A Project Report Submitted in Partial fulfillment of the requirements For the degree of Bachelor of Technology In Civil Engineering By Patel Kaushal Ashokbhai ID No: D12CL067 Under the supervision of Ms. Neha Chauhan Mr. Hiren Desai M. S. PATEL DEPARTMENT OF CIVIL ENGINEERING FACULTY OF TECHNOLOGY AND ENGINEERING CHAROTAR UNIVERSITY OF SCIENCE & TECHNOLOGY CHANGA – 388421, GUJARAT, INDIA May 2015
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A Project Report
Submitted in
Partial fulfillment of the requirements
For the degree of
Bachelor of Technology
In
Civil Engineering
By
Patel Kaushal Ashokbhai
ID No: D12CL067
Under the supervision of
Ms. Neha Chauhan
Mr. Hiren Desai
M. S. PATEL DEPARTMENT OF CIVIL ENGINEERING
FACULTY OF TECHNOLOGY AND ENGINEERING
CHAROTAR UNIVERSITY OF SCIENCE & TECHNOLOGY
CHANGA – 388421, GUJARAT, INDIA
May 2015
ii
CERTIFICATE
This is to certify that I have been supervising the work of Patel Kaushal Ashokbhai
(D12CL067) for the Degree of Bechlor of Technology in Civil Engineering.
The project report is comprehensive, complete and fit for evaluation. To the best of
my knowledge, the matter embodied in the project has not been submitted to any
other University / Institute for the award of any Degree or Diploma.
Ms. Neha Chauhan Dr. A.V. Thomas
Faculty Supervisor Professor & Head
Date:
Examiner
__________________________
Examiner
__________________________
Examiner
_________________________
iii
ACKNOWLEDGEMENT
I express my deep gratitude to Mr. Hiren Desai, owner of Sai Consultant, Surat for his
valuable suggestions and guidance rendered in giving shape and coherence to this
endeavor. I also thankful to his team members for their support and guidance throughout
the period of project.
I like to express my heartfelt gratitude and regards to my project supervisor Ms Neha
Chauhan, Civil Engineering Department of Charotar University of Science and
Technology, for her unconditional guidance.She always bestowed parental care upon
us and evinced keen interest in solving my problems. An erudite teacher, a magnificent
person and a strict disciplinarian, I consider myself fortunate to have worked under her
supervision.
I am highly grateful to Dr A.V Thomas, Head of Department, Civil Engineering,
for providing necessary facilities during the course of the work.
Patel Kaushal Ashokbhai
D12CL067
iv
ABSTRACT
Among the many ongoing construction projects in Surat held by ‘SAI
CONSULTANTS’, this report deals with the designing of Low Rise Buildings. Low
Rise Building is a combination of residential and commercial project. SAI
COUNSULTANT is also involved in other Commercial projects and plotted
developments across Surat, Bardoli, Navsari, and Delhi, Jaipur and many others.
This report encloses elements of Structural Engineering, one of the main branches in
Civil Engineering. By both manual and software based methods, an attempt has been
made to relate the theoretical concepts to field work and have a comparative study based
on analysis and designing of project.
Sample analysis and design have been compiled in the report along with necessary
theoretical concepts to validate the attempts. However, deviations may be observed
between theoretical and on-field data, which is the main purpose of preparing this
report, i.e., application of theoretical concepts to field and noting the deviations and
analyzing why the deviations occurs and adopting those deviations on field after
thorough knowledge.
v
CONTENT ANNEXURES
I. Training Certificate i
II. Certificate ii
III. Acknowledgement iii
IV. Abstract iv
V. Content v
VI. List of Figures ix
VII. List of Table xi
SR.
NO. DESCRIPTION
PAGE
NO.
1.0 INTRODUCTION 01-02
1.1 Introduction About ‘SAI CONSULTANT’ 01
1.2 List of Projects 01
1.2.1 High-Rise Building
1.2.2 Public/Intuitional/Community Buildings
1.2.3 Industrial Buildings
1.2.4 Bungalows, Row Houses and Low high Rise
1.2.5 Commercial Building
01
01
01
01
02
1.3 Objectives of the Training 02
2.0 ESTIMATION OF R.C.C FOOTING 03-11
2.1 General Detail of Structure 03
2.2 Plan of Footing 04-05
2.3 Quantity Sheet of R.C.C. Raft Footing 06
2.4 Quantity Sheet of R.C.C. Raft Footing Reinforcement 08
3.0 SITE WORK 12-17
3.1 General Details 12
3.2 Excavation 14
3.3 R.C.C. Raft Footing 14
vi
3.4 Laying of Foundation 16
4.0 LITERATURE REVIEW & DESIGN PROCEDURE 18-43
4.1 Introduction to Structural Design 18
4.1.1 Introduction
4.1.2 Structural Design Process
4.1.3 Philosophy of Designing
4.1.4 Design Aids
18
18
19
20
4.2 Stages in Structural Design 20
4.2.1 Structural Planning
4.2.1.1 Positioning and Orientation of Columns
4.2.1.2 Position of Beams
4.2.1.3 Spanning of Slabs
4.2.1.4 Selecting Proper Type of Footing
4.2.2 Actions of Forces and Computation of Loads
4.2.3 Analysis of a Structure
4.2.4 Member Design
4.2.5 Detailing, Drawing, and Preparation of Schedule
21
21
23
24
25
26
27
27
27
4.3 The Design Process 27
4.3.1 Functional Design
