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SEISMIC DESIGN OF RC RESIDENTIAL BLDG”
B.TECH. Dissertation Report
In
Civil Engineering
By
KHAN ASADULLAH :- CV/12/45
Under Supervision of
Mr. MIRZA AAMIR BAIG
Department of Civil Engineering
AL-FALAH School of Engg. & Tech.
AL-FALAH UNIVERSITY
Faridabad, Haryana (India)
June, 2016
CERTIFICATE
I hereby certify that the work which is being presented in the Btech. Dissertation “SEISMIC
DESIGN OF MULTI STORIED RC RESIDENTIAL BUILDING”in partial fulfillment of
the requirements for the award of the Bachelor of Technology in CIVIL ENGINEERING and
submitted to the Department of CIVIL ENGINEERING is an authentic record of my own
work carried out during a period from January 2016 to May 2016 under the supervision of Mr.
MIRZA AAMIR BAIG Assistant Professor Department of Civil Engineering, ALFALAH
UNIVERSITY, Faridabad.
The matter presented in this thesis has not been submitted by me for the award of any other
degree elsewhere.
Signature
KHAN ASADULLAH-
CV/12/45
This is to certify that the above statement made by the candidate is correct to the best of my
knowledge.
Signature of Supervisor
Date: Mr. MIRZA AAMIR BAIG
Assist Prof. (CE dept.)
Special Thanks to Aamir Baig Sir Danish Sir
ACKNOWLEDGEMENT
This is our proud privilege in expressing deep sense of obligation and gratitude to “Mr. Mirza
Aamir Baig” who has assigned us to carry our project on such a rising and interesting topic,
which is “Seismic Design of Multi Storied RC Residential building”. We are also thankful to
him for his support and valuable guidance, rejuvenating encouragement, positive criticism and
constant supervision all through our project session.
We see greatly indebted to be associated with him for his everlasting impression,
scientific temperament and humanitarian sensibility. He has always been a source of inspiration
to us throughout the work.
My sincere and intense thanks to our H.O.D “Dr Syyed Khursheed Ahmad” and to the
civil engineering department for arranging these kinds of projects, for the students and also
would like to thank “Mr Parvez Ansari” for his Supervision and guidance which he
enthusiastically imparts to all the students of 8th
semester.
We further wish to record our applause to our friends and family members for their co-
operation, prayers and sacrifices.
ABSTRACT
The principle objective of this project is to analyze and design a multistoried building [G +
23+2B] (3 dimensional frame)] using STAAD Pro. The design involves load calculations
manually and analyzing the whole structure by STAAD Pro. The design methods used in
STAAD-Pro analysis are Limit State Design conforming to Indian Standard Code of Practice.
STAAD.Pro features a state-of-the-art user interface, visualization tools, powerful analysis
and design engines with advanced finite element and dynamic analysis capabilities. From
model generation, analysis and design to visualization and result verification, STAAD.Pro is
the professional’s choice. Initially we started with the analysis of simple 2 dimensional
frames and manually checked the accuracy of the software with our results. The results
proved to be very accurate. We analyzed and designed a G+23+2B storey building [2-D
Frame] initially for all possible load combinations [dead, live, wind and seismic loads].
STAAD.Pro has a very interactive user interface which allows the users to draw the frame
and input the load values and dimensions. Then according to the specified criteria assigned it
analyses the structure and designs the members with reinforcement details for RCC frames.
We continued with our work with some more multi-storeyed 2-D and 3-D frames under
various load combinations. Our final work was the proper analysis and design of a
G+23+2B 3-D RCC frame under various load combinations.
The ground floor height was 3.05m and rest of the 23 floors had a height of 3.05m.The
structure was subjected to self weight, dead load, live load, wind load and seismic loads
under the load case details of STAAD.Pro. The wind load values were generated by
STAAD.Pro considering the given wind intensities at different heights and strictly abiding
by the specifications of IS 875-3. Seismic load calculations were done following IS 1893-
2002/2005. The materials were specified and cross-sections of the beam and column
members were assigned. The supports at the base of the structure were also specified as
fixed. The codes of practice to be followed were also specified for design purpose with
other important details. STAAD Pro was used to analyze the structure and design the
members. In the post-processing mode, after completion of the design, we can worked on
the structure and studied the bending moment and shear force values with the
6
generated diagrams. We also checked the deflection of various members under
the given loading combinations. The design of the building is dependent upon
the minimum requirements as prescribed in the Indian Standard Codes. The
minimum requirements pertaining to the structural safety of buildings are being
covered by way of laying down minimum design loads which have to be
assumed for dead loads, imposed loads, and other external loads, the structure
would be required to bear. Strict conformity to loading standards recommended in
this code, will help ensure the structural safety of the buildings which are being
designed. Structure and structural elements were normally designed by Limit
State Method.
Complicated and high-rise structures need very time taking and cumbersome
calculations using conventional manual methods. STAAD Pro provides us a fast,
efficient, easy to use and accurate platform for analyzing and designing structures.
7
OBJECTIVE
Seismic design and analysis of multi storied RC residential building as per
given architectural drawing using STAAD pro. and manually. The building has
(2B+G+23) floors and an area of about 520 m2. It has four lifts as well as two
staircases.
The site is located at PLOT NO 12A, SECTOR ZETA-1, GREATER NOIDA,
U.P.
Bearing capacity of soil 180KN/m2
Dry bulk density of soil 20KN/m3
Angle of repose 30°
8
INDEX
Chapter 1 12-20
1.1 Introduction 12
1.1.1 Salient features of the building.
1.1.2 Architectural Plan of the building.
1.2 Use of STAAD 19
1.2.1 STAAD Pro.V8i.
1.2.2 Procedure for Design using STAAD PRO.
Chapter 2 22-55
2.1 Gravity Design 22
2.1.1 Analysis for Gravity Loads 22
2.2 STAAD Editor 24
2.2.1 STAAD PRO Model Responses 24
2.3 Manual Design of Slab Panel 27
2.4 Manual Design of Stair case 30
2.5 Manual Design of Beam 36
2.6 Manual Design of Column 46
Chapter 3 56-66
3.1 Wind loads 56
3.1.1 Design consideration for Wind load 57
3.1.2 Natural Wind 58
3.1.3 Type of Wind 59
3.1.4 Characteristics of Wind 60
3.2 Code based Method for Wind Load Design 60
3.2.1 Design for Wind load 62
3.2.2 Load Combinations 66
Chapter 4 67-81
4.1 An introduction to Seismic Design 67
4.1.1 Building Behavior 70
4.1.2 Influence of soil 71
4.1.3 Damping 71
4.1.4 Building Drift and Separation 74
4.2 Seismic Design Concepts 75
4.2.1 Structural Response 75
4.2.2 Ductility 76
4.2.3 Load combinations 78
Chapter 5 82-97
5.1 Materials required by Gravity Design method 82
5.2 Ductility consideration 83
5.2.1 Requirements for Ductility 83
5.3 Foundation 91
5.3.1 Raft Foundation 91
5.3.2 Raft Foundation Design 92
5.3.3 STAAD PRO Foundation Design summary 96
9
Chapter 6 98-100
6.1 Detailing and drawing 98
6.1.1 Architectural Plan 98
Conclusion 104
Appendices 105
References 106
List of figures and tables
Figure no. Page no.
1.1 14
1.2 15
1.3 16
1.4 17
1.5 18
2.1 23
2.2 24
2.3 25
2.4 28
2.5 31
2.6 35
2.7 35
2.8 35
2.9 36
2.10 36
2.11 37
2.12 39
2.13 48
2.14 49
2.15 50
2.16 51
2.17 52
2.18 54
3.1 62
3.2 63
3.3 64
4.1 68
4.2 72
4.3 73
4.4 76
4.5 79
4.6 80
5.1 84
5.2 84
5.3 85
10
5.4 86
5.5 87
5.6 88
5.7 88
5.8 89
5.9 90
5.10 91
5.11 94
6.1 97
6.2 98
6.3 99
6.4 100
6.5 102
Table no 1……….…12
Table no 2……….….65
Table no 3………....78
11
ABBREVIATIONS
Unless specified otherwise, the symbols and notations used in the report
shall have the following meaning.
a0…………………………………… Basic Horizontal seismic coefficient
Ag……………………………………Gross area of section
Ah ……………………………………Horizontal seismic coefficient
Asc ………………………………… Area of compression steel
Ast…………………………………… Area of tension steel
b………………………………….. Width of member
C………………………………….. Flexibility co-efficient
d…………………………………... Effective depth of member
D…………………………………… Overall depth of member
d’……………………………………..Nominal cover in compression
Dia………………………………........Nominal Diameter of the bar
Fck………………………Characteristic compressive strength of concrete
Fy……………………………………Characteristic yield strength of steel
I…………………………………….Importance factor
K……………………………………Performance factor
K1………………………………… Probability factor
K2………………………………Terrain, height and structure size factor
K3………………………………Topographical factor
Ld………………………………Development length
Lex………………………………Effective length of column about X-X axis
Ley………………………………Effective length of column about Y-Y axis
L0……………………………… Unsupported length of column
Mu………………………………Factored Moment
Mx………………………………Moment about X-X axis
My………………………………Moment about Y-Y axis
P/Pu…………………………… Axial load
Pc………………………………Percentage compressive steel
Pt………………………………Percentage tension steel
12
Pz………………………………Design wind pressure at level z
T………………………………….......Fundamental Time period
𝜏c ……………………………………Design shear strength of section
𝜏v…………………………………… Normal shear stress
V/Vu …………………………………Factored shear force
Vb ……………………………… ……Basic wind speed/ Base shear
Vz…………………………………… Design wind speed at level z
W……………………………………..Tidal weight of building
Z…………………………Height or level with respect to mean ground level
13
CHAPTER 1
1.1 INTRODUCTION
The project is to analyze and design the proposed building. This building is
to be used as a residential building and it is located in the Greater Noida, U.P. The
project came under the final year project work scheme of department of Civil
Engineering. The project includes generation of floor plan in AutoCAD, design of
several component of the building viz. beams, columns, slabs, staircase, shear wall
etc manually as well as by using STAAD Pro. Embedded with structural analysis of
the building on application of several load combination specially wind and seismic
loads.
1.1.1 SALIENT FEATURE OF THE BUILDING
Purpose Residential
No of Storeys 26(2B+G+23)
Storey height 3.05m
Built up Area 520 m2
No of Staircase 2
No of Lifts 3
Foundation Used Raft
Type Multi-storey
Table no 1
14
1.1.2 ARCHITECTURAL PLAN OF YHE BUILDING
The Building covers a plan area equal to 520 m2, consists of 2 basements
plus ground floor plus twenty three upper floors.
