Soham Mantra
ARCHITECT - ENGINEERS & INTERIOR DESIGNER
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 RCC Framed Buildings Basics

FAQ

Q            

What is a Framed Structure? How is load supported in a Framed Structure?

What are the different types of structural elements in a building? 

What are the different types of loads for which a structure must be designed?

What are the common types of Foundations?

Who are the main people behind the construction of a building? What are their roles?

What is a Framed Structure? How is load supported in a Framed Structure?

What are the different types of structural elements in a building? 

What are the different types of loads for which a structure must be designed?

What are the common types of Foundations?

Who are the main people behind the construction of a building? What are their roles?

Q             What is a Framed Structure? How is load supported in a Framed Structure?

A             An RCC Framed Structure is an assembly of slabs, beams, columns and foundation connected to one another so that it behaves as one unit. It is a methodology, which enables the construction of tall buildings and building with stilts. Majority of urban structures and multistoried buildings are built as RCC framed structures. In an RCC framed structure, the load is transferred from a slab to the beams then to the columns and further to lower columns and finally to the foundation which in turn transfers it to the soil. The walls in such structures are constructed after the frame is ready and are not meant to carry any load.  As against this, in a load bearing structure, the loads are directly transferred to the soil through the walls, which are capable of carrying them.

  Q           What are the different types of structural elements in a building? 

A             The flat ceiling of a story is called a 'Slab'.

The peripheral horizontal members supporting the slab are called 'Beams'.

The beams at ground level or plinth level (the lowermost habitable level) are called 'Plinth Beams'.

The vertical members supporting the beams are called 'Columns'.

The system below ground transferring the entire load of the structure to the soil is called 'Foundation'.

A slab or a beam supported only on one side and projecting horizontally on the other side is called a 'Cantilever' slab or beam e.g. balconies, lofts and canopies. 

 Q            What are the different types of loads for which a structure must be designed?

A             There are basically two types of loads which a structure must support or resist.

Gravity loads: These loads act vertically downward such as the Dead Load (the weight of the structure itself along with the walls, overhead water tanks, immovable furniture etc) and Live Load (the weight of inhabitants or users, movable furniture etc)

Lateral loads: These loads act horizontally on the structure such as wind load and seismic (earthquake) load. These may act in any direction depending on the incidence of wind or earthquake. 

  Q           What are the common types of Foundations?

A             The common types of foundations used for RCC framed buildings are:

Footings: In these sufficient area of contact with soil is provided around each column when good quality soil is available at a shallow depth.

Raft foundation: This is used when basement is to be provided and the soil available at a shallow depth is not very firm. In this case the entire base slab of the basement transfers the load to the soil.

Pile foundations: This type of foundation is used when the loads to be supported are large and the necessary type of firm soil is not available at a shallow depth. Sometimes a combination of the above types may be found to be more appropriate than a single type. Foundations should be designed so that the loads are safely transferred to the soil in such a way that the soil is able to withstand them.

  Q           Who are the main people behind the construction of a building? What are their roles?

A             Architect: He plans the utilization of space in the building and around and prepares drawings and specifications depicting apartments on various floors and the services required for the occupants of the apartments. He also designs the building aesthetically and obtains the necessary approvals from various authorities. He monitors the construction work through periodic site visits.

Structural Engineer: Based on the architectural drawings, the structural engineer designs a structural system so as to support the various loads that would act upon the building. In order to transfer these loads in a safe and stable manner to the ground, he decides the location, size and details of various structural components (such as slabs, beams, columns, foundations etc) of the building and prepares structural drawings and specifications. He visits the site at important stages of the construction work to inspect the quality of the structural work.

Soil - Foundation Engineer: He inspects (and carries out necessary tests on) the soil and recommends the appropriate type of foundation, which would safely transfer the loads to the ground. He may also recommend ways of strengthening soil, if necessary.

Contractor: Contractor executes the construction work in accordance with the drawings and specifications set out by the architect and the structural engineer. Strict adherence to these drawings and specifications would mean use of good quality materials and standards of workmanship through the necessary quality control.

The overall quality of a building is a result of the inputs from the above three.

Q             What is a Framed Structure? How is load supported in a Framed Structure?

A             An RCC Framed Structure is an assembly of slabs, beams, columns and foundation connected to one another so that it behaves as one unit. It is a methodology, which enables the construction of tall buildings and building with stilts. Majority of urban structures and multistoried buildings are built as RCC framed structures. In an RCC framed structure, the load is transferred from a slab to the beams then to the columns and further to lower columns and finally to the foundation which in turn transfers it to the soil. The walls in such structures are constructed after the frame is ready and are not meant to carry any load.  As against this, in a load bearing structure, the loads are directly transferred to the soil through the walls, which are capable of carrying them.

  Q           What are the different types of structural elements in a building? 

A             The flat ceiling of a story is called a 'Slab'.

The peripheral horizontal members supporting the slab are called 'Beams'.

The beams at ground level or plinth level (the lowermost habitable level) are called 'Plinth Beams'.

The vertical members supporting the beams are called 'Columns'.

The system below ground transferring the entire load of the structure to the soil is called 'Foundation'.

A slab or a beam supported only on one side and projecting horizontally on the other side is called a 'Cantilever' slab or beam e.g. balconies, lofts and canopies. 

   Q          What are the different types of loads for which a structure must be designed?

A             There are basically two types of loads which a structure must support or resist.

Gravity loads: These loads act vertically downward such as the Dead Load (the weight of the structure itself along with the walls, overhead water tanks, immovable furniture etc) and Live Load (the weight of inhabitants or users, movable furniture etc)

Lateral loads: These loads act horizontally on the structure such as wind load and seismic (earthquake) load. These may act in any direction depending on the incidence of wind or earthquake. 

  Q           What are the common types of Foundations?

A             The common types of foundations used for RCC framed buildings are:

Footings: In these sufficient area of contact with soil is provided around each column when good quality soil is available at a shallow depth.

Raft foundation: This is used when basement is to be provided and the soil available at a shallow depth is not very firm. In this case the entire base slab of the basement transfers the load to the soil.

Pile foundations: This type of foundation is used when the loads to be supported are large and the necessary type of firm soil is not available at a shallow depth. Sometimes a combination of the above types may be found to be more appropriate than a single type. Foundations should be designed so that the loads are safely transferred to the soil in such a way that the soil is able to withstand them.

 Q            Who are the main people behind the construction of a building? What are their roles?

A             Architect: He plans the utilization of space in the building and around and prepares drawings and specifications depicting apartments on various floors and the services required for the occupants of the apartments. He also designs the building aesthetically and obtains the necessary approvals from various authorities. He monitors the construction work through periodic site visits.

Structural Engineer: Based on the architectural drawings, the structural engineer designs a structural system so as to support the various loads that would act upon the building. In order to transfer these loads in a safe and stable manner to the ground, he decides the location, size and details of various structural components (such as slabs, beams, columns, foundations etc) of the building and prepares structural drawings and specifications. He visits the site at important stages of the construction work to inspect the quality of the structural work.

Soil - Foundation Engineer: He inspects (and carries out necessary tests on) the soil and recommends the appropriate type of foundation, which would safely transfer the loads to the ground. He may also recommend ways of strengthening soil, if necessary.

Contractor: Contractor executes the construction work in accordance with the drawings and specifications set out by the architect and the structural engineer. Strict adherence to these drawings and specifications would mean use of good quality materials and standards of workmanship through the necessary quality control.

The overall quality of a building is a result of the inputs from the above three.

List of I.S. Codes generally required to be reffered for Building Design

7.1 The important I.S. Codes (with their latest editions/ amendments) to be referred to for design of building are as follows :

(i) I.S. 456-1978 : Code of practice for plain and reinforced concrete .

(ii) I.S. 800-1962 : Code of practice for use of structural steel in general building constriction.

(iii) I.S. 875-1987 : Designs loads other than (part I toV) earthquake for building Design.

Part-I : Dead loads .

Part-II : Imposed loads .

Part-III : Wind loads .

Part IV : Snow loads .

Part V : Special loads and load combinations.

(iv) I.S. 1080-1965 : Code of practice for design and construction of shallow foundation in soils (other than Raft, Ring and shell )

(v) I.S:1642-1988 : Fire safety of Bldgs. (General) Detail 3 of construction.

(vi) I.S.: 1643-1988: Code of practice for Fire safety of Bldgs(General) Exposure Hazard.

(vii) I.S. 1644-1988 : Code of practice for Fire safety of Bldgs(General) Exit requirements and personal Hazards.

(viii) I.S. 1888-1972 : Methods of load test on soils.

(ix) I.S. :1893-1984 : Criteria for earthquake resistant design of structures.

(x) I.S : 1904-1986 : Code of practice for design & construction of pile foundation in soil structural safety of building foundation.

(xi) I.S. 2911-1990 : Code of practice for design and construction of pile (Part I to IV) foundation.

(xii) I.S. 2950-1981 : Code of practice for design and construction of raft foundation.

(xiii) I.S. 3370-1965 : Code of Practice for water retaining structures .

(xiv) I.S. 3414-1987 : Code of Practice for Design and Installation of joints in buildings.

(xv) I.S. 4326-1993 : Code of practice for earthquake resistant design of structure .

(xvi) I.S. 6403-1981: Code of practice for Determination of bearing pressure of shallow foundation .

(xvii) I.S. 13920-1993 : Code of practice for ductility detailing of reinforced concrete structures subjected to seismic forces .

I.S. Codes are also available for design of special types of structures like folded plate ,shell structures etc. Refer publication list of BIS for the same .

Similarly there are special publications of I.S. which are useful for design of buildings such as .

(i) SP-16 : Design Aids to I.S. : 456-1978

(ii) SP-22 : Explanation to I.S. : 1893 & I.S. :4326.

(iii) SP-23 : Concrete Mix .

(iv) SP-24 :Explanation of I.S. 456-1978.

(v) SP-25 : Cracks in buildings and their repairs .

(vi) SP- 34 : Detailing in R.C.C. structures .

(vii) SP-38 : Design of steel trusses .

Besides above mentioned I.S. Codes ,Hand Book for R.C. Member " (Limit State Design ) Vol .I and II by P.L. Bongirwar and U.S. Kalgutkar ,published by P.W.D. (Govt.of Maharashtra) is very useful .

For general instructions regarding carring out R.C.C. works in field refer to Design Circle’s Technical Note No . 7502 and 7503 are kept at page 46 and page 59. respectively .

For aspects which are not covered by any other I.S. codes available, relevant British Standard Codes may be referred to .

7.2 While designing R.C.C. structures, important provisions of I.S. codes must be borne in mind . Some of the important provisions of I.S. :456-1978 are as follows.

7.2.1 The code has been divided into 6 sections.

Section-I : General .

Section-II : Material, Workmanship, inspection and testing .

Section-III : General Design requirements for structural members and systems .

Section-IV : Special Design requirement for structural members and systems.

Section-V : Structural Design .(Limit State Method ).

Section-VI : Structural Design (Working Stress Method ).

7.2.2 General Provisions.

Clause No. 19 : Deals with stability of the structure against overturning and sliding.

Clause No. 25.2.1 : Development length of bars.

Clause No. 25.3.1 : Minimum distance between individual bars .

Clause No.25.3.2 : Maximum distance between bars in tension .

Clause No.25.4 : Cover to reinforcement .

Clause No.26 : Expansion joints .

7.2.3 Provision regarding slabs :

Clause No.21.2 : Effective span.

Clause No.21.4.1 : Arrangement of live load .

Clause No.21.5 : Moment and shear co-efficient for continuous beams .

Clause No.22.2 : Control of deflection.

Clause No.23.1 : Provisions regarding solid slabs .

Clause No. 25.5.2.1 : Minimum reinforcement.

Clause No.25.5.2.2 : Maximum diameter.

7.2.4 Provisions regarding beams :

Clause No.21.2 : Effective span

Clause No.21.4.1 : Arrangement of live load .

Clause No. 21.5 : Moment and shear co-efficient for continuous beams.

Clause No. 22.2 : Control of deflection.

Clause No. 22.3 : Slenderness limits for beams.

Clause No. 25.5.1.1 : Requirement of tensile reinforcement for beams .

Clause No. 25.5.1.2 :Compression reinforcement.

Clause No. 25.5.1.3 : Side face reinforcement.

Clause No.25.5.1.5 : Maximum spacing of shear reinforcement.

Clause No.25.5.1.6 : Minimum shear reinforcement.

Clause No.25.5.1.7 : Distribution of torsion reinforcement.

7.2.5 Provisions for columns;

Clause No.24.1.2 : Short and slender compression members .

Clause No.24.1.3 : Unsupported length .

Clause No.24.2 : Effective length of compression members.

Clause No.24.3 : Slenderness limits for columns .

Clause No.24.4 : Minimum eccentricity .

Clause No.25.5.3 : Longitudinal reinforcement.

Clause No. 25.5.3.2 : Transverse reinforcement.

Clause No.42.2 : Cracking Consideration .

7.2.6 Provisions for footings :

Clause No. 33.1.2 : Thickness at the edge of footing .

Clause No.33.4 : Transfer of load at the base of column .

Other references /Literature generally referred to are

(i) Reinforced Concrete Designer’s Hand Book by Reynolds & Steelman.

(ii) Limit State Theory & Design of Reinforced Concrete by Karve and shah .

(iii) Hand Book of Reinforced Concrete Design (I.S.:456-1978)by Karve .