4.3.2 Structural Design
4.3.2.1 Structural Details of a Framed Structure:
28
28
29
4.4 Design of Members 29
4.4.1 Design of Slab
4.4.1.1 Design of One-Way Slab
4.4.1.2 Design of Two-Way slabs:
4.4.2 Design of Beams
4.4.3 Design of Columns (Exact Theoretical Method)
4.4.3.1 Axially Loaded Short Columns
4.4.3.2 Short Columns Subjected to Axial Compression and
Uniaxial Bending
4.4.3.3 Short Columns Subjected to Axial Compression and
Bi-axial Bending
29
30
33
36
38
39
39
40
vii
4.4.3.4 Slender Columns
4.4.4 Design of Footings
4.4.4.1 Design of Isolated Footing
41
41
41
5.0 MODELLING, ANALYSIS AND DESIGN OF A LOW RISE
BUILDING USING STRUDS 44-93
5.1 Introduction 44
5.2 Modeling of Structural Systems 45
5.3 Struds Analysis Techniques 46
5.3 Analysis and Design 46
5.4.1 Analysis
5.4.2 Design Features
46
46
5.5 Output From STRUDS 47
5.6 Overview of the Mode 47
5.7 Results 48
5..8 Design of a Low Rise Building Using STRUDS 49
5.8.1 Introduction
5.8.2 Typical Section of Building
5.8.3 Typical Floor Plans of Building
49
49
50
5.9 Modeling of a Low Rise Building 52
5.9.1 Starting STRUDS
5.9.2 Creating a New Model
5.9.3 Set Floors and Heights
5.9.4 DXF File into STRUDS
5.9.5 Column Marking, Column Size, Shape and Section in
STRUDS
5.9.6 Attach Support
5.9.7 Defining and Attaching Materials and Section
5.9.8 Attaching Walls
5.9.9 Slab Attachment
5.9.10 Analysis
5.9.11 RCC Design
5.9.11.1 Slab Design
52
52
53
55
57
60
62
66
67
69
72
73
viii
5.9.11.2 Beam Design
5.9.11.3 Column Design
5.9.11.4 Footing Design
76
79
82
5.10 3D Model of a Low Rise Building 85
5.11 Sample Schedule of STRUDS 86
5.11.1 Beam Schedule Report 86
5.11.2 Column Schedule Report 92
5.11.3 Slab Schedule Report 93
6.0 SAMPLE MANUAL DESIGN OF SRUCTURAL
MEMBERS 94-106
6.1 Sample Manual Design of Structural Members 104
6.1.1 Design of One-Way Slab 94
6.1.2 Design of Beam 98
6.1.3 Design of Column 100
6.1.4 Design of Footing 102
CONCLUDING REMARKS 107
REFERENCES 108
ix
LIST OF FIGURES
NO DESCRIPTION PAGE
NO
2.01 Plan of Layout of Foundation 4-5
3.01 Front Elevation of Omorose 14
3.02 Bird View of Omorose 14
3.03 Excavation of Soil for Foundation 15
3.04 R.C.C Raft Pads 16
3.05 Reinforced Steel Mash for Raft Foundation 17
3.06 Laying Out of Reinforcement Cage for Column 18
3.07 Casting of R.C.C Column 18
4.01 Column Position for Rectangular Pattern Building 22
5.01 Section of Building 51
5.02 Section 1-1 of Building 52
5.03 Basement Floor Plan 52
5.04 Ground Floor Plan 53
5.05 First Floor Plans 53
5.06 Second Floor Plan 53
5.07 Third Floor Plan 54
5.08 Terrace Floor Plan 54
5.09 STRUDS: Adding New File 55
5.10 STRUDS: New Model Initialization 55
5.11 STRUDS: Building Story Data 56
5.12 STRUDS: Working Space Selection 57
5.13 STRUDS: Import DXF File 57
5.14 STRUDS: DXF File Setting 58
5.15 STRUDS: Imported Grid 58
5.16 STRUDS: Column Marking 59
5.17 STRUDS: Defining Column Location 59
x
5.18 STRUDS: Defining Column Shape 61
5.19 STRUDS: Defining Column Size 62
5.20 STRUDS: Attaching Support 62
5.21 STRUDS: Defining Column Grouping 63
5.22 STRUDS: Defining Materials 64
5.23 STRUDS: Section Define 65
5.24 STRUDS: Attachment of Elements 67
5.25 STRUDS: Attachment of Section 68
5.26 STRUDS: Adding Wall Properties 68
5.27 STRUDS: Defining Slab Properties 69
5.28 STRUDS: Attached Slabs 71
5.29 STRUDS: Pre-Analysis Enquiry 72
5.30 STRUDS: Analysis Options 73
5.31 STRUDS: Design of Slab 75
5.32 STRUDS: Deflection Check Dialog Box 76
5.33 STRUDS: Section of One Slab 78
5.34 STRUDS: Shear Capacity Error 78
5.35 STRUDS: Stirrup Detailing 79
5.36 STRUDS: Section of Beam B28 (terrace) 80
5.37 STRUDS: Maximum Percentage Error 81
5.38 STRUDS: View Column Design 82
5.39 STRUDS: Section of One Column 83
5.40 STRUDS: Bond Check Error 84
5.41 STRUDS: Footing Design 85
5.42 STRUDS: Design Parameters 85
5.43 STRUDS: Design of One Isolated Footing 86
5.44 STRUDS: 3D View of Building 87
6.01 Location of Designed Slab (First Floor, S10) 94
6.02 Location of Beams on First Floor 98
6.03 Location of Column on First Floor 100
6.04 Location of Footing 102
xi
LIST OF TABLE
NO DESCRIPTION PAGE
NO
2.01 General Detail of Building 3
3.01 General Detail of Building 12
4.01 Maximum Span Limit of Beam 22
4.02 Maximum Span Limit of Slab 24
4.03 Span / Depth Ratio 34
4.04 Design Moment Coefficient 35
5.01 Beam Schedule Report 86
5.02 Column Schedule Report 92
5.03 Slab Schedule Report 93
6.01 Dimension of Beam 98
6.02 Loading on Beam 98
6.03 Column Dimension 100
6.04 Loading on Column 100
6.05 Dimensions & Design Data 102
1
CHAPTER 1
INTRODUCTION
1.1 INTRODUCTION ABOUT ‘SAI CONSULTANT’
‘SAI CONSULTANT’ was originally set up in 1990 as a result of one man’s dream and
passion, Mr. Hiren G. Desai, a Civil Engineer M.E. (structure) by qualification, with an
ardent intention to create residential and commercial spaces that exceeded consumer’s
aspirations. He is consulting structure engineer and Government approved Valuer.
