training report at structural consultancy
DESCRIPTION
Training Report for Civil engineering Students(B.TECH)TRANSCRIPT
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.
22
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.
23
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.
24
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.
25
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.
26
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.
27
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.
28
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.
29
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.
30
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’.
31
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
32
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.
33
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
span Lx and total depth D.
Table No. 4.03 Span / Depth Ratio (IS 456-2000, Cl 24.1)
Allowable L/D Ratio for span ≤ 3.5m and loading class ≤ 3kN/m2
End Condition L/D Ratio
Grade of steel
Fe 250 Fe 415 or Fe 500
Simply Supported Slab 35 28
Continuous Slab 40 32
34
5. LOADS :-
Calculate load for one meter width strip of slab. Wu = 1.5(25D + FF + LL) kN/m
6. DESIGN MOMENTS
Obtain the bending moments by using the relation Mu = α Wu Lx2 using IS CODE.
7. CHECK FOR CONCRETE DEPTH FROM BENDING MOMENT
CRITERIA :-
In the case of a two way slab, effective depths for reinforcement in short span steel
and effective depths for reinforcement in short span and long span is placed above
short span steel. The effective depth do is for outer layer of short span steel and
effective depth di is for inner layer of long span steel at mid span. As far as support
section is concerned, the effective depth is do only for both spans.
do = D – (nominal cover + Ø/2) where Ø = diameter of the bar.
di = do – Ø for mid span long span steel.
8. MAIN STEEL :-
Calculate the area of steel required at four different locations.
Main steel calculated is provided only in the middle strips of width equal to 3 4⁄𝑡ℎ
the
slab width. There will be no main steel parallel to the support in edge strip of width
equal to 18⁄
𝑡ℎ of slab width. In this edge strip, only distribution steel will be
provided. Distribution steel will be provided for middle strip bars at top of supports.
9. CHECK FOR DEFLECTION :-
If Lx ≤ 3.5m and L.L≤ 3kN/m2, check that (L/D)prov > (L/D)req then,
Table No. 4.04 Design Moment Coefficient
Design Moment Coefficient for Approximate Analysis
End Condition No. EC=1 EC=2 EC=3
Design Moment Coefficient α=1/8 α=1/10 α=1/12
35
EC=1:- Simply Supported Slab
EC=2:- Slab Simply Supported One End and Continuous at Other End
EC=3:- Slab Continuous at Both End
For Lx > 3.5m or L.L > 3kN/m2, the deflection check should be similar to that
explained in one way slab.
10. TORSION STEEL :-
At corners where slab is discontinuous over both edges, At = (3/4) Ast.
At corners where slab is discontinuous over only one edge, At = (3/8) Ast.
At corners where slab is discontinuous over both the edges, At =0.
11. CHECK FOR SHEAR :-
a) Design maximum shear in two way slab may be obtained using the following
relation.
At middle of short edge, Vu.max = WuLx / 3 per unit width.
At middle of long edge, Vu.max = WuLx [𝛽/ (2𝛽 + 1)] where, β = Ly / Lx.
Increase above value by 20% for shear at continuous edge and decrease the
same by 10% at simply supported discontinuous edge and continuous over the
other.
b) Shear resistance and hence shear check is obtained in the same way as it is
obtained for one way slab.
c) Load carried by supporting beams of two way slab.
Long edge: Trapezoidal load with ordinate WuLx /2
Equivalent UD load for bending Weqs = W𝑢L𝑥
2[1 −
1
3𝛽2]
Equivalent UD load for shear Weqs = W𝑢L𝑥
2[1 −
1
2𝛽]
Short edge:
Equivalent UD loading for bending Weqb = WuLx /3
Equivalent UD loading for shear Weqs = WuLx /4.
12. CHECK FOR DEVELOPMENT LENGTH :-
It will be applied similar to that of one way slab
36
4.4.2 Design of Beams
A beam is a structural member that is capable of withstanding load by primarily
resisting bending.
The designing of the beam mainly consists of fixing the breadth and depth of the
beam and arriving at the area of steel and the diameter of bars to be used. The breadth
of the beam is generally kept equal to the thickness of the wall to avoid offset inside
the room. It shall also not exceed the width of the column for effective transfer of load
from beam to column. The depth of the beam is taken between L/10 to L/16.
The dimensions of the beam that we have chosen common are: breadth=150, 200,
230, 250, 300, 350, 380, 400mm and depth=300, 380, 450, 530, 600, 680, 750, 840,
900mm.
Procedure to design beams:
1. Analysis: The beam is analyzed first in order to calculate the internal actions
such as Bending Moment and Shear Force. A simplified substitute frame
analysis can be used for determining the bending moments and shearing forces
at any floor or roof level due to gravity loads. The Moment distribution
method is used for this purpose.
2. Loads: In order to analyze the frame, it is needed to calculate the loads to
which the beams are subjected to. The different loadings are as follows:
a) Uniformly Distributed Load : (w) in kN/m
The load transferred from the slab per meter length will be either rectangular from one
way slab or trapezoidal/triangular from two-way slab. Depending on the position of
the slab, the loading may be decided. In the case of two way slabs, trapezoidal load
comes from the longer side while the triangular load comes from the shorter side.
i. Slab load: The load transferred from the slab on the right side is denoted as ws2
and the slab from the left side is denoted as ws1.
ii. Masonry wall : ww=ϒ tw Hw where tw=thickness in m, Hw=height in m and
ϒ=unit weight of masonry=19.2 kN/m3
iii. Self-weight :ws= 25 b.D
iv. Total working load (w) = (ws1+ws2) + ww + ws for calculation of B.M and S.F.
37
v. Design (ultimate) load: wu= 1.5w kN/m.
b) Point Loads: Given total No. of point loads = Number of secondary beams
supported.
3. Design Moment: While designing it should first be noted if it is a flanged
section or a rectangular section. Most of the intermediate beams are designed
as rectangular sections. The main beams may be designed as flanged sections.
For rectangular beams, the maximum depth of N.A lies at the center. For
flanged sections, check if the N.A lies within the flange or not and then
proceed to calculate the moment. The dimensions of flanged section as
designed as per the code IS: 456-2000 as per Cl-23.1. Either way, for a singly
reinforced section:
Mu (xu=Df) = 0.36 fck bf Df (d-0.42Df)
If design moment Md calculated through frame analysis is less than Mu
(xu=Df), then N.A is known to lie within the flange. This is the case that
usually governs the slab-beam construction.
4. Main steel : Ast= 𝑀𝑑
0.87𝑓𝑦(d−0.42𝑥𝑢)
If it is a flanged section, replace d by Df.
The continuous beams at supports are generally required to be designed as a
doubly reinforced section.
Steps to design a doubly reinforced section:
i. Calculate Mu.max= 0.36 fck b d (d-0.42xu.max)
ii. If M>Mu.max, then the design should be as a doubly reinforced.
iii. Ast1= 𝑀𝑢.𝑚𝑎𝑥
0.87𝑓𝑦(d−0.42𝑥𝑢.𝑚𝑎𝑥)
iv. Ast2= 𝑀𝑢−𝑀𝑢.𝑚𝑎𝑥
0.87𝑓𝑦(d−𝑑𝑐)
v. Total area of tension = Ast1+Ast2
vi. Calculate Asc= 0.87𝑓𝑦𝐴𝑠𝑡2
𝑓𝑠𝑐 Where fsc = 0.0035
(𝑥u.max – d’)
𝑥u.max
38
5. Detailing of Reinforcement:
Select number and diameter of bars. Required spacing may be calculated as
per the code.
6. Check for shear & shear reinforcement
i. Find the shear force (acting), F from the frame analysis.
ii. Find the shear strength of the beam given by F’=k τ b.d, where the
parameters are as designated in the code.
iii. If F<F’, then provide minimum reinforcement, the spacing of the bars
given by 0.87𝑓𝑦𝐴𝑠𝑡
0.4b
iv. F>F’, then shear reinforcement need to be provided given for F-F’, with
the spacing S= 0.87𝑓𝑦𝐴𝑠𝑡d
F−F’
v. Incase bars are bent up for provision of shear reinforcement, then the
additional force coming in due to the bent up must also be considered.
Vusb=0.87fyAsb sin α < 0.5F”, where F”=F-F’
7. Check for deflection:
In the case of beam, deflection criteria is normally satisfied, because L/d <16
and hence computations are skipped.