(iv) Limit State Design of Reinforced Concrete by Vergis .

 

   Design of R.C.C. Members of Buildings , procedure followed in the Designs Circle .

1 INTRODUCTION :

Instructions about the preparation of R.C.C. design of building works have been issued vide Govt. in P.W.D. Circular No .BDG-1080/80838 (394) /Desk -2 dt.3rd Nov.1980 (Kept at page 35)

1.1 This circular states that R.C.C. design of all load bearing structures and R.C.C. framed structures up to four stories i.e.G+3 upper, except in case of structures requiring wind and or seismic analysis , shall be prepared by the field engineers.

1.2 The design of R.C.C. frame structures having more than G+3 upper floors as well as structure with more than G+2 upper floors requiring wind and /or seismic analysis , are required to be prepared by Designs Circle.

1.3 Designs Circle will undertake the work of preparing R.C.C, design for a structure only after the receipt of the following information from the field engineers.

(a) Copy of Administrative approval to the estimate of the structure, (based on approved Architectural drawings .) along with a blue print set of original Architect’s plans (No traced copies are acceptable ) .

(b) Copy of Technical sanction from the competent authority .

(c) If the work is budgeted, item number of work and its page number in the Budget Book .

(d) Proposed construction programme i.e. proposed dates of start of different stages of construction and scope of different phases of construction ,in case of phased construction .

(e) "Field Data" in standard proforma prescribed by the Design Circle .Copy of standard proforma is kept at page 37.

1.4 It is also desired that Field Engineer should communicate to Designs Circle, the present position of the tender for the work i.e. the date of issue of tender notice ,date of receipt of the tender and likely date of issue of work order .This information will be helpful to Designs Circle , in planning the design work and there will be less likelihood of delay in supply of R.C.C. schedules from time to time i.e. as per the construction programme proposed by field engineers.

It is a prerequisite that, before undertaking actual design work, the design engineer should have basic knowledge of "Strength of materials" , "Properties of materials","Behaviour of structures", "Analysis of structures" and through knowledge about detailing of reinforcement ,etc. Also he should be acquainted with various I.S. Codes which are required to be referred to in the design work .It is, therefore ,advised that the designer should refresh his knowledge by referring to the various technical books and codes .

 

 

 

2  RCC  Design Philosophy

2.1. R.C.C design of buildings is being carried out mainly by three methods of design .They are namely : (1) Working stress method, (2) Ultimate load method and (3) Limit state method .

2.2. The Limit state method is now in vogue in all government design offices and premier private consulting firms .The B.I.S. have published I.S.:456-1978 incorporating the use of Limit state Method of design . The designer should therefore get well versed with the theory of Limit State Method of design .

Working Stress Method : Used over decades , this method is now practically outdated in many advanced countries of the world ,because of its inherent limitations

The I.S :456-1978 code gives emphasis on Limit State Method which is the modified form of Ultimate Load Method .

Limit State Method is a judicious amalgamation of Working Stress Method and Ultimate Load Method ,removing the drawbacks of both of the methods but retaining their good points .It is also based on sound scientific principles and backed by 25 years of research .The Limit State Method has proved to have an edge over the Working Stress Method from the economic point of view . Consequently we need not stick to Working Stress Method any more .

Accordingly ,Designs Circle in P.W. Department is designing the R.C.C. structure as per Limit State Method , since early eighties .

2.3. Codes: In carring out the design calculations ,one has to comply to the provisions of various I.S. Codes .Use of special publications of B.I.S. and Hand Books for design methodology and readymade design tables can also be made.A list of frequently referred codes /hand books is given on page 7.

2.4. Departmental Circulars: Designs Circle Circulars to field officers namely 7502 and 7503 should also be studied .Copies of the same are kept at page 46 & page 59 .

The designer is advised to study these circulars/I.S. codes carefully and also discuss the provisions among his colleagues/superior officers for clarification/s for better understanding.

2.5. Besides analytical part of structural design ,following factors should also be kept in mind while designing the structure .

(a) Strength of structure .

(b) Durability of structure .

(c) Serviceability of structure ,during construction as well as

during design life time of structure .

(d) Economy in building materials and ease of constructions.

(e) Economy in centering and form work .

(f) Aesthetics of structure .

3 . Computer Aided Design

Personal computers of sufficiently high speed and large memory capacity have been made available to Designs Circle .Designs Circle has developed various Design software and same are being used . Software available presently in designs Circle are discussed in para 19,20. Designer should get conversant with the Users Manuals of these programmes so that he can work independently on the computer

 

3  Steps involved in RCC Design :

The R.C.C. design of a building is carried out in following steps .

(i) Study the architectural drawings.(see page 5)

(ii) Study the field data .(see page 6)

(iii) Prepare R.C.C. layouts at various floor levels .(See page 11)

(iv) Decide the imposed live load and other loads such as wind , seismic and other miscellaneous loads, (where applicable ), as per I.S. 875 ,considering the contemplated use of space ,and seismic zone of the site of proposed building .

(v) Fix the tentative slab and beam sizes and then prepare preliminary beam design .Using values of support reactions from preliminary beam design ,prepare preliminary column design and based on these load calculations ,fix tentative column section and it’s concrete mix. As far as possible, for multistoried buildings, the same column size and column mix should be used for at least two stories so as to avoid frequent changes in column size and concrete mix facilitate easy and quick construction. Concrete Mix to be adopted for beams and slabs at all floors is M 15 for Non Coastal Region and M 20 for Coastal Region .

(vi) Group the member such as columns, beams , slabs , footings etc. wherever possible ,on the basis of the similarity of loading pattern ,spans, end conditions etc. It reduces the quantum of calculation work .

(vii) Prepare R.C.C. Layouts and get approval from the Architect to the R.C.C.layouts and tentative sizes of beams and columns and other structural members if any .In the R.C.C. Layouts ,show the structural arrangement and orientation of columns ,layout of beams ,type of slab (with its design live load) at different floor levels . Also indicate how the different structural members will transfer the load of each floor successively to the foundation level .

For a building , generally following R.C.C. layouts are prepared :

(a) R.C.C. layout at pile cap/ plinth level .

(b) R.C.C. layout at various floor levels or at typical floor level (depending on Architectural plans.)

(c) R.C.C. layout at terrace level.

(d) R.C.C. layout at staircase roof level and where lifts are provided .

(e) R.C.C. layout at lift machine room floor level .

(f) R.C.C. layout at lift machine room roof level .

Where good foundation is available at reasonably shallow depth, provision of plinth beams in Non Seismic Areas can be omitted .However ,this should be got approved from Superintending Engineer /competent authority .In such case the R.C.C. layout at plinth level may be prepared accordingly .

(viii) Finalise various structural frames in X-direction and Y- direction followed by preparation of frame sketches and filling in, data of the frames on coding sheets , for computer aided frame analysis .

(ix) Feed the data of frames on computer and recheck the data so stored , by getting print out .

(x) Analyse the frames using Design Circle’s "computer programme "SEDC" (based on stiffness matrix method ) and obtain the analysis printout . The computer programme "SEDC" incorporates the beam design programme (as per Limit State Method )and regarding columns member it gives only horizontal and vertical force along with moment acting on the column section, in the plane of the frame , for different load combinations as per I.S. :456/1978.

(xi) Calculations of Horizontal forces :Whenever the structure is to be designed for horizontal forces (due to seismic or wind forces ) refer I.S. : 1893 for seismic forces and I.S. :875 Part-III for wind forces.

All design parameters for seismic /wind analysis shall be got approved from Superintending Engineer before starting design calculations and frame analysis. The proper selection of the various parameters is a critical stage in design process .

(xii) Design column sections Assemble the design data for column design, using results obtained in analysis of respective X and Y direction frames, which include the column under consideration .The design of column can be done using computer programme "ASP2" or manually by referring to Hand Book of R.C. members (Limit State Design ) Volume II’ (Govt. of Maharashtra Publication ).

(xiii) Design footings manually using Hand Book of R.C.C. members (Limit State Design ) Volume II’ or by using the computer programme ‘FOOT’ for design of isolated /combined footing . For design of other types of footing refer standard text books .

(xiv) Design slabs manually by using Hand Book for R.C. members Vol.I’ or by using computer programme ‘SLAB’ .

(xv) Design beams by using the frame analysis output. It gives required area of reinforcement at various locations and diameter and spacing of shear reinforcement.

Designer’s work now involves.

(a) Fix the bar diameter and number of bars(at top and bottom) at various locations along the beam span, as per codal provisions and practice .

(b) Finalise the diameter and spacing of shear reinforcement as per analysis results and as per codal provisions of detailing where ever applicable .

Design secondary beams, is not included in "SEDC" and shall be done manually on similar lines on finalisation of R.C.C. design of main beams.

(xvi) Preparation of R.C.C. schedules for footings , slabs, beams and columns at various levels, on completion of respective design .As these R.C.C. schedules are to be used during the execution ,designer should take maximum care in preparing them .Schedules should be prepared by one Engineer ,and thoroughly cross checked by another Engineer , before submitting the same for approval to the competent authority . In schedules ,special instructions to the field engineers should be highlighted and sketches should be drawn wherever necessary .General notes to be mentioned on schedules are kept at page 46.

Form of schedule of footing schedule of columns ,schedule of beams , schedule of slabs are kept at page 71, page 70, page72,page 73, respectively.

. Study of Architectural Drawings

5.1 As the building is to be constructed as per the drawings prepared by the Architect .it is very much necessary for the Designer to Correctly visualize the structural arrangement as proposed by the Architect .A Designer ,after studying Architect’s plans, can suggest necessary change like additions/deletions and orientations of columns and beams as required from structural point of view .

5.2 For this, the designer should have a complete set of prints of original approved architectural drawings of the buildings namely i) Plans at all the floor levels ,ii) Elevations,(front, back and sides ), iii) Salient cross sections where change in elevation occurs and any other sections that will aid to visualize the structure more easily .The cross sections should show the internal details like locations of windows ,doors. toilets staircases, lift machine room, staircase rooms, and any other special features like gutter at roof level ,projections proposed to give special elevation treatment, etc.

5.3 During the study following points should be noted. The drawings should be examined to find out ,

(i) Whether the plan shows all the required dimensions and levels so that the designer can arrive at the lengths and sizes of different members .Wherever necessary ,obligatory member size as required by Architect (on architectural grounds ) are given or otherwise .

(ii) Whether the plans and schedules of doors and windows etc. are supplied so as to enable designer to decide beam size as these locations .

(iii) Whether thickness of various walls and their height (in case of partition walls) is given .

(iv) Whether functional requirements and utility of various spaces are specified in the plans. These details will help in deciding the imposed load on these spaces.

(v) Whether material for walls is specified .

(vi) The structural arrangement and sizes proposed by the Architect should not generally be changed except where structural design requirements can not be fulfilled by using other alternatives like using higher grade of concrete mix or by using higher percentage of steel or by using any other suitable alternate structural arrangement .Any change so necessitated be made in consultation with the Architect . Further design should be carried out accordingly .

(vii) Note the false ceiling ,lighting arrangement, lift/s along with their individual carrying capacity (either passenger or goods ), Air Conditioning ducting, acoustical treatment ,R.C.C. cladding ,finishing items, fixtures, service/s’ opening proposed by the Architect .

(viii) Note the position/s of expansion joints, future expansion (horizontal and/ vertical) contemplated in the Architect’s plan and check up with the present scope of work (indicated in the "Field Data" submitted by the field engineers).The design of the present phase will account for future expansion provision such as loads to be considered for column and footing design ( combined /expansion joint footing ) resulting if any .

If this aspect is neglected it will create design as well as execution problems in the next phase of work . In case of vertical expansion in future, the design load for the present terrace shall be maximum of the future floor level design load or present terrace level design load .

(ix) whether equipment layout has been given ,particularly in the areas where heavy machinery is proposed to be located .

(x) Special features like sun breakers ,fins, built- in cupboards with their sections so as to enable designer to take their proper cognizance .

(xi) Whether the location/s of the over head water tanks specified by the Architect and whether "Field Data" submitted by field engineer furnishes the required capacity of each over head water tank .

(xii) What type of water proofing treatment is proposed in toilet blocks and on terrace .

The findings of the above scrutiny should be brought to the notice of the Architect and his clear opinion in this matter should be obtained before proceeding ahead with R.C.C. design.

  4 . Computer Aided Design

Personal computers of sufficiently high speed and large memory capacity have been made available to Designs Circle .Designs Circle has developed various Design software and same are being used . Software available presently in designs Circle are discussed in para 19,20. Designer should get conversant with the Users Manuals of these programmes so that he can work independently on the computer

5 Steps involved in RCC Design :

The R.C.C. design of a building is carried out in following steps .

(i) Study the architectural drawings.(see page 5)

(ii) Study the field data .(see page 6)

(iii) Prepare R.C.C. layouts at various floor levels .(See page 11)

(iv) Decide the imposed live load and other loads such as wind , seismic and other miscellaneous loads, (where applicable ), as per I.S. 875 ,considering the contemplated use of space ,and seismic zone of the site of proposed building .

(v) Fix the tentative slab and beam sizes and then prepare preliminary beam design .Using values of support reactions from preliminary beam design ,prepare preliminary column design and based on these load calculations ,fix tentative column section and it’s concrete mix. As far as possible, for multistoried buildings, the same column size and column mix should be used for at least two stories so as to avoid frequent changes in column size and concrete mix facilitate easy and quick construction. Concrete Mix to be adopted for beams and slabs at all floors is M 15 for Non Coastal Region and M 20 for Coastal Region .