The building is that of a framed structure type. In the plan, each floor
consists of three flats and each flat consists of 3 bed rooms, 1 dining room, 1
drawing room, 1 study, 1 kitchen and 3 toilets, and is provided with 4 lifts and 2
staircase.
Some open area is provided in different parts of all floors in the same
vertical plane through all the floors. This open space will facilitate enough
ventilation and natural light. It is surrounded by steel railings on all the four sides.
All the rooms are provided with a wide balcony at the back face and a wide
corridor at the front face.
15
FIG 1.1: Typical Floor Plan
16
FIG 1.2 :Typical Centre Line Diagram
17
MAJOR PROJECT REPORT:-
1:- Structural Layout of the Building Frame:
The following figure shows the structural frame of the building. The
columns, beams and shear wall have been shown here.
Beam and Column Position:- FIG 1.3
18
Structural Model:- FIG 1.4
19
Raft Foundation:- FIG 1.5
20
61.2 Use of STAAD
The analysis and the design for the project is done by STAAD. So a brief
concept of STAAD PRO software is dealt with.
1.2.1 STAAD Pro V8i has been prominently and widely used to analyze and
design a structure. It is an automated software for structural analysis and design. It
can generate the building frame (beams, columns, and foundation) in 3D. Several
types of loads along with certain load combinations can then be applied on the
framed structure. After the application of load, the software generates the required
data viz. moments forces, deflections, stresses etc. these responses can be viewed
graphically as well as in tabular form. Based on this response we can design the
building in STAAD. It can design the desired section for the beams, columns, slabs
and foundation as well as provide us with the reinforcement details too.
This software is also enabled with various codes of practice with regards to
the Indian Codes of Practice.
STAAD software has been used for analyses of the structure under wind
loads and seismic loads and the building has been designed for the critical case. IS-
Code has been considered the base for defining all the necessary parameters that are
relevant in the design. Apart from this certain manual modifications have also been
made to satisfy the economic aspects of the building.
1.2.2 Procedure for Design using STAAD Pro
1. Preparation of general layout of the building.
2. Decide the position of beams and columns based on
architectural point of view.
3. Generate the plan of the building in Auto CAD.
4. Based on the Auto CAD drawing, generate a 3D model of the
building in STAAD.
5. Assume suitable size of section for beams and columns based on
experience and knowledge.
6. Estimate all kinds of probable loads that might act on the
building.
7. Apply the estimated loads on the building.
21
8. Apply proper load combinations on the building based on IS-
Code (wind load and seismic load have to be applied
separately).
9. Analyze the structure in application of the above load
combinations and find out the response of the structure i.e. BMD, SFD, and
deflections etc.
10. Based on these responses design the different components of the
building.
11. Modify the design obtained and check for economic
considerations.
22
CHAPTER 2
2.1 GRAVITY DESIGN
The basic analysis of the structure starts with the gravity load combinations
applied to the structure. This includes dead load due to self-weight of different
components of the building structure itself (beams, columns, Slabs, stairs etc.) live
load due to miscellaneous moveable components on the floors (furniture, electrical
appliances etc.). The presence of occupants also adds to the live load of the
structure.
Here we have analyzed the structure for one load combination
1. 1.5(Dead load + Live load)
2. (Dead Load+ Live load)
The beams and columns have been designed on the basis of responses
obtained in preliminary analysis for gravity loads using STAAD.Pro Software.
However the slab panels have been designed manually for one floor of the building
a model calculation for the slab panels and stair case has also been discussed.
2.1.1 ANALYSIS FOR GRAVITY LOADS
Dead Loads:
Self-weight factor =1
Weight of 230mm thick Walls on Beams =12.096 KN/m
Weight of 115mm thick Walls on Beams =6.15 KN/m
Weight of parapet Walls on Beams =4.72 KN/m
Weight of Floor slabs =3 KN/m2 (Discussed Later)
Weight of Floor finish =1.2 KN/m2
Live Loads:
All floors =2 KN/m2
Corridors and Staircases including fire escapes and store
rooms =3 KN/m2
Roof Top = 1.5 KN/m2
Based on application of these loads the structure has been designed for load
combination of 1.5(DL+LL). While the slab panels and staircases have been
23
designed manually or by Microsoft Excel program for the above mentioned load
conditions, the beams and columns have been designed based on the responses
obtained by STAAD pro.
BASIC LOADING
Dead Load
(A) Dead Load on Floor Slab
Thickness of the Slab = 120.0mm
Dead Load of Slab = 0.120 x 25 = 3.0 kN/m2
Finishing = 0.02 x 26.70 = 0.534 kN/m
Cement slurry = 0.03 x 14.10 = 0.423 kN/m2
Plaster = 0.006 x 20.4 = 0.12 kN/m
2
Miscellaneous = 0.50 kN/m2
4.57 kN/m
2
(B) Dead Load on Roof Slab
Thickness of the Slab = 120.0mm
Dead Load of Slab = 0.120 x 25 = 3.0 kN/m2
Wt. of mortar = 0.20 x 5.0 = 2.50 kN/m2
Plaster = 0.006 x 20.4 = 0.12 kN/m2
5.62 kN/m2
(C) Brick Wall Load
1. 230mm thick = (0.230 x 20 + 22 x 0.02) x2.45m(ht)
= 12.34 kN/m2.
115mm thick = (0.115 x 20 + 22 x 0.012) x 2.45m(ht)
= 8.43 kN/m
24
2.2 STAAD EDITOR
2.2.1 STAAD Pro MODEL RESPONSES
Before we move ahead let’s have a look at the STAAD Pro model
responses:
Loads:-FIG 2.1
25
S.F.D:-FIG 2.2
26
Bending Moment Diagram:- FIG 2.3
27
2.3 MANUAL DESIGN OF FLOOR SLAB PANEL:
Slab of size (3.088x4.0.38)
Short span, Lx=3.088m
Long span, Ly =4.038m
Depth of slab, D=120mm,
Two adjacent edges discontinuous
Load Calculation:
Self wt of slab=0.120*25 = 3.0KN/m2
D.L due to finishing=0.05*26.75 + 0.02*22 = 1.77KN/m2
L.L on slab = 2.0KN/m2
Total load on slab (W) = 6.77KN/m2
Ultimate load on slab (Wu) = 1.5×6.77 = 10.16KN/m2
Hence design as a two way slab
ɑx+=0.043 ɑx
-= 0.056
ɑy+=0.035 ɑy
-= 0.047
Mux(+) = ɑx+*Wu*Lx
2
= 0.043*10.16*3.088
2 = 4.17 kNm
Mux(-) = 0.056*10.16*3.0882 = 5.43 kNm
Muy(+) = 0.035*910.16*3.0882
= 3.39 kNm
Muy(-) = 0.047*10.16*3.0882 = 4.55 kNm
Depth of slab required = sqrt(Mmax/(0.138*Fck*b))
= (5.43×106)/ (0.138*25*1000)
= 39.67 mm (<120mm) O.k
Design of reinforcement:
Shorter span:
Moment of resistance = 0.87*Fy*Ast*[d(-
0.42*(0.87*Fy*Ast/0.36*Fck*b*d)]
5.43 x 106 = 0.87*415*Ast*100[1-
0.42(0.87*415*Ast/0.36*25*1000*100)]
= 154.41 mm2
Minimum area of steel required, Ast min = 0.12%
= (0.12*b*D)/100 = (0.12*1000*100)/100
= 120mm2 (154.41 mm
2>120 mm
2) O.K
28
Let us provide diameter of bar 8mm
Required spacing = (1000*50.26)/154.41
= 324 mm 320 mm
Longer span:
Moment of resistance = 0.87*Fy*Ast*[d(-
0.42*(0.87*Fy*Ast/0.36*Fck*b*d)]
4.55 x 106 = 0.87*415*Ast*100[1-
0.42(0.87*415*Ast/0.36*25*1000*100)]
= 130 mm2
Minimum area of steel required, Ast min =0.12%
= (0.12*b*D)/100 = (0.12*1000*120)/100
= 120 mm2 (130 mm
2> 120 mm
2) O.K
Let us provide diameter of bar 8mm
Required spacing = (1000*50.26)/148
= 339mm
Maximum spacing for reinforcement:
1. Three times the effective depth,3d=3*101=303mm
2. 300mm
Provide 8mm dia bar @250m c/c on shorter span
Area of steel provided = (1000*50.26)/250=201mm2
Provide 8mm dia bar @200mmc/c on longer span
Area of steel provided = (1000*50.26)/250=201mm2
Check for deflection:
Pt = 201/ (103*10
2))*100=0.201
Fs = 0.58*415*(198.9/201)
= 238
Modification factor = 2.15N/mm2
(l/d)max = 20*2.15 = 43
(l/d)provided = 4207/100 = 42.07(<43) O.K
Check for shear:
Vu=Wu*(0.5*Lx-d)
29
=10.16 *(0.5*3.088-0.099)
=15.17 KN/m
Τv=(15.17*103)/(1000*100)=0.156
For Pt =0.201 and Fc=25KN/m3
Tc=0.32
From above Tc>Tv O.K
Section at A-A:- FIG 2.4
Where
As1 =201mm2 As2 =201mm
2 L1 =4.038 m L2 =3.088 m
30
2.4 Design of Staircase
Let us assume
Thickness of Waist slab = 125mm,
Riser = 160mm,
Tread = 270mm,
Fe 415, M 25,
Thickness of wall = 230mm,
The supporting beam = 230mm wide
Effective cover = 15+20/2 = 25mm
Effective Depth available = 125-25 = 100mm
Load Calculation:
Dead load of waist = 0.31*0.26*25/0.27 = 7.46 kN/m2
Ceiling Finish = 0.02*22+0.05*26.75 = 01.77 kN/m2
Dead load of steps = 0.27*0.16*0.5*25/0.27 = 2 KN/m2
Live Load = 2 KN/m2
Total Load = 13.23 KN/m2
Factored load = 1.5*13.23 = 19.85 KN/m2
Flight AB
Number of steps = 6
Effective span = c/c distance b/w the supporting wall
= 0.23/2+1.62+1.5+0.23/2
= 3.35 m
Considering a one meter wide strip of the flight
Reaction at support(Ra) = Ra*3.42-13.23*1.77*(1.77/2+1.65)-10*1.6502/2
= 18.59 KN
Reaction at support(Rb) = 39.92-18.59
= 21.33 KN
Maximum bending moment = Rb*(1.65+1.77/2)-10*1.65*(1.65/2+1.77/2)-
13.23*1.77/2*1.77/4
= 14 KN.m
Equating moment of resistance to the max bending moment
.138*fck*b*d2 = 14*10
6N-mm
.138*25*1000* d2= 14*10
6N-mm
d = 64 mm
31
Calculated d < assumed d (100mm) O.K.