4.4.3 Design of Columns (Exact Theoretical Method)
This method of designing column depends upon the type of column (short or slender)
and the type of loading and whether the column is subjected to axial load only or
subjected to combined axial load and uniaxial bending or combined axial load and
biaxial bending. The columns are easy to design using the design aids given in SP-16.
If Leff/h <12, then the column is said to be short and if Leff/h > 12, the column is
slender.
4.4.3.1 Axially Loaded Short Columns
The column shall be designed as a short axially loaded compression member if the
minimum eccentricity does not exceed 0.05 times the lateral dimension.
Pu= 0.4 fck Ac + 0.67 fy Asc
39
Where,
Pu= axial load on the member.
fck= characteristic compressive strength of concrete
Ac= Area of concrete
fy= characteristic strength of compression reinforcement
Asc= area of longitudinal reinforcement.
Here Ac= Ag-Asc, where Ag is the total cross sectional area of the column.
Assume diameter of lateral ties (Ø not less than 5mm or 14⁄
𝑡ℎ the diameter (Ø) of
main bar, whichever is greater). Normally, 6mm diameter ties are used for main bar
diameter less than 25mm. Decide the pitch S of ties such ‘S’ is not greater than least
of (300mm, width b)
4.4.3.2 Short Columns Subjected to Axial Compression and Uniaxial Bending
Determine the bending moments in columns. Assume arrangement of bars.
If the column is subjected to large bending moment M as compared to axial load P
(say e/D = M/ (PD) ≥ 0.5), assume bars to be equally placed on opposite faces like a
doubly reinforced section. On the contrary, if P is large compared to bending moment
M (e/D = M/ (PD) < 0.5), assume bars to be uniformly placed all around the
periphery.
These charts can be used without significant error for any number of bars greater than
8, provided the bars are equally distributed on the four sides. It may be noted that the
second arrangement requires large area of steel than that required by the first
arrangement. In case of ambiguity of deciding the arrangement, the second one is
definitely safer.
Procedure:
(a) For bending about x-axis bisecting the depth of column
i. Calculate Pu/(fckbD) and Mu/(fckbD2)
ii. Calculate d’/D where d’= effective cover
40
iii. Select appropriate chart corresponding to d’/D, grade of steel and
distribution of reinforcement. Obtain point of intersection of Pu/(fckbD)
and Mu/(fck.b.D2)
iv. Interpolate the value of p/fck where, p=As/(bD)
v. Calculate total area of steel required= As= fck (pbD/100)
(b) For bending about y-axis bisecting the width of the column the chart to be referred
to is having value of d’/b and use Mu/(fckbD2). Rest of the procedure is the same as
given above.
4.4.3.3 Short Columns Subjected to Axial Compression and Bi-Axial Bending
i. Assume steel percentage between 1% and 3% and the number-diameter
combination of bars for the same. Assume bars to be placed uniformly all
around the periphery as this is better for bi axial bending. Calculate p/fck
where p=100As/(bD) and Pu/(fckbD)
ii. Select appropriate chart corresponding to d’/D. Draw a horizontal line from
Pu/(fckbD) and continue it till it reaches a point corresponding to the value of
p/fck. Drop a perpendicular on x-axis to give the value of Mux1/(fckbD2).
Calculate Mux1.
Repeat the process by selecting appropriate chart corresponding to d’/b and
obtain the coefficient by dropping the perpendicular on x-axis which gives
Muy1/(fck.b2.D). Calculate Muy1.
iii. Calculate Puz = 0.45 fck Ac + 0.75 fy Asc and calculate Pu/Puz and hence the
value of αn (As per IS:456-2000 Pg:71)
iv. Check that (𝑀𝑢𝑥
𝑀𝑢𝑥1)
𝛼𝑛
+ (𝑀𝑢𝑥
𝑀𝑢𝑥1)
𝛼𝑛
≤ 1
If this equation is not satisfied, then the section is unsafe. Increase the section
and/or reinforcement and revise the calculations. If the left hand side of the
equation is less than 0.8, the section is uneconomical. Reduce the
reinforcement or reduce the section and repeat the procedure if desired.
Continue with the trials until the section and economical.
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4.4.3.4 Slender Columns
i. Calculate additional moment due to slenderness. Obtain Puz and Pub as
mentioned earlier.
ii. Calculate initial moments and obtain total moment Mut. This is now the design
moment for the column accompanied by given Pu.
iii. Check the safety of column for combined effect of Pu and total moment Mut
using the procedure for axial loading with uniaxial bending.
Note: For safe side, most of the columns, which could be designed as axially loaded
were designed considering them as axially loaded columns with uniaxial bending.
4.4.4 Design of Footings
Footings are of two types:
1) Isolated footing
2) Rectangular sloped footing.
We have designed isolated footing and the procedure is given below.
4.4.4.1 Design of Isolated Footing
The footing for an axially loading column of size b*D is designed as an inverted
cantilever outstanding from column and loaded with uniform upward soil pressure.
The various steps involved in the design are given below:-
Proportion of Base Size:-
Initially suitable footing dimensions are required to be selected to ensure that under
serviceability conditions the soil bearing pressure is not exceeded. The maximum load
transferred to the soil is equal to axial load on column plus self-weight of the footing.
Since the size of the footing is unknown, its self-weight is assumed to be equal to
10% of the axial load on the column.
If the axial load (working) on column is P then,
Area of footing = Aƒ = 1.1P/fb =Lf x Bf
Where
Lf = Length of the footing
Bf = breadth of the footing.
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fb = safe bearing capacity of soil
Once the area of footing is known the size of footing gets fixed. The shape of the
footing may be square or rectangular or circular.
The size of the rectangular base is selected such that the cantilever projections of the
footing from the faces of the column are equal. This gives approximately the same
depth for bending about x and y axes. The length or breadth of the footing based on
equal projection is obtained as under:
Cantilever projection of footing for bending about x-axis = Cx = (Lf – D)/2
Cantilever projection of footing for bending about y-axis = Cy = (Bf – b)/2
For equal projections, (Lf - D)/2 = (Bf - b)/2 or Bf = Lf – D+b
Substituting the value of Bf in the below equation and solving quadratic equation in Lf
we get,
Lf = 𝐷−𝑏
2+ √(
𝐷−𝑏
2)
2
+ 𝐴𝑓
Select the length of the footing by rounding out the value of Lf,
Recalculate Cx = (Lf – D)/2 and Cy = (Bf – b)/2
Where, breadth of footing = Bf = b + 2 x Cx
and Lf and Bf are the length and breadth of footing provided.
For square footing, Lf = Bf = √𝐴𝑓
Area of the footing provided =Af = Lf x Bf
Upward factored soil reaction = Wu = Pu/Af.
Where, Pu = load factor x axial force = 1.5 x P
Comments:-
1. In calculating the upward factored soil reaction the self-weight of the footing
is not considered because the dead load of the footing acts in the opposite
direction of soil pressure and hence does not induce any moment or shear in
the footing
2. The value of Wu will work out to be greater than the bearing capacity of the
soil. But this is not unsafe because the comparison can be made with the
upward working soil reaction which can be obtained by dividing Wu by the
load factor of 1.5. Then it will be seen that the value of working soil reaction
so obtained (Wu/1.5) will be less than the bearing capacity of the soil.
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Depth of Footing from Bending Moment Considerations
The maximum bending moment is calculated at the face of the column or pedestal by
passing through the section a vertical plane which extends completely across the
footing and computing the moment of forces acting over the entire area of the footing
on one side of the said plane.
Bending moment at the column face parallel to x-axis:- Mux =Wu Bf Cx2 / 2
Bending moment at the column face parallel to y-axis:- Muy = Wu Bf Cy2 / 2
Required effective depth for bending about x-axis:- dx = √𝑀𝑢𝑥
𝑅𝑢.𝑚𝑎𝑥 × 𝑏1
Required effective depth for bending about y-axis:- dy = √𝑀𝑢𝑦
𝑅𝑢.𝑚𝑎𝑥 × 𝐷1
Where,
b1 = b + 2e
D1 = D + 2e
b = width of column,
D = depth of column,
e = offset provided at the top of footing for seating column form work
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CHAPTER 5
MODELLING, ANALYSIS AND DESIGN OF A LOW
RISE BUILDING USING STRUDS
5.1 INTRODUCTION
STRUDS is an ideal software solution for the usage of structural engineers for the
analysis of 2D & 3D structures and the design of different R.C.C. / Steel components
such as Slabs, Beams, Columns, Footings and Trusses with design sketches running on
Windows 95/98/2000/XP/NT platforms.