His mission is to provide economical & innovative structural designs and detailed
drawings so as to make structure easy to construct, safe and durable, requiring bare
minimum maintenance and fulfilling all its functional requirements throughout its life
span.
1.2 LIST OF PROJECTS
1.2.1 High-rise Buildings
OMO Rose
Corona Height
Regaliya, Navsari
1.2.2 Public/Institional/Community Buildings
B.C.C School, Gaziyabad
Bharthana Swimming Pool
1.2.3 Industrial Buildings
SRK diamond factory
Dream Honda, car showroom
1.2.4 Bungalows, Row Houses and Low high Rise
Ibrahimbhai Lalgate
1.2.5 Commercial Building
Fortune mall
2
Palash paladiya
1.3 OBJECTIVES OF THE TRAINING
The objectives of present study over a period of two months of industrial training
include the following:
1. To gain practical knowledge and understanding the practices done on site by a
structural consultancy firm.
2. To know the methods used by structural consultancy for estimation and the fees
charged for respective projects.
3. To learn about structural changes required in an existing building during repairs or
in distress.
4. Detailed study of Architectural drawings, interpretations, and gain of analytical skills
as a structural engineer.
5. To learn Manual design of low rise building using Codes as and when needed.
6. Modeling, analysis and design of G + 3(with basement) low rise Building using
STURDS 2010.
3
CHAPTER 2
ESTIMATION OF R.C.C FOOTING
2.1 General Detail
Table No 2.01 General Detail of Building
1. Name of Building Omorose.
2. Designated Use Residential high rise
3. Address Pratham Ganesa
Near Trinity Business Hub, Green City
Rd, Adajan Gam, Surat, Gujarat
395009, India
4. No.of floors Basement Floor (Parking) + Ground
Floor +Typical 1st to 12th Floors
(Building A)+ Typical 1st to 11th
Floors ( Building B )
5. Floor to Floor Hieght 3.05 mts. (10'-0")
6. Type of structure RCC framed structure with brick infill
walls
7. Walls
Exterior walls
Interior walls
9” thick brick mortar walls
41
2 ” thick brick mortar walls
8. Roofing RCC Slab
Length Width Height Quantity Total
(m) (m) (m) (Cu.m) (Cu.m)
1 Raft-1 1 12.34 3.35 0.762 31.5003
F-1 1 0.75 1.14 0.45 0.38475
F-7 & 11 2 0.68 0.99 0.45 0.60588
F-17 & PC 1 1.091 1.55 0.45 0.76097
33.2519205
2 Raft-2 1 12.65 8.68 0.914 100.359
F-2 1 0.98 0.514 0.45 0.22667
F-3 1 0.981 1.66 0.45 0.73281
F-8 1 1.141 1.97 0.45 1.0115
F-12 1 2.53 1.06 0.45 1.20681
F-18 & 19 2 1.13 2.82 0.45 2.86794
106.4047555
3 Raft-3
36'' Pad 1 8.07 13.99 0.914 103.19
60'' Pad 1 8.07 6.99 1.524 85.9678
F-13 &14 2 1.141 1.97 0.45 2.02299
F- 20 & 21 2 1.92 1.92 0.45 3.31776
194.4984864
4 Raft-4 1 12.65 8.68 0.914 100.359
F-4 1 0.981 1.66 0.45 0.73281
F-5 1 0.98 1.514 0.45 0.66767
Sr No.Descpition No
2.3 Quantity Sheet of R.C.C Raft Footing
6
F-9 1 1.141 1.97 0.45 1.0115
F-15 1 2.53 1.06 0.45 1.20681
F-22 & 23 2 1.13 2.82 0.45 2.86794
106.8457555
5 Raft-5 1 12.34 3.35 0.762 31.5003
F-6 1 0.75 1.14 0.45 0.38475
F-10 & 16 2 0.68 0.99 0.45 0.60588
F- 24 1 0.75 1.55 0.45 0.52313
35.882013
6 P.C 4 1.37 1.22 0.45 3.00852
3.00852
Total 479.8914509
7
No Length Weight Quantity Total
(m) (kg/m) (kg) (kg)
1 Raft -1
(Bottom Reinforcement)
(A.T.L)
16 mm Dia 17 12.92 1.58 347.0312
12 mm Dia 17 12.92 0.89 195.4796
(A.T.W)
16 mm Dia 62 3.93 1.58 384.9828
12 mm Dia 62 3.93 0.89 216.8574
(Top Reinforcement)
(A.T.L)
12 mm Dia 28 12.92 0.89 321.9664
(A.T.W)
12 mm Dia 100 3.93 0.89 349.77
1816.0874
2 Raft-2
(Bottom Reinforcement)
(A.T.L)
16 mm Dia 88 13.38 1.58 1860.355
(A.T.W)
Sr No. Decription
2.4 Quantity Sheet of R.C.C Raft Footing Reinforcement
8
20 mm Dia 64 9.41 2.47 1487.533
16 mm Dia 64 9.41 1.58 951.5392
(Top Reinforcement)
(A.T.L)
12 mm Dia 88 13.38 0.89 1047.922
(A.T.W)
12 mm Dia 128 9.41 0.89 1071.987
6419.336
3 Raft-3
(Bottom Reinforcement)
(A.T.L-1)
20 mm Dia 82 8.38 2.47 1697.285
(A.T.L-2)
20 mm Dia 41 9.75 2.47 987.3825
16 mm Dia 41 9.75 1.58 631.605
(A.T.W-1)
20 mm Dia 71 9.4 2.47 1648.478
(A.T.W-2)
16 mm Dia 91 9.4 1.58 1351.532
(Top Reinforcement)
(A.T.L-1)
12 mm Dia 41 8.38 0.89 305.7862
9
16 mm Dia 41 8.38 1.58 542.8564
(A.T.L-2)
12 mm Dia 82 9.75 0.89 711.555
(A.T.W-1)
12 mm Dia 36 9.4 0.89 301.176
16 mm Dia 36 9.4 1.58 534.672
(A.T.W-2)
12 mm Dia 91 9.4 0.89 761.306
9473.6343
Raft-4
(Bottom Reinforcement)
(A.T.L)
16 mm Dia 88 13.38 1.58 1860.355
4
(A.T.W)
20 mm Dia 64 9.41 2.47 1487.533
16 mm Dia 64 9.41 1.58 951.5392
(Top Reinforcement)
(A.T.L)
12 mm Dia 88 13.38 0.89 1047.922
(A.T.W)
10
12 mm Dia 128 9.41 0.89 1071.987
