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