STRUDS has an in-built graphical data generator to model the geometry of building
structure. The basic approach is to create two-dimensional floor plans (Plane Grids) and
provide column locations with the help of which the program automatically generates
2D Plane Frames and 3D Space Frame. Appropriate material and section properties can
be created or assigned from STRUDS libraries. Standard boundary conditions and
different types of loads can then be applied.
At every step of the modelling process, we will receive graphical verification of our
progress. We never have to worry about making a mistake as the deleting or editing of
any part of the geometry is possible using available menu commands. Immediate visual
feedback provides an extra level of assurance that the model we have constructed agrees
with our intentions.
When our structure geometry is complete, STRUDS performs analysis using Stiffness
Matrix Method and Finite Element Method for maximum solution, accuracy, speed and
reliability.
After the analysis, the Post Processor mode of STRUDS provides powerful
visualization tools that let us quickly interpret our analysis results and numerical tools
to search, report and understand the behavior of the structure. Herein, the analysis
results for different load combinations for a part of structure or the whole geometry can
be seen in the graphical as well as the text form.
45
STRUDS then performs the integrated design by Limit State Method of all R.C.C.
components of the structure by directly reading the analysis results. All the relevant
Indian Standard codes & British standard codes are followed to confirm to the design
parameters and checks. If any component fails, the program gives us warning messages
and suggests us the possible alternatives for design. STRUDS prepares graphical
outputs in the form of drawings and diagrams. Design results in the text form of
Schedules, Quantities and Details are also produced. The design process is highly
interactive and extremely user-friendly. We can change the design parameters
anywhere in between the design process and redesign the structure. These changes are
automatically reflected in graphical and numerical output form. STRUDS also enables
us to produce the working drawings in AUTOCAD.
Documentation is always an important part of analysis and design and the Windows
user interface enhances the results and simplifies the effort. STRUDS provides direct
high quality printing and plotting of both text and graphics data to document our model
and results.
5.2 MODELING OF STRUCTURAL SYSTEMS
Use a single and modern intuitive interface
Import architectural plan from CAD drawings
Import models from other structural software such as Staad Pro and ETABS
Generate irregular shaped slabs
Create L, C, T shape shear walls
Generate true curved beams
Design flat slabs with drop and capital
Design rectangular, T and L shaped beams
Design rectangular, T, L and circular shaped columns
Design differential footing levels (footings on sloping ground)
Model floating columns on beams
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5.3 STRUDS ANALYSIS TECHNIQUES
This module performs the analysis of the building structure defined by us, by the
advanced "Finite Element method". We have the option of analyzing the structure by
the 2D Plane Grid / Plane Frames or 3D Space Frame method. In this mode, the analysis
results are written in the text format, so that they are directly accessible for design.
5.4 ANALYSIS AND DESIGN
5.4.1 Analysis
Perform advanced 3D space frame analysis, with optional plane grid and plane
frame analysis
Perform wind load analysis to code IS:875
Apply seismic analysis by response spectrum analysis
Consider floor diaphragm effect in analysis
Perform torsion analysis due to eccentricity between centre of mass and centre
of rigidity
Undertake shear wall analysis
5.4.2 Design Features
In this mode, the data of the analysis results is automatically read from the text files,
produced by the analysis module and it is then processed for the R.C.C. / Steel design
of all the components of the selected structure. All the relevant IS codes are followed
for the design of Slabs, Beams, Columns, Footings and Trusses. In this mode, we can
also generate the detail design reports, schedules, drawings and bills of quantities for
all the components. The design process is highly interactive and the user has the choice
of modifying the final details as per his discretion.
Design slabs (Rectangular, Triangular, Trapezoidal and Flat)
Design beams (Rectangular, T section , L section and curved in plan)
Design columns (Rectangular, Circular, T shape and L shape)
Design foundations:
- Footings (flat, sloping, combined, strip),
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- Piles (Under reamed and end bearing),
- Raft (beam supported)
Design shear walls
Perform grouping to rationalize design of all building components
Handle project changes easily and effectively
5.5 OUTPUT FROM STRUDS
Produce analysis results for forces and displacements
Produce clear diagrams for shear force, bending moment and deflections
Product written and graphical representation for end moments and end
reactions
Produce detailed calculation reports
Prepare floor-wise design schedules for all components
Adopt ductile detailing as per IS:13920 and normal detailing as per SP-35
Generate multi-layered DXF drawings for slabs, beams, columns, shear walls
and footings
Produce BOQ / material lists of concrete and steel components including
slabs, beams, columns, foundations.
Export models to other structural software
5.6 OVERVIEW OF THE MODE
This menu option is used to toggle between the modes available.
The following five modes are available in STRUDS
1. Prepro
2. Postpro
3. R.C.C Design
4. Steel Design
5. Individual Design
48
The functionality of each of these modes has been briefly enlisted below:
PREPRO: This is the module, in which the user can model/ edit the structure.
By default, this is the module which is opened when we starts the program, or
opens a BLD file. This icon can be used to select Preprocessor mode.
POSTPRO: In this module, we are capable of visualising the Post Analysis
results. Before going to this mode, it is essential that the analysis of the structure
should have been completed. This icon can be used to select postprocessor
mode.
R.C.C DESIGN: This mode is to be selected, if we want to perform the R.C.C
design of the structure. In this module, the analysis results would be directly
read from the output files of the analysis. This icon can be used to select
RCC Design mode.
STEEL DESIGN: This mode enables that we can perform the Steel design of
the structure. This module is currently useful, for the design of Steel Trusses.
This icon can be used to select steel design mode.
INDIVIDUAL DESIGN: This mode needs to be selected, if we want to design
individual components of the structure. In this module, the input data needs to
be given by the user. This module of STRUDS is referred to as STRUDS – IDM
5.7 RESULTS
The Results menu option enables that we can view the Post Analysis results. To view
the results, it is essential, that we should have completed the analysis of the structure,
for at least a single Structure Type (i.e. Plane Grid/ Plane Frame/ Space Frame).
Before selecting this option, we must set the current mode as "Postpro", unless and
otherwise, all the options under this menu caption will appear inactive.
This menu has the following options:
RESULTS - STRUCTURE TYPE RESULTS - CONTROL
RESULTS - VECTOR DIAGRAM RESULTS - GEOMETRY
49
RESULTS - ELEMENTAL RESULTS RESULTS - REPORTS
5.8 DESIGN OF A LOW RISE BUILDING USING STRUD
5.8.1 Introduction
This building is constructed under the SAI COUNSULTANTS. Project was directly
allotted to us without any previous work done on it. Site of the project is situated at
Lalgate, Surat. Building is a combination of Showroom till First floor and residential
above it.
5.8.2 Typical Sections of Building
Figure 5.01 Section of Building
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Figure 5.02 Section 1-1 of Building
5.8.3 Typical Floor Plans of Building
Figure 5.03 Basement Floor Plan
51
Figure 5.04 Ground Floor Plan
Figure 5.05 First Floor Plan
Figure 5.06 Second Floor Plan
52
Figure 5.07 Third Floor Plan
Figure 5.08 Terrace Floor Plan
5.9 MODELING OF A LOW RISE BUILDING
5.9.1 Starting STRUDS
If STRUDS is not already open, start the program by clicking on the appropriate
desktop shortcut or by selecting STRUDS from Windows Start menu. This will open
the STRUDS main window.
5.9.2 Creating a New Model
We can start a new model using the following steps:
1. Select the FILE Menu > NEW
1 1
53
Figure 5.09 STRUDS: Adding New File
2. A dialog box will appear. Type the name of project, owner name, job and
reference No., Date of project etc. we can also change code from this dialog
box.
3. Set the units to meter, “m”, using the drop-down box in the lower right
corner of the dialog box.
4. Now click on the “OK” button.
Figure 5.10 STRUDS: New Model Initialization
54
5.9.3 Set Floors and Heights
After clicking “OK” another dialog box is open in which we can add our floor no., floor
Description, Floor height and Level height by click on “ADD” button. After all floors
are added select “CLOSE” button.
Figure 5.11 STRUDS: Building Story Data
This dialog box also appears, at the start, when you model a new BLD file. It has various
fields, which have been described in detail below.
No of Floors: This field displays the total number of floors, which are present in the
existing structure.
Floor Description: This field is used to display the name of the floor.