6419.336
Raft -5
(Bottom Reinforcement)
(A.T.L)
16 mm Dia 17 12.92 1.58 347.0312
5
12 mm Dia 17 12.92 0.89 195.4796
(A.T.W)
16 mm Dia 62 3.93 1.58 384.9828
12 mm Dia 62 3.93 0.89 216.8574
(Top Reinforcement)
(A.T.L)
12 mm Dia 28 12.92 0.89 321.9664
(A.T.W)
12 mm Dia 100 3.93 0.89 349.77
1816.0874
Total 25944.4811
25.95 tonnes
11
12
CHAPTER 3
SITE WORK S
3.1 GENERAL DETAILS
Table No. 3.01 General Detail of Building
1. Name of Building Omorose.
2. Designated Use Residential high rise
3. Address Pratham Ganesa
Near Trinity Business Hub, Green City
Rd, Adajan Gam, Surat, Gujarat
395009, India
4. No.of floors Basement Floor (Parking) + Ground
Floor +Typical 1st to 12th Floors
(Building A)+ Typical 1st to 11th
Floors ( Building B )
5. Floor to Floor Hieght 3.05 mts. (10'-0")
6. Type of structure RCC framed structure with brick infill
walls
7. Walls
Exterior walls
Interior walls
9” thick brick mortar walls
41
2 ” thick brick mortar walls
8. Roofing RCC Slab
13
Figure 3.01 Front Elevation of Omorose
Figure 3.02 Bird View of Omorose
14
3.2 Excavation
Excavation was carried out both manually as well as mechanically. Normally 1-2 earth
excavators (JCB’s) were used for excavating the soil. Adequate precautions are taken
to see that the excavation operations do not damage the adjoining structures. Excavation
is carried out providing adequate side slopes and dressing of excavation bottom. The
soil present beneath the surface was too clayey so it was dumped and was not used for
back filling. The filling is done in layer not exceeding 20 cm layer and then it’s
compacted. Depth of excavation was 5’4” from Ground Level.
Figure 3.03 Excavation of Soil for Foundation
3.3 R.C.C Raft Footing
A raft foundation consists of a raft of reinforced concrete under the whole of a building.
This type of foundation is described as a raft in the sense that the concrete raft is cast
on the surface of the ground which supports it, as water does a raft, and the foundation
is not fixed by foundations carried down into the subsoil.
Raft foundations may be used for buildings on compressible ground such as very soft
clay, alluvial deposits and compressible fill material where strip, pad or pile foundations
would not provide a stable foundation without excessive excavation. The reinforced
concrete raft is designed to transmit the whole load of the building from the raft to the
ground where the small spread loads will cause little if any appreciable settlement.
The two types of raft foundation commonly used are the flat raft and the wide toe raft.
The flat slab raft is of uniform thickness under the whole of the building and reinforced
to spread the loads from the walls uniformly over the under surface to the ground. This
15
type of raft may be used under small buildings such as bungalows and two storey houses
where the comparatively small loads on foundations can be spread safely and
economically under the rafts.
Figure 3.04 R.C.C Raft Pads
The concrete raft is reinforced top and bottom against both upward and downward
bending. Vegetable top soil is removed and a blinding layer of concrete 50 mm thick is
spread and levelled to provide a base on which to cast the concrete raft. A waterproof
membrane is laid, on the dry concrete blinding, against moisture rising into the raft. The
top and bottom reinforcement is supported and spaced preparatory to placing the
concrete which is spread, consolidated and finished level.
The concrete raft may be at ground level or finished just below the surface for
appearance sake. Where floor finishes are to be laid on the raft a 30”, 36” thick layer of
concrete is spread over the raft, between the walls, to raise the level and provide a level,
smooth finish for floor coverings. As an alternative a raised floor may be constructed
on top of the raft to raise the floor above ground.
16
3.4 Laying of Foundation
At our site, Raft foundations are used to spread the load from a structure over a large
area, normally the entire area of the structure. Normally raft foundation is used when
large load is to be distributed and it is not possible to provide individual footings due
to space constraints that is they would overlap on each other. Raft foundations have the
advantage of reducing differential settlements as the concrete slab resists differential
movements between loading positions. They are often needed on soft or loose soils with
low bearing capacity as they can spread the loads over a larger area.