(vi) Group the member such as columns, beams , slabs , footings etc. wherever possible ,on the basis of the similarity of loading pattern ,spans, end conditions etc. It reduces the quantum of calculation work .

(vii) Prepare R.C.C. Layouts and get approval from the Architect to the R.C.C.layouts and tentative sizes of beams and columns and other structural members if any .In the R.C.C. Layouts ,show the structural arrangement and orientation of columns ,layout of beams ,type of slab (with its design live load) at different floor levels . Also indicate how the different structural members will transfer the load of each floor successively to the foundation level .

For a building , generally following R.C.C. layouts are prepared :

(a) R.C.C. layout at pile cap/ plinth level .

(b) R.C.C. layout at various floor levels or at typical floor level (depending on Architectural plans.)

(c) R.C.C. layout at terrace level.

(d) R.C.C. layout at staircase roof level and where lifts are provided .

(e) R.C.C. layout at lift machine room floor level .

(f) R.C.C. layout at lift machine room roof level .

Where good foundation is available at reasonably shallow depth, provision of plinth beams in Non Seismic Areas can be omitted .However ,this should be got approved from Superintending Engineer /competent authority .In such case the R.C.C. layout at plinth level may be prepared accordingly .

(viii) Finalise various structural frames in X-direction and Y- direction followed by preparation of frame sketches and filling in, data of the frames on coding sheets , for computer aided frame analysis .

(ix) Feed the data of frames on computer and recheck the data so stored , by getting print out .

(x) Analyse the frames using Design Circle’s "computer programme "SEDC" (based on stiffness matrix method ) and obtain the analysis printout . The computer programme "SEDC" incorporates the beam design programme (as per Limit State Method )and regarding columns member it gives only horizontal and vertical force along with moment acting on the column section, in the plane of the frame , for different load combinations as per I.S. :456/1978.

(xi) Calculations of Horizontal forces :Whenever the structure is to be designed for horizontal forces (due to seismic or wind forces ) refer I.S. : 1893 for seismic forces and I.S. :875 Part-III for wind forces.

All design parameters for seismic /wind analysis shall be got approved from Superintending Engineer before starting design calculations and frame analysis. The proper selection of the various parameters is a critical stage in design process .

(xii) Design column sections Assemble the design data for column design, using results obtained in analysis of respective X and Y direction frames, which include the column under consideration .The design of column can be done using computer programme "ASP2" or manually by referring to Hand Book of R.C. members (Limit State Design ) Volume II’ (Govt. of Maharashtra Publication ).

(xiii) Design footings manually using Hand Book of R.C.C. members (Limit State Design ) Volume II’ or by using the computer programme ‘FOOT’ for design of isolated /combined footing . For design of other types of footing refer standard text books .

(xiv) Design slabs manually by using Hand Book for R.C. members Vol.I’ or by using computer programme ‘SLAB’ .

(xv) Design beams by using the frame analysis output. It gives required area of reinforcement at various locations and diameter and spacing of shear reinforcement.

Designer’s work now involves.

(a) Fix the bar diameter and number of bars(at top and bottom) at various locations along the beam span, as per codal provisions and practice .

(b) Finalise the diameter and spacing of shear reinforcement as per analysis results and as per codal provisions of detailing where ever applicable .

Design secondary beams, is not included in "SEDC" and shall be done manually on similar lines on finalisation of R.C.C. design of main beams.

(xvi) Preparation of R.C.C. schedules for footings , slabs, beams and columns at various levels, on completion of respective design .As these R.C.C. schedules are to be used during the execution ,designer should take maximum care in preparing them .Schedules should be prepared by one Engineer ,and thoroughly cross checked by another Engineer , before submitting the same for approval to the competent authority . In schedules ,special instructions to the field engineers should be highlighted and sketches should be drawn wherever necessary .General notes to be mentioned on schedules are kept at page 46.

Form of schedule of footing schedule of columns ,schedule of beams , schedule of slabs are kept at page 71, page 70, page72,page 73, respectively.

Study of Architectural Drawings

5.1 As the building is to be constructed as per the drawings prepared by the Architect .it is very much necessary for the Designer to Correctly visualize the structural arrangement as proposed by the Architect .A Designer ,after studying Architect’s plans, can suggest necessary change like additions/deletions and orientations of columns and beams as required from structural point of view .

5.2 For this, the designer should have a complete set of prints of original approved architectural drawings of the buildings namely i) Plans at all the floor levels ,ii) Elevations,(front, back and sides ), iii) Salient cross sections where change in elevation occurs and any other sections that will aid to visualize the structure more easily .The cross sections should show the internal details like locations of windows ,doors. toilets staircases, lift machine room, staircase rooms, and any other special features like gutter at roof level ,projections proposed to give special elevation treatment, etc.

5.3 During the study following points should be noted. The drawings should be examined to find out ,

(i) Whether the plan shows all the required dimensions and levels so that the designer can arrive at the lengths and sizes of different members .Wherever necessary ,obligatory member size as required by Architect (on architectural grounds ) are given or otherwise .

(ii) Whether the plans and schedules of doors and windows etc. are supplied so as to enable designer to decide beam size as these locations .

(iii) Whether thickness of various walls and their height (in case of partition walls) is given .

(iv) Whether functional requirements and utility of various spaces are specified in the plans. These details will help in deciding the imposed load on these spaces.

(v) Whether material for walls is specified .

(vi) The structural arrangement and sizes proposed by the Architect should not generally be changed except where structural design requirements can not be fulfilled by using other alternatives like using higher grade of concrete mix or by using higher percentage of steel or by using any other suitable alternate structural arrangement .Any change so necessitated be made in consultation with the Architect . Further design should be carried out accordingly .

(vii) Note the false ceiling ,lighting arrangement, lift/s along with their individual carrying capacity (either passenger or goods ), Air Conditioning ducting, acoustical treatment ,R.C.C. cladding ,finishing items, fixtures, service/s’ opening proposed by the Architect .

(viii) Note the position/s of expansion joints, future expansion (horizontal and/ vertical) contemplated in the Architect’s plan and check up with the present scope of work (indicated in the "Field Data" submitted by the field engineers).The design of the present phase will account for future expansion provision such as loads to be considered for column and footing design ( combined /expansion joint footing ) resulting if any .

If this aspect is neglected it will create design as well as execution problems in the next phase of work . In case of vertical expansion in future, the design load for the present terrace shall be maximum of the future floor level design load or present terrace level design load .

(ix) whether equipment layout has been given ,particularly in the areas where heavy machinery is proposed to be located .

(x) Special features like sun breakers ,fins, built- in cupboards with their sections so as to enable designer to take their proper cognizance .

(xi) Whether the location/s of the over head water tanks specified by the Architect and whether "Field Data" submitted by field engineer furnishes the required capacity of each over head water tank .

(xii) What type of water proofing treatment is proposed in toilet blocks and on terrace .

The findings of the above scrutiny should be brought to the notice of the Architect and his clear opinion in this matter should be obtained before proceeding ahead with R.C.C. design.

6. Study of Field Data :

6.1 The architectural drawings give the details only from architectural point of view. As such the designer must also have through information of the site where the structure is proposed to be constructed. For this a standard proforma has been prescribed by Designs Circle . The field engineer has to submit the field data in this proforma while requesting Designs Circle for supply of R.C.C. designs .Copy of the form of "Field Data" is kept at page 37.

6.2 The "Field Data" is a must before starting design work. However, it is generally noticed, that the "Field Data" lacks vital information such as bearing capacity of the founding strata, proposed location and capacity of over head water tank/s ,electrical lift loads, future horizontal and/or vertical expansion etc. so on receipt of "Field Data" it should be checked thoroughly and if any data is found to be missing, the same should be called from field engineer immediately, to avoid delay in starting the design work .

6.3 Besides information on the points mentioned in prescribed proforma, information on special points also is to be supplied where applicable by the field officers, like :

(i) Machinery and/or equipment layout .

(ii) Air cooling /air conditioning ducting layouts including exhaust arrangements.

(iii) Flase celing arrangements, proposed acoustical treatment, electrical lighting and audio system fixtures .

(iv) Fire fighting pipeline/s or any other special ducting layouts .

(v) Sub soil and sub soil water properties particularly Sulfide and Chloride contents where the building is located in coastal and or highly polluted industrial area.

(vi) Importance factor (I) and value of (Beta) for soil foundation system as per I.S. 1893, to be considered for the proposed building when the building is being constructed in seismic zone.It may be noted that the importance factor more than 1.0 leads to increased seismic forces consequently the reinforcement requirement increases considerably .Also improper value of (Beta) will lead to erroneous higher value of seismic forces and ultimately unnecessary uneconomical design. Therefore before starting Seismic Analysis Importance factor (I) and value of (Beta)should be got approved from the Superintending Engineer .

(vii) In case foundations other than open type of foundation proposed (with reasons) and safe bearing capacity of the founding strata and its depth from the general ground level along with trial bore log details and test results on rock samples .

7. List of I.S. Codes generally required to be reffered for Building Design

7.1 The important I.S. Codes (with their latest editions/ amendments) to be referred to for design of building are as follows :

(i) I.S. 456-1978 : Code of practice for plain and reinforced concrete .

(ii) I.S. 800-1962 : Code of practice for use of structural steel in general building constriction.

(iii) I.S. 875-1987 : Designs loads other than (part I toV) earthquake for building Design.

Part-I : Dead loads .

Part-II : Imposed loads .

Part-III : Wind loads .

Part IV : Snow loads .

Part V : Special loads and load combinations.

(iv) I.S. 1080-1965 : Code of practice for design and construction of shallow foundation in soils (other than Raft, Ring and shell )

(v) I.S:1642-1988 : Fire safety of Bldgs. (General) Detail 3 of construction.

(vi) I.S.: 1643-1988: Code of practice for Fire safety of Bldgs(General) Exposure Hazard.

(vii) I.S. 1644-1988 : Code of practice for Fire safety of Bldgs(General) Exit requirements and personal Hazards.

(viii) I.S. 1888-1972 : Methods of load test on soils.

(ix) I.S. :1893-1984 : Criteria for earthquake resistant design of structures.

(x) I.S : 1904-1986 : Code of practice for design & construction of pile foundation in soil structural safety of building foundation.

(xi) I.S. 2911-1990 : Code of practice for design and construction of pile (Part I to IV) foundation.

(xii) I.S. 2950-1981 : Code of practice for design and construction of raft foundation.

(xiii) I.S. 3370-1965 : Code of Practice for water retaining structures .

(xiv) I.S. 3414-1987 : Code of Practice for Design and Installation of joints in buildings.

(xv) I.S. 4326-1993 : Code of practice for earthquake resistant design of structure .

(xvi) I.S. 6403-1981: Code of practice for Determination of bearing pressure of shallow foundation .

(xvii) I.S. 13920-1993 : Code of practice for ductility detailing of reinforced concrete structures subjected to seismic forces .

I.S. Codes are also available for design of special types of structures like folded plate ,shell structures etc. Refer publication list of BIS for the same .

Similarly there are special publications of I.S. which are useful for design of buildings such as .

(i) SP-16 : Design Aids to I.S. : 456-1978

(ii) SP-22 : Explanation to I.S. : 1893 & I.S. :4326.

(iii) SP-23 : Concrete Mix .

(iv) SP-24 :Explanation of I.S. 456-1978.

(v) SP-25 : Cracks in buildings and their repairs .

(vi) SP- 34 : Detailing in R.C.C. structures .

(vii) SP-38 : Design of steel trusses .

Besides above mentioned I.S. Codes ,Hand Book for R.C. Member " (Limit State Design ) Vol .I and II by P.L. Bongirwar and U.S. Kalgutkar ,published by P.W.D. (Govt.of Maharashtra) is very useful .

For general instructions regarding carring out R.C.C. works in field refer to Design Circle’s Technical Note No . 7502 and 7503 are kept at page 46 and page 59. respectively .

For aspects which are not covered by any other I.S. codes available, relevant British Standard Codes may be referred to .

7.2 While designing R.C.C. structures, important provisions of I.S. codes must be borne in mind . Some of the important provisions of I.S. :456-1978 are as follows.

7.2.1 The code has been divided into 6 sections.

Section-I : General .

Section-II : Material, Workmanship, inspection and testing .

Section-III : General Design requirements for structural members and systems .

Section-IV : Special Design requirement for structural members and systems.

Section-V : Structural Design .(Limit State Method ).

Section-VI : Structural Design (Working Stress Method ).

7.2.2 General Provisions.

Clause No. 19 : Deals with stability of the structure against overturning and sliding.

Clause No. 25.2.1 : Development length of bars.

Clause No. 25.3.1 : Minimum distance between individual bars .

Clause No.25.3.2 : Maximum distance between bars in tension .

Clause No.25.4 : Cover to reinforcement .

Clause No.26 : Expansion joints .

7.2.3 Provision regarding slabs :

Clause No.21.2 : Effective span.

Clause No.21.4.1 : Arrangement of live load .

Clause No.21.5 : Moment and shear co-efficient for continuous beams .

Clause No.22.2 : Control of deflection.

Clause No.23.1 : Provisions regarding solid slabs .

Clause No. 25.5.2.1 : Minimum reinforcement.