Area of steel required, Ast = (fck*b*d/2fy)(1-sqrt(1-(4.6Mu/bd2 fck)))
=(25*1000*100/2*415)(1-sqrt(1-(4.6*14*/1000*1002 *25)))
Ast=925 mm2
=1000 mm2
Providing 12mm diameter bar
Number of bar required = 1000/ (π*122)
= 8.84 = 9 No.
Spacing of the bar = 1000/ (9-1) = 125 mm
Provide 12mm bar at 125 mm c/c
DISTRIBUTION Reinforcement
Ast req. = 0.0012*bD
= 0.0012*1000*125 = 150mm2 /m
Assume 8 dia bar
No of bars = 150*4/π*82
= 3 No.
Spacing = 1000/3 = 333.3 mm
Provide 8 dia at 250 mm c/c.
32
Staircase:- FIG 2.5
33
2.4 DESIGN OF BEAM
All beams have been designed as rectangular section, of different sizes as per optimum
requirement.
The general design considerations are taken from IS: 456 -2000
Effective depth – is the distance from the centre of the tensile reinforcement to the outermost
compression fibers.
Control of deflection – the vertical deflection limit may generally assumed to be satisfied
provided that the span to depth ratios are not greater than the values obtained as below :
a) Span to effective depth ratio for span up to 10m
Cantilever 7
Simply supported 20
Continuous 26
b) Depending upon the area and stress of steel for tension
reinforcement, values in(a) shall be modifying by
multiplying with modification factor obtained as per fig
5(IS: 456-2000).
c) Depending upon the area of compression reinforcement, the
value of span to depth ratio is further modified by multiplying
with the modification factor obtained as per fig 5 (IS: 456-
2000).
Development stresses in reinforcement Ld is taken directly from SP 16 (table
65), for deform bars conforming to IS: 1786 these values shall be increased
by 60% for bars in compression, the values of bond stress for bar in tension shall be
increased by 25%.
34
Curtailment of tension reinforcement shall extend beyond the point at which it is
no longer required to resist flexure for distance equal to the effective depth of the
member or 12 times the bar diameter, whichever is greater except at simple support
or end of cantilever.
Positive moment reinforcement: – at least 1/3 +ve moment reinforcement in
simple member and ¼ +ve reinforcement in continuous member shall extend
along the same face of the member into the support , to length equal to Ld/3.
Spacing of reinforcement: - min. distance b/w the individual bar not be greater
than the dia. of bar if dia. are equal or dia. of larger bar if dia. are of different size
and 5mm more than the nominal maximum size of course aggregate.
Maximum distance should not be exceeded than 180mm for Fe 415 from table
IS: 456:-2000
Min. reinforcement should not be less than As =0.85bd/fy
Maximum reinforcement both in tension and compression shall not exceed
0.04bD.
Maximum spacing of shear reinforcement shall not exceed 0.75d for vertical
stirrups and d for inclined stirrups and in no case shall the spacing exceed 300mm
and minimum reinforcement provided as per this formula
= Asv/bsv > (0.4 /0.87fy).
The maximum spacing of shear stirrups has been kept at 200mm, subjected to
detailing consideration with respect to earthquake detailing.
At least two bars have been provided continuous over the entire span of beam.
At external joints bars with columns, top and bottom bars have been provided
with anchorage length of Ld in tension + 10 dia. of bar.
At internal joints bars have been taken continuous through the column.
35
The tension steel ratio on any section is not less than (0.24 fck0.5
)/fy and not
greater than 0.025Mpa.
Provision for laps has been provided wherever required. Hooks shall be provided
wherever lap occurs at spacing not greater than 150mm. Further it has been taken
care not to be provided any laps in the joint within distance of 2d from any face and
within quarter length of any member. Also not more than 50% bars have been
curtailed at a section.
36
2.5 MANUAL DESIGN OF BEAM
LIVE LOAD ON BEAM No. 2:- FIG 2.6
DEAD LOAD ON BEAM No. 2:- FIG 2.7
1.5(DL+LL) ON BEAM No. 2:- FIG 2.8
37
1.5(DL+LL) ON BEAM No. 2:- FIG 2.9
On STAAD Pro Analysis of the whole structure ,we get the follwing responses.
Shear Force Diagram:- FIG 2.10
38
Bending Moment Diagram:- FIG 2.11
Sample Design Calculation for Beam No: 3
Steel Reinforcement for= Tor grade 500
Concrete = M25 Grade
B= 300 D= 600 mm
Effective L = 4.608 m
Determination of area of steel reinforcement:
Maximum Positive Moment = 311 KN-m
Maximum Negative Moment = 220 KN-m
Top Reinforcement Tor 16 mm @ 85 C/C
Bottom Reinforcement Tor 20 mm@ 175 mm C/C
Check for shear:
𝑉𝑢= 147 KN
𝜏𝑣= 𝑉𝑢
𝑏∗𝑑=
147∗1000
300∗600= 0.82
𝜏𝑐 = 0.47 from IS 456 Table-19
𝜏𝑐,𝑚𝑎𝑥=3.1
Since 𝜏𝑐<𝜏𝑣<𝜏𝑐,𝑚𝑎𝑥 shear reinforcement is required
𝑉𝑢𝑠=𝑉𝑢 − 𝜏𝑐𝑏𝑑
= 147-0.47*300*600= 62.4 KN
Provide 8 mm, 2-legged stirrups@220 mm c/c
39
Strength of shear reinforcement
𝑉𝑠 = .87𝑓𝑦 ∗ 𝐴𝑠𝑣 ∗ 𝑑
𝑠𝑣
𝑉𝑠=.87∗415∗ 100.53 ∗ 600
220 = 98.9KN > 81.9KN
OK
Development length
𝑙𝑑 = ∅∗087∗𝑓𝑦
4∗𝜏𝑏𝑑 =
20∗0.87∗415
4∗2.24 = 805 mm
Provide (8*20mm = 160mm) anchorage length and provide a 90 degree
bend in the 20 mm bars.
Provide (8*16mm = 128mm) anchorage length and provide a 90 degree
bend in 16 mm bars
40
Column Reinforcement:- FIG 2.12
STAAD DESIGN
B E A M N O. 2 D E S I G N R E S U L T S
M25 Fe500 (Main) Fe415 (Sec.)
LENGTH: 4608.5 mm SIZE: 300.0 mm X 600.0 mm COVER: 25.0 mm
SUMMARY OF REINF. AREA (Sq.mm)
----------------------------------------------------------------------------
SECTION 0.0 mm 1152.1 mm 2304.2 mm 3456.4 mm 4608.5 mm
----------------------------------------------------------------------------
TOP 1641.07 1293.34 1218.03 1280.23 1579.34
REINF. (Sq. mm) (Sq. mm) (Sq. mm) (Sq. mm) (Sq. mm)
BOTTOM 1148.22 1350.67 1425.03 1392.57 1191.75
REINF. (Sq. mm) (Sq. mm) (Sq. mm) (Sq. mm) (Sq. mm)
41
----------------------------------------------------------------------------
SUMMARY OF PROVIDED REINF. AREA
----------------------------------------------------------------------------
SECTION 0.0 mm 1152.1 mm 2304.2 mm 3456.4 mm 4608.5 mm
----------------------------------------------------------------------------
TOP 9-16í 7-16í 7-16í 7-16í 8-16í
REINF. 2 layer(s) 2 layer(s) 2 layer(s) 2 layer(s) 2 layer(s)
BOTTOM 3-25í 3-25í 3-25í 3-25í 3-25í
REINF. 1 layer(s) 1 layer(s) 1 layer(s) 1 layer(s) 1 layer(s)
SHEAR 2 legged 8í 2 legged 8í 2 legged 8í 2 legged 8í 2 legged 8í
REINF. @ 200 mm c/c @ 200 mm c/c @ 200 mm c/c @ 200 mm c/c @ 200 mm
c/c
----------------------------------------------------------------------------
SHEAR DESIGN RESULTS AT DISTANCE d (EFFECTIVE DEPTH) FROM
FACE OF THE SUPPORT
-----------------------------------------------------------------------------
SHEAR DESIGN RESULTS AT 1106.3 mm AWAY FROM START SUPPORT
VY = 153.56 MX = 0.46 LD= 22
Provide 2 Legged 8í @ 200 mm c/c
SHEAR DESIGN RESULTS AT 1112.5 mm AWAY FROM END SUPPORT
VY = -149.91 MX = -0.60 LD= 24
Provide 2 Legged 8í @ 200 mm c/c
42
2.6 DESIGN OF COLUMNS
The columns of proposed structure have been designed as short columns
with axial load and biaxial moments. All columns have been designed using
method outlined in SP 16, (Design Aids to IS: 456-2000) using the columns
interaction diagrams with all the reinforcement distributed equally on all sides.
DESIGN APPROACH
As mentioned, all columns have been designed as short columns along both
axes in accordance with clause 25.1.1 of IS: 456-2000.
A column is said to be short when the slenderness ratio as given by the
expression is less than 12 and greater than 3
Slenderness ratio along X-X axes
Lex /b and
Slenderness ratio along Y-Y axes
Ley/D
Where:
Lex = Effective length of column along X-X axis
Ley = Effective length of column along Y-Y axis
B = width of column along X-X axis
D = Depth of the column along Y-Y axis
UNSUPPORTED LENGTH
The length of column ,LO was taken as the clear distance b/w the floor and
the underside of the shallower beam framing into the columns in each direction at
the next higher floor level in accordance with clause 25.1.3 of IS : 456-2000
The limit to slenderness, in accordance with clause 25.3.1 of IS: 456-2000
was also taken into consideration.
43
EFFECTIVE LENGTH OF COLUMNS
The columns being restrained along both axes the effective length of
columns was taken as 0.65 Lo in accordance with table – 28 of IS: 456-2000
All columns have been designed for the following forces:-
1. Axial load
2. Moment about X-X axis
3. Moment about Y-Y axis
4. Moment due to minimum eccentricity as mentioned in clause 25.4 of
IS: 456-2000
5. Shear force analysis (see article below), and
6. Torsion shear due to seismic forces.
DESIGN OF COLUMNS FOR SHEAR
As mentioned above, all columns have been designed for greater of the two.
1. Factored shear force from analysis
2. Shear given by the expression in IS: 13920 -1993.
In all the cases that were encountered, the factored shear force from analysis was
found greater and thus the columns designed for the same.
Design for shear was done in accordance with clause 40.1 of IS: 456-2000
by calculating the nominal shear stress given by the expression
𝛕v = Vu/bd
Where
44
Vu = Design shear force
b = Width of member
d = effective depth
Depending upon the area of tensile reinforcement and grade of the concrete
used, the design shear strength of concrete was obtained from modified given in
clause 40.2.2 of IS: 456-2000
NOTE: - While calculating the design shear strength 50% area of steel was taken
into consideration by assuming that half of the steel would be in compression and
the total steel is distributed equally on all sides.