In laying of raft foundation, special care is taken in the reinforcement and construction
of plinth beams and columns. It is the main portion on which ultimately whole of the
structure load is to come. So a slightest error can cause huge problems and therefore all
this is checked and passed by the engineer in charge of the site.
Figure 3.05 Reinforced Steel Mash for Raft Foundation
17
Figure 3.06 Laying Out of Reinforcement Cage for Column
Apart from raft foundation, individual footings were used in the mess area which was
extended beyond the C and D blocks.
Figure 3.07 Casting of R.C.C Column
18
CHAPTER 4
LITERATURE REVIEW & DESIGN PROCEDURE
4.1 INTRODUCTION TO STRUCTURAL DESIGN
4.1.1 Introduction
Structural design is the methodical investigation of the stability, strength and rigidity
of structures. The basic objective in structural analysis and design is to produce a
structure capable of resisting all applied loads without failure during its intended life.
The primary purpose of a structure is to transmit or support loads. If the structure is
improperly designed or fabricated, or if the actual applied loads exceed the design
specifications, the device will probably fail to perform its intended function, with
possible serious consequences. A well-engineered structure greatly minimizes the
possibility of costly failures.
4.1.2 Structural Design Process
A structural design project may be divided into three phases, i.e. planning, design and
construction.
Planning: This phase involves consideration of the various requirements and
factors affecting the general layout and dimensions of the structure and results
in the choice of one or perhaps several alternative types of structure, which
offer the best general solution. The primary consideration is the function of the
structure. Secondary considerations such as aesthetics, sociology, law,
economics and the environment may also be taken into account. In addition
there are structural and constructional requirements and limitations, which
may affect the type of structure to be designed
Design: This phase involves a detailed consideration of the alternative
solutions defined in the planning phase and results in the determination of the
most suitable proportions, dimensions and details of the structural elements
19
and connections for constructing each alternative structural arrangement being
considered.
Construction: This phase involves mobilization of personnel; procurement of
materials and equipment, including their transportation to the site, and actual
on-site erection. During this phase, some redesign may be required if
unforeseen difficulties occur, such as unavailability of specified materials or
foundation problems.
4.1.3 Philosophy of Designing
The structural design of any structure first involves establishing the loading and other
design conditions, which must be supported by the structure and therefore must be
considered in its design. This is followed by the analysis and computation of internal
gross forces as well as stress intensities, strain, reflection and reactions produced by
loads, changes in temperature, shrinkage, creep and other design conditions. Finally
comes the proportioning and selection of materials for the members and connections
to respond adequately to the effects produced by the design conditions. The criteria
used to judge whether particular proportions will result in the desired behavior reflect
Accumulated knowledge based on field and model tests, and practical experience.
Intuition and judgment are also important to this process. The traditional basis of
design called elastic design is based on allowable stress intensities which are chosen
in accordance with the concept that stress or strain corresponds to the yield point of
the material and should not be exceeded at the most highly stressed points of the
structure, the selection of failure due to fatigue, buckling or brittle fracture or by
consideration of the permissible deflection of the structure. The allowable Stress
method has the important disadvantage in that it does not provide a uniform overload
capacity for all parts and all types of structures. The newer approach of design is
called the strength design in reinforced concrete literature and plastic design in steel-
design literature. The anticipated service loading is first multiplied by a suitable load
factor, the magnitude of which depends upon uncertainty of the loading, the
possibility of it changing during the life of the structure and for a combination of
loadings, the likelihood, frequency, and duration of the particular combination. In this
approach for reinforced-concrete design, theoretical capacity of a structural element is
20
reduced by a capacity reduction factor to provide for small adverse variations in
material strengths, workmanship and dimensions. The structure is then proportioned
so that depending on the governing conditions, the increased load cause fatigue or
buckling or a brittle-facture or just produce yielding at one internal section or sections
or cause elastic-plastic displacement of the structure or cause the entire structure to be
on the point of collapse.
4.1.4 Design Aids
The design of any structure requires many detailed computations. Some of these are
of a routine nature. An example is the computation of allowable bending moments for
standard sized, species and grades of dimension timber. The rapid development of the
computer in the last decade has resulted in rapid adoption of Computer Structural
Design Software that has now replaced the manual computation. This has greatly
reduced the complexity of the analysis and design process as well as reducing the
amount of time required to finish a project. Standard construction and assembly
methods have evolved through experience and need for uniformity in the construction
industry. These have resulted in standard details and standard components for
building construction published in handbooks or guides.
4.2 STAGES IN STRUCTURAL DESIGN
The process of structural design involves the following stages:
Structural planning
Action of forces and computation of loads
Methods of analysis
Detailing, drawing and preparation of schedules
21
4.2.1 Structural Planning
After getting an architectural plan of the buildings, the structural planning of the
building frame is done. This involves determination of the following:
Positioning and orientation of columns
Position of beams
Spanning of slabs
Selecting proper type of footing
The basic principle in deciding the layout of members is that the loads should be
transferred to the foundation along the shortest path.
4.2.1.1 Positioning and Orientation of Columns
Positioning of columns
1) Columns should be preferably located at or near the corners of a building and
at the intersections of beams/walls.
Since the basic function of the columns is to support beams which are normally
placed under the walls to support them, their position automatically gets fixed as
shown in the figure 4.01
Figure 4.01 Column Position for Rectangular Pattern Building
2) Select the position of columns so as to reduce bending moments in beams.
When the locations of two columns are very near, then one column should be
provided instead of two at such a position so as to reduce the beam moment.
3) Avoid larger spans of beams.
When the center to center distance between the intersection of walls is large or when
there are no cross walls, the spacing between two columns is governed by limitations
of spans of supported beams because spacing of columns decides the span of beam.
