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For internal circulation of BSNL only E4 E4-E5 CIVIL E5 CIVIL (TECHNICAL) (TECHNICAL) Structural Design of RCC Bldg Structural Design of RCC Bldg Components Components (Session (Session – 1) 1)
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  • For internal circulation of BSNL only

    E4E4--E5 CIVIL E5 CIVIL

    (TECHNICAL)(TECHNICAL)

    Structural Design of RCC Bldg Structural Design of RCC Bldg Components Components (Session (Session –– 1)1)

  • WELCOME

    • This is a presentation for the E4-E5 Civil Technical

    Module for the Topic: Structural Design of RCC Bldg

    Components (Session -1)

    • Eligibility: Those officers of civil wing who have got the

    Upgradation from E4 to E5.

    • This presentation is last updated on 21-4-2011.

    • You can also visit the Digital library of BSNL to see this

    topic.

    For internal circulation of BSNL only

  • For internal circulation of BSNL only

    AGENDA

    Basic Codes for Design.

    General Design Consideration of IS: 456-2000.

    Steps for design of a multi-storied building.

    Calculation of horizontal loads on buildings.

    Vertical load analysis.

    Horizontal load analysis.

  • INTRODUCTION

    � Analysis & design of building depends on type of building, its

    complexity, number of stories etc.

    � Structural system is finalized after thorough Study of

    architectural drawings.

    � Choice of an appropriate structural system is important for its

    economy and safety. There are two type of building

    systems:-

    (a) Load Bearing Masonry Buildings.

    (b) RCC Framed Buildings.

    � Structural frame is finalized & sizes of structural members

    are conveyed to the concerned architect.

    For internal circulation of BSNL only

  • INTRODUCTION

    Load Bearing Masonry Buildings

    • Low rise buildings with small spans generally constructed as

    load bearing brick walls with RCC slab & beams.

    • Suitable for building up to four or less stories.

    • Adequate for vertical loads & also serves to resists

    horizontal loads like wind & earthquake by box action.

    • Provisions of IS: 4326 e.g. providing horizontal RCC Bands

    & vertical reinforcement in brick wall etc. need to be followed

    to ensure safety against earthquake

    • Design to be done as per BIS code IS:1905

    For internal circulation of BSNL only

  • INTRODUCTION

    RCC Framed Structures

    • RCC frames are provided in both principal directions

    and

    • Loads are transmitted to ground through vertical framing

    system i.e Beams, Columns and Foundations.

    • Effective in resisting both vertical & horizontal loads.

    • Brick walls are non load bearing filler walls only.

    • Suitable for multi-storied building as it is very effective

    in resisting horizontal loads due to earthquake / wind.

    For internal circulation of BSNL only

  • INTRODUCTION

    RCC Framed Structures

    • Before starting structural design of a RCC building, the

    following information/ data are required:

    (i) Set of architectural drawings;

    (ii) Soil Investigation report

    (iii) Location of the place or city in order to decide on

    wind and seismic loadings

    (iv) Data for lifts, water tank capacities on top, special

    roof features or loadings, etc.

    For internal circulation of BSNL only

  • BASIC CODES OF DESIGN

    Useful Codes/Hand Books For Structural Design of RCC

    Structures

    (i) IS 456 : 2000 – Plain and reinforced concrete – code of practice

    (ii) Loading Standards:

    IS 875 (Part 1-5) – Code of practice for design loads (other than

    earthquake) for buildings and structures

    Part 1 : Dead loads

    Part 2 : Imposed (live) loads

    Part 3 : Wind loads

    Part 4 : Snow loads

    Part 5 : Special loads and load combinations

    For internal circulation of BSNL only

  • BASIC CODES OF DESIGN

    Earthquake Resistant Design

    • IS 1893 : 2002 – Criteria for earthquake resistant design of

    structure.