DETAILING OF REINFORCEMENT
1. The cross-section of longitudinal reinforcement was kept b/w 0.8% to 4% in
accordance with clause 26.5.3.1 of IS : 456-2000
2. All bars used for longitudinal reinforcement are greater than 12mm.
3. Spacing of bars along periphery of column has been kept less than 300mm.
4. All transverse reinforcement provided is of greater than ¼ of the largest
longitudinal bar and not exceeding the 16mm.
5. The pitch of ties should not exceed 300mm.
6. All transverse reinforcement has been arranged in accordance with clause
26.5.3.2 of IS : 456-2000
Apart from these considerations, following provision of IS 13920-1993 has
been conformed to
7. The least lateral dimension of the column is greater than 300mm.
8. The ratio of the least lateral dimension to the perpendicular dimension is
more than 0.4.
45
9. Lap splices wherever they occur have been proposed in the central half of the
member. Hoop with a pitch not exceeding 150mm c/c have been provided
over entire splice length.
10. The transverse reinforcement consists of square hoops having 135 degree
with a 10 dia. extended at each end confined in the core.
11. The parallel edges of hoops are not spaced greater than 300mm as far as
possible. A cross tie or a pair of overlapping hoops have provided engaging
all peripheral bars.
46
MANUAL DESIGN OF COLUMN
COLUMN NO: - 2040
Concrete fck=40 N/mm2
Steel fy =500 N/mm2
Cover (gross) =40 mm
Unsupported length =3050 mm
Factored load (Pu) = 2348.98 KN
Factored Moment
Factored moment about major axis (Mux) = 100.46 KN.m
Factored moment about minor axis (Muy) = 46.98 KN.m
Depth in respect of major axis (b) = 1100 mm
Width of member (D) = 300 mm
Check for slenderness ratio
Effective length=le=1.0*L=1*3200=3200mm
Effective Length/Depth(D)=3050mm/1100mm=2.72(<12)
Effective Lenth/Width(B) =3050mm/300mm=10.17(<12)
It is designed as a short column.
Check for eccentricity:
ex=𝑀𝑢𝑥
𝑃𝑢=
100.46×106
2348.98×103= 42.77 mm
ey=𝑀𝑢𝑦
𝑃𝑢=
46.98×106
2348.98×103= 20 mm
Minimum eccentricity as per code:
ex min = 3050
500+
1100
30 = 42.76 mm
ey min = 3050
500+
300
30 = 16 mm
As a first trial assume the reinforcement percentage, p=0.86%
𝑝
𝑓𝑐𝑘⁄ = 0.8640⁄ =0.021
Uniaxial moment capacity of the section about xx-axis:
47
𝑑′𝐷⁄ =
40
1100 = 0.036
Chart for 𝑑′𝐷⁄ = 0.05 will be used.
Pu/fck bD =110030025
1098.2348 3
= 0.177
Referring to chart 47,
Mu/fck bD2 = 0.32
∴ Mux1 = 62 1011003002532..0 = 2904 kNm
Uniaxial moment capacity of the section about yy-axis:
1100
40'
D
d = 0.036
Chart 𝑑′𝐷⁄ = 0.1 will be used.
Referring to chart 47,
Mu/fck bD2 = 0.32
∴ Muy1 = 62 1011003002532..0 = 792 kNm
Calculation of Puz:
Referring to chart 63 corresponding to p=0.86, FY=500 and fck = 40
Puz/Ag = 11.6 N/mm2
∴ Puz = 11.6Ag = 11003006.11 310 KN = 3828 KN
Pu/Puz = 2348.98
3828 = 0.61
Mux/Mux1 = 100.46
2904 = 0.03
Muy/Muy1 = 46.98
792 = 0.6
48
Referring to chart 64 SP16, the permissible value of Mux/Mux1
corresponding to the above values of Muy/Muy1 and Pu/Puz is equal to 0.61
Area of steel = 0.61×1100×300
100 = 2013 mm
2
Providing 16mm diameter bar
No. of bar = 2013
𝜋×8×8= 10.23 = 12 bar
Providing 8mm dia lateral ties
The spacing of the column should not exceed
1. Least dimension of the column=300mm
2. Sixteen times the dia of longitudinal bar=16*16=256mm
3. 300mm
Provide 8mm lateral ties at 190mm c/c spacing
49
DESIGN CHARTS USED FOR COLUMN DESIGN:-
FIG 2.13
50
FIG 2.14
51
FIG 2.15
52
FIG 2.16
53
Column Detailing:- FIG 2.17
54
STAAD DESIGN
C O L U M N N O. 29016 D E S I G N R E S U L T S
M40 Fe500 (Main) Fe415 (Sec.)
LENGTH: 3050.0 mm CROSS SECTION: 300.0 mm X 1100.0 mm COVER:
40.0 mm
** GUIDING LOAD CASE: 22 END JOINT: 13111 SHORT COLUMN
DESIGN FORCES (KNS-MET)
-----------------------
DESIGN AXIAL FORCE (Pu) : 2348.98
About Z About Y
INITIAL MOMENTS : 92.25 30.58
MOMENTS DUE TO MINIMUM ECC. : 100.46 46.98
SLENDERNESS RATIOS : - -
MOMENTS DUE TO SLENDERNESS EFFECT : - -
MOMENT REDUCTION FACTORS : - -
ADDITION MOMENTS (Maz and May) : - -
TOTAL DESIGN MOMENTS : 100.46 46.98
REQD. STEEL AREA : 1053.35 Sq.mm.
REQD. CONCRETE AREA: 131669.25 Sq.mm.
MAIN REINFORCEMENT : Provide 16 - 12 dia. (0.55%, 1809.56 Sq.mm.)
(Equally distributed)
TIE REINFORCEMENT : Provide 8 mm dia. rectangular ties @ 190 mm c/c
SECTION CAPACITY BASED ON REINFORCEMENT REQUIRED (KNS-
MET)
----------------------------------------------------------
Puz : 6316.05 Muz1 : 918.51 Muy1 : 237.73
INTERACTION RATIO: 0.18 (as per Cl. 39.6, IS456:2000)
SECTION CAPACITY BASED ON REINFORCEMENT PROVIDED (KNS-
MET)
----------------------------------------------------------
WORST LOAD CASE: 30
END JOINT: 13111 Puz : 6586.01 Muz : 691.92 Muy : 171.62 IR: 0.54
55
FIG 2.18
56
CHAPTER 3
3.1WIND LOAD
Wind pressure on a building surface depends primarily on its velocity, the
shape and surface structure of the building, the protection from wind offered by
surrounding natural terrain or man-made structures, and to a smaller degree, the
density of air which decreases with altitude and temperature. All other factors
remaining the same, the pressure due to wind is proportionate to the square of the
velocity:
P = 0.6Vz2
Where p is the pressure, in kN/m2
V is the velocity of wind, in meter per second.
In an engineered structure, wind loads have long been a factor in the design
of lateral force resisting system, with added significance as the height of the
building increased. For many decades, the cladding system of high rise buildings,
particularly around the corners of the buildings have been scrutinized for the effect
of wind on building enclosure. Glass and curtain wall system are regularly
developed and tested to resist cladding pressures and suctions are introduced by the
postulated wind events.
As wind hits the structure and flows around it, several effects are possible as
illustrated in fig 3.1. Pressure on the windward face and suction on the leeward face
creates drag force.
Analogous to flow around an airplane, unsymmetrical flow around the
structure can create lift forces. Air turbulence around the leeward corners and edges
can create vortices, which are high- velocity air currents that create circular
updrafts and suction streams adjacent to the building.
Periodic shedding of vortices causes the building to oscillate in a direction
transverse to the direction of the wind and may result in unacceptable accelerations
at the upper floors of tall buildings.
The effects of downdrafts must also be considered: Downdrafts have been
known to completely strip trees in plaza areas and to buffet pedestrians
dangerously. Some tall buildings that extend into high wind velocity regions have
been known to sway excessively in strong wings. High suction forces have blown
off improperly anchored lightweight roofs
57
3.1.1 DESIGN CONSIDERATIONS FOR THE WIND LOAD
In designing for wind, a building cannot be considered independent of its
surroundings because configuration of nearby buildings and natural terrain has
substantial influence on the design loads, and hence on the sway response of the
building. Sway is defined as the horizontal displacement at the top of a building.
The sway at the top of a tall building caused by wind may not be seen by a
passerby, but may be of concern to those experiencing wind -motion problems
at the top floors. There is scant evidence that winds, except those due to a
tornado or hurricane, have caused major structural damage to buildings.
Nevertheless, it is prudent to investigate wind-related behavior of modern
skyscrapers, typically built using lightweight curtain walls, dry partitions, and high-
strength materials, because they are more prone to wind-motion problems than the
early skyscrapers, which had the weight advantage of heavy masonry partitions,
stone facades, and massive structural members.
To be sure, all buildings sway during windstorms, but the motion in old tall
buildings with heavy full-height partitions has u been imperceptible and, therefore,
has not been a cause for concern. Structural innovations coupled with lightweight
construction have reduced the stiffness, mass, and damping characteristics of
modern buildings. In these buildings, objects may vibrate, doors and chandeliers
may swing, pictures may lean, and books may fall off shelves. Additionally if the
building has a twisting action, its occupants may get an illusory sense that the world
outside is moving, creating symptoms of vertigo and disorientation. In more violent
storms, windows may break, creating safety problems for pedestrians below.
Sometimes, strange and frightening noises may be heard by occupants as
the wind shakes elevators, strains floors and walls, and whistles around the building
sides.
It is generally agreed that acceleration response that includes the effects of
torsion at the top floors of a tall building, is the best standard for evaluation of
motion perception. A commonly used criterion is to limit accelerations of the
building’s upper floors to no more than 2% of gravity (20 milli-g) for a 10
year wind. Other commonly applied guidelines include those published by the
Council on Tall Buildings and Urban Habitat (CTBUH), and the
International Organization for Standardization (ISO 6899-1984)
58
3.1.2 NATURAL WIND
Wind is not constant either with height or time, is not uniform over the
windward side of the building, and does not always cause positive pressure. In fact,
wind is a complicated phenomenon; it is air in turbulent flow, which means that
motion of individual particles is so erratic that in studying wind, one ought to be
concerned with statistical distributions of speeds and directions rather than with
simple averages.
Wind is the term used for air in motion and is usually applied to the natural
horizontal motion of the atmosphere. Motion in a vertical or nearly vertical
direction is called a current. Movement of air near the surface of the earth is three-
dimensional, with horizontal motion much greater than the vertical motion.