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As the span of the beam increases, the required depth of the beam, and hence it’s self-
weight, and the total load on beam increases.
It is well known that the moment governing the beam design varies with the square of
the span and directly with the load. Hence with the increase in the span, there is
considerable increase in the size of the beam.
On the other hand, in the case of column, the increase in total load due to increase in
length is negligible as long as the column is short. Therefore the cost of the beam per
unit length increases rapidly with the span as compared to beams on the basis of unit
cost. Therefore the larger span of the beams should be preferably avoided for
economy reasons.
In general, the maximum spans of beams carrying live loads up to 4 kN/m2 may be
limited to the following values.
Table No.4.01 Maximum Span Limit of Beam
Beam type Cantilevers Simply supported Fixed / continuous
Rectangular 3 meters 6 meters 8 meters
Flanged 5meters 10 meters 12 meters
4) Avoid larger center to center distance between columns. Larger spacing of columns
not only increases the load on the column at each floor posing problem of stocky
columns in lower storeys of a multistoried building. Heavy sections of column lead to
offsets from walls and obstruct the floor area.
5) The columns on property line need special treatment. Since column footing
requires certain area beyond the column, difficulties are encountered in providing
footing for such columns. In such cases, the column may be shifted inside along a
cross wall to make room for accommodating the footing within the property line.
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Orientation of Columns
1) Avoid projection of column outside wall. According requirements of
aesthetics and utility, projections of columns outside the wall in the room
should be avoided as they not only give bad also obstruct the use of floor
space and create problems in furniture flush with the wall. Provide depth of
the column in the plane of the wall to avoid such offsets.
2) Orient the column so that the depth of the column is contained in the major
plane of bending or is perpendicular to the major axis of bending. When the
column is rigidly connected to right angles, it is subjected to moments of
addition to the axial load. In such cases, the column should be so oriented that
the depth of the column is perpendicular to major axis of bending so as to get
larger moment of inertia and hence greater moment resisting capacity. It will
also reduce Leff/D ratio resulting in increase in the load carrying capacity of the
column.
3) It should be borne in mind that increasing the depth in the plane of bending
not only increases the moment carrying capacity but also increases its
stiffness, there by more moment is transferred to the column at the beam
column junction.
4) However, if the difference in bending moment in two mutually perpendicular
directions is not large the depth of the column may be taken along the wall
provided column has sufficient strength in the plane of large moment. This
will avoid offsets in the rooms.
4.2.1.2 Position of Beams
1) Beams shall normally be provided under the walls or below a heavy
concentrated load to avoid these loads directly coming on slabs. Since beams
are primarily provided to support slabs, its spacing shall be decided by the
maximum spans of slabs.
2) Slab requires the maximum volume of concrete to carry a given load.
Therefore the thickness of slab is required to be kept minimum. The maximum
practical thickness for residential/office/public buildings is 200mm while the
minimum is 100mm.
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3) The maximum and minimum spans of slabs which decide the spacing of
beams are governed by loading and limiting thickness given above. In the case
of buildings, with live load less than 5kN/m2, the maximum spacing of beams
may be limited to the values of maximum spans of slabs given below.
Table No. 4.02 Maximum Span Limit of Slab
Support
condition
Cantilevers Simply supported Fixed / continuous
Slab Type One-
way
Two-
way
One-way Two-way One-way Two-way
Maximum
Recommended
span
of slabs
1.5 m 2.0 m
3.5 m
4.5 m 4.5 m 6.0 m
4) Avoid larger spacing of beams from deflection and cracking criteria. Larger
spans of beams shall also be avoided from the considerations of controlling the
deflection and cracking. This is because it is well known that deflection varies
directly with the cube of span and inversely with the cube of depth i.e., L3/D3.
Consequently, increase in D is less than increase in span L which results in
greater deflection for larger span.
5) However, for large span, normally higher L/D ratio is taken to restrict the
depth from considerations of head room, aesthetics and psychological effect.
Therefore spans of beams which require the depth of beam greater than one
meter should be avoided.
4.2.1.3 Spanning of Slabs
This is decided by supporting arrangements. When the supports are only on
opposite edges or only in one direction, the slab acts as a one way supported slab.
When rectangular slab is supported along its four edges, it acts as one way slab when
Ly / Lx > 2 and as two way slab for Ly / Lx < 2.
However two way action of the slab not only depends on the aspect ratio Ly / Lx
and but also on the ratio of reinforcement in the two directions. Therefore, designer is
free to decide as to whether the slab should be designed as one way or two way.
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1) A slab normally acts as a one way slab when the aspect ratio Ly / Lx >2 since in
this case one way action is predominant. In one way slab, main steel is
provided along the short span only and the load is transferred to two opposite
supports only. The steel along the long span just acts as distribution steel and
is not designed for transferring the load but to distribute the load and to resist
shrinkage and temperature stresses.
2) A two way slab having aspect ratio Ly / Lx< 2 is generally economical
compared to one way slab because steel along the spans acts as main steel and
transfers the load to all its four supports. The two way action is advantageous
essentially for large spans and for live loads greater than 3kN/m2. For short
spans and light loads, steel required for two way slab does not differ
appreciably as compared to steel for one way slab because of the requirement
of minimum steel.
3) Spanning of the slab is also decided by the continuity of the slab.
4) Decide the type of the slab. While deciding the type of the slab whether a
cantilever or a simply supported slab or a continuous slab loaded by UDL it
should be borne in mind that the maximum bending moment in cantilever (M
= wL2/2) is four times that of a simply supported slab (M=wL2/8), while it is
five to six times that of a continuous slab or a fixed slab (M=wL2/10 or
wL2/12) for the same span length.