Level Description: This field is used to display the name of the level in the floor (The
level of the floor denotes the height of the floor from the footing top).
Height of Floor: This field displays the height of the floor.
Level of Floor: This field displays the level of the floor.
Copy: This option allows us to copy the floor plan geometry from one floor to another.
This option can be used to generate more than one floor with same plan geometry by
drawing only one floor. Thus we can make a number of copies of a typical floor plan.
We can then open any of these floor plans by using VIEW > FLOOR PLAN > SET
55
FLOOR option and modify the geometry as per your requirement. When we select this
option, STRUDS displays following window.
Then by selecting floor using drop-down box click on “OK” button.
Figure 5.12 STRUDS: Working Space Selection
5.9.4 Importing DXF File into STRUDS
For importing the DXF file (floor plan) in to STRUDS, take the path as follows:
VIEW>FLOOR PLAN>IMPORT>DXF FILE
Figure 5.13 STRUDS: Import DXF File
Once the DXF file is added a pop up appears asking for the layer to be imported as
shown in figure 5.06. Here the layer imported was zero as we worked in layer zero in
AUTOCAD file. In the same pop up we can change the scale factor to 0.0833 and the
unit used in DXF file.
56
Figure 5.14 STRUDS: DXF File Setting
The grid imported looks like as below in fig. no. 5.07 and the digits in pink color are
the NODES.
Figure 5.15 STRUDS: Imported Grid
Once the grid is imported for one floor level grid for rest of the floors are copied and
edited as required by following the below steps: MODIFY>BUILDING>SKELETON
57
as explained in 5.8.3
5.9.5 Column Marking, Column Size, Shape and Section in STRUDS
Marking
Columns can be marked at the required nodes by following the below steps: select
MARK COLUMN SEQUNTLIALLY ON DEFINED NODES
Figure 5.16 STRUDS: Column Marking
Selecting and Rotating of Column:
To change the orientation, shape and size of column select MODIFY Menu >
COLUMN > ORIEN or select .
Figure 5.17 STRUDS: Defining Column Location
58
Rotate:
This option allows us to rotate a column along the axis of connected beams. To use this
option, first click on the ‘Select Column’ button. A box cursor appears on the screen.
Select the column by the cursor. STRUDS highlights the selected column. Click
anywhere on the screen. Now press the ‘Enter’ key from the keyboard repeatedly to see
the rotation of column along beam axis.
Select Column:
When we select this option, a box cursor appears on the screen. We can select any
column by the cursor to change its size, orientation or flushing.
Select Multi Column:
This option is used when we want to select more than one column to change the
orientation. When we use this option and then choose the columns, the chosen columns
turn blue. All the columns starting and ending at the same level can only be selected
together.
Rotate by 90:
This option should be used after the columns are selected by the above option. On using
it the selected columns rotate by 90 degrees.
Move Column:
This option can be used to move a column along the axis of connecting beams. When
we select this option STRUDS displays following window.
Type the value of X and Y offset in the fields to specify the distance by which we want
to move the column. The sign for left (along X) and below (for Y) should be negative.
When we move a column, the effect in the drawings and center line diagram is taken
by STRUDS automatically. However, the extra moments due to eccentricity are not
considered for analysis.
59
Shape & Size:
This option allows us to specify the size and shape of columns. When we select this
option STRUDS displays following window.
Figure 5.18 STRUDS: Defining Column Shape
This window has a drop down menu having the group numbers of all the columns. We
should select the column group number for which we want to modify the column size.
NOTE - we can group the columns having same size for all floors and same orientation
by using the options COLUMN - GROUPING. If we do not group the column,
STRUDS assumes that every column is in its own group. When we group the columns
and change the size or orientation of that group, the sizes and orientation of all the
columns in that group will be changed. There are four icons in the window that indicate
the shape of columns such as Rectangular, Circular, L shape, and T shape. Select the
shape that we want to assign to the columns in the selected group.
Column Sizes:
Click on this button to see or modify the sizes of columns in the selected group. When
we select the option for rectangular columns, STRUDS displays following window.
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Figure 5.19 STRUDS: Defining Column Size
5.9.6 Attach Support
For attaching support select CREATE > BUILDING > CONSTRAINTS > SUPPORT
> SPACE FRAME
Using this option, we can assign the boundary conditions, to the nodes, in the modelled
geometry, for the Space Frame structure Type.
Figure 5.20 STRUDS: Attaching Support
When we select this option to attach the boundary conditions for the Space Frame
structure type, another level called as the "Footing Level" is automatically added in the
61
combo box, comprising the floors available in the structure. When, we set the "Footing
level" as the current floor level, the screen will appear somewhat as shown below:
Figure 5.21 STRUDS: Defining Column Grouping
This view displays the plan of the footing nodes. By selecting this level, in the list of
floors, we can attach the selected boundary conditions, to the footing nodes, for the
Space Frame structure type.
The "Footing Level", would be present in the list of available floors, only till this
command, for constraints are active. Once we end this command, by using the CLOSE
option in the Splitter, this level would be automatically deleted from the list of available
floors, so that we cannot modify or edit the geometry at this level.
It must be remembered that all the other menu options, apart from the ones related to
display would be unavailable, until this command is active. Once we end this command,
using the Close button, all the other menu option would be available.
62
5.9.7 Defining and Attaching Materials and Section
Material
For defining material first select CREATE Menu > BUILDING > PROPERTIES >
DEFINE > MATERIAL or select .
By using this option, we can create material properties to be assigned to the elements
drawn in the plan geometry. By default the standard properties of various grade of
concrete are available with STRUDS. When we select this option STRUDS displays
following window.
Figure 5.22 STRUDS: Defining Materials
Section
For defining Section first select CREATE Menu > BUILDING > PROPERTIES >
DEFINE > SECTION or select .
This option allows us to define the sectional properties to be assigned to the elements
in plan geometry. You must provide sectional properties to all the elements in plan
otherwise the program will not be able to perform the analysis of the defined structure.
When we select this option, STRUDS displays following window.
63
Figure 5.23 STRUDS: Section Define
In this window we can select the type of sectional properties we want to define by
clicking on the RCC or Steel option.
SECTION ID - STRUDS automatically assigns an identification number to every
section we define.
NAME – We can give any name to the each of the sectional properties. By default
STRUDS assumes names sec1, sec2, sec3 etc. If we want to provide any other name,
we can overwrite the default name after giving the section dimensions.
SECTION TYPES - STRUDS displays a drop-down menu for the type of sections
available. Click on the down arrow of this menu and select the type of section we want
to define. STRUDS shows the figure for the selected type in the window above this
menu. The type of sections available are Rectangular, Circular, T Section, L Section, V
Section, U section and I section.
When we select the type of section, STRUDS asks for corresponding input. For
example for rectangular section, we are asked to provide the width and depth. For
Circular Section, we are asked to give the diameter.
64
In case of L and T sections, if you specify the web width and web depth, STRUDS will
automatically find out the thickness of flange and width of flange from the data of
connecting slabs when we attach the section to an element.
On the right side of the ‘Section Define’ window buttons are available to invoke
different options.
NEW - By clicking on this button we can start defining a section.
SAVE - Click on this option to save the defined section after we have provided relevant
dimensions and section name. This option should also be used when we modify an
already defined section by using EDIT option.
EDIT - This option allows we to modify the dimensions of an already defined section.
Select the section to be changed from the list at the right side column and click on this
option. STRUDS again asks us for the revised dimensions keeping the section type as
same. Please note that if we have attached a section to some elements and then modify
the dimensions, then the dimensions of all the elements to which this section is attached
are also changed automatically by STRUDS.
Attaching Material:
For attach material CREATE Menu > BUILDING > PROPERTIES > ATTACH >
MATERIAL or select .
We can assign the defined material properties to any of the elements. We can also assign
different material properties to different elements. When we select this option,
STRUDS displays following window.
65
Figure 5.24 STRUDS: Attachment of Elements
This window has a drop-down menu. Click on the down arrow of this menu and select
the type of material we want to assign from the defined set of materials. The properties
of this material type are displayed by STRUDS in the top half portion of this window.
Below the drop down menu several buttons are available to decide the way of attaching
material to elements.
ALL - When we click on this button STRUDS assigns the selected material to all the
elements in the plan geometry.
CLOSE - Click on this option to close the window.
LOCATE - When we click this button, a box cursor appears on the screen. Select the
elements by moving cursor along the elements and clicking left button of mouse. We
can select all the desired elements one by one.