    • IS 13920: 1993 – Ductile detailing of reinforced concrete

    structure subject to seismic forces – Provisions of IS 13920-

    1993 shall be adopted in all reinforced concrete structures

    located in seismic zone III, IV or V

    Design Handbooks (Bureau of Indian standards) -

    • SP 16 : 1980 – Design Aids to IS 456 : 1978 (Based on

    previous version of code but still useful)

    • SP 34 : 1987 – Handbooks on Reinforced Concrete Detailing

    For internal circulation of BSNL only

  • BASIS OF DESIGN

    Aim Of Design

    • To design structures with appropriate degree of safety to –

    • Perform satisfactorily during its intended life.

    • Sustain all loads/ deformations of normal construction & use

    • Have adequate durability & resistance to fire.

    Method of Design

    • Structure and structural elements to be normally designed by

    Limit State Method.

    • Working Stress Method may be used where Limit State

    Method can not be conveniently adopted

    For internal circulation of BSNL only

  • LOADS

    DESIGN LOAD –

    Design load to be taken in appropriate method of design is –

    • Characteristic load with appropriate partial safety factors for

    limit state design

    • Characteristic load in case of working stress method

    For internal circulation of BSNL only

  • LOAD COMBINATIONS

    BASIC LOAD CASES USED FOR ANALYSIS

    No. Load case Directions

    1 DL Downwards

    2 IL(Imposed/Live load) Downwards

    3 EXTP (+Torsion) +X; Clockwise torsion due to EQ

    4 EXTN (-Torsion) +X; Anti-Clockwise torsion due to EQ

    5 EZTP (+Torsion) +Z; Clockwise torsion due to EQ

    6 EZTN (-Torsion) +Z; Anti-Clockwise torsion due to EQ

    For internal circulation of BSNL only

  • LOAD COMBINATIONS

    LOAD COMBINATIONS

    • 1.5 (DL + IL)

    • 1.2 (DL + IL ± EL)

    • 1.5 (DL ± EL)

    • 0.9 DL ± 1.5 EL

    • EQ load must be considered for +X, -X, +Z and –Z directions.

    Moreover, accidental eccentricity can be such that it causes

    clockwise or anticlockwise moments.

    • Thus, ±EL above implies 8 cases, and in all, 25 cases must be

    considered. It is possible to reduce the load combinations to

    13 instead of 25 by not using negative torsion considering

    symmetry of the building. For internal circulation of BSNL only

  • Grade of Concrete

    Minimum Grade of Concrete

    For internal circulation of BSNL only

  • BIS 456 EXTRACT

    26.4 Nominal Cover to Reinforcement

    • Nominal cover is the design depth of concrete cover to

    all steel reinforcements, including links.

    • It shall be not less than the diameter of the bar.

    • Minimum values for nominal cover of normal weight

    aggregate concrete which should be provided to all

    reinforcement, including links depending on the condition

    of exposure shall be as given in Table 16 of IS 456.

    For internal circulation of BSNL only

  • BIS 456 EXTRACT

    26.4 Nominal Cover to Reinforcement (Table 16 )

    Exposure Nominal Concrete Cover

    in mm not Less Than

    Mild 20

    Moderate 30

    Severe 45

    Very Severe 50

    Extreme 75

    • For longitudinal reinforcing bar in column nominal cover shall

    in any case not be less than 40 mm, or less than bar dia.

    • For footings minimum cover shall be 50 mm.

    For internal circulation of BSNL only

  • Steps of Design

    Steps for Design of Multi-Storeyed

    RCC Framed Buildings

    Step1: Study of architectural Drawings

    Step2: Finalization of Structural Configuration.

    Step3: Preliminary Sizes of Structural members.

    Step4: Load Calculation and

    Step5: Analysis for various load combinations.

    Step6: Design of various structural components for

    most critical load combination.

    For internal circulation of BSNL only

  • Preliminary Sizes

    Finalising Preliminary Sizes

    • Slab: Slab thickness is decided based on span/depth ratio.

    • Beam: Width of beam to be at least equal to width of wall

    (230 or 300 mm). Larger beam width is helpful in placement

    of reinforcement in one layer & for resisting shear & torsion.

    - Depth of beam generally taken as 1/12th (for Heavy Loads)

    to 1/15th (for Lighter Loads) of span.

    • Column: Size of column depends upon axial load &

    moments from both directions and is finalized after

    approximate calculations.