Vertical air motion is of importance in meteorology but is of less importance near
the ground surface. On the other hand, the horizontal motion of air, particularly the
gradual retardation of wind speed and high turbulence that occur near the ground
surface, are of importance in building engineering. In urban areas, this zone
of wind turbulence often referred to as surface boundary layer, extends to a height
of approximately one-quarter of a mile aboveground. Above this layer, the
horizontal airflow is no longer influenced by the retarding effect of the ground
surface. The wind speed at this height is called gradient wind speed, and it is
precisely within this boundary layer where human construction activity occurs.
Therefore, how wind effects are felt within this zone is of concern in
building design.
Although one cannot see wind, we know by experience, its flow is quite
random and turbulent. Imagine taking a walk on a windy day. You will no doubt
experience a constant flow of wind, but intermittently you may also experience
sudden gusts of rushing wind. This sudden variation in wind speed, called gustiness
or turbulence, is an important factor in determining dynamic response of tall
buildings.
Air flowing over the earth’s surface is slowed down and made turbulent by
the roughness of the surface. As the distance from the surface increases, these
friction effects are felt less and less until a height is reached where the influence of
the surface roughness is negligible. This height, as mentioned earlier, is referred to
59
as the gradient height, and the layer of air below this, where the wind is turbulent
and its speed increases with height, is referred to as the boundary layer. The
gradient height or depth of the earth’s boundary layer is determined largely by the
terrain roughness and typically varies from 900ft over country to about 1660ft over
built up urban areas.
The wind -tunnel testing provides information regarding the response of
buildings subject to differing wind speed and direction. In order to make the most
rational use of this aerodynamic information, it is necessary to synthesize test
results with the actual wind climate characteristics at the site
3.1.3 TYPES OF WIND
Winds that are of interest in the design of buildings can be classified into
three major types: prevailing winds, seasonal winds, and local winds.
1. Prevailing winds: Surface air moving toward the low-pressure equatorial
belt is called prevailing wind or trade wind. In the northern hemisphere, the
northerly wind blowing toward the equator is deflected by the rotation of the earth
to a northeasterly direction, and hence commonly known as the northeast
trade wind. The corresponding wind in the southern hemisphere is the southeast
trade wind.
2. Seasonal winds: Air over the land is warmer in summer and colder in
winter than the air adjacent to oceans during the same seasons. During summer, the
continents become seats of low pressure, with wind blowing in from the colder
oceans. In winter, the continents experience high pressure with winds directed
toward the warmer oceans. These movements of air caused by variations in
pressure difference are called seasonal winds.
The monsoons of the China Sea and the Indian Ocean are examples of these
movements of air.
3. Local winds: These are associated with the regional weather patterns and
include whirl-winds and thunderstorms. They are caused by daily changes in
temperature and pressure, generating local effects in winds. The daily variations in
temperature and pressure may occur over irregular terrain, causing valley and
mountain breezes.
60
All three types of wind are of importance in building design. However, for
the purpose of determining wind loads, the characteristics of prevailing and
seasonal winds are grouped together, whereas those of local winds are studied
separately. This grouping is to distinguish between the widely differing scales of
fluctuations of the winds; prevailing and seasonal winds fluctuate over a period of
several months, whereas local winds may vary every few seconds. The variations in
the mean velocity of prevailing and seasonal winds are referred to
as fluctuations whereas the variations in local winds occurring over a very short
period of time are referred to as gusts.
Flow of wind unlike that of other fluids, is not steady and fluctuates in a
random fashion. Because of this, wind loads for building design are studied
statistically.
3.1.4 CHARACTERISTICS OF WIND
Wind flow is complex because numerous flow situations arise from the
interaction of winds with structures. However, in winds engineering, simplifications
are made to arrive at the design winds loads by distinguishing the following
characteristics:
Variation of winds velocity with height (velocity profile)
• Winds turbulence
• Statistical probability
• Vortex shedding
• Dynamic nature of winds–structure interaction
.
.
3.2 Code based method for wind load design
IS 875 part -3 gives basic wind speed map of India as applicable to 10 m
height above mean ground level for different zones of the country. Basic wind
speed is based on peak gust velocity average over a short time interval of about 3
sec and corresponds to mean heights above ground level in an open terrain.
61
Basic wind speed considered in our considered in our project for
Greater Noida is 47m/s
Design Wind Speed (Vz)
The basic wind speed for any site shall be obtained from Fig. 1 and shall be
modified to include the following effects to get design wind speed, Vz at any
height, Z for the chosen structure:
(a) Risk level,
(b) Terrain roughness and height of structure,
(c) Local topography, and
(d) Importance factor for the cyclonic region.
It can be mathematically expressed as follows:
Vz = Vb k1 k2 k3
where Vz = design wind speed at any height z in m/s,
k1 = probability factor (risk coefficient),
k2 = terrain roughness and height factor,
k3 = topography factor
NOTE: The wind speed may be taken as constant up to a height of 10 m.
However, pressures for buildings less than 10m high may be reduced by 20% for
stability and design of the framing
Design Wind Pressure
The wind pressure at any height above mean ground level shall be obtained
by the following relationship between wind pressure and wind speed:
Pz = 0.6 Vz2
Where Pz = wind pressure in N/m2at height z, and
Vz = design wind speed in m/s at height z.
The design wind pressure pd can be obtained as,
pd = Kd . Ka. Kc. Pz
where Kd = Wind directionality factor
Ka = Area averaging factor
Kc = Combination factor (See 6.2.3.13)
62
NOTE 1 – The coefficient 0.6 (in SI units) in the above formula depends on
a number of factors and mainly on the atmospheric pressure and air temperature.
The value chosen corresponds to the average Indian atmospheric conditions.
NOTE 2 –Ka should be taken as 1.0 when considering local pressure
coefficients.
Wind load on individual member
When calculating the wind load on individual structural elements such as
roof and walls, an individual cladding unit and their fittings, it is essential to take
account of the pressure difference between opposite faces of such elements or units.
For clad structure, it is therefore necessary to know the internal pressure as well as
external pressure. Then the wind load, F acting in the direction normal to the
individual structural elements or cladding unit is:
F = (Cpe-Cpi)*A*pd
Where, Cpe=external pressure coefficient
Cpi=internal pressure coefficient
A=surface area of cladding unit,
Pd =design wind pressure
3.2.1 Design for wind load
Height of building=73.20m+1m (parapet wall) =74.20 m
Length of building=37.385 m
Width of building=28.13m
Basic wind speed, V=47m/s
Now Design wind speed,Vz =k1*k2*k3*Vb
Where,
K1=1(for Vb=47m/s and life=50years)
63
Fig:- 3.1
64
Fig:- 3.2 For K2,
Terrain category=2
Class=B (Greatest horizontal and vertical dimension between 20m-
50m)
Based on terrain category and structure class, we calculate the value of K2
for different height of building as given below.
65
For K3
K3=1(skewness of wind direction less than 30)
Fig:- 3.3
Now substituting this values in given formula of design Wind Speed,
Design wind speed,Vz = K1*K2*K3*Vb
We get the corresponding value at different height of the building
For Design wind pressure, Pz =0.6Vz2
Now, Design Wind Pressure at different height of the building is calculated
accordingly in the tabular form:
66
3.2.2 On application of other forces, for the following load combination
Table no 2
NO Load Combination
1 1.5(DL+LL)
2 1.2(DL+LL+WLX)
3 1.2(DL+LL+WLZ)
4 1.2(DL+LL-WLZ)
5 1.2(DL+LL-WLZ)
6 1.5(DL+WLX)
7 1.5(DL-WLX)
8 1.5(DL+WLZ)
9 0.9DL+1.5WLX
10 0.9DL-1.5WLX
11 0.9DL+1.5WLZ
67
CHAPTER 4
4.1 AN INTRODUCTION TO SEISMIC DESIGN
Although structural design for seismic loading is primarily concerned with
structural safety during major earthquakes, serviceability and the potential for
economic loss are also of concern .As such, seismic design requires an
understanding of the structural behavior under large inelastic, cyclic deformations.
Behavior under this loading is fundamentally different from wind or gravity
loading. It requires a more detailed analysis, and the application of a number of
stringent detailing requirements to assure acceptable seismic performance
beyond the elastic range. Some structural damage can be expected when the
building experiences design ground motions because almost all building codes
(here we consider IS 1893-2002) allow energy dissipation in structural system.
The seismic analysis and design of buildings has traditionally focused on
reducing the risk of the loss of life in the largest expected earthquake. Building
codes base their provisions on the historic performance of the buildings and their
deficiencies and have developed provisions around life- safety concerns by
focusing their attention to prevent collapse under the most intense earthquake
expected at a site during the life of a structure. These provisions are based on the
concept that the successful performance of the building in areas of high seismicity
depends on a combination of strength; ductility manifested in the details of
construction; and the presence of a fully interconnected ,balanced and complete
lateral force-resisting system. Very brittle lateral force –resisting system can be
excellent performers as long as they are never pushed beyond their elastic
strength.
Seismic provisions typically specify criteria for the design and the
construction of new structures subjected to earthquake ground motions with three
goals: (1) minimize the hazard to life from all structures, (2) increase the expected
performance of structures having a substantial public hazard due to
occupancy or use, and (3) improve the capability of essential facilities to function
after an earthquake.
68
Some structural damage can be expected as a result of design ground motion
because the codes allow inelastic energy dissipation in the structural system. For
ground motions in excess of the design levels, the intent of codes is for structures to
have a low likelihood of collapse.
In most structures that are subjected to moderate –to-strong earthquakes,
economical earthquake resistance is achieved by allowing yielding to take place in
some structural members. It is generally impractical as well as uneconomical to
design a structure to respond in the elastic range to the maximum expected
earthquake induced inertia forces. Therefore, in seismic design, yielding is
permitted in predetermined structural members or locations, with the provisions
that the vertical load carrying capacity of the structure is maintained even after
strong earthquakes. However, for certain types of structures such as nuclear
facilities, yielding cannot be tolerated and as such, the design needs to be elastic.
Structures that contain facilities critical to post-earthquake operations- such as
hospitals, fire stations, power stations, and communication centers- must not only
survive without collapse, but must also remain operation after an earthquake.
Therefore, in addition to life safety, damage control is an important design
consideration for structures deemed vital post-earthquake functions.
In general, most earthquake code provisions implicitly require that
structures be able resist
1. Minor earthquakes without any damage.
2. Moderate earthquakes with negligible structural damage and some non-
structural damage.
3. Major earthquakes with some structural and non-structural damage but
without collapse.
The structure is expected to undergo fairly large deformations by yielding in some
structural members.
An idea of the behavior of a building during an earthquake may be grasped by
considering the simplified response shape shown in figure 4.1. As the ground on
which the building rests is displaced, the base of the building moves with it.