Clause No.25.5.2.2 : Maximum diameter.

7.2.4 Provisions regarding beams :

Clause No.21.2 : Effective span

Clause No.21.4.1 : Arrangement of live load .

Clause No. 21.5 : Moment and shear co-efficient for continuous beams.

Clause No. 22.2 : Control of deflection.

Clause No. 22.3 : Slenderness limits for beams.

Clause No. 25.5.1.1 : Requirement of tensile reinforcement for beams .

Clause No. 25.5.1.2 :Compression reinforcement.

Clause No. 25.5.1.3 : Side face reinforcement.

Clause No.25.5.1.5 : Maximum spacing of shear reinforcement.

Clause No.25.5.1.6 : Minimum shear reinforcement.

Clause No.25.5.1.7 : Distribution of torsion reinforcement.

7.2.5 Provisions for columns;

Clause No.24.1.2 : Short and slender compression members .

Clause No.24.1.3 : Unsupported length .

Clause No.24.2 : Effective length of compression members.

Clause No.24.3 : Slenderness limits for columns .

Clause No.24.4 : Minimum eccentricity .

Clause No.25.5.3 : Longitudinal reinforcement.

Clause No. 25.5.3.2 : Transverse reinforcement.

Clause No.42.2 : Cracking Consideration .

7.2.6 Provisions for footings :

Clause No. 33.1.2 : Thickness at the edge of footing .

Clause No.33.4 : Transfer of load at the base of column .

Other references /Literature generally referred to are

(i) Reinforced Concrete Designer’s Hand Book by Reynolds & Steelman.

(ii) Limit State Theory & Design of Reinforced Concrete by Karve and shah .

(iii) Hand Book of Reinforced Concrete Design (I.S.:456-1978)by Karve .

(iv) Limit State Design of Reinforced Concrete by Vergis .

 

8. General practice followed in Design Circle :

(i) The loading to be considered for design of different parts pf the structure including wind loads shall be generally as per I.S. 875-1987 (Part I to IV) and I.S. 1893-1984 (seismic loads )with there latest amendments .

(ii) Live load for sanitary block shall be 200 kg/m2.

(iii) Lift machine room slab shall be designed for live load of 1000 kg/m2 .

(iv) Lift load shall be considered as per relevant I.S. codes as per capacity of lift and the same shall be increased by 100% for impact while designing .

(v) Loading due to electrical installation e.g. AC. ducting , exhaust fans etc.shall be got confirmed from the Executive Engineer, electrical wing of P.W. Department .

(vi) Seismic loads shall be as per I.S. 1883-1984 and I.S. 4326-1993. The method of analysis and values of various parameters shall be taken as per relevant provisions of codes .

(vii) Ductility provisions specified in I.S. 4326-1993 and I.S. 13920-1993 shall be adopted in design, if the value of (Alpha h) is greater than or is equal to 0.05.

(viii) Any other loads which may be required to be considered in the designs due to special type or nature of the structure shall be got approved in advance from the Superintending Engineer .

(ix) Deduction in dead loads for opening in walls need not be considered.

(x) Unless otherwise specified ,the weight of various materials shall be considered as given below .

(a) Brick masonry :1920kg/m3

(b) Reinforced cement concrete : 2500kg/m3

(c) Floor finish : 100kg/m3

(d) Brick Bat Coba of 112mm thickness

laid on terrace for water proofing treatment : 200kg/m2

(a) Brick Bat Coba in bath &W.C. depending on

thickness of water proofing treatment : 1920 kg/m3

(xi) The analysis shall be carried out separately for dead loads, live loads, seismic loads, wind loads . All the structural components shall be designed for the worst combination of the above loads as per relevant codal provisions.

(xii) In case of tall building, if required Model analysis shall be done for horizontal forces, as per I.S. : 1893 and I.S. 875 (Part III).

(xiii) Minimum reinforcement in all structural members shall be as per relevant clause I.S. 456-1978.

(xiv) The R.C.C. detailing in general shall be as per SP:34 .

(xv) High Yield Stress Deformed bars shall be used for main reinforcement .Mild Steel bars are used only as distribution steel .

(xvi) Diameter of bars in footings shall be not less than 10 mm .

(xvii) Spacing of stirrups in beams shall not exceed 30cm.

(xviii) Thickness of slab shall not be less than 10cm and in toilet blocks not less than 15cm.

(xix) Depth of beam shall not be less than 23cm .

(xx) Spacing of ties in columns shall not exceed 30cm.

(xxi) The longitudinal bars in columns shall not be less than 12mm in diameter .

9. Guidelines for Preparation of R.C.C. Layouts

9.1 The preparation of R.C.C. layouts involves fixing of locations of columns and beams, denoting slabs with respect to design live load, type of slab and numbering these structural elements .

9.2 There are two types of joints which need to be considered in the layouts .They are (a) Movements joints, (b) Expansion joints .

9.3 If the length of building exceeds 45m, expansion joints shall be provided to split into suitable parts which are individually less than 45m. in length Building having wings in different directions shall be provided with expansion joints at the connection of the wings to the central core to avoid torsional effects .Expansion joints may also be provided when there is a sudden change in plan dimensions. For details of the joints refer to I.S.3414-1968,I.S. 4326-1976 and I.S. 3370-1965 (Part-I) Discussion with Executive Engineer will be quite useful in fixing the proper location/s of expansion joint/s .

9.4 In case of the building is having different number of stories for different parts of the building, thus having different dynamic characteristics, then such parts shall be kept separated by a movement joint to avoid unequal loading, unequal settlement and collusion during an earthquake . Movement joints may also to be provided if the different parts of building are located on different stratas and of different safe bearing capacities .such movements joints, however shall be provided right to the bottom of the foundation, unlike the expansion joints which are provided only up to the top of the foundation .In this regard refer to S.P.34( explanatory Hand Book of I.S. 456-1978) Clause 26.1 and also refer Clause 5.1.1 of I.S. 4326-1993. As per this clause the minimum total gap between these joints shall be 25mm .

9.5 Separate R.C.C. layouts are to be prepared for different levels i.e. plinth, typical or at each floor level (if the plans are not identical at all floor levels ) terrace floor level, staircase block roof level and where applicable lift machine room roof level.

9.6 R.C.C. layouts are generally prepared on tracing paper from the architectural drawings, by tracing only the walls, columns and other structural members. In the layout, the door and window positions are not shown .

10. Guidline for fixing the Position and Orientation of Columns in the Layout

This is an important stage . It is skillful job and economy in design is achieved by locating columns at proper and / ideal locations.

(i) Normally the positions of the columns are shown by Architect in his plans .

(ii) Columns should generally and preferably be located at or near corners and intersection /junction of walls.

(iii) If the site restrictions make it obligatory to locate column footings within the property line the column may be shifted inside along a cross wall to accommodate footings within the property line . Alternatively trapezoidal footing, eccentric footing can also be adopted .In residential buildings, generally columns should be located at 3 to  4m.c/c to avoid large spans of beam .This will also control deflection and cracking .

(iv) While fixing the orientation columns care should be taken that it does not change architectural elevation. This can be achieved by keeping the column orientations and side restrictions as proposed in plans by the Architect .

(v) As far as possible, column projection/s outside the walls should be avoided, unless Architect’s plans show contrary or same is required as structural requirement.

(vi) Columns should not obstruct door and window position/s shown in the Architect’s plans.

(vii) As far as possible, column should be so positioned, that continuous frames from one end to the other end of building in both X and Y directions are available. This will increase the global stiffness of the building against horizontal forces .

(viii) When the locations of two columns are near to each other (for e.g. the corner of the building and intersection of the walls ) then as for as possible only one column should be provided .

(ix) As far as possible, column should not be closer than 2m.c/c to avoid stripped /combined /continuous footings. Generally the maximum distance between two column should not be more than 8m.c/c.

(x) Columns should be normally provided around staircases and lift wells.

(xi) Preferably overhead water tank should rest on the columns as shown in the Architect’s plan. The height of water tank should be up to 2.0m.

(xii) Twin columns of equal size are desirable at expansion joints from asthetic point of view .

(xiii) As far as possible every column must be connected (tied) in both directions with beams at each floor level, so as to avoid slender columns.

(xiv) As far as possible column supported on beem should be avoided.

(xv) When columns along with connecting beams from a frame, the columns should be so orientated that as far as possible the larger dimension of the column is perpendicular to the major axis of bending. By this arrangement column section and there reinforcement are utilised to the best structural advantage.

 

11. Guidelines for finalising the beam positions:

(i) Normally beams shall be provided below all the walls.

(ii) Beams shall be provided for supporting staircase fights at floor levels and at mid landing levels .

(iii) Beams should be positioned so to restrict the slab thickness, to 15 cm, satisfing the deflection criteria . To achieve this, secondary beams shall be provided where necessary .

(iv) Generally we come across with the situation that there is a gap between the floor level beam and beam supporting the chajja. Here the depth of floor beam shall be so chosen that it can suport chajja also. However if depth so required is large (distance between floor beam bottom and lintel top, greater than 30cm ) provide separate beam .

(v) If two slabs are at different levels, provisions of para roman four above shall be followed.

(vi) As far as possible, cantilever beams should not be projected from beams, to avoid torsion .

(vii) Beams of equal depths shall be provided on both side of the expansion joint from aesthetical point of view .

(viii) To get the required minimum head room, following alternatives can be tired .

(a) Reduce the beam depth without violating deflection criteria and maximum percentage of steel criteria for beams .

(b) In case there is a wall, over the beam without any opening, inverted beam may be provided in consultation with Architect.

(ix) Where secondary beam are proposed to reduce the slab thickness and to form a grid of beams, the secondary beams shall preferably be provided of lesser depth than the depth of supporting beams so that main reinforcement of secondary beams shall always pass above the main beams .

(x) In toilet block provide minimum number of secondary beams so that casting slabs and beam will be simple .’No secondary beam’ condition would be ideal .

(xi) Beams which are required to give a planer look from the underside shall be provided as Inverted Beams, e.g. canopies. Alternatively hidden beams inside the slab having the same depth as thickness of slab may be adopted .Such hidden beams can be provided in toilet blocks, under partition wall etc. where a cluster of beams can be avoided.

12. Guidelines for fixing the Slab Directions :

(I) Slab shall be designed as one way slab if ratio of Ly to Lx is more than 2 and two way slab, if the ratio is equal or less than 2.

Where Lx is shorter span and Ly is longer span of the slab.

(II) However as per Designs Circle practice slabs up to 2.5m spans may be designed as one way slabs .

(III) Canopy, Chajja, balcony slabs are generally provided as cantilever slabs.

(IV) W.C. slab is generally made sloping or sunk by about 50cm .below general floor level for Indian type water closet .Slabs for toilet block and Nahani slab are generally sunk by 20cm. below general floor level .

(V) Staircase waist slab shall be generally one way slab .

(VI) Loft slabs over toilets are generally supported on partition walls of toilet and W.C.Loft load should be considered while designing the beams supporting these walls .

13. Numbering System and notations to be adopted in Layouts:

13.1 Columns:

Columns are numbered serially with integer number suffixed to letter "C" i.e. C1,C2,C3 etc. The columns are numbered from lower most left corner of the R.C.C. layout. Numbering shall proceed from left to right in X direction and proceeding successively in positive Y direction .R.C.C. layout showing column numbering is kept at page 65.

13.2 Beams:

(i) Beam actually supported over a column is called main beam. Beam supported over other beam is called secondary beam.

(ii) A beam number is composed of two parts e.g. 5.1,5.2 etc. The part to the left of decimal point denotes the leftside reference column number. The part to the right represents serial number of the beam.

Beams in X direction here the reference column is left supporting column If left supporting column is is absent then right supporting column is considered as reference column . For X direction beam serial number (2nd part) is always odd e.g. 1,01,3,03 etc. Beams to the right side of reference column is numbered as 5.1 etc. while beams to the left of reference column is numbered 5.01, where the reference column is C5.

Beams in Y direction in this case reference column is bottom most column. If the bottom column is absent then the upper supporting column can be considered as the reference column. For Y direction beam serial number (2nd part )is always even number e.g. 5.2,5.02,5.4 etc. Beams in positive Y direction of reference column are numbered as 5.2 while beams in negative Y direction of the reference column are numbered as 5.02, where the reference column number is C5.

(iii) for numbering the secondary beams in"X" direction the first part of beam number shall be a reference column which shall be the nearest left side column of the beam . The second part shall be odd number except ‘I’ i.e. 3, 5 etc.serially in X direction e.g. 5.3,5.5 etc.

Similarly secondary beams in Y direction can be numbered e.g.5.4,5.6etc. except "2" .

(iv) If the beams are at intermediate level above the floor under consideration then the beam number will be suffixed with a letter like A,B & M. e.g. If 5.1 is main beam at 1st floor level, 5.1 A is beam in X direction at 1st floor lintel level, and 5.2 M is a beam in Y direction at MIDLANDING LEVEL between the 1st floor and 2nd floor levels. "A" refers to floor level and "B" refers to lintel level And "M" refers midlanding level.

(v) A.R.C.C.layout showing the beam numbering is kept as page 65.

13.3 Slabs :

13.3.1 The slab notation is composed of four parts .The first, second and third part are written on the left side of the decimal point and 4th is written on the right hand side of the decimal point e.g. 200SI.I, 500S2.2.