Similarly deflection of a cantilever loaded by a uniformly distributed load is given by:
δ = wL4 /8EI = 48/5 *(5wL4 / 38EI)
Which is 9.6 times that of a simply supported slab = (5wL4 / 384 EI).
While designing any slab as a cantilever slab, it is utmost importance to see whether
adequate anchorage to the same is available or not.
4.2.1.4 Selecting Proper Type of Footing
1) The type of footing depends upon the load carried by the column and bearing
capacity of the supporting soil. It may be noted that the earth under the
foundation is susceptible to large variations. Even under one small building
the soil may vary from soft clay to hard murum.
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2) It is necessary to conduct the survey in the area where the proposed structure
is to be constructed to determine the soil properties. Drill holes and trail pits
should be taken and in situ plate load test may be performed and samples of
soil tested in the laboratory to determine the bearing capacity of soil and other
properties.
3) For framed structure under study, isolated column footings are normally
preferred except in case of soils with very low bearing capacities. If such soil
or black cotton soil exists for great depths, pile foundations can be appropriate
choice.
4) If columns are very closely spaced and bearing capacity of the soil is low, raft
foundation can be an alternative solution. For column on the boundary line, a
combined footing or a strap footing may be provided.
4.2.2 Actions of Forces and Computation of Loads
Basic Structural Actions
The various structural actions which a structural engineer is required to know are as
follows:-
Axial force action: - This occurs in the case of one dimensional (discrete)
members like columns, arches, cables and members of trusses, and it is caused
by forces passing through the centroid axis and inducing axial (tensile or
compressive) stresses only.
Membrane action: - This occurs in the case of two dimensional (continuum)
structures like plates and shells. This induces forces along the axial surface
only.
Bending action: - The force either parallel or transverse, to the membrane axis
and contained in the plane of bending induces bending (tensile and
compressive) stresses. The bending may be about one or both axes which are
perpendicular to the member axis.
The bending action is essentially by transverse forces or by moments about
axes lying in the plane of the slab.
Shear action: - The shear action is caused by in-plane parallel forces inducing
shear stresses.
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Twisting action :- This action is caused by out of plane parallel forces i.e.,
forces not contained in the plane of axis of the member but in a plane
perpendicular to axis of the member inducing torsional moment and hence
shear stresses in the member
Combined action: - It is a combination of one or more of above actions. It
produces a complex stress condition in the member.
4.2.3 Analysis of a Structure
The different approaches to structural analysis are:-
1) Elastic analysis
2) Limit analysis
Elastic analysis is used in working stress method of design.
Limit analysis is further bifurcated as plastic theory applied to steel structures
and ultimate load method of design, and its modified version namely Limit
State Method for R.C. Structures, which includes design for ultimate limit
state at which ultimate load theory applies and in service state elastic theory
applies and in service elastic theory applies and in services state elastic theory
is used.
4.2.4 Member Design
The member design consists of design of slab, beam, column, and footing. These
topics will be covered step wise in detail at later stage of report as and when needed.
4.2.5 Detailing, Drawing, and Preparation of Schedule
Detailing is a process of evolution based on an understanding of structural behavior
and material properties. The good detailing ensures that the structure will behave as
designed and should not mar the appearance of the exposed surface due to excessive
cracking. The skillful detailing will assure satisfactory behavior and adequate strength
of structural members.
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4.3 THE DESIGN PROCESS
The design process of structural planning and design requires not only imagination
and conceptual thinking but also sound knowledge of science of structural
engineering besides the knowledge of practical aspects, such as recent design codes,
bye laws, backed up by ample experience, intuition and judgment. The purpose of
standards is to ensure and enhance the safety, keeping careful balance between
economy and safety.
The process of design commences with planning of the structure, primarily to meet its
functional requirements. Initially, the requirements proposed by the client are taken
into consideration. They may be vague, ambiguous or even unacceptable from
engineering point of view because he is not aware of the various implications
involved in the process of planning and design, and about the limitation and
intricacies of structural science.
It is emphasized that any structure to be constructed must satisfy the need efficiently
for which it is intended and shall be durable for its desired life span.
Thus, the design of any structure is categorized into the following two main types:-
1) Functional design
2) Structural design.
4.3.1 Functional Design
The structure to be constructed should be primarily serve the basic purpose for which
it is to be used and must have a pleasing look.
The building should provide happy environment inside as well as outside. Therefore,
the functional planning of a building must take into account the proper arrangements
of rooms / halls to satisfy the need of the client, good ventilation, lighting, acoustics,
unobstructed view in the case of community halls, cinema halls, etc. sufficient head
room, proper water supply and drainage arrangements, planting of trees etc. bearing
all these aspects in mind the architect/engineer has to decide whether it should be a
load bearing structure or R.C.C framed structure or a steel structure etc.
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4.3.2 Structural Design
Structural design is an art and science of understanding the behavior of structural
members subjected to loads and designing them with economy and elegance to give a
safe, serviceable and durable structure.
4.3.2.1 Structural Details of a Framed Structure
In a framed structure the load is transferred from slab to beam, from beam to column
and then to the foundation and soil below it.
The principle elements of a R.C building frame consist of:
Slabs to cover large area
Beams to support slabs and walls
Columns to support beams
Footings to distribute concentrated column loads over a large of the supporting
soil such that the bearing capacity of soil is not exceeded.
4.4 DESIGN OF MEMBERS
4.4.1 Design of Slabs
This procedure involves the design of slab. Primarily to design a slab we have to
confirm if it is a one way slab or two way slab
A. One Way Slab
It supports on opposite edges or when Ly/Lx > 2, predominantly bends in one
direction across the span and acts like a wide beam of unit width.
If a continuous slab/beam loaded by using UDL has equal spans or if spans do
not differ by more than 15% of the longest they are designed using IS: Code. For
accurate analysis a continuous slab carrying ultimate load is analyzed using elastic
method with redistribution of moments.