GRID - When we select this option, a box cursor appears on screen. When we click on
any element, all the elements in the line of selected element shall be assigned that
material.
REST - When we have attached material already to some of the elements, we can attach
the selected material to all the remaining elements by clicking this option.
66
Attaching Section:
For attach section CREATE > BUILDING > ATTACH > SECTION or select .
You can assign the defined sectional properties or sections to different elements. On
selection of this option, STRUDS displays following window.
This window has a drop-down menu. Click on the down arrow of this menu and select
the name of the section you want to assign from the defined set of sections. The
dimensions of this section type are displayed by STRUDS in the top half portion of this
window.
Figure 5.25 STRUDS: Attachment of Section
5.9.8 Attaching Walls
Follow the steps CREATE>BUILDING>WALL>DEFINE or select . As we select
the above option a dialogue box appears as show in below figure.
Figure 5.26 STRUDS: Adding Wall Properties
67
For attaching wall to desired location Follow the steps CREATE >BUILDING
>WALL>ATTATCH or select
5.9.9 Slab Attachment
The slab can be attached to the building by following the steps: CREATE> BUILDING
> SLAB > RECTANGULAR or select to Draw the slab. Once the slab is traced as
required below dialogue box appears
Figure 5.27 STRUDS: Defining Slab Properties
The load from rectangular slab on the supporting beams is calculated by STRUDS
automatically as per the yield line pattern given in IS: 556 - 2000. STRUDS also designs
this slab as per the IS / BS code coefficients. The boundary conditions for slab such as
continuous/discontinuous edges are taken automatically by STRUDS from the plan
geometry.
At the top of the dialog box, icons are displayed to specify the Load transfer type from
slab to beams. We can specify the One Way, Two Way or Cantilever slab by selecting
the respective icon. The Auto icon is to decide the load transfer of slab automatically
from aspect ratio. When we click ‘Auto’ icon, STRUDS computes the length to width
ratio of slab and decides whether it is a One Way slab or Two Way slab.
68
Thickness: There is a field to specify the thickness of the slab. By default the thickness
is taken as 100 mm. We can change the thickness as per our description. The self-weight
of slab is computed from the thickness provided here. If we change the thickness,
STRUDS will re-compute the self-weight of slab.
Material Density: We can specify the Material Density for slab in the field provided.
By default the density is taken as 25 kN/m3 for concrete.
Dead Load: We can view the dead load (Self-weight) of slab in a field. When we change
the thickness, we can see the corresponding change in this field.
Live Load: We can specify the Live Load on the slab in the field provided. By default
STRUDS takes Live Load on slab as 2kN/m2. We can change the value of Live Load
on the slab as per your requirements. If we want to know what are the IS code provisions
for Live Load for different loading classes, click on “CATEGORY REF.” button.
STRUDS will display the relevant pages from IS 875.
Floor Finish Load: We can specify the extra load on the slab as due to flooring etc. in
the field provided for it.
Sunk Slab: Sunk slab is the slab whose level is depressed with respect to surrounding
slabs, for example the slab at the bottom of toilet is depressed to accommodate pipes
and waterproofing. We can specify a slab as sunk by giving the level of slab. For
example if the depression is by 300mm, we can type 0.3m in the field provided for sunk
level. This sunk slab may be filled with some material such as brickbats. If we provide
the density of this fill material in the field provided for Material Density, STRUDS will
calculate the extra load on slab due to this filling and show its value in the field provided
for Sunk Load.
Note - When you specify a slab as sunk, STRUDS considers the boundary condition of
this slab as all four edges discontinuous for design.
69
Figure 5.28 STRUDS: Third Floor Slab
5.9.10 Analysis
This top level file menu has several sub menu options, related to saving the analysis
files, and performing analysis, which have been listed below:
1. Pre-Analysis Enquiry
2. Analysis Options
3. Perform Analysis
4. Front Optimization
70
1. Pre-Analysis Enquiry:
This option can be used to verify the input data before preparing data for analysis. If
you are not sure that the input created is not fully correct, you can use this option to
check the same. When you select this option, STRUDS displays following window.
Figure 5.29 STRUDS: Pre-Analysis Enquiry
For creating data for analysis, following criteria must be satisfied.
1. All the elements at all floors must be assigned sectional and material properties.
2. There should not be any zero length element or coincident nodes.
3. Proper boundary conditions should be attached to the nodes. That is there must
be some columns in the geometry.
In the above window STRUDS displays the discrepancies if any in the input regarding
above requisitions.
2. Analysis Options:
This option enables you to save the analysis related files, depending upon the structure
type, before performing the analysis.
When you select this option, STRUDS displays following window.
71
Figure 5.30 STRUDS: Analysis Options
This dialog has four checkboxes, corresponding to each Structure Type. By default, the
Space Frame option is always checked when you click on this option.
Depending upon the checkboxes, which you select, the dialog box, is further expanded
3. Perform Analysis:
Using this option, you can directly perform the analysis of the structure, for any
structure type. Before, using this option, make sure that you go to the option,
ANALYSIS - ANALYSIS OPTIONS, to save the analysis related files.
Once the files, have been saved using the above mentioned option, the "Perform
Analysis", will simply perform the analysis for the all the files of the structure type,
which have been saved.
For example, if you select, a few files for the Plane Grid structure, some files, for the
Plane Frame structure, as well as the Space Frame files, the analysis would be
performed sequentially, starting from the Plane Grid, the Plane Frame, and then the
Space frame. This icon can be used to give Perform Analysis command.
4. Front Optimization:
STRUDS uses the Frontal Solution Technique for solution of the simultaneous
equations. The efficiency of this solution is based on "Front Width", which in turn
depends on how the numbering of elements is done. STRUDS has an in-built 'Front
Optimization Algorithm' to renumber the elements such that front width is reduced to
minimum possible. This enhances the Solver performance and thereby reduces the
analysis time. Moreover it needs less CPU memory for the same number of equations.
72
By default, when a particular file is opened, this flag is always checked, and STRUDS
automatically optimizes the front width by numbering of elements of structure, when
we save the structure.
5.9.11 R.C.C. Design
This module of STRUDS allows you to design the structure you have generated in Pre-
Processor mode and have analyzed it as Grid, Plane Frame or Space Frame. You can
analyze the structure by either one or all of these three methods.
The results of analysis are directly read by STRUDS. Before performing the R.C.C
design of any component, you must set the current mode to R.C.C design, using the
Mode - RCC Design option.
STRUDS performs the design of all the components by the Limit State Method.
This menu has several menu options, which have been listed below:
Set Structure Type
Design Parameters
Load Combination
Design All
Slab
Beam
Column
Shear Wall
Footing
RCC DESIGN > SET STRUCTURE TYPE
This option is used to set the structure type for design, before you proceed to the design
of any component.
When the model is created in the preprocessor, you can analyze it using any of the three
methods, namely the Plane Grid, Plane Frame or the Space Frame method.
73
Similarly, once the analysis results are available for the all the three types, the design
of the RCC components can be performed for any of the structure types. When the
Structure type has been set to any one of the options, the design of all the components
would be performed using the results for the current structure Type. Before starting
with the design, set the structure type to any one of the above mentioned structure types.
This Structure type will be used to design all the RCC components, namely the beams,
Columns, Shear Walls as well as the Footings. Before, setting the structure type, ensure
that the analysis pertaining to that Structure Type has been completed, in all respects.
The default Structure Type is set to the Plane Grid, by STRUDS, when the mode is set
to Design.
This can be changed at any stage while executing the design module.
5.9.11.1 Slab Design
RCC DESIGN >SLAB > NEW > ALL
When you select this option, STRUDS designs all the slabs in the selected floor.
Figure 5.31 STRUDS: Design of Slab
If you have not previously designed slabs in the selected floor, the above message will
not occur and STRUDS will design all the slabs. During design process, STRUDS
74
checks the slab for deflection and flexure. If any of the slabs fails in deflection,
STRUDS displays following message.
Figure 5.32 STRUDS: Deflection Check Dialog Box
At the top of this window STRUDS displays the slab id number, the required effective
thickness to satisfy the deflection check and clear cover. Below this STRUDS displays
the dimensions of the slab and its boundary conditions.
The available thickness, area of steel provided, modification factor and base factor as
per IS code are displayed below. Please refer to SP: 10 for the values of modification
factor and base factor.