(i) The first part denotes the imposed live load intensity in kg/sqm . for which the particular slab is designed . This load is decided on basis of designated use of the particular space (the slab ) as shown in the Architect’s plans and as per provisions of I.S.875. This practice is useful and advantageous for maintaining a proper record especially when different slab panels are designed for different live loads. This record is also useful to avoid over loading of the slab in future change of usage .

(ii) The second part represents the type of the slab for e.g.

"S" denotes general floor slab,

"SF" denotes staircase flight slab,

"SR" denotes room roof level slab/ staircase room roof level slab

"SM" denotes machine room floor slab

"SC" denotes cantilever slab and

"ST" denotes terrace slab .

(iii) The third part is either "I"or"2", "I" denotes the slab is one way .The "2"denotes the slab is two way .

(iv) The forth part is the serial number of the slab is one way /two way category . Slabs having different end conditions shall be treated as different slabs for this notation .

(v) Slabs shall not be grouped on the basis of panel dimensions, loading pattern and end conditions.

(vi) The notation for one way slab , two way slab, 23cm . brick wall ,15cm thick brick wall, R.C.C. layout kept at page 65.

The dead load of various materials and live loads adopted for different slabs and the R.C.C.layouts shall be got approved from Superintending Engineer before starting preliminary Beam and Column Design (P.B.D.& P.C.D.)

14. Preparation of priliminary Beam Design (P.B.D.)

14.1 P.B.D.for each beam in the layout at all floors is prepared on the standard printed fromNo.3 (kept at page ) All beams of the same types having approximately equal span (+) or (-) 5% variation), magnitude of loading, support conditions and geometric property are grouped together . the heaviest beam of the group is considered for the design

In the preliminary beam design, value of reaction at both ends are worked out for all the loadings acting on the beam . All secondary beams may be treated as simply supported beams .

14.2 Begin with fixing the dimensions of beam.The width of beam under a wall is preferably kept equal to the width of that wall to avoid offsets i.e. if the wall is of 23cm. then provided beam width of 23cm.

14.3 Minimum width of main and secondary beam had shall 23cm.However secondary beams can be of 15cm. incase of beams of toilet block. The width of beam should also satisfy architectural considerations.

14.4 The span to depth ratio for beam be adopted as follows :

For building in seismic zone between 10 to12 and for non seismic zone 12 to 15 . The ratio "D/b" (depth divided by width ) of beam should not generally exceed 4 if it is a slender beam . The depth so calculated shall be as shown in the Architect’s plan.

14.5 To limit deflection, of a beam (up to 10m span ) within the permissible limit, under service load, the I.S. 456 clause 22.2.1 provides the following span to depth ratios.

(i) For cantilever not more than 7.

(ii) For simply supported beam not more than 20.

(iii) For continuous beam not more than 26.

These ratios can be further modified according to Modification Factor depending upon percentage steel used in section as per I.S. : 456 Clause 22.2.1(e) .

14.6 The beams shall be designed as deep beam /slender beam as the case may be .

14.7 The beam shall be treated as

(i) A rectangular beam if it does not support any slab on either side also if it is an inverted beam .

(ii) As Ell beam if it supports a slab on one side and

(iii) As Tee beam if it supports slab on both sides.

14.8 P.B.D. form is kept at page 66.

14.9.1 The beam and slabs carrying live loads more than 75% of dead load shall be designed or the following load combinations as per Clause 21.4.1 of I.S. 456-1978.

(i) Design dead load on all spans with full design live load on two adjacent spans.

(ii) Design dead load on all spans with full design live load on alternate spans.

14.9.2 When design live load does not exceed 75% of the Design Dead load, the loading arrangement may be, Design Dead load and Design live load, on all spans.

14.9.3 For beams and slabs continuous over supports ,Load Combinations given in 14.9.1 may be assumed.

14.9.4 Find out reactions and fixed end moments, at supports of a beam by using standard beam formulae .

14.9.5 Computer programme "SEDC.PCD" for doing P.B.D. is also now available. See para 20.1.

While using programme "SEDC" for frame analysis the Designer is not required to calculate the values of Stiffness to beam, Fixed End Moment at support and Simply Supported Bending Moment at the midspan . the Programme "SEDC" automatically calculates these values while analysing.

15. Preliminary column design and determination of Preliminary column design and determination of size of column section ( P.C.D.)

15.1 In P.C.D. of column section at particular floor, total load acting on the section is worked by adding .

(a) load from upper column section .

(b) The support reactions ( calculated in PBD )of all relevant X and Y direction beams connected to the column at particular floor level.

(c) Self weight of the particular column .

The P.C.D. of a column is to be started from the top of the most section and proceed to next lower section till you reach footing level

15.2 The dimension of a particular column section, is decided in the following way.

(i) A column shall have minimum section 23cm. X 23cm. if it is not an obligatory size column

(ii) The size of obligatory column/s shall be taken as shown on the architect’s plan. For non obligatory columns as far as possible the smaller dimension shall equal to wall thickness as to avoid any projection inside the room. The longer dimension should be chosen such that it is a multiple of 5cm. and ratio Pu/ fckbd is restricted to, for non-seismic area 0.4 (for corner columns it may be 0.35) and for seismic region 0.35( for corner columns it may be 0.30)

Where Pu, Fck, B, D, have the following meaning.

Pu is the factored load on the column .(in Newton)

Fck is characteristic compressive strength of concrete. (Newton/mm2)

b is the breadth of the column .(mm)

d is the depth of the column .(mm)

15.3 The above ratios will ultimately help in keeping requirements of steel for columns within 0.8 to 2.5% which is economical and will avoid congestion of steel Generally the concrete mix in R.C.C. work shall be of minimum M:15 grade. However for the structures in coastal area and highly polluted (Aggressive Atmosphere and/ or subsoil conditions ) areas the minimum mix shall not be less than be less than M20 grade .

15.4 If the size of column is obligatory or if size can not be increased to the desired size due to Architectural constraints and if the ratio of Pu / Fckbd works out to be more than the limit specified above it will be necessary to upgrade the mixof concrete. For ease of construction frequent changes in column size should be avoided As far as possible in multistoried building at least two floors should have the same column section. Preferably least number of column size should be adopted in the entire building. And mix of all the columns on a particular floor should be same. P.C.D. form is kept at page 67.

15.5 While using programme "SEDC.PCD" filling of PBD and PCD forms is not necessary .see para 20.1.

15.6 Effective length of column shall be calculated as per figure 24 and 25 of I.S. : 456:1978. (pp142)

15.7 Columns shall be designed for direct load and uniaxial or biaxial bending considering different for load, combinations as given in I.S.456:4978.

In addition, all columns shall be designed for minimum eccentricity equal to [(unsupported length of column /500)+(lateral dimension /30] subject to minimum eccentricity of 20mm.

15.8 Grouping of columns can be done on the basis of size, orientation and forces acting on it.

15.9 A computer Programme "SEDC.PCD" has now been developed to give P.B.D. and P.C.D. results directly, along with the data files for plane frame Analysis Programme "SEDC" for details refer Users Manual for "SEDC.PCD" Programme .The use of this new Programme will save lot of time and efforts. See para 20.1.

15.9.1 All R.C.C. layouts, tentative sizes of the beam, and column sections should be got approved from the Architect before starting analysis of frames.

16. Analysis for Building Frames

16.1.1 In Designs circle, at present, frame analysis is done by treating the building as composed of only plane frames .

A building may be required to be designed for Non Seismic/Seismic Forces and/ wind forces (whichever is governing ) depending on the location, plan dimensions and height of the building .

16.1.2 For buildings located in seismic zone I and II, only (Dead Load +Live Load ) Analysis is sufficient and seismic analysis is not required to be carried out .

Building up to Ground +2 floors in Seismic Zone I and II are generally designed by following the provisions of Design Circle’s Technical Note 7502.

However for building having G+3 stories and above located in Seismic Zone III and IV the seismic analysis of the building frames is required to carried out . The magnitude of seismic nodal horizontal forces are worked out .

Before started the analysis of frames the forces for which the building is to be designed and the design parameters and particularly Importance Factor (I) and (Beta) for soil foundation system for Seismic Design to be adopted should be got approved from Superintending Engineer .

16.2 SEISMIC ANALYSIS

16.2.1 For calculating seismic forces refer provisions of I.S.: 1893-1994 .

16.2.2 It should be noted that provisions of I.S : 1893-1994 do not apply for .

(i) Buildings constructed in steps, in hilly area.

(ii) Plaza type buildings, where there is sudden change in stiffness (highrise building with the side flanks ).

(iii) Building with flexible first storey including buildings like assembly halls and cinema theatres where the central auditorium (in one storey) covers up to three stories of the side flank as per provisions of I.S. 1993 clause 4.2.1.1

16.2.2.2 In general in all seismic zones the buildings having height upto40m, can be designed for seismic forces by static Approach. For building greater than 40m and up to 90m height, Model Analysis is recommended. However the static approach may also be used for design of structures in zone I to III.

For building greater in height than 40m, checking for dirft and torsion is necessary .

For building taller than 90m in zone I and II, detailed Dynamic Analysis shall be made based on expected ground motion and model analysis.

At present most of the buildings we come across, use of static approach is adequate .

However for important buildings where it is felt necessary to carry out Dynamic Analysis, The Superintending Engineer may advice to carry out the Response Spectrum Method or Model analysis.

16.2.3 STATIC APPROACH FOR SEISMIC ANALYSIS

16.2.3.1 In this approach the structure is treated as a discrete system, having concentrated masses at the different floor levels which compose of mass that of columns and walls of half the floor above and half of the floor below.

16.2.3.2 Using details from P.C.D. the base shear can be worked out as follows.

(i) Find the total load i.e. (Dead load+ Live load ) on each floor by summing up loads of all columns at that floor level……………(1)

(ii) Find the Total live load acting on every floor ……………(2)

Total live load =Live load intensity X Area on which this live load intensity acts,

In case of areas having different live load intensities, work out separately for each case and sum up to get total live load.

(iii) Total Dead load at each floor = (1) - (2) ……………(3)

(iv) Find out Total Appropriate Live Load to be taken for working out horizontal seismic force as per clause 4.1 and 4.1.2 of I.S. : 1893. ……………(4)

(v) For calculating the earthquake forces on terrace (roofs) the live load may be not be considered.

(vi) Total weight of building to be taken for Seismic Design W=(3)+ (4)

(vii) From the seismic map of India find the Zone of the location of a building. Using the ‘Importance factor ‘ (I.S.: 1893-table 4) and soil foundation system factor (beta) (as per I.S. : 1893- table 3) given the "Field Data" using value of Alpha (Zero) for the zone (as per I.S: 1893 - table 2)calculate seismic coefficient (Alpha h ) for the building .

(Alpha h) = (Alpha zero) x (I) x (Beta)

(viii) Calculate base shear (Vb), using formulas given in I.S. 1893 clause 4.2.1.1, using value of C as given in Graph (Fig.3) and note 1&2 of the said clause.

(Vb) = C x(Alpha h) x W .

(ix) Distribute the base shear between all floors of building as per clause 4.2.1.2 of I.S: 1893 . these are floor lateral share forces for frame analysis .

The computer programme "SEDC.PCD" referred earlier, also works out the seismic load calculations .

16.2.4 The frame analysis for seismic forces by the "Static Approach" is done in programme "SEDC" in 3 phases.

16.2.5 Seismic Analysis is carried out based on the following assumptions

(i) The Seismic forces acts, at a time along one direction only, i.e. when seismic force along with dead and live load forces are acting on a frame along X direction then on Y direction, only dead and live load forces are acting and vice versa. Also, earthquake is not likely to occur simultaneously with wind .

(ii) The nature of seismic force action if reversible in direction (i.e. + and - forces can act on the frame .)

(iii) Horizontal deflection of all joints of a frame, at particular floor level is same .

(iv) The individual frame shares the storey shear in proportion to its stiffness.

(v) The inverse of deflection of a frame is treated as a measure of its stiffness.

16.2.6 A judicious choice of beam sections ( as explained in para 13.2)and column sections ( as explained in para 14.2) will ensure deflection of the frames within permissible limits.

16.2.7 In the first phase of Analysis, Programme "SEDC" gives only Dead local and Live Load Results.

16.2.8 To find the deflection of each frame apply value of Total storey shear (i.e. 100% of the horizontal force calculated for entire building ) at the appropriate nodes and run programme ‘SEDC’ for 2nd phase of Analysis which gives the displacement at a particular level for all the X and Y direction frames .

Generally the deflection in a fame at terrace level, is maximum .

As stated earlier the total base shear is shared in all X/Y frames of the buildings in inverse proportion of their deflections. The inverse of deflection for each frame is calculated .Then using these values, ratio of (inverse of deflection of a particular frame (X/Y) Direction /sum of inverse of Deflection of frames) is worked out in percentage for each and every frame .

16.2.9 In the third phase of "SEDC" the percentage value of total base shear being acting on a particular frame is used as input (horizontal forces acting on the frame at appropriate floor levels ) and detailed frame analysis printout is obtained.

16.3 WIND ANALYSIS:

As per I.S. 875:1987(Part-III) wind analysis is generally not necessary except for Tall Buildings and Chimneys .Para 7.1 of the code stipulates that "flexible slender structure and structural elements shall be investigated to ascertain the importance of wind induced oscillations or excitations along and across the direction of wind.

In general the following guide lines may be used for examining the problem of wind introduced oscillations.