However, the building above the base is reluctant to move with it because the
inertia of the building mass resists motion and causes the building to distort. This
distortion wave travels along the height of the structure, and with continued shaking
of the base; cause the building to undergo a complex series of oscillations.
69
Although both wind and seismic forces are essentially dynamic, there is a
fundamental difference in the manner in which they are induced in a structure.
Wind loads, applied as external loads, are characteristically proportional to the
exposed surface of the structure, while the earthquake forces are principally internal
forces resulting from the distortion produced by the inertial resistance of the
structure to earthquake motions.
The magnitude of earthquake forces is a function of the mass of the
structure rather than its exposed surface. Whereas in wind design, one would feel
greater assurance about the safety of a structure made up of heavy sections, in
seismic design, this does not necessarily produce a safer design.
Building behavior during Earthquake:- FIG 4.1
70
4.1.1 BUILDING BEHAVIOR
The behavior of a building during an earthquake is a vibration problem. The
seismic motions of the ground do not damage a building by impact, as does a
wrecker’s ball, or by externally applied pressure such as wind, but by internally
generated inertial forces caused by the vibration of the building mass. An increase
in mass has two undesirable effects on the earthquake design. First, it results an
increase in the force, and second, it can cause buckling or crushing of columns and
walls when the mass pushes down on a member bent or moved out of plumb by the
lateral force. The distribution of dynamic deformations caused by the ground
motions and the duration of motion are of concern in seismic design, although the
duration of ground motion is an important design issue.
In general, tall buildings respond to seismic motion differently than low rise
buildings. The magnitude of inertia forces induced in an earthquake depends on
the building mass, ground acceleration, the nature of the foundation, and the
dynamic characteristics of the structure. I f a building and its foundation were
infinitely rigid, it would have the same acceleration as the ground, resulting in an
inertia force, F=ma, for a given ground acceleration, a.
However, because buildings have certain flexibility, the force tends to be
less than the product of building mass and acceleration. Tall buildings are
invariably more flexible than low-rise buildings, and in general, they experience
much lower accelerations than low rise building. But a flexible building subjected
to ground motions for a prolonged period may experience much larger forces if its
natural time period is near that of the ground waves. Thus, the magnitude of lateral
force is not a function of the acceleration of the ground alone, but is influenced to a
great extent by the type of response of the structure itself and foundation as well.
This interrelationship of building behavior and seismic ground motion also
depends on the building period as formulated in the so- called response spectrum.
71
4.1.2 INFLUENCES OF SOIL
The intensity of ground motion reduces with the distances from the
epicenter of the earthquake. The reduction, called attenuation, occurs at a faster rate
for higher frequency (short period) components than for lower frequency (long
period) components. The cause of change in attenuation rate is not understood, but
its existence is certain. This is a significant factor in the design of tall buildings,
because a tall building, although situated farther from a causative fault than a low
rise building, may experience greater seismic loads because long-period
components are not attenuated as fast as the short period components. Therefore,
the area influenced by ground shaking potentially damaging to, say, a 50-story
building is much greater than for a 1-story building.
As a building vibrates due to ground motion, its acceleration will be
amplified if the fundamental period of the building coincides with the period of
vibrations being transmitted through the soil. This amplified response is called
resonance. Natural periods of soil are in the range of 0.5-1.0 s. Therefore, it is
entirely possible for the building and the ground it rests upon to have the same
fundamental period. This was the case for many 5 to 10 storeys building in
September 1985 earthquake in Mexico City. An obvious design strategy is to
ensure that buildings have a natural period different from that of the expected
ground vibration to prevent amplification.
4.1.3 DAMPING
Buildings do not resonate with the purity of a tuning fork because they are
damped; the extent of damping depends upon the construction materials, the type of
connections, and the influence of non-structural elements on the stiffness
characteristics of the building. Damping is measured as a percentage of critical
damping.
In a dynamic system, critical damping is defined as the minimum amount
of damping necessary to prevent oscillation altogether. To visualize critical
damping, imagined a tensioned string immersed in water. When the string is
plucked, it oscillates about its rest position several times before stopping. If we
replace water with a liquid of higher viscosity, the string will oscillate, but certainly
not as many times as it did in water. By progressively increasing the viscosity of the
liquid, it is easy to visualize that a state can be reached where the string, once
plucked, will return to its natural position without ever crossing it. The minimum
72
viscosity of the liquid that prevents the vibration of the string altogether can be
considered equivalent to the critical damping.
The damping of the structures is influenced by a number of external and
internal sources. Chief among them are
1. External viscous damping caused by air surrounding the building. Since
the viscosity of air is low, this effect is negligible in comparison to other types of
damping.
2. Internal viscous damping associated with the material viscosity. This is
proportional to velocity and increases in proportion to the natural frequency of the
structure.
3. Friction damping, also called Coulomb damping, occurring at
connections and support points of the structure. It is a constant, irrespective of the
velocity or amount of displacement.
4. Hysteric damping that contributes to a major portion of the energy
absorbed in ductile structures.
For analytical purposes, it is a common practice to lump different sources of
damping into a single viscous damping. For non-base isolated buildings, analyzed
for code prescribed loads, the damping ratios used in practice vary anywhere from
1% to 10% of critical. The low –end values are for wind, while those of the upper
end are for seismic design. The damping ratio used in the analysis of seismic base
isolated building is rather large compared to values used for non-isolated buildings,
and varies from about 0.20 to 0.35(20% to 35% of critical damping).
Base isolation, consists of mounting a building on an isolation system to
prevent horizontal seismic ground motions from entering the building. The strategy
results in significant reductions in inter-storey drifts and floor accelerations, thereby
protecting the building and its contents from earthquake damage.
73
Linear viscous program:- FIG 4.2
A level of ground acceleration on the order of 0.1g, where ‘g’ is the
acceleration due to gravity, is often sufficient to produce some damage to weak
construction. An acceleration of 0.1g, or 100% of gravity, is analytically
equivalent, in the static sense, to a building that cantilevers horizontally
from a vertical surface.
As stated previously, the process by which free vibration steadily
diminishes in amplitude is called damping. In damping, the energy of the
vibrating system is dissipated by various mechanisms, and often more than one
mechanism may be present at the same time. In simple laboratory models, most of
the energy dissipation arises from the thermal effect of the repeated elastic
straining of the material and from the internal friction. In actual structures,
however, many other mechanisms also contribute to the energy dissipation. In a
vibrating concrete building, these include the opening and closing of micro
cracks in concrete, friction between the structure itself and non-structural elements
such as partition walls. Invariably, it is impossible to identify or describe
mathematically each of these energy- dissipating mechanisms in an actual building.
Therefore, the damping in actual structures is usually represented in a highly
idealized manner. For many purposes, the actual damping in structures can be
idealized satisfactorily by a linear viscous damper or dashpot. The damping
coefficient is selected so that the vibration energy that dissipates is equivalent to the
energy dissipated in all the damping mechanisms. This idealization is called
equivalent viscous damping.
Figure 4.2 shows a linear viscous damper subjected to a force, fD. The
damping force, fD, is related to the velocity across the linear viscous damper by
fD = c
Where the constant c is the viscous damping coefficient; it has units of
force*time/length.
Displacement
Force
74
Bilinear force-displacement hysteresis loop:FIG 4.3
Unlike the stiffness of the structure, the damping coefficient cannot be
calculated from the dimension of the structure and the sizes of the structural
elements. This is understandable because it is not feasible to identify all the
mechanisms that dissipate the vibrational energy of actual structures.
Thus, vibration experiments on actual structures provide the data for
evaluating the damping coefficient. These may be free-vibration experiments that
lead to measured rate which motion decays in free vibration. The damping property
may also be determined from forced- vibration experiments.
The equivalent viscous damper is intended to model the energy dissipation
at deformation amplitudes within the linear elastic limit of the overall structure.
Over this range of deformation, the damping coefficient c determined from the
experiments may vary with the deformation amplitude. This non linearity of the
damping property is usually not considered explicitly in dynamic analysis. It may
be handled indirectly by selecting a value for the damping coefficient that is
appropriate for the expected deformation amplitude, usually taken as the
deformation associated with linearly elastic limit of the structure. Additional energy
is dissipated due to the inelastic behavior of the structure at large deformations.
Under cyclic forces or deformations, this behavior implies the formation of a force-
displacement hysteresis loop (figure 4.3). The damping energy dissipated during
one deformation cycle between deformation limit ±up is given by the area within
the hysteresis loop abcd (figure 4.3). This energy dissipation is usually not modeled
by a viscous damper, especially if the excitation is earthquake ground motion.
Instead, the most common and direct approach to account for the energy dissipation
through inelastic behaviour is to recognize the inelastic relationship between
resisting force and deformation. Such force-deformation relationships are obtained
from experiments on structures or structural components at slow rates of
deformation, thus excluding any energy dissipation arising from rate dependent
effects.
4.1.4 BUILDING DRIFT AND SEPERATION
Drift is generally defined as the lateral displacement of one floor relative to
the floor below. Drift control is necessary to limit damage to interior partitions,
elevator and stair enclosure, glass, and cladding systems. Stress and strength
limitations in ductile materials do not always provide adequate drift control,
75
especially for tall buildings with relatively flexible moment-resisting frames or
narrow shear walls.
Total building drift is the absolute displacement of any point relative to the
base. Adjoining buildings or adjoining sections of the same building may not have
identical modes of response, and therefore may have a tendency to pound against
one another. Building separations or joints must be provided to permit
adjoining buildings to respond independently to earthquake ground motion.
4.2 SEISMIC DESIGN CONCEPT
An effective seismic design generally includes
1. Selecting an overall structural concept including layout of a lateral force-
resisting system that is appropriate to the anticipated level of ground shaking. This
includes providing a redundant and continuous load path to ensure that a building
responds as a unit when subjected to ground motion.
2. Determining code-prescribed forces and deformations generated by the
ground motion, and distributing the forces vertically to the lateral force-resisting
system. The structural system, configuration, and site characteristics are all
considered when determining these forces.
3. Analyzing the building for the combined effects of gravity and seismic
loads to verify that adequate vertical and lateral strengths and stiffness are achieved
to satisfy the structural performance and acceptable deformation levels prescribed
in the governing building code.
4. Providing details to assure that the structure has sufficient inelastic
deformability to undergo large deformations when subjected to a major earthquake.
Appropriately detailed member possess the necessary characteristics to dissipate
energy by inelastic deformations.