STRUDS also displays the ratio of span to depth and the product of the basic deflection
factor for the slab and the modification factor. The current deflection status is also
indicated in the field for the same. If we manually want to control the deflection then
we can take help of the buttons as defined below. But if we want the software to find
the optimum thickness which would satisfy the deflection criterion by itself then we
tick the checkbox "Change thickness internally" and then click on the "OK" button.
Below this are two buttons to take action on the deflection check.
75
Change Thickness:
When you click on this button, the field for available thickness becomes active. Type
the value of new thickness in the field and click on the `OK' button. STRUDS will
check the slab for deflection for the new thickness. If the check is still not satisfied,
STRUDS displays the same window with computed values of Ast, Base Factor and
Modification factor.
Change Ast:
This option allows you to see the change in modification factor and base factor by
changing the area of steel. When you click on this button, the field for Ast (Area of
Steel provided) becomes active. Overwrite the value in this filed and click on the
`Compute' button to see the corresponding change in Base Factor and Modification
Factor.
Compute:
This button becomes active only when you have selected the ̀ Change Ast' option. When
you click on this button, STRUDS computes the Modification and Base Factor as per
the change in Ast and displays it in their fields.
Ignore:
You can click on this button, to ignore the deflection check. When you click on this
option, STRUDS finds out the extra steel to be provided to change the modification
factor to satisfy the deflection check and provides this steel in the slab design.
Save:
This option allows you to save the design data after you have designed the slabs. You
can then open the design data by using the previous option.
RCC DESIGN > DESIGN SKETCH > ALL OR ONE
When you select this option, STRUDS displays the graphical representation of
reinforcement in all the slabs in the floor.
76
Figure 5.33 STRUDS: Section of One Slab
5.9.11.2 Beam Design
RCC DESIGN > BEAM > NEW or select
Select this option if we have not designed the beams at the current floor level earlier. If
we have already designed them and we then select this option, STRUDS will once again
perform the design, overwriting previous design results. During design if the beam fails
in shear capacity then you will get following dialog box.
Figure 5.34 STRUDS: Shear Capacity Error
77
In this dialog box by default the section is changed internally in depth by 25 mm. If we
want we can change the material also if we select on Change material radio button.
Change the grade of concrete or steel from drop down menu.
In the dialog box user can give the dimensions as per requirement as well can select the
type of section. These changes could be implemented using various 3 options
1) Change to current beam. Will change in the current beam only.
2) Change to all beams in current gridline will change the selected option in all beams
present on the grid line of beam which is failing in shear.
3) Change in all beams in all gridlines will change the value for all beams which are
failing in shear on that particular floor.
On selecting redesign option the design will be done for selected changes. If we want
we can break the design.
After this if the beam is failing in Stirrups detailing then we will get following dialog
box.
Figure 5.35 STRUDS: Stirrup Detailing
78
Here we can increase the diameter of bar or can increase the number of legs from the
corresponding drop downs which will get activated on selection of specific options.
These changes also could be implemented to all beams by selecting the appropriate
option.
RCC DESIGN > BEAM > SELECT GRID
This option allows us to choose any continuous beam for viewing its analysis and
design results. When we select this option, a box cursor appears on the screen. Select
the gridline of beams of which we want to see the design results. STRUDS displays the
continuous beam on screen with a new menu at top.
DESIGN RESULT > SECTION GARPHICS
Figure 5.36 STRUDS: Section of Beam B28 (Terrace)
79
5.9.11.3 Column Design
RCC DESIGN > COLUMN > ALL or select
Select this option to design the columns in our project. This option is activated only if
the current mode has been set as "RCC Design". We can set the mode, using the Mode
option.
Once the mode has been set to RCC Design, set the Structure Type, for which we want
to design all the columns in the structure. The Structure Type can be set to the Plane
Grid, Plane Frame, or the Space Frame.
When we select this option, STRUDS will design All the columns, in the structure, for
the Design Type (Axial / Uniaxial/ Biaxial) which has been set by us in the Column
Design Parameters, irrespective of the Structure type, set using the RCC DESIGN -
DESIGN PARAMETERS option.
For example, if the Design type has been set as Axial, all the columns will be designed
for axial loads purely, irrespective of the Structure Type, which has been set.
Again, if the Design Type has been set as Uniaxial, all the columns would be designed
about the axis, which has been specified by us (That is either about the X axis, or the Y
axis).
Similarly, if the Design Type has been set as Biaxial, all the columns would be designed
biaxial.
During designing columns if we fail due to exceeding maximum steel percentage given
in design parameters then we will get following dialog box.
80
Figure 5.37 STRUDS: Maximum Percentage Error
We can change the required parameter from list of parameters given in the dialog box
and can proceed for further design using redesign option.
RCC DESIGN > COLUMN > VIEW DESIGN
This option allows us to view the design results for the selected column. This option
will be activated only when we have completed the design process for all the columns.
When we select this option, a box cursor appears on the screen. Select the column of
which we want to see the design results by the cursor. STRUDS displays following
window.
Figure 5.38 STRUDS: View Column Design
81
This window displays the design results for the selected column at all floors in the
building.
These design results are displayed in a tabular format. The results for the column
design, serially from the bottom most floors to the top most floors are shown along the
rows in this table.
The above dialog box shows two windows. The window at the bottom is used for
modifying the column design and the upper one is to View the Design. The window at
the bottom displays the design attributes for the column at the Floor level selected in
the drop down menu, named Floor - Level, situated at the bottom left of this dialog box.
If we need to modify the design attributes, for any particular floor level, select that floor
in the drop down menu.
Cross Section
This option allows us to visualize the cross sectional diagram of a column. When we
select this option, a box cursor appears on the screen. Select any of the columns by
cursor. STRUDS displays the cross section diagram of the column on screen.
Figure 5.38 STRUDS: Section of One Column
82
5.9.11.4 Footing Design
RCC DESIGN > FOOTING > NEW or select
When we select this option, STRUDS will perform the design of all the footings in the
building. We must have designed the column of the building to use this option.
While designing, if any check is not satisfied, STRUDS displays following messages.
Figure 5.39 STRUDS: Bond Check Error
If the Development length check for column bars is not satisfied, STRUDS
displays the above message. At the top STRUDS shows the footing group
number for which the check has failed. Below this the required and available
development length for column bars embedded in footing is displayed in two
fields. To satisfy the checks, we can use following options.
We can change the grade of concrete and steel and redesign the footing. To do
this select CHANGE MATERIAL button.
We can ask STRUDS to increase the depth of footing for present group or for
all groups. Select on the FOR ONE GROUP or FOR ALL GROUPS option and
click on the DEPTH button.
WE can ignore the check for present or all groups. Select on the FOR ONE
GROUP or FOR ALL GROUPS option and click on the IGNORE button.
We can ask STRUDS to increase the size of footing for present group or for all
groups. Select on the FOR ONE GROUP or FOR ALL GROUPS option and
click on SIZE button. We can ignore the check for present or all groups. Select
83
on the FOR ONE GROUP or FOR ALL GROUPS option and click on the
button.
RCC DESIGN > FOOTING > VIEW DESIGN
This option allows us to visualize the design results of any footing on screen. When we
select this option, a box cursor appears on the screen. Select the footing of which we
want to see the design results by cursor. STRUDS displays following window. This
window displays the design results of selected footing in table form. At the top
STRUDS shows the footing group number, the shape type of footing and the worst load
combination for design. Below this the design table is shown. The design table shows
X and Y Dimensions of footing, minimum and total depths, diameter and number of
bars along x and y dimensions of footing.
Figure 5.40 STRUDS: Footing Design
Properties
This option allows us to modify the default properties of the selected footing. When we
select this option, STRUDS displays following window.
Figure 5.41 STRUDS: Design Parameters
84
We can then modify the properties or design parameters of the selected footing by using
various options in this window. For detail explanation of this window, refer to the pages
for RCC DESIGN > DESIGN PARAMETERS menu in Footing Design Module.
RCC DESIGN > FOOTING VIEW PLAN + ELEVATION
This option allows us to visualize the reinforcement plan and cross sections about X
and Y axis for the selected footing. When we select this option, a box cursor appears
on the screen. Select the footing node by the cursor. STRUDS displays for
Isolated Footing
Combined Footing
Piles
In the left portion of screen, STRUDS graphically displays the reinforcement plan of
footing. The X & Y dimensions of footing, number of bars along both sides, diameter
of bars and spacing between bars is also displayed in the drawing.