(a) Building and closed structures with height to minimum lateral dimension ratio more than 5.and

(b) Buildings and closed structures whose natural frequency in the first mode is less than 1 Hz.

Any structure or building which does not satisfy either of the two criteria shall be examined for dynamic effects of wind .for this modal analysis (on similar lines of modal seismic analysis ) will be carried out .If the wind introduced oscillations are significant, analytical methods like use of wind tunnel modeling will have be carried out.

16.3.1 wind analysis for structure which are not required to be examined by dynamic analysis, is carried out by static approach and based on the following assumptions.

(i) the wind force act at a time only along one direction, i.e. when dead load ,live load and wind forces are assumed to act on a frame along X direction then on Y direction only Dead and live load forces are acting and vice versa .

(ii) Horizontal deflection of all joints of frame at particular floor level, is same .

(iii) The individual frames share the storey horizontal force in proportion to it’s stiffness.

16.3.2 Analysis for wind forces by static approach is done in the same manner as described for Seismic Analysis above but here the horizontal wind forces acting at each floor level shall be calculated as per provisions of I.S: 875(Part-3)-1987

16.3.3 The wind analysis is carried out on the similar assumptions of Seismic Analysis as stated in 16.2.5 above .

16.3.4 The designer should be note that Seismic and wind forces can act in either direction i.e. they are reversible forces. The overall effect is that these forces induce moments at supports both at top and bottom .

17 Preparation of frame sketches, filling coding sheets and creating data files

17.1 The data of frames shall be written on the frame sketches .Following steps shall be considered in preparing the frame sketch.

Name all the frames of the layout starting with X direction frames i/e. X1, X2, etc. from left to right and then Y direction frames i.e. Y1, Y2, etc. from bottom to top in R.C.C. layout .

(i) Draw frame sketch indicating the number of stories (including the vertical expansion proposed for design).and number of columns forming the particular frame .

(ii) Write the relevant column and beam numbers involved in the frame.

(iii) Dimension the storey heights (including plinth to footing level ) and spans of beams.

(iv) Draw a sketches of column as per orientation as applicable to the frame, just bellow the footing level joint.

(v) Show the type of joint at foundation assumed for analysis (i.e. fixed or hinged at bottom ).

(vi) Show all the loads coming on the beams and nodal vertical and horizontal forces.

(vii) Number the joints. Start from lower left most joint and proceed left to right and then bottom to top giving joint number serially.

(viii) Number the members. .Start with beams first and then number columns. For beam member number start from lower left most beam and proceed left to right and then bottom to top numbering serially. For column number give immediate next number of the last beam member from the left most bottom column section. Proceed serially bottom to top and then left to right .

(ix) Group beams and columns according to span and loading. Indicate for each member, the group number to which belongs.

As the Analysis programme "SEDC" caters only for cyclic frame, all the frames shall be treated as cyclic i.e. every floor must have the same number of bays .The bay width should be same on every floor. If particular frame is non-cyclic then it shall be converted to cyclic frame by insertion of additional imaginary (dummy) members having sizes 1 cm. X1 cm. Form of "Frame sketch" is kept at page68.

17.2 With the help of frame sketch, data of all frames shall be written on coding sheets in the manner & format, required by frame analysis Programme ‘SEDC’ . The data on coding sheets is then stored on a floppy disk as data files

17.3 Filling of coding sheets is necessary only when PBD and PCD have been done manually. With Programme "SEDC.PCD" it is not more necessary to prepare frame sketches and filling coding sheets, as it automatically creates required data files for executing Programme "SEDC" .

17.4 Designer is advised to study the Users Manuals of "SEDC.PCD" and "SEDC".

(Vol.I and II)

18. Analysis of Plane Frame using Computer Program "SEDC":

18.1 Checking of Input Data

Before execution of programme in the computer it is very essential to check the input data thoroughly so as to avoid any errors to design, wastage of computer time and stationery . Always bear in mind "Garbage In, Garbage Out"., in case of Computer Aided Analysis .

18.2 Guidelines for checking the Data file:

(i) Check whether the format of the particular data is correct or otherwise .The programme will not get executed if there is format error .

(ii) Check each and every data, particularly data regarding frame geometry (number of byes, number of joints ) member properties (breadth, depth, mix ) and loading details. Any error in this data will execute the programme fully, however output will give misleading results.

(iii) Data given in line No .4 onwards should be compatible with the data given in line No 3 .Any non compatibility will abort the execution of programme.

18.3 Running of the Frame Analysis program "SEDC":

The programme "SEDC" uses Stiffness Matrix method of Analysis.

18.3.1 This programme can be run only after installing FRS.

18.3.2 Programme "SEDC" is designed to give results for various load combinations with the appropriate load factors as per I.S: 456-1978(when so specified in input data of frame) namely

(1) 1.5 [Dead Load + Live Load ] for non seismic analysis.

(2) 1.2 [Dead Load + Live Load + Seismic Load] for Seismic analysis

(3) 1.2 [Dead Load + Live Load + Wind Load] for wind analysis

The designer has to decide which of these load combinations are required and accordingly give the details of horizontal loads.

18.3.3 For executing the programme the Input file shall be stored in file named FRAME1.DAT. The output is given in file named FRAME2.DAT.

18.3.4 Programme output gives values of axial force, moment and deflections for each member and R.C.C. Design of beams (i.e. values of area of reinforcement, required at supports, quarter span and center of span and details of shear reinforcement ).

18.4 Output results from Computer

The results obtained by running programme "SEDC.EXE" should be thoroughly checked before accepting the same in the final design .

(A) The checking of input data is already discussed .

(B) Checking of displacements.

(i) Displacement of joint are printed in meters. For fixed end of a frame the value of displacement must be zero.

 

(ii) At hinged end of a frame horizontal and vertical displacement must be zero.

 

(iii) The maximum horizontal displacement due to earthquake forces between successive floors shall not exceed 0.004 times the difference in level between these floors .

 

(iv) Displacement of all joints on a particular floor should be equal.

 

(v) While checking of forces, at every joint following 3 equilibrium equation must be satisfied .

(a) Sum of all vertical forces must be zero .

(b) Sum of all horizontal forces must be zero.

(c) Sum of all moments at the joint must be zero.

Designer should personally check these points and check some joints for his own satisfaction.

19 Design of various R.C.C. elements of Building

After the analysis is over, the designer will undertake the detailed design of various members of the building in the following order of actual construction, to be in tune with construction programme decided by the field Engineers.

(i) Design of piles caps/ open footings (depending on the site and foundation conditions).

(ii) Design of columns.

(iii) Design of beams. (Plinth Level to Terrace Level ).

(iv) Design of slabs. (Plinth Level to Terrace Level ).

(v) Design of water tank/s.

19.1 Design of Pile and Pile Cap

Piles are required to be provided where the strata of adequate bearing capacity is not available at reasonable depth, and site conditions dicate that open foundation is not feasible and economical. This is generally the case in black cotton soils and reclaimed areas.

For very low bearing capacity strata, and where pile foundation is not economical, we may adopt raft foundation. For codal provisions refer I.S.:2911.

It is good design practice to provide minimum two piles or 3 piles in triangular pattern and generally not more than 4 piles (in square pattern ) be provided under a column .

For piles, where the subsoil water is polluted and presence of sulfides and/ chlorides is more than the safe limits, sacrificial cover shall have to be provided. However, the same shall be neglected while working out the area of concrete required to sustain the load on pile . The diameter of pile and pattern of pile cap for twin or triple pile group shall be so chosen that the adjoining pile caps do not get overlapped and there is at least minimum distance between the two adjacent pile caps as stipulated in the code. The mix of the concrete for casting of pile shall be always stipulated as M-20 however, for design purpose it shall be always treated as M-15 only .

19.2 Design of open Footings

19.3 Isolated footings:

(i) write down the different load combination values for the section "plinth to footing" of the column footing in question from the relevant X and Y direction Frame Analysis output.

(ii) The working load for each load combination is then worked out by dividing each load by the appropriate load factor of the particular load combination .

(iii) The maximum value of all these working loads is taken as design working load. on footing .

(iv) The isolated footings are designed manually by using the design process as explained in HANDBOOK FOR R.C. MEMBERS (Vol.II pages 359 to 380).

(v) Normally trapezoidal footing is provided except where the site conditions demand otherwise.

(vi) Designer shall check that with the designed dimensions, the isolated footings are not getting overlapped, If they are getting overlapped, suitable combined footings shall be designed .

19.3.1 Combined footings :

These are provided

(1) at the expansion joint locations and

(2) when it is noticed thats designed as isolated footings, the footings are getting over lapped or encroaching on adjoining property. The design working load for combined footing shall be sum of design working loads of columns constituting the combined footing. For manual analysis and design of combined footing, refer any standard text book.

19.3.2 Special types of footings :

For design of pedestal or any other special type of footing like strip footing etc. refer standard text books.

19.3.3 Design Checks for all types of footings :

The design shall be checked for following,

(1) Check single shear, double shear.

(2) Check for negative moment( if active) .

(3) Check for bearing pressure on top of footing.

19.4 DESIGN OF COLUMN SECTION:

19.4.4 A column is subjected to direct load and moment across its axes .Find out design loads and design moments across appropriate axes from the output of relevant X direction Y direction frame analysis, for the design section under consideration .

The data for column design by Limit State Method shall be as per following combinations.

-------------------------------------------------------------------------------------------------

Design Load Load Moment Moment

Case on XX on YY on XX on YY

-------------------------------------------------------------------------------------------------

Non 1.5(D+L) 1.5(D+L) 1.5(D+L) 1.5(D+L)

Seismic

-------------------------------------------------------------------------------------------------

1.5(D+L) 1.5(D+L) 1.5(D+L) 1.5(D+L)

S -------------------------------------------------------------------------------------

E 1.2(D+L+E) 1.2(D+L) 1.2(D+L+E) 1.2(D+L)

I -------------------------------------------------------------------------------------

S 1.2(D+L) 1.2(D+L+E) 1.2 (D+L) 1.2(D+L+E)

M ------------------------------------------------------------------------------------

I 1.2(D+L-E) 1.2(D+L) 1.2(D+L-E) 1.2(D+L) C -------------------------------------------------------------------------------------

1.2(D+L) 1.2(D+L-E) 1.2 (D+L) 1.2(D+L-E)

---------------------------------------------------------------------------------------------------

Similar combinations will be applicable in case of wind analysis i.e. replacing Seismic forces by wind forces.

The columns shall be designed as uniaxial or biaxial depending upon whether the moments are acting across one or both axes of column and their relative magnitudes.

Effective length of column member shall be worked out considering end conditions and used in the calculations .

The column design is done manually as per "HANDBOOK FOR DESIGN R.C. MEMBERS" (Limit State Method) Vol. II as explained in pages 20 to 33 for uniaxial columns and for biaxial columns pages 322 to 337 and for circular columns page 342. Computer programme "ASP2" is also available.

The design section and the reinforcement shall satisfy all the combinations stated above.

19.4.5 Approach for Economic Design of Column

19.3.2.21 In the design of column, two factors are to be keenly watched namely pu/ fckbd and interaction factor .

The pu/ fckbd factor is a measure of compressive force in column and by keeping the value of this factor is equal to or less than 0.4, it is seen that the concrete section provided is utilised to the maximum extent .

The interaction factor is a measure of degree of utilisation of stell reinforcement provided in the column section .The value of this factor (calculated as per clause 38.6 & 38.7 of I.S.456 ) as close to 1.00 ensures that the external loads and moments are resisted optimally by the proposed concrete section along with the (proposed ) steel reinforcement pattern .

19.3.2.1 Always begin by designing the top most section of a column and then proceeding successively to the lower section .

19.3.2.2 Begin the design by choosing "One bar at each corner " i.e. 4 bar pattern (giving total area of reinforcement required on the basis of minimum steel criteria ) and if this first approximation is not safe then modify the diameter of bars and / or reinforcement pattern till you get the interaction Ratio as close to 1.0

As far as possible, for the next lower story column section , continue the same bar diameters and reinforcement pattern.

19.3.3 Choosing proper reinforcement pattern

While deciding the pattern it should bourn in mind that when the C.G. of the steel provided is away from the N.A., it gives higher moment of resistance . to the section

19.3.3.1 If the first approximation of steel reinforcement proves inadequate , try to increase the diameter and /number of bars .It shall ensured that the pattern selected , the bigger diameter bars are always placed near the corner /faces away from axis of bending . Each successive trial shall be taken by gradually changing reinforcement , and the final trail should provide just adequate steel reinforcement . The reinforcement pattern should fulfill the minimum spacing criteria . The reinforcement bars are required to be laterally tied by providing links of proper shape .

19.3.3.2 While choosing the reinforcement pattern provide adequate number of bars so that it satisfies spacing criteria as per I.S. 456.

19.3.3.3 A sketch giving the suitable link arrangements for column reinforcement which will create least congestion and aid easy flow of concrete in steel cage is kept at page number for guidance.

19.3.3.4 The number of reinforcement bars shall be so chosen that for uniaxial column, equal area of steel on opposite faces is provided and for biaxial column , equal area of steel on opposite faces is provided .

19.3.3.5 For requirements of ductility detailing refer para 22.(page 31)

 19.4 Design of Beams

(I) The Computer output of programme "SEDC" gives the area of required steel at supports, at quarter span (from each end ) and at centre of span .The Designer has only to choose the diameter and numbers of top and bottom bars such that actual steel area is just over the design value and there is no congestion of steel .