    For internal circulation of BSNL only

  • Loads

    Types of Loads –

    Vertical Loads –

    • Dead Load (Self Weight) – Dl – As per IS-875(part-1)

    • Imposed Load (Live Load) – LL Or IL – As per IS-875 (Part-2)

    • Snow Load

    Horizontal Loads –

    • Earthquake Load (Seismic) – EQX & EQZ (As per IS-1893)

    • Wind Load – WL –As Per IS-875 (Part-3)

    • Special Loads & Load Combinations

    For internal circulation of BSNL only

  • Dead Loads – Unit Wt of Bldg Materials (IS 875 Pt-1)

    For internal circulation of BSNL only

    MATERIAL

    UNIT WEIGHT

    kN/m3 kN/m2

    PLAIN CONCRETE 24

    REINFORCED CONCRETE 25

    BRICK MASONRY 19-20

    STONE MASONRY 21-27

    TIMBER 6-10

    CEMENT-PLASTER 21

    LIME -PLASTER 18

    STEEL 78.5

    AC SHEET -ROOFING 0.16

    GI SHEET -ROOFING 0.15

    MANGLORE TILES 0.65

    STEEL WORK -ROOFING 0.16-0.23

  • Live Loads on Floors of T.E. Bldgs

    For internal circulation of BSNL only

    TYPE OF FLOOR USAGE

    LIVE LOAD

    (kN/m2)

    � SWITCH ROOM(NEW TECHNOLOGY) 6.0

    � OMC ROOM,DDF ROOM,POWER PLANT,

    BATTERY ROOM

    6.0

    � MDF ROOM 10.0

    � WEATHER MAKER 12.0

    LIVE LOADS ON ROOFS

    � ROOF WITH ACCESS 1.5

    � ROOF WITHOUT ACCESS 0.75

  • Loads

    Procedure for Vertical load calculation on Columns–

    Step(i): Transfer slab floor load (both LL & DL) to beams

    using formulae for equivalent UDL as :-

    Equivalent UDL on short span beam = w B/4

    Equivalent UDL on long span beam = w B/4 x [2-(B/L)]

    where w is the total load on slab panel in KN/Sqm &

    L & B respectively are long span & short spans of slab

    panel.

    For internal circulation of BSNL only

  • Loads

    Procedure for Vertical load calculation on Columns–

    Step(ii): Add weight of wall (if any), self weight of beam etc.

    to obtain load on beam (in running meter). Calculate

    similarly for each beam

    Step(iii): Transfer loads from beams to columns.

    Step(iv):Repeat Step (i) to Step (iii) for each floor.

    Step(v): Add for each column for all floors to get total load on

    each column at footing level for entire building.

    For internal circulation of BSNL only

  • Loads

    Procedure for Horizontal (Seismic) Load Calculation–

    • Load Calculations for Seismic Load case is carried out as

    per IS:1893-2002 clause 7.5.3.

    • The Seismic Shear at various floor levels is calculated for

    the whole Building using the values from IS 1893-2002.

    • Design Seismic base shear is –

    Vb = Ah W

    Where W= Seismic weight as per clause 7.4.2 (Full dead load

    + appropriate percentage of imposed load of building as

    given in Table 8)

    For internal circulation of BSNL only

  • Procedure for Horizontal (Seismic) Load Calculation :

    Design Imposed Load for eq. Force Calculation

    Table 8 (IS 1893)

    Percentage of Imposed Load to be Considered

    in Seismic Weight Calculation (Clause 7.3.1 )

    Imposed Uniformity Percentage of

    Distributed Floor Load Imposed Loads

    ( kN/ m2 )

    (1) (2)

    Upto and including 3.0 25

    Above 3.0 50

    For internal circulation of BSNL only

    Load Calculation

  • Loads

    Procedure for Horizontal (Seismic) Load Calculation –

    Ah = Design Horizontal acceleration spectrum value (cl. 6.4.2)

    = (Z/2) (I/R) (Sa/g)

    Where Z = Zone factor as per table 2 of IS 1893

    I= Importance factor as per table 6 of IS-1893

    = 1.5 (If the bldg. is T.E. Bldg.)