In the right portion of the screen, STRUDS displays the cross sectional diagrams of the
selected footing about both X and Y axis. The dimensions of footing are also displayed
in the drawing.
Figure 5.42 STRUDS: Design of One Isolated Footing
85
5.10 3D Model of a Low Rise Building
Then for the 3D view of the model of the building select the button, we can see the
3D view of building.
Figure 5.43 STRUDS: 3D View of Building
92
5.11.2 Column Schedule Report
Floor - Level : 2nd Floor-Default Level
Column
Group
Columns Concrete
Grade
Column
size
(mm)
Main Steel
(mm)
Stirrup
Steel
(mm)
CG1 C1 M20 230 x 450 #12 - 6 + #16 -
4 #8 @ 190
CG2 C2 M20 230 x 450 #16 - 8 #8 @ 230
CG3 C3 M20 230 x 450 #12 - 8 #8 @ 190
CG4 C4 M20 230 x 450 #12 - 8 #8 @ 190
CG5 C6 M20 230 x 450 #12 - 8 #8 @ 190
CG6 C5 M20 230 x 450 #12 - 8 #8 @ 190
CG7 C9 M20 230 x 450 #12 - 8 #8 @ 190
CG8 C7 M20 230 x 230 #12 - 4 #8 @ 190
CG9 C8 M20 230 x 230 #12 - 4 #8 @ 190
CG10 C10 M20 230 x 450 #12 - 8 #8 @ 190
CG11 C11 M20 230 x 230 #12 - 4 #8 @ 190
CG12 C12 M20 230 x 230 #12 - 4 #8 @ 190
CG13 C13 M20 230 x 450 #12 - 8 #8 @ 190
CG14 C14 M20 230 x 450 #12 - 8 #8 @ 190
CG15 C15 M20 230 x 450 #12 - 8 #8 @ 190
CG16 C17 M20 230 x 450 #12 - 8 #8 @ 190
CG17 C16 M20 230 x 380 #16 - 8 #8 @ 230
93
5.11.3 Slab Schedule Report
Slab Schedule Report: (Default Level at 12.45 m)
Slab
Group
Slab
ID
Concrete
Grade
Thk Bottom
Reinforcement(c/c)
Top Reinforcement
Extra Steel(c/c)
Remark
Main Other Left Right Up Down
SG1 S1 M20 200 #12 @ 75 #8 @ 205 --- --- --- --- OneWay
SG2 S2 M20 100 #10 @ 200 #8 @ 200 -- -- -- -- TwoWay
SG3 S3 M20 100 #10 @ 200 #8 @ 300 --- --- -- --- OneWay
SG4 S4 M20 115 #10 @ 200 #8 @ 300 --- --- --- --- OneWay
SG5 S5 M20 115 #10 @ 200 #8 @ 300 --- --- --- --- OneWay
SG6 S6 M20 125 #10 @ 200 #8 @ 200 -- -- -- -- TwoWay
SG7 S7 M20 125 #10 @ 200 #8 @ 300 --- --- -- -- OneWay
SG8 S8 M20 150 -- #8 @ 275 --- ---
#10
@
200
--- Cantilever
SG9 S9 M20 200 #10 @ 200 #8 @ 195 -- -- -- -- General
Notes :
1.Dia of Reinforcement bars is in mm
2.Spacing of Reinforcement bars is in mm
3.Thickness of Slab is in mm
94
1
CHAPTER 6
SAMPLE MANUAL DESIGN OF STRUCTURAL MEMBERS
6.1 Sample Manual Design of Structural Members:
6.1.1 Design of One - Way Slab
Figure 6.01 Location of Designed Slab (First Floor ,S10)
1) Floor Mark: First Floor
Slab Mark: S10
Span of slab: 1.616 m
Grade of concrete = M20
Grade of steel = fe415
2) Section:
Total Depth= 125mm
Effective Cover= 20mm
Effective Depth=105mm
Effective Length = 6.161 mm
3) Loads:
Dead Load = 3.125 KN/m2
95
Self-Weight = 25*0.125*1 = 3.125 KN/m2
Floor Finish = 1 KN/m2
Total Dead Load = 3.125+3.125+1
= 7.25 KN/m2
Live Load = 2 KN/m2
Total Working Load = 7.25 + 2
= 9.25 KN/m2
Total Factored Load = 9.25*1.5 = 13.88 KN/m2
4) Design Moments:
Design moment Mu =
𝑤𝑙2
2
= 13.88∗6.1612
2
= 263.43 KN.m
Mu, limit = 0.36*fck*Xumax*(d-0.42fck)*b
= 333.84 KN.m
Where,
Mu, limit = maximum ultimate moment
Fck = strength of concrete
d = effective depth
b = breadth (1meter).
5) Main steel reinforcement:
Mu = 0.87*FY*Ast*(d-0.42Xu)
Ast = 868.91mm2
Provide 6-14# HYSD Bars
Required Spacing(S) = (1000*153.93) / (868.91)
= 177.15mm
= 180mm
96
Provide 6Nos - #14mm @ 180mm Spacing C/C
6) Distribution steel reinforcement:
Ast = 0.12% b.D
= 150 mm2
Required Spacing(S) = (1000*50.2) / (150)
= 334.66 mm
= 340 mm
Provide 3Nos - #8mm @340mm C/C
7) Check for cracking:
For Main Steel
1) 3d = 3*105 = 315 mm
2) 300 mm
For Distribution
1) 5d = 5*105 = 525 mm
2) 450 mm
8) Check for deflection
Allowable 𝑙
𝑑 = 7 * M.F
% Pt = 100 ∗ 923
1000∗105 = 0.87%
M.F = 1
Allowable 𝑙
𝑑 = 7 * 1 = 7
Actual 𝑙
𝑑 =
6161
105 = 58.67
7 < 58.67 ……………… Not O.K.
9) Check for shear:
Vu = 22.80 KN
Tv =
vu
bd = 0.217 N/mm2
Pt = (100*Ast) / b.d
= (100 * 923) / (1000 * 105)
97
= 0.879%
Tc = 0.59 N/mm2
For D = 125 mm
K = 1.30
Tc’= k.tc = 1.30 * 0.59
= 0.767 N/mm2
Tv < Tc’ …………………… O.K.
98
6.1.2 Design of Beam
Design Data
Floor Id: First floor
Beam Id: B14
Figure 6.02 Location of Beams on First Floor
1) Dimensions:
Table No 6.01 Dimensions
Beam type ‘Rectangular Beam’
Width (b) 230 mm
Total Depth (D) 540 mm
Effective tension cover 33 mm
Effective compression cover 33 mm
Clear side cover 25 mm
Effective depth (d) 507 mm
Span 1.499 m (1499 mm)
Clear span 1.499 m (1499 mm)
2) Loads:
Table No 6.02 Loading on Beam
Self-weight of beam 3.105 kN/m
Slab load 4.310 kN/m
Masonry wall 10.96 kN/m
Total load 18.375 kN/m
Total Factored Load 27.56 kN/m
99
3) Design moment:
Maximum bending moment: Mumax= wl2
8
= 7.740x106 N.mm
Mu = 0.36 fck b d(d-0.42xumax)
= 10.034x106N.mm
Design the beam as doubly R.C. beam.
4) To find tension reinforcement:
Ast1= Mu.max
0.87fy(d−0.42xu.max) = 623.42 mm2
Ast2= Mu−Mu.max
0.87fy(d−dc) = 275.39 mm2
Total area of tension = Ast1 + Ast2
= 623.42 + 275.39
= 900 mm2
5) To find compression reinforcement;
Asc= 0.87fyAst2
fsc Where fsc = 0.0035
(xu.max – d’)
xu.max
= 331.43 mm2 = 0.0030
6) Detailing of reinforcement:
I. For tension reinforcement:
Ast = 900mm2
Provide 6nos - #14mm dia bars
II. For compression reinforcement
Asc = 331.43 mm2
Provide 3nos - #12mm dia bars
III. Shear reinforcement: Provide 8nos -190mm C/C
7) Minimum and Maximum Steel CHECKS:
a) Minimum steel check as per IS456:200 clause 26.5.1.1(a)
Ast = (0.85 x b x d) / fy
100
= 238 mm2
b) Maximum steel check ( as per IS456:2000 clause 26.5.1.1(b)
Ast = 0.04 x b x D
= 4968 mm2
6.1.3 Design of Column
Design Data
Floor Id: 1st Floor
Column Id: C17
Figure 6.03 Location of Column on First Floor
1) Dimensions
Table no: 6.03 Column Dimensions
Column type Rectangular column
Width (b) 340 mm
Total Depth (D) 600 mm
Clear cover 40 mm
Effective depth (d) 560 mm
2) Loads
Table no.6.04 Loading on Column
Axial load 467.22 kN
Factored load 694.08 kN
101
3) To check if the column is short or slender
D = 600 mm
B = 340 m
L = 3048 mm
lex /D = 3048/600 = 5.08 < 12
ley/b = 3048/340 = 10.16
Hence, it is a short column.