Non congestion can be ensured by keeping horizontal distance between the bars as the greatest of the following ,

(a) The diameter of bar (in mm) if the diameters are Equal.

(b) The maximum diameter (in mm) of bar if the diameters are Unequal.

(c) 5 mm more than the nominal maximum size of coarse aggregate.

For ensuring better compaction of concrete with needle vibrator , it is desirable that this minimum clear distance be 50 mm .

(ii) The anchor bars (at top and bottom) shall be minimum 2 Nos. of 12 mm diameter.

(i) Where it is not possible to accommodate all the bars in one layer , provide them in layers .The vertical distance between these layers shall not be less than the greatest of following :

(a) 15mm.

(b) 2/3 of the nominal maximum size (in mm) of coarse aggregate.

(c) Nominal size of bars (in mm).

(ii) as per Design Circle’s practice bars at the bottom of beam are taken straight without bending .

(iii) when there are collinear beams over a support the extra steel over the support (at top and/ bottom as the case may be ) shall be maximum required for the either of the two .

For collinear beams the extra steel over support shall be continued in the adjoining span for a length equal to anchorage length or 25% of the adjoining span whichever is more .

For non collinear beams the extra steel over support shall be anchored

in supporting column for full anchorage length .

(iv) The stirrups of shear reinforcement shall be provided with appropriate diameter of mild steel or H.Y.S.D. bars so that there is no congestion of reinforcement in beam and it shall be seen than the ductility criteria where applicable is also fulfilled . The philosophy of ductility its explained in para 22.

19.4.1 For requirements of ductility detailing refer para 22.(page 31)

19.5 Design of Slabs

(i) The slabs may be one way or two way depending on the panel dimensions .The design moment coefficients of a particular slab shall be taken in accordance with its boundary conditions.

(ii) Design of slabs is done manually by referring to "Hand Book for R.C.C." Members (Limit State Method ) Vol. I pages 161 To 173 for one Way slabs and pages 196 to 203 for two way slabs .

(iii) As per Design Circle’s practice minimum diameter of bars for slabs shall be 8 mm.

(iv) In case of future vertical expansion , the R.C.C. layout of the top floor shall be as per Architect’s plan. However the slab reinforcement shall be maximum of that required for future floor or present terrace .

19.6 Design of overhead water tanks

The design of water tank is carried out as per procedure given in the "Reinforced Concrete Designer’s Hand Book " by Reynolds, and conforming to I.S.3370.

 

20 Computer aided design using inhouse developed software

With the availability of high speed and large memory capacity desk top computers in Designs Circle, much of the analysis is now carried out on these computers .

Following is the list of computer programmes available in Designs Circle with User’s Manual.

20.1 "SEDC.PCD": This programme is an aid for plane frame Analysis programme "SEDC"

Using data of beam loading and geometry etc. the "SEDC .PCD" works out P.B.D. and P.C.D. On going through the P.C.D. results the designer should finalise the column sizes and rerun the programme to get final output . The programme will create the data files of all the frames ready for use with SEDC for further analysis

20.2 "SEDC" This programme carries out analysis of the plane frame with/without horizontal nodal forces , using Stiffness Matrix Method. The output gives the design of beams based on Limit State Method and for column member forces for various load combinations( with appropriate load factors).

20.3 "FOOT" : This programme design isolated footing as per limit state method of design .Column Size , concrete mix , safe bearing capacity of the founding strata and working load on the column are the basic inputs. All the checks as per code are included in the programme .

20.4 "EC FOOT": This programme designs combined footing along the expansion joint Column details along with their orientation expansion joint details etc. are basic inputs . All the checks as per code are included .

20.5 "SLAB" : This programme designs one way and two way slabs as per "Limit State Method "design. The basic data is concrete mix , span/s , clever cover to reinforcement bars, slab loading . and end conditions.

20.6 "ASP2" The basic input required to run this programme are section dimensions , unsupported length and effective length in both X and Y direction ,reinforcement pattern and different load combinations .

The main limitation of this programme is that it is workable only with rectangular column section .

The programme designs from given column section, reinforcement pattern and load combination and checks the adequacy of section .For this programme the X axis is always assumed to be along the smaller dimension of column . The programme output gives the results for the chosen column section and reinforcement pattern the values of [pu/(fck x b xd)] and Interaction Factor Values for each load combination case under consideration .

21 Earthquake resistant design guidelines as per I.S. 4326

21.1 The Seismic Design philosophy is to be accept damage to a building during a earthquake . Hence the I.S1893 code specifies design seismic force for a building , only a fraction of the seismic force that it will experience if it were remain Linear elastic during serve ground motions. Thus the structure in serve seismic zones should be necessarily ductile.

21.2 Meaning there by the member of reinforced concrete shall be under shall be under reinforced so as to cause tension failure. Also it should be so designed that the parameter failure due to shear or bond may not occur subjected to the provisions of I.S. 456-1978. Ductile failure will be enable structure to absorb energy during earthquake to avoid sudden collapse of structure .

21.3 I.S. 4326-1993 deals with earthquake resistant design and construction of design .some important clause are as under.

Clause 4.4 Building Configuration

4.4.0 In order to minimize torsion and stress concentration, provisions given in 4.4.1 to 4.4.3 should be complied with as relevant.

4.4.1 The building should have a simple rectangular plan and by symmetrical both with respect with mass and rigidity so that the centers of mass and rigidity of the building coincide with each other in which case no separation sections other than expansion joints are necessary . For provision of expansion joints reference may be made to I.S. 3414 -1968.

4.4.2 If symmetry of the structure is not possible in plan , elevation or mass , provision shall be made for torsional and other effects due to earthquake forces in the structural design or the parts of different rigidities may be separated through crumple sections . The length of such building between separation sections shall not preferably exceed three times the width .

4.4.3 Buildings having plans with shapes, like L, T, E. and Y shall preferably separated in to rectangular parts of providing separation sections` at appropriate places.

Note 1.The building with small lengths of projections forming L,T,E or Y shapes need not be provided with separation section . In such cases the length of the projection may not exceed 15 to 20 percent of the total dimension of the building in the direction of the projection .

Note 2. For building with minor asymmetry in plan and elevation, separation sections may be omitted.

Clause 4.5 Strength in various Directions

The structure shall be designed to have adequate strength against earthquake effect along both the horizontal axes . The design shall also be safe considering the reversible nature of earthquake forces.

Clause 4.6 Foundations

The structure shall not be founded on such loose soils which will subside or liquefy during an earthquake , resulting in large differential settlements.

Clause 4.7 Ductility

The main structural elements and their connection shall be designed to have a ductile failure. This will enable the structure to absorb energy during earthquakes to avoid sudden collapse of the structure .providing reinforcing steel in masonry at critical sections, as provided in this standard will not only increase strength and stability but also ductility . The important sketches from I.S. 13920-1993 are kept at page 74 to 75 .

Clause 5 Special Construction Features

Clause 5.1 Separation of Adjoining Structures

5.1.1 Separation of adjoining structures or parts of the same structures is required for the structures having different total heights or story heights and different dynamic characteristics. This is to avoid collision during an earthquake . Minimum total gap shall be 25 mm.

Clause 5.2 Separation or Crumple Section

5.2.1 In case of farmed construction, members shall be duplicated on either side of the separation or crumple section as an alternative ,in certain cases, such duplication may not be provided , if the portions on either side can act as cantilevers to take the weight of the building and other relevant loads .

22. Ductile Detailing as per 13920: 1993.

I.S. 4326 , The code of practice for earthquake resistant design and construction of building, while commenting on certain special features for the design and construction of earthquake resistant buildings, included some details for achieving ductility in reinforced concrete buildings.

The I.S. : 13920 has taken note of latest developments, experiences gained from the performance of structures which were designed and detailed as per I.S. 4326, during the recent earthquakes . It covers provisions for earthquake resistant design and detailing of reinforced concrete structures in particular .(as such it includes provisions of I.S. 4326also) Now all ductility detailing shall comply I.S. :13920.

Some important clause of this code are as follows

CLAUSE1.1.1

Provisions of this code shall be adopted in all reinforced concrete Structures which satisfy one of the following 4 conditions .

(i) The structure is located in seismic zone IV or V.

(ii) The structure is located in Seismic Zone III and has importance factor (I) greater than 1.0.

(iii) The structure is located in Seismic Zone III and is an industrial structure.

(iv) The structure is located in Seismic Zone III and is more than 5 storeys.

Clause 3.4 :

Hoop- It is closed stirrup having a 135 degree hook with 10 diameter extension (but not less than 75 mm ) at each end that is embedded in the confined core of the section .

Clause 5.2 :

For all buildings which are more than 3 storeys in height the minimum grade of concrete shall be M20.

Clause 5.3 :

Steel reinforcement of grade Fe 415 or less only shall be used .

Clause 6

For flexural members

6.1.1 The factored axial stress on the member under earthquake loading shall not exceed 0.1 fck.

6.1.2 The member shall have a width to depth ratio of more than 0.3

6.1.3 Width of flexural member not less than 200mm.

6.1.4 Depth if member not less than 0.25 of the clear span .

Clause 6.2 Longitudinal reinforcement :

6.2.1

(a) At least two bars at top and two bars at bottom shall be provided through out the member length .

(b) The tension steel ratio on any fact at any section shall not be less than

Rho (min)= 0.24 [(square root of fck)/fy] .

6.2.2 The maximum steel ratio on any face at any section shall be not exceed Rho(max) = 0.025.

6.2.3 The positive steel at joint face must be at least equal to half the negative steel at that face.

6.2.4 The steel provided at each of the top and bottom face of the member at any section along its length shall be at least equal to one fourth of the maximum negative moment steel provided at the face of either joint .

6.2.5 In an external joint both the top and bottom bars of the beam shall be provided with anchorage length beyond the inner face of column equal to development length in tension plus 10 times the bar diameter minus the allowance for 90 degree bends (s) In an internal joint, both face bars of the beam shall be taken continuously through the column.

6.2.6 The longitudinal bars shall be spliced, only if hoops are provided over the entire splice length at a spacing not exceeding 150 mm.The lap length shall not be less than the bar development length in tension.

Lap splices shall not be provided

(a) Within joint.

(b) Within a distance of 2 d from joint face and

(c) Within a quarter length of member where flexural yielding may generally occur under the effect of earthquake forces . Not more than 50 percent of bars shall be spliced at one section .

6.3.5 The spacing of hoops over a length of 2 d at either end of a beam shall not exceed.

(a) d/4.

and

(b) 8x dia of smallest bar ,But not less than 100 mm.

The first hoop shall be at a distance not exceeding 50 mm from the joint face. Vertical hoops at the same spacing as above shall also be provided over a length equal to 2 d on either side of a section where flexural yielding may occur under the effect of seismic forces . Elsewhere the beam shall have vertical hoops at a spacing not exceeding d/2.

Clause 7 Columns subjected to bending and axial load.

7.1.1 These requirement apply to columns which have factored axial force in excess of (0.1 fck) under the effect of earthquake forces.

7.1.2 The minimum dimension of column shall be 200 mm . However where in frames where beams have c/c span exceeding 5m, or column having unsupported length exceeds 4m the shortest dimension shall not be less than 300 mm.

7.1.3 The ratio of shortest dimension to the perpendicular dimension shall be preferably NOT less than 0.4.

Clause 7.2 Longitudinal Reinforcement

7.2.1 Lap splices shall be provided only in the central half of the member length.Itshould be proportioned as a tension splice .Hoops hall be provided over entire the splice length at spacing not exceeding 150 mm center to center .

Not more than 50 percent of bars shall be spliced at one section.

7.2.2 Any area of column that extends more than 100 mm beyond the confined core due to Architectural requirements shall be detailed in the matter .

In case of the contribution of the area to strength has been considered then it will have the minimum longitudinal and transverse reinforcement asper this code .

However if this area has been treated as non structural the minimum reinforcement shall be governed by I.S. 456 provisions .

Clause 7.3 Transverse Reinforcement

7.3.2 The spacing of rectangular hoops shall not be more than 300 mm c/c .If the length of any side of stirrup , exceeds 300 mm a cross tie shall be provided or a pair of overlapping hoops may be provided .

Clause 7.4 Special Confining Reinforcement

7.4.1 This shall be provided over a length of (lo) from each joint face towards mid span on either side of any section lo shall not be less than

(a) larger lateral dimension of the member .

(b) 1/6 of clear span of member and

(c) 450 mm.

7.4.2 When a column terminates in to a footing or mat special confining reinforcement shall extended at least 300 mm in to the footing or mat.

7.4.3 The spacing of hoops used as a special confining reinforcement shall not exceed ¼ of minimum member dimension but need not be less than 75 mm nor more than 100 mm.

7.4.4 The minimum area of cross section of bar forming circular hoops or spiral to be used as special confining reinforcement shall not be less than

Ash = .09 S Dk (fck/fy) [(Ag/Ak) -1.0]

Where

Ash = area of the bar cross section .

S = Pitch of spiral or spacing of hoops.

Dk = diameter of core measured to the outside of spiral or hoop .

Fck = characteristic compressive strength of concrete cube .

Fy = yield stress of (spiral/ hoop ) steel

Ag = gross area of column cross section .