4.2.1 STRUCTURAL RESPONSE
If the base of a structure is suddenly moved, as in a seismic event,
the upper part of the structure will not respond instantaneously, but will lag because
of the inertial resistance and flexibility of the structure. The resulting stresses and
distortions in the building are the same as if the base of the structure were to remain
stationary while time varying horizontal forces are applied to the upper part of the
building. These forces, called inertia forces, are equal to the product of the mass of
the structure times acceleration, that is, F=ma (the mass m is equal to weight
divided by the acceleration of gravity, i.e., m=w/g). Because earthquake ground
76
motion is three dimensional ( 3D; one vertical two horizontal), the structure, in
general, deforms in a 3D manner. Generally, the inertia force generated by the
horizontal components of ground motion require greater consideration for
seismic design since adequate resistance to vertical seismic loads is usually
provided by the member capacities required for gravity load design. In the
equivalent static procedure, the inertia forces are represented by equivalent static
forces.
4.2.2 DUCTILITY
It will soon become clear that in seismic design, all structures are designed
for forces much smaller than those the design ground motion would produce in a
structure with completely linear elastic response. This reduction is possible for a
number of reasons. As the structure begins to yield and deform inelastically, the
effective period of response of the structure tends to lengthen, which for many
structures, results in a reduction in strength demand. Furthermore, the inelastic
action results in a significant amount of energy dissipation, also known as
hysteretic damping. The effect, which is also known as the ductility reduction,
explains why a properly designed structure with a fully yielded strength that is
significantly lower than the elastic seismic force demand can be capable of
providing satisfactory performance under the design ground motion excitations.
The energy dissipation resulting from hysteretic behaviour can be measured
as the area enclosed by the force deformation curve of the structure as it
experiences several cycles of excitation. Some structures have far more energy
dissipation capacity than do others. The extent of energy dissipation capacity
available is largely dependent on the amount of stiffness and strength degradation
that the structure undergoes as it experiences repeated cycles of inelastic
deformation. Figure 4.4 indicates representative load deformation curves for two
simple structures, such as beam-column assembly in a frame. Hysteretic curve in
figure 4.4a is representative of the behaviour of substructures that have been
detailed for ductile behaviour. The substructure can maintain nearly all of its
strength and stiffness over a number of large cycles of inelastic deformation. The
resulting force deformation “loops” are quite wide and open, resulting in a large
amount of energy dissipation capacity. Hysteretic curve in Figure 4.4b represents
the behaviour of a substructure that has not been detailed for ductile behaviour.
It rapidly loses stiffness under inelastic deformation. The energy dissipation
capacity of such a substructure is much lower than that for the substructure in figure
77
4.6a. Hence structural systems with large energy dissipation capacity are assigned
higher R values, resulting in design for lower forces, than systems with relatively
limited energy dissipation capacity.
Hysteresis behaviour: a) curve representing large
energy dissipation and
b) curve representing limited energy dissipation
FIG 4.4 A ductile material is one that can undergo large strains while resisting loads
when applied to reinforced concrete members and structures, the term ductility
implies the ability to sustain significant inelastic deformations prior to collapse. The
capability of a structure to absorb energy, with acceptable deformations and
without failure, is a very desirable characteristic in any earthquake-resistant design.
Concrete, a brittle material, must be properly reinforced with steel to provide the
ductility necessary to resist seismic forces. In concrete columns, for example, the
combined effects of flexure (due to frame action) and compression (due to action
of the overturning moment of the structure as a whole) produce a common mode of
failure: buckling of the vertical steel and spalling of the concrete cover near the
floor levels. Columns must, therefore, be detailed with proper spiral reinforcing or
hoops to have greater reserve strength and ductility.
Ductility may be evaluated by the hysteretic behaviour of critical
components such as a column-beam assembly of a moment frame. It is obtained by
78
cyclic testing of moment rotation (or force-deflection) behaviour of the
assembly. Ductility or hysteretic behaviour may be considered as an energy
dissipating mechanism due to inelastic behaviour of the structure at large
deformations. The energy dissipated during cyclic deformations is given by
the area of hysteric loop ( see figure 4.4a and b). the areas within the loop may be
full or fat, or lean and pinched. Structural assemblies with loops enclosing
large areas representing large dissipated energy are regarded as superior systems for
resisting seismic loadings.
79
Following load combination have been used for Earthquake analysis of the
structure:
Table no 3
NO Load Combination
1 1.5(DL+LL)
2 1.2(DL+LL+EQX)
3 1.2(DL+LL+EQZ)
4 1.2(DL+LL-EQX)
5 1.2(DL+LL-EQZ)
6 1.5(DL+EQX)
7 1.5(DL-EQX)
8 1.5(DL+WQZ)
9 0.9DL+1.5EQX
10 0.9DL-1.5EQX
11 0.9DL+1.5EQZ
80
Deflection Depiction:- FIG 4.5
81
Axial Force- FIG 4.6
82
CHAPTER 5
This chapter deals with the miscellaneous topics. First of all we provide a
comparative study of the economy involved in the design with and without
seismic design. Then we move to ductile design of the building. Some theories and
codal provision have been discussed. A special mention of the reinforcement in the
beam, column and joints according to the provision of IS:13920 have been
discussed. A discussion about the type of foundation used and its design has also
been given. Finally some design details have been given from the ductile design
STAAD Pro. output file.
5.1 MATERIAL REQUIRED BY GRAVITY LOAD DESIGN METHOD
83
5.2 DUCTILITY CONSIDERATION
The basic approach of earthquake resistant design should be based on lateral
strength as well as deformability and ductile capacity of the structure with limited
damage but no collapse. The IS 13920:1993 is based on this approach .Ductility of
the structure is one of the most important factor affecting its seismic performance.
The gap between the actual and lateral force is narrowed down by providing
ductility in the structure. Ductility in the structure will arise from inelastic material
behaviour and detailing of reinforcement in such a manner that brittle failure is
avoided and ductile behaviour is induced by allowing steel to yield.
5.2.1 REQUIREMENT FOR DUCTILITY
In order to achieve a ductile structure we must give stress on three key areas
during the design process. Firstly, the overall design concept of the building
configuration must be sound. Secondly, individual member must be designed for
ductility, and finally connection and other detail need careful attention
Detail consideration
1. GENERAL
1. The design and construction of reinforced concrete buildings shall be
governed by the provisions of IS 456: 2000, except as modified by the
provisions of this code.
2. For all buildings which are more than 3 storeys in height, the minimum
grade of concrete shall be M20 ( fck = 20 MPa ).
The concerned structure is G+23+2B storied, that’s why we have used
M25 grade of concrete
3. Steel reinforcements of grade Fe 500 or less only shall be used.
84
2. FLEXURAL MEMBERS
2.1 General
The factored axial stress on the member under earthquake loading shall not
exceed 0.1 fck.
The member shall preferably have a width-to-depth ratio of more than 0.3.
The width of the member shall not be less than 200 mm.
The depth D of the member shall preferably be not more than 1/4 of the
clear span.
2.2 Longitudinal Reinforcement
The top as well as bottom reinforcement shall consist of at least two bars
throughout the member length.
The tension steel ratio on any face, at any section, shall not be less than
ρmin = 0.24(fck/fy) ; where fck and fy are in MPa.
The maximum steel ratio on any face at any section, shall not exceed ρmax
= 0.025.
The positive steel at a joint face must be at least equal to half the negative
steel at that face.
In an external joint, both the top and the bottom bars of the beam shall be
provided with anchorage length, beyond the inner face of the column, equal
to the development length in tension plus 10 times the bar diameter minus
the allowance for 90 degree bend(s) ( see Fig. 1 ). In an internal joint, both
face bars of the beam shall be taken continuously through the column.
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 a joint, (b) within a distance of 2d from joint face,
and (c) within a quarter lengh of the member where flexural yielding may
generally occur under the effect of earthquake forces. Not more than 50
percent of the bars shall be spliced at one section.
85
FIG:-5.1
Use of welded splices and mechanical connections may also be made, as per
25.2.5.2 of IS 456 : 1978. However, not more than half the reinforcement shall be
spliced at a section where flexural yielding may take place
Lap sploces in beam FIG:-5.2
86
2.3 Web Reinforcement
Web reinforcement shall consist of vertical hoops. A vertical hoop is a
closed stirrup having a 135° hook with a 10 diameter extension (but not <
75 mm) at each end that is embedded In confined core.
The minimum diameter of the bar forming a hoop shall be 6 mm. However,
in beams with clear span exceeding 5 m, the minimum bar diameter shall
be 8 mm.
The shear force to be resisted by the vertical hoops shall be the maximum
of :
a) calculated factored shear force as per analysis, and
b) shear force due to formation of plastic hinges at both ends of the
beam plus the factored gravity load on the span.
FIG:-5.3
The contribution of bent up bars and inclined hoops to shear resistance of
the section shall not be considered.
The spacing of hoops over a length of 2d at either end of a beam shall not
exceed (a) d/4, and (b) 8 times the diameter of the smallest longitudinal bar;
however, it need not be less than 100 mm.
87
Beam Reinforcement FIG:-5.4
3. Compression Member:
3.1 General
These requirements apply to frame members which have a factored axial
stress in excess of 0.1 fck under the effect of earthquake forces.
The minimum dimension of the member shall not be less than 200 mm.
However, in frames which have beams with centre to centre span exceeding
5 m or columns of unsupported length exceeding 4 m, the shortest
dimension of the column shall not be less than 300 mm.
The ratio of the shortest cross sectional dimension to the perpendicular
dimension shall preferably not be less than 0.4.
3.2 Longitudinal Reinforcement
Any area of the column that extends more than 100mm beyond the
confined core due to architectural requirement shall be detailed as in
diagram.
88
FIG:-5.5
3.3 Transverse Requirement
The detailing of the transverse reinforcement should be done in the diagram below
89
FIG:-5.6
Transverse Reinforcement in Column:- FIG:-5.7
1. Special Confining reinforcements
Special confining reinforcement shall be provided over a length lo from each
joint face, towards midspan, and on either side of any section, where
flexural yielding may occur under the effect of earth quake forces. The
length ‘lo’ shall not be less than :
Larger dimension of the member at the section where yielding
occur,
1/6 of clear span of member, and
90
450mm
When a column terminate into a footing or mat, special confining reinforcement
shall extend at least 300mm into the footing or mat.
Column-Joint Detailing FIG:-5.8
91
Provision of special confining reinforcement in footing FIG:-5.9
5.3 FOUNDATION
5.3.1 RAFT OR MAT FOOTING
A raft or mat is a combined footing that covers the entire area
beneath a structure and supports all the wall and columns. When the allowable soil
pressure is low, or the building loads are heavy, the use of spread footing
would cover more than one-half of the area and it may prove more economical to
use mat or raft foundation. They are also used where the soil Mass contains
compressible lenses or the soil is sufficiently erratic so that the differential
settlement would be difficult to control. The raft tends to bridge over the erratic
deposits and eliminates the differential settlement. Raft foundation is also used to
reduce settlement above highly compressible soil, by making the weight of
structure and raft approximately equal to the weight of soil excavated.