    R = Response reduction factor as per table 7 of IS 1893

    = 3.0 for OMRF or 5.0 for SMRF

    (Sa/g) = Average response acceleration coefficient based on

    soil type & natural periods and damping of structure. (Refer

    Fig. 2 page 16 of IS 1893)

    For internal circulation of BSNL only

  • • Procedure for Horizontal (Seismic) Load Calculation :

    For calculating (Sa/g) value as above we have to calculate

    T i.e. Fundamental Natural Time Period (in Seconds)

    (Clause 7.6 of IS Code)

    • T = 0.075 h0.75 (For RC Frame building)

    where h = Height of building in Meter

    • In case of RCC building with brick in fills walls.

    T = 0.09 h / d ½ where h = height of building in meter

    & d = Base dimension of the building at plinth level in

    meter along the considered direction of lateral force.

    For internal circulation of BSNL only

    Load Calculation

  • Procedure for Horizontal (Seismic) Load Calculation :

    • Distribution of base shear (Clause 7.7 of IS 1893) –

    Distribution of total design base shear to different floor

    levels along height of building is done using formula –

    Fi = w i h i2 / ∑(i=1 to n) w i h i

    2 x VbWhere Fi = Design lateral force at floor i

    Wi = Seismic weight of floor i

    hi = height of floor in m from base.

    n = number of storyes in the building is equal to

    number of levels at which masses are located.

    Vb = Total Design base shear

    For internal circulation of BSNL only

    Load Calculation

  • ANALYSIS OF STRUCTURE

    VERTICAL LOAD ANALYSIS

    a) GENERAL:

    • It is presumed that all joints of the frame are monolithic.

    • To simplify analysis, three dimensional multistoried R.C.C.

    framed structure is considered as combination of planer

    frames in two directions.

    • It is assumed that each of these planer frames act

    independently of other frames.

    For internal circulation of BSNL only

  • ANALYSIS OF STRUCTURE

    Vertical Load Analysis

    • Procedure for Frame analysis for calculation of moments

    in Columns & beams:

    • Step(i): First, the load from slab is transferred to adjoining

    beams using formula given below:-

    • For computation of Bending Moments in beams, equivalent

    uniformly distributed load of beam is taken as

    Equivalent UDL on short beam of slab panel = w B/3.0

    Equivalent UDL on long beam of slab panel = w B/6 x [ 3-(B/L)2 ]

    where w is the total load on the slab panel in KN/Sqm &

    L & B are long span & short spans of slab respectively.

    For internal circulation of BSNL only

  • ANALYSIS OF STRUCTURE

    Vertical Load Analysis

    • Procedure for Frame analysis for calculation of

    moments in Columns & beams:

    Step(ii): Over this load, weight of wall, self weight of beam

    etc. are added to get load on beam (in running metre).

    Step(iii): The load (in running Metre) on each beam is

    calculated as in Step (i) & Step (ii).

    Step(iv): Step (i) to Step (iii) is repeated for each floor

    Step(v): Then these loads are used as u.d.l on a particular

    frame for analysis by moment distribution method.

    For internal circulation of BSNL only

  • ANALYSIS OF STRUCTURE

    METHOD OF ANALYSIS:

    • Analysis of large framed structures is too Cumbersome

    with classical methods of structure analysis such as –

    – Clapeyron’s theorem of three moments,

    – Castingiliano’s therefore of least work,

    – Poison’s method of virtual work etc.

    Therefore, simpler methods are mostly followed in 2-D

    manual analysis of structures. These are –

    • Hardy cross method of moment distribution.

    • Kani’s method of iteration.

    For internal circulation of BSNL only

  • ANALYSIS OF STRUCTURE

    Horizontal Load Analysis

    • Frame analysis for horizontal loads calculated in step 4

    may be carried out by using Approximate Methods:-

    (i) Cantilever method.

    (ii) Portal method.

    • Approximate methods are used for preliminary designs

    only.

    • For final design exact methods are used which are –

    (i) Slope deflection or matrix methods

    (ii) Factor method.

    For internal circulation of BSNL only

  • For internal circulation of BSNL only


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