B. Two Way Slab
A rectangular slab supported on four edges with ratio of long span to short
span less than 2 (Ly/Lx <2) deflects in the form of a dish. It transfers the transverse
load to its supporting edges by bending in both directions.
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4.4.1.1 Design of One-Way Slab
SLAB MARK: - write the slab mark or designation such as S1, S2 etc.
1. END CONDITION: - for approximate analysis write the end condition No.
according to the category of the slab.
SPAN LENGTH (L): - depending upon end conditions determines the
effective span of the slab.
In fact, since the depth of slab is not known in advance and the width of
support is normally greater than the effective depth of slab, in practice the
effective depth of slab is taken equal center to center distance between the
supports to be on safer side.
2. TRIAL SECTION :-
Effective depth required d = Effective Span L
Basic L𝑑⁄ Ratio∗α
Where,
Basic l/d ratio
= 7 (for cantilever)
= 20 (for simply supported)
= 26(for continuous).
α= depends upon Pt% and steel stress (fs)
Initially assume Pt = 0.5% - 0.9% for steel of steel grade Fe-250
= 0.25% - 0.45% for steel of steel grade Fe-415
= 0.2% - 0.35% for steel of Fe-500
Obtain the nominal cover from IS: Code, and add half the diameter of main
steel, to get effective cover.
Therefore,
Effective cover=d’=nominal cover + half dia.
Total depth of slab = effective depth + effective cover
= d + d’.
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3. LOADS :-
Calculate load in kN/m on one meter wide strip of slab
Dead load: - Self weight = Ws = 25D where, D shall be in meter.
Floor Finish = FF = 1.5 kN/m
Total dead load =DL = Wd = Ws + FF
Imposed load = LL
Total working load W = DL + LL
Total ultimate load Wu = 1.5W
4. DESIGN MOMENTS :-
Design moment Mu = WL2/2 (for cantilever)
= WL2/8 (for simply supported)
= according to the code (for continuous).
5. CHECK FOR CONCRETE DEPTH :-
Mu.limit = 0.36 fck b.d(d-0.42xu.max)
Where,
Mu.limit = maximum ultimate moment
fck = strength of concrete
d = effective depth
b = breadth (1meter).
If Mu < Mu.limit then we will find area of steel (Ast) from the following formula:-
Mu = 0.87 fy Ast (d-0.42Xu)
If Mu > Mu.limit redesign depth.
Minimum area of steel (Ast) =0.15% of b.D (for Fe=250)
=0.12% of b.D (for Fe=415 or 500)
Assume bar diameter (8mm or 10mm for steel grade Fe415, and 10mm or 12mm for
Fe250).
Required spacing(S) = 1000*ast/Ast where, ast is area of one bar.
Maximum spacing (Smax) < (3d or 300mm) whichever is less.
From practical consideration minimum spacing is 75<S<100
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6. CHECK FOR DEFLECTION:-
Calculate required Pt% (maximum value at mid-span of continuous slab or simply
supported slab).
(Pt) assumed < (Pt) required
Then the check may be considered to be satisfied else detailed check should be carried
out as given in the code as under:-
Calculate steel stress of service load (fs):-
fs = 0.58 fy (Ast)reqd / (Ast)prov.
Obtain modification factor (α) corresponding to (Pt) prov and fs.
Required depth (d) = L
BasicL
d Ratio∗α
<effective depth provided.
7. DISTRIBUTION STEEL :-
Required Ast.min = 1.2D for HYSD bars,
= 1.5D for Fe250 where D in mm
Assume bar diameter (6mm for steel grade Fe 250 and 8mm for Fe 415).
Required spacing, S=1000𝑎𝑠𝑡
𝐴𝑠𝑡 min, to be rounded off on lower side in multiple of
10mm or 25mm as desired.
Maximum spacing, S=< (5d or 450mm) whichever is less.
In practice spacing is kept between 150mm to 300mm.
8. CHECK FOR SHEAR :-
a) Calculate design (maximum) shear.
In case of slabs, design shear may be taken equal to maximum shear Vu.max at support
and is given by:-
Vu.max = Wu*L*shear coefficient
= Wu*L/2 for simply supported slab.
Where, Wu = ultimate UDL on slab/ unit width.
In other cases, the maximum shear may be calculated from principles of mechanics.
b) Calculate shear resistance (Vuc) of slab:
This may be obtained from the relation (Vuc) = τuc b.d k (b=1000mm in case of slabs).
τuc depends upon Pt = 100Ast /bd.
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Where
Ast = area of tension steel. It is the bottom steel at simply supported end and
top steel at Continuous end.
Ast =Ast /2 if alternate bars from mid span are bent to top at simple support.
Check that Vuc > Vu.max. If not, increase the depth.
This check for shear is mostly satisfied in all case of slabs subjected to uniformly
distributed load and therefore many times omitted in design calculations.
It may be noted that when the check of shear is obtained, it is not necessary to provide
minimum stirrups as they are required in the case of beams.
9. CHECK FOR DEVELOPMENT LENGTH:-
Required Ld ≤ 1.3 M V⁄ + Lo
For slabs alternate bars are bent at support M = Mu.max / 2
And Lo =b2⁄ -x + 3Ø for HYSD bars using 90 degrees bend.
= b 2⁄ -x + 13Ø for mild steel using 180 degrees bend.
Where x = end clearance.
4.4.1.2 Design of Two Way Slabs
1. SLAB MARK: - write the slab designation e.g. S1, S2 etc…
2. END CONDITION: - Write end boundary condition No
3. SPANS:- Determine short span Lx , long span Ly, check that Ly / Lx < 2
4. TRIAL DEPTH (D):- It will be decided by deflection criteria based on short