Ordinarily, raft are designed as reinforced concrete flat slabs .If the C.G of
loads coincide with the centroid of the raft ,the upward load is regarded as uniform
pressure equal to the downward load divided by the area of the raft. The weight of
raft is not considered in structural design because it is assumed to be carried
directly by the subsoil .
92
Fig:- 5.10 5.3.2 Design of RAFT Foundation
1. Depth of foundation
H=𝑞
𝑊𝑒(
1−𝑠𝑖𝑛∅
1+𝑠𝑖𝑛∅)2
H=180
20(
1−sin (30)
1+sin (30))2 =1 m
The base of foundation is located at a depth of 3.55 m below which is not
subjected
To seasonal volume changes caused by alternate wetting and drying.
2-Footing Dimensions
Total load of columns = 127566.42 KN
Area of footing =127566.42
180 =708.82 m
2
Provided Area ((34x32)-56) = 1048 m2
3- Thickness of footing
The thickness of footing may be governed either by the maximum moment and
maximum one way shear.
Net upward intensity= 127566.42
34.5𝑋32−56 = 83.62 KN/m
2
93
Net upward reaction/m=83.62X34.5=2884.84 KN/m
a) Thickness of footing based on moment
b* d2
=Mumax/.36(xu/d)fck(1-0.416*(xu/d))
(xu/d)=0.479 for steel grade Fe 415
Mumax= 1382 KN-m/m
b=1m
1000* d2
=1382*106/0.36*0.476(1-0.416*0.476)
d =634.22 mm
b) Thickness of footing based on punching shear
d =Vumax/tcb Vumax=5.48051 * 10
6
KN/m
2
d=5.48051*106/1.25*2*(400+d+700+d)
d=807.5 mm
Therefore thickness of footing governed by punching,
D=807+75+assume dia 20=892
Take it as 900 mm
Take D=900 mm
4-Design for moments:
Moment per unit width
KNm/m
Effective depth in
(mm) d
Reinforcement
End span longitudinal
Moment
Mu=275KNm/m
d=D-75-20/2=815m
Ast=1140 mm2
Not less than
.0012x1000x950=1140 mm2
Provide
25mm dia@250 c/c distance
94
1472 mm2
Interior span
longitudinal moment
Mu=281 KNm/m
d =D-75-20/2=815 Ast=1140 mm2
min reinforcement
=0.0012x1000x950=1140mm2
provide 20 mmdia@250 c/c
=1472mm2
Interior support
longitudinal moment
Mu=1368 KNm/m
d =D-75-10=815mm Ast=5670
25 mm dia @100 mm2
Min reinforcement =1140
mm2
Transverse support
moment
Mu=72KNm/m
d =D-75-25-10=790
mm
Ast=1140 mm2
Provide 20 mm dia@300 c/c
Transverse span
moment
Mu=694 KNm/m
d =D-75-25-10=790
mm
Ast=2543mm2
Provide 20mm dia 125 c/c
Development length in 20 mm dia. bars
𝐿𝑑=0.87𝑓𝑦𝑥𝑑𝑖𝑎
4𝜏𝑏𝑑
=0.87𝑥415𝑥𝑑𝑖𝑎.
4𝑥1.4 (obtained from IS 456: 2000 cl. 26.2.1.1 )
=1612 mm
Check for shear:
KsTc>=Vu/bd
95
b=2x(700+815)+(400+815))= 5460
Where Ks=0.5+B<= 1.0
=0.5+0.4/0.7=1.07
Take Ks=1.0
Tc=0.25xsqrt Fck=1.25
5.48051 * 10
6 /5460x815 =1.2 <1.25 OK
Fig:- 5.11
96
5.3.3 STAAD PRO
Foundation DESIGN SUMMARY
ELEMENT DESIGN SUMMARY
----------------------
ELEMENT LONG. REINF MOM-X /LOAD TRANS. REINF MOM-Y
/LOAD
(SQ.MM/ME) (KN-M/M) (SQ.MM/ME) (KN-M/M)
60000 TOP : 876. 0.00 / 0 876. 0.00 / 0
BOTT: 876. 0.00 / 60 876. 0.00 / 60
60001 TOP : 876. 0.00 / 0 876. 0.00 / 0
BOTT: 876. 0.00 / 60 876. 0.00 / 60
60002 TOP : 876. 0.00 / 0 876. 0.00 / 0
BOTT: 876. 0.00 / 60 876. 0.00 / 60
60003 TOP : 876. 0.00 / 0 876. 0.00 / 0
BOTT: 876. 0.00 / 60 876. 0.00 / 60
60004 TOP : 876. 0.00 / 0 876. 0.00 / 0
BOTT: 876. 0.00 / 60 876. 0.00 / 60
60005 TOP : 876. 0.00 / 0 876. 0.00 / 0
BOTT: 876. 0.00 / 60 876. 0.00 / 60
60006 TOP : 876. 0.00 / 0 876. 0.00 / 0
BOTT: 876. 0.00 / 60 876. 0.00 / 60
60007 TOP : 876. 0.00 / 0 876. 0.00 / 0
BOTT: 876. 0.00 / 60 876. 0.00 / 60
60008 TOP : 876. 0.00 / 0 876. 0.00 / 0
BOTT: 876. 0.00 / 60 876. 0.00 / 60
60009 TOP : 876. 0.00 / 0 876. 0.00 / 0
BOTT: 876. 0.00 / 60 876. 0.00 / 60
60010 TOP : 876. 0.00 / 0 876. 0.00 / 0
BOTT: 876. 0.00 / 60 876. 0.00 / 60
60011 TOP : 876. 0.00 / 0 876. 0.00 / 0
BOTT: 876. 0.00 / 60 876. 0.00 / 60
60012 TOP : 876. 0.00 / 0 876. 0.00 / 0
BOTT: 876. 0.00 / 60 876. 0.00 / 60
60013 TOP : 876. 0.00 / 0 876. 0.00 / 0
BOTT: 876. 0.00 / 60 876. 0.00 / 60
97
60014 TOP : 876. 0.00 / 0 876. 0.00 / 0
BOTT: 876. 0.00 / 60 876. 0.00 / 60
60015 TOP : 876. 0.00 / 0 876. 0.00 / 0
BOTT: 876. 0.00 / 60 876. 0.00 / 60
98
Chapter 6
6.1 Architectural plan Details
By observing the plan of the building it is very clear that the shape of the
building is a regular one with 3 flats on each floor of the building.
It is very much necessary to study the plan in detail for a good and sound
understanding of the structural detailing of the structural members of the building i.e. beams,
columns, shear wall.
To accomplish the detailed study the above mentioned sections of the
members of the building, the diagrams are listed below.
Column Section at basement
Fig:- 6.1
99
Column Section at 3rd
to 6th
floor
Fig:- 6.2
100
Column Section at 7th
to 11th
floor
Fig:- 6.3
101
Shear wall section
Fig:- 6.4
102
Raft Foundation
Fig:- 6.5
103
Raft foundation section
Fig:- 6.5
104
CONCLUSION
In this project Seismic design and analysis of building which consists of G+2B+23
floors and area 520 m2 situated in Sector zeta Greater Noida UP.
The building has each floor of height 3.05m and has three similar flats at each floor.
Each flat have 3 bed rooms, 1 dining room, 1 drawing room, 1 study, 1 kitchen and
3 toilets, 3 lifts and 2 stair case is provided.
The designing has been done both manually and using STAAD.Pro V8i According
to Indian Standard codes. The dead load, live loads and Wind load of the building
are taken as per IS 875 part I and II, III respectively. The code provisions for
seismic load estimation as per IS 1893 have been followed , SP 34 used for
Reinforcement detailing, IS 13920 used for Ductile detailing, the manual design of
columns and beams and staircase , Slabs, foundation, Shear wall is done by taking
the forces from STAAD results and the key results are summarized.
The building lies in zone IV therefore zone factor of 0.24 is taken, Basic wind
speed is taken as 47m/s. Safe soil bearing capacity of the soil is taken as 180kN/m2,
The building is provided with raft foundation of overall depth of 1000 mm as it is
the most suitable foundation for this building.
Modal participation factor of the building was found to be 90% after considering 18
modes.
Storey drifts of the building were found to be well within the permissible limit i.e.
0.004h where h is the height of the building.
Design results of building components obtained manually were approximately
similar to results obtained by STAAD.Pro V8i.
Total volume of Concrete of grade M25 used is 1563 𝑚3 , Total weight of steel of
grade Fe 415 used is 118.2 Ton.
105
APPENDICES
SOIL REPORT
106
REFERNCES
IS: 875 (Part 1) – 1987 for Dead Loads, Indian Standard Code Of Practice for
Design Loads (Other Than Earthquake) For Buildings and Structures, Bureau of
Indian Standards, Manak Bhavan, 9 Bahadur Shah Zafar Marg, New Delhi
110002.
IS: 875 (Part 2) – 1987 for Imposed Loads, Indian Standard Code Of Practice
for Design Loads (Other Than Earthquake) For Buildings and Structures, Bureau
of Indian Standards, Manak Bhavan, 9 Bahadur Shah Zafar Marg, New Delhi
110002.
IS: 875 (Part 3) – 1987 for Wind Loads, Indian Standard Code Of Practice for
Design Loads (Other Than Earthquake) For Buildings And Structures, Bureau of
Indian Standards, Manak Bhavan, 9 Bahadur Shah Zafar Marg, New Delhi
110002.
IS: 875 (Part 5) – 1987 for Special Loads and Combinations, Indian Standard
Code Of Practice for Design Loads (Other Than Earthquake) For Buildings and
Structures, Bureau of Indian Standards, Manak Bhavan, 9 Bahadur Shah Zafar
Marg, New Delhi 110002.
IS 1893 (Part 1)-2002, Indian Standard Criteria for Earthquake Resistant Design
of Structures, (Part 1-General Provisions and Buildings), Bureau of Indian
Standards, Manak Bhavan, 9 Bahadur Shah Zafar Marg, New Delhi 110002.
IS 456-2000, Indian standard code of practice for plain and reinforced concrete
(fourth revision), Bureau of Indian Standards, New Delhi, July 2000.
SP: 16-1980, Design aids for reinforced concrete to IS: 456, Bureau of Indian
standards, New Delhi, 1980.
SP: 34-1987, Hand Book of Concrete Reinforcement and Detailing, Bureau of
Indian Standards, New Delhi, 1987.
Pilli, S.U. And Menon .D, “Reinforced concrete design”, Second edition, Tata
Mc Graw Hill Publishing Company Limited, New Delhi, 2003.
Jain, A.K. “Reinforced Concrete – Limit State Design”, Sixth edition, New
Chand & Bros, Roorkee, 2002.
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