4) Minimum eccentricity
ex min = Greater of (lex/500 + D/30) and 20 mm = 26.096 mm
ey min = Greater of (ley/500 + b/30) and 20 mm = 16.096 mm
0.05 D = 0.05(600) = 30 mm > 26.096 mm
0.05 b = 0.05(340) = 17mm < 16.096 mm
5) Area of steel
Pu = 0.4 fck Ac + 0.67 fy Asc
694.08(103) = 0.4(20){(340)(600)-Asc} + 0.67(415)Asc
Asc = 889.09 mm2
Acs Provide = 904 mm2
Provide 8nos-#12mm dia bars
6) Lateral ties
Dia of lateral ties:
i. ≥ 1
4 x largest dia of longitudinal bar = 3 mm
ii. < 16 mm
Provide 6 mm dia lateral ties.
Pitch:
i. 340mm
ii. 16 x 12 = 192 mm
iii. 300 mm
So, Provide #6 mm @300 mm C/C
102
6.1.4 Design of Isolated Footing
Design Data
Footing Id: F16
Figure 6.04 Location of Footing
1) Dimensions
Table No.6.05: Dimension & Design Data
Colum size 340 x 600
Axial load 959.77 kN
Factored load 1439.66 kN
S.B.C 280 kN/m2
Grade of concrete M20
Grade of steel Fe415
1) Size of footing:
Characteristic load of column (working load) = 959.77 kN
Assume self-weight of footing 10% of column load = 95.97
Total load = 1055.74 kN
S.B.C of soil = 280kN/m2
103
Area of footing required = Total load
SBC =
1055.74
280 = 3.78 m2
Difference between dimension of column = 0.60 – 0.34 = 0.26 m
If b is width of footing,
b (b+0.26) = 3.78
b2 + 0.26b – 3.78 = 0
b = 1.81m say b = 1.85 m
d = 1.85 + 0.26 = 2.11 m say d = 2.15 m
provide size of footing = 1.85 m x 2.15 m
A = 3.98 m2 > 3.78 m2 …..O.K.
2) Net upward pressure (p) :
P = Factored column load
Area of footing provided
= 1439.66
3.78 = 380.86 kN/m2
3) Bending moment :
u.d.l along x-direction
= p x 1.85
= 380.86 x 1.85
= 704.60 kN/m
u.d.l along y-direction
= 380.86 x 2.15
=818.85 kN/m
Muy = 𝑤𝑙2
2 = 704.60 x
0.7752
2 = 211.60 kN.m
Mux = 𝑤𝑙2
2 = 818.85 x
0.7752
2 = 245.91 kN.m
4) Depth of footing :
Fy = 415 N/mm2
fck = 20 N/mm2
Mux = 0.138 fck b dx2
104
245.91 x 106 = 0.168 x 20 x 750 x dx2
dx = 312.38 mm
Muy = 0.138 fck b dy2
211.60 x 106 = 0.138 x 20 x 490 x dy2
dy = 395.55 mm
Assume #12 mm bars for footing
Try overall depth = 600 mm
dy = 600 – 50 – 6 = 544 mm
dx = 544 – 12 = 532 mm
Assume d = (544 + 532)/2 = 538 mm
Assume edge depth = 125 mm
5) Reinforcement :
Reinforcement along x :
Muy
bd2 =
211.60 𝑥 106
490 𝑥 5442 = 1.46
Pt = 0.443%
Ast = 0.443
100 x 490 x 544
= 1180.86 mm2 (for 1.85 m)
Provide #14 – 8 nos. (Ast = 8 x 154 = 1232 mm2)
Minimum steel = 0.12
100 x (
125+600
2) x 1850
= 804.75 mm2
Check for cracking:
Clear distance between bars
= 1850−100−12
7 = 248 mm
c/c distance = 248 – 14 = 234 mm < 180 mm
Provide 180 mm Spacing c/c
Reinforcement along y :
105
Mux
bd2 =
245.91 𝑥 106
750 𝑥 5322 = 1.158
Pt = 0.343 %
Ast = 0.343
100 x 750 x 532
= 1368.57 mm2
Considering the reinforcement parallel to shorter direction are equally spaced.
No. of #12 mm bars = 1368.57
113 = 12.11 Nos
= 14 Nos
Ast = 14 x 113 = 1582 mm2
Check for cracking:
Clear distance between bars
= 2150−100−12
13 = 156.77 mm < 180 mm ……O.K.
6) Check for one way shear :
About y:
475
775 =
𝑦′
231
y’ = 141.58 mm
d’ = y’ + (125 – 50 - 𝜙
2)
= 141.58 + (125 – 50 – 6)
= 210.58 mm (for lower layer)
b’ = width of col. + 2d
= 340 + 2 x544
= 1428 mm
Vu = S.F. at critical section
= p x hatched area
= 380.86 x (1.85 x 231)
= 162.76 kN
106
Mu at critical section = w𝑙2
2 = 704.60 x
0.2312
2 = 18.79 kN.m
Tan β = 475
775 = 0.61
tv = (Vu - Mu
d′ tan β)
b’d’
= [162.76 - 18.79
0.210 x 0.61] x 103
1428 x 210
= 0.36 N/mm2
Pt = (100 Ast) / (b’d’)
= (100 x 1232) / (1428 x 210.58)
= 0.40 N/mm2
tc = 0.45 N/mm2
tv < tc ……….. O.K.
Similarly, one way shear may be checks along x
7) Development length :
For M20 and Fe 415
Ld = 47 𝜙 = 47 x 14 = 658 mm (required)
Ld provided
= 775 – 50
= 725 mm > 658 mm …….O.K.
107
CONCLUDING REMARKS
I have designed a residential project which was being carried out by ‘SAI
CONSULTANCY’ at Lalgate, Surat. It enlightens trainee such as me, an excellent
opportunity to get to the ground level and experience the things that I would have never
gained going straight into a job. I also learnt about construction techniques, labor
management, time and cost management and techniques best suitable for site activities.
I also got practical knowledge which is used on construction site and how to improvise
theoretical concept on construction site. It not only helped me to get experience on
technical practices but also to observe management practices and to interact with fellow
workers. Also I learnt the way to work in an organization, the importance of being
punctual, the importance of maximum commitment, and the importance of team spirit.
This report is mainly concerned with important aspect of civil engineering, such as,
Analysis and design of R.C.C. Structure, by using both methods – STRUDS and manual
design method using codes, which will be useful for me as civil engineer.
To review the analysis and design concepts in order to carry out modeling of a structure
using STRUDS, making me proficient in one of the widely used software for structure
design.
108
REFERENCES
1. Shah V. L, Karve S. R , “Illustrated Design of Reinforced Concrete Buildings”,
“Structures Publication”
2. Rethaliya R. P, “Design of Structure-II (RCC)”,”Atul Prakashan”
3. Shah H. J., Vol-I & II, “Design of Structures R.C.C.”, “Charotar Publication”
4. General drawing of foundation detail
5. General and Detail Specification and site work instructions
6. Working drawings of building
7. Centre line drawing of building
8. Architectural drawing of building
9. IS 456: 2000 Plain and Reinforced Concrete - Code of Practice
10. SP16: 1980 Design Aids for Reinforced Concrete
11. IS 875 (Part II): 1987 Code of Practice for Design Load (Other than Earthquake)
For Buildings and Structures Part 2: Imposed Loads
12. www.civilengineersportal.com
13. https://en.wikipedia.org/wiki/Limit_state_design
14. file:///E:/FOR%20REPORT/Types%20of%20Foundation%20and%20Methods%
20of%20Construction%20of%20Foundation.html
15. www.engineeringcivil.com
16. file:///E:/FOR%20REPORT/Types%20of%20Foundation%20and%20Methods%
20of%20Construction%20of%20Foundation.html