Ak = area of concrete core should not exceed 300mm (see figure 7)

7.4.8 The area of cross section Ash of the bar forming rectangular hoop to be used as special confining reinforcement shall not be less than

Ash = 0.18 S.h. (fck/fy) [(Ag/Ak) -1.0]

Where

H = longer dimension of rectangular hoop.

Ak = Area of concrete core in the rectangular hoop measured to its outside dimensions.

Clause 8 Joints of frames

8.1 The special confining reinforcement as required at the end of column shall be provided through the joint is confined as specified by 8.2

8.2 A joint which has beams framing in to all vertical faces of it and where each beam which is at least ¾ of the column width, may be provided with half the special confining reinforcement required at the end of column . The specing of hoops shall not exceed 150 mm.

Important sketches from I.S. : 13920 are kept at page 76 to 79.

 

 

23. Copy of G.R. Dated 03.11.80

Preparation of R.C.C. design For building works, plans & estimate for Bridge .

Public Works and Housing Department,

Mantralaya, Bombay 400 032.

Govt. circular No BDG -1080/80838(394) /Desk-2 3rd November, 1980

Read : Government Circular No. B &C Department .

(i) No. BDG-1864/22208/N(I) ,dated 12.11.1964.

(ii) No. BDG-3869/5340/K dated 13.07.1970.

1. Instructions about the preparation of R.C.C. Designs for building works have been issued vide Government references cited above. Similarly , in respect of bridge works, so far, it was a practice that the Design Circle used to prepare detailed plans and estimates, only for major bridges where linear waterway exceeds 100’ (i.e.30M). Since then there has been substantial increase in the construction activities and eventual increases in the work load of Design Circle.

2. The question of relieving the Design Circle from some of its routine work load, was under consideration of Government of some time past. In order to enable the Designs Circle to devote more time and energy for preparing sophisticated type of designs in case of more complicated structures and to give guidance to the field officers on planning and monitoring technique of PERT /CPM for works of large magnitude Government is now pleased to issue the following orders.

(A) Preparation of Bridge Projects:-

(i) Bridge up to 30 m linear waterway shall be designed and estimated by the concerned Road Project Division.

(ii) (a) Only preliminary design indicating the waterway the type of foundation, the span arrangement and brief project report will be prepared by the Design Circle for bridge between 30m to 60 m linear waterway.

(b) Detailed plans and estimates for the above bridges shall be done by the concerned Road Project Division .

(i) The Design Circle will henceforth prepare detailed plans and estimates only for bridges where linear waterway exceeds 60m.

(B) Designs of Bridges:-

The Design Circle will continue to prepare Type-Design for various bridge-components as well as detailed structural designs for bridges as per the present practice.

(C) Designs of Buildings :-

(i) Designs of all load bearing structures shall be prepared by the concerned field Executive Engineer, irrespective of number of stories and cost of structure.

(ii) Design of R.C.C. farmed structure up to 4 stories (Ground plus 3 upper) shall be prepared by the Executive Engineers of P.W. Division of zilla Parishads irrespective of the cost of the structure except in case of structures requiring wind and seismic analysis.

 

24. Field data proforma,  standard proforma for finishing field data for commencing design of building projects

1. Name of work :

2. Location :

(i) Location with Seismic Zone.

(ii) "Importance Factor " for structure as per I.S.1893.

1. General description & salient Features :

2. Architect’s Plan No .& Job No. :

3. G.R. number and date of administrative approval with cost :

4. Technical sanction order and its date (authority with cost). :

5. Foundation conditions. :

(a) Foundation details of exciting building near to the site .

(b) Distance between the nearest exciting building and proposed building.

(c) Plan showing location /s of trial pits/ trial bores including level of subsoil water table.

(give date of observation) .

(d) Results of chemical tests on sub soil water for Sulphite, Chloride contents, Ph value.

(e) Safe bearing capacity of foundation strata including depth in case of open footing (mention basis i.e. test results with report etc.)

(f) Details of sub soil exploration or test with the results like.

(i) Nature of sub soil beneath and around with respect to Compressibility and shear strength.

(ii) Penetration test results of Different Strata.

(iii) In case of rock, description of rock to convey physical characteristics and strength .

(iv) In case of weathered rock, description regarding physical behaviour and excepted behaviour .

(g) Value of ‘Beta’ for soil foundation as per I.S. : 1893.

(h) Tidal effects if any . :

8. Special points about foundations and site . :

8.1 If open footings are not feasible give recommendations about :

(a) Raft : Depth and safe bearing capacity of strata :

(b) Piles :

(I) Depth.

(II) Safe bearing pressure for the hard strata.

(III) Type - frictional /bearing/ under reamed .

(IV) Dia of pile proposed (if specific dia is to be provided).

(V) Proposed pile cap level.

(VI) Proposed top level of finished pile .

(VII) Undrained shear strength of soil .

(VIII) Horizontal Modulus of soil .

8.2 Nature of ground e.g. plain, undulating, sloping etc. (attach contour plan at 0.5 m interval if ground slope exceeds 1:30) :

9. Water storage tanks (show requirements are present and future extension separately .) :

(a) Overhead tanks : Type (M.S. /R.C.C. )capacity (show location on plan) :

(b) Underground tank (Location, capacity and special requirements if any). :

10. Lift loads including impact with load transfer points and depth on lift pit below plinth.

11. Extra ordinary Load If any to be considered for Design :

12. Provision to be made in design for future extension if any .

(a) Horizontal :

(b) Vertical :

(c) Authority for the above (Architect’s plan, provisions in A.A. or Tech . Sanctioned estimate reference to master plan etc. :

(d) Whether structural sections assumed in sanctioned estimate take in to account the envisaged expansion at (a) & (b) above . :

(e) Detailed plans of the future extension . :

13. Special requirements of Architectural plans if any . :

(a) Restriction on column sizes and their orientation with locations. :

(b) Restriction on sizes of beam and their orientations. :

(c) Lift machine room floor clearance from general terrace level. :

(d) Minimum headway if any, with locations. :

(e) Any specific or suggested positions of expansion joints if required at particular places. :

14. If the Building is to be designed for wind load give value K1 =

of ‘K1’, ‘K2’, ‘K3’, as per I.S. 875 (part 3) K2 =

to calculate design wind speed. K3 =

15. Special feature of the stair cases if any . :

(a) Clearance on sides.

(b) Restrictions on No.of steps in a flight

(c) Restrictions on tread widths and heights of risers etc.

16. Any other special requirements or points such as. :

(i) Type of water proofing with its loading.

(ii) Exposure to saline and chemical atmosphere.

Note :- The following plans must be supplied with this proforma .

(i) Index plan.

(ii) Site plan showing locations of trial pits.

(iii) Sub surface data including test results.

(iv) Contour plan incase ground slope exceeds 1:30.

(v) Architect’s plan (original and not traced copies) Marked with location of

over head tank/s with individual capacity.

(vi) plans and sketches showing special requirements, if any .

25. Notes to appear on various schedules

[A] General( applicable for all schedules)

1. For general instructions and detailing of reinforcement, refer to Designs Circle’s Technical Note No.7502, and SP-34 (S and T) 1987 of bureau of Indian Standards.

2. Unless otherwise specified in the respective schedules, the concrete mix shall be M15 (characteristic strength 15N/ sq.mm.) for non-coastal region and M 20 (characteristic strength 20N/ sq.mm.) for coastal region.

3. Reinforcement except 6 mm shall be high yield strength deformed bars (Fe 415) conforming to I.S. 1986 with latest amendments.

4. 6 mm. reinforcement shall be mild steel (grade I) conforming to I.S.:4332 with latest amendments.

5. Any deviation from designed size, found necessary on site shall be got approved well in advance before execution from Superintending Engineer .

6. Development length of reinforcing bars shall be in accordance with clause 25.2.1 of I.S. :456.

7. Approval to R.C.C. layouts and to the sizes of columns and beams above plinth level shall be obtained from Architect prior to the execution .

8. For narration of slabs, beams and columns and column orientation refer to R.C.C. layouts of respective floors.

[B] R.C.C. Layouts

1. This R.C.C. layout is based on the Architect’s Drawing No. -----Job No.----Dated---/--/--.

2. R.C.C. layout at a particular level indicates (i) beams and slabs at that level(ii) supporting column below that level & (iii) walls above that level.

3. Any discrepancies between these layouts and Architect’s drawings shall be communicated to office of ---------(where designs are prepared) for clarification before starting execution .

4. Any change in the location of beams, oriented of column/s other than the shown in the layouts, shall be got approved in advance from Superintending Engineer .

[C] Footings / Piles and Pile Caps

1. For column numbers and their orientation refer to R.C.C. layout at plinth level drawing No.----/---

2. The difference in levels between adjoining footings shall not exceed than that permitted vide clause No. 9.7 of I.S. : 1904 .

3. The larger dimension of footing shall be oriented along the longer side of a column, unless the sketch indicates the contrary.

4. Clear cover to reinforcement shall be 50 mm for non- coastal region and 65 mm for coastal region .

5. Reinforcement parallel to breadth of footing shall be laid first .

6. Reinforcement bars shall be bent up at the edges of footing as shown in the sketch.

7. The sub -soil & sub-soil water are assumed to be free from harmful elements.

8. Footings /pile and pile caps are designed for (ground +----) (number of stories for which footings are designed)

9. Footings are designed for safe bearing capacity of -----t/ sq.m.

10. For detail of dowel arrangement refer to schedule of columns from footing to plinth level drawing No. ---/---.

[D] Columns :

1. For orientation of columns refer R.C.C. layout at plinth drawing No. -----/------.

2. Reduction in column size shall be effected from the top of the slab at relevant floor level.

3. For any change proposed at site, in the size of column section and /or their orientation, approval of superintending Engineer shall be obtained before execution .

4. Clear cover shall be 40 mm. for non-coastal region and 55 mm for coastal region.

5. Larger diameter bars shall be provided at corners, unless otherwise indicated in the sketch .

6. Arrangement of main vertical reinforcement should not be modified .

7. Arrangement of binders shown in the sketch is suggestive, any other alternative arrangement in accordance with the relevant provisions in IS : 2502 may be adopted.

[E] Beams

1. For notation of beams refer R.C.C. layout at ---floor level Drawing No. ----/---.

2. Clear cover to reinforcement shall be 25mm or maximum diameter of bar . Whichever is more for non-coastal region and 40mm. for coastal region .

3. In case of collinear beams, top reinforcement over a support for non-seismic region and both top and bottom reinforcement at a support for seismic region shall be continued in adjacent span for full development length or span/4 of adjoining span whichever is more.

4. In case of nonlinear beam and incase there is no beam on the other side, the top reinforcement at a support for coastal region shall be anchored in the supporting column for full development length . Incase of grid beams it shall be Anchoredthe supporting beams and columns.

5. Minimum and maximum distances between individual bars shall be as per clause no 25.3 of I.S. :456 with latest amendments.

6. The end of beam except in a grid not having either a column support or collinear beam shall be considered to be a discontinuous end.The top and bottom reinforcement as such a discontinuous end shall be tremiated in the supporting beams instead of anchoring for full development length .

7. In case diameter and number of bars of adjacent collinear beams are same then these bars shall be kept continuous .

8. If the spacing of stirrups in any region of a beam (such as 0 to D, D to 2D, etc.) is not a submultiple of the depth of the beam, then the same spacing shall be continued in the next region for one or more spacing before starting the new spacing to be provided in the next region .

9. Extra steel at top of support between adjacent beams is shown in any one beam . This extra steel is to be continued on both sides of the support for required anchorage length or span/4 of respective beam, whichever is more .

10. Top of internal plinth beams shall be 15 cms .below plinth level and top of external plinth beams shall be 15 cms. below ground level.

11. Beams at toilet portion shall be cast 20 cm. below general floor level.

12. Necessary provision for reinforcement of chajja, facias, canopy, fins, pardi and brackets etc. shall be made while casting of relevant beams.

[F] Slabs

1. For notations of slabs refer R.C.C. layouts at ---floor level drawing No.---/----.

2. Slabs of toilet portion shall be cast at 20 cm. below general floor level.

3. Clear cover to reinforcing bars shall be 15mm. for non-coastal region and 30mm. for coastal region

4. Reinforcement in chajjas shall be provided as per the sketch no 4A of Designs Circle’s Technical Note No .7502

5. In slab notation, the first figure indicate the imposed live load assumed in design. It shall be ensured by the field engineers that the actual live load on the slabs does not exceeds this specified load.

[G] Water Tank

1. Mix of the concrete for water tank shall be M20.

2. All dimensions are in cms , unless otherwise specifically mentioned .

3. Plans and sections are not to scale.

4. Clear cover to reinforcement shall be 25 mm . for non-coastal region and 40 mm. for coastal region

5. Necessary water proofing treatment, load of which shall not exceed 100 kg/ sq. m. shall be given to the tank .

6. The drawing shows only structural details .Air vents, over flow pipes, inlets, scour pipes, man holes etc. have NOT been shown on the drawing.

7. Manholes of adequate diameter shall be provided as per requirement/s with extra trimmer bars below main reinforcement of slab as shown in the drawing .

8. The horizontal and vertical bars of the walls shall be continued beyond the bend for full development length.

9. The diameter and position of over flow pipe shall be such that it will ensure a free board of 15 cms.

10. Column reinforcement shall be continued up to top of bottom slab of water tank.

11. R.C.C. Tank/s of ----- Liters capacity shall rest on columns nos ---,---,---,---,---,and ---.