Steel design.pdf

STEEL BULDING DESIGN
PROF. LATHI KARTHI
INITIAL APPROACH
AND
SAFE ECONOMIC ASPECTS IN
MEMBER SELECTION

CONTENTS
§ Structural Steel and its application
§ Popular Steel Structures
§ What makes Steel Structures special
§ Advantages or merits of steel structures
§ Behaviour of Structural Steel systems under loading
§ Structural Steel Sections – An Overview
§ Steel Building Design

To know and understand a building structure
requires
• an intuitive ability to read and feel a building as
a structural object
• a skill to identify the functional requirement of
the building
• an ability to distinguish between the structural
and non structural part of the building
Prelude
3

Structural Steel and Its Applications
4
Characteristics
Elasticity: Ability to return to its original shape after loading and unloading
Endurance limit: Cyclic loading and unloading stresses of material above its
endurance limit and leads to failure – Fatigue limit
Ductility:Deformation without fracture beyond the elastic limit - High Ductility
Toughness: Combination of strength and ductility or resist impact loads without
fracture High toughness
Maintenance: Susceptible to corrosion. Use paints, or weathering steels
Fireproofing:Strength reduces with increased temperature - Fireproofing required

Structural Steel and Its Applications contd..
5
Structural Steel – The Evolution
1780 - 1840 Cast Iron. ( iron-carbon alloys, >2% C)
arch-shaped bridges upto 30m span.
1840 - 1890 Wrought Iron. (soft, ductile fibrous, <0.1% C)
Spans upto 100m.
1870 - 1920 Bessemer Converter
Introduction to Carbon Steel (from pig iron)
1920 - Till date Steel (C - 0.002% -2.1%)
Third most popular construction material after Concrete and Timber.

Advantages
§ Durability
§ Design flexibility
§ Simplicity and Speed of Construction
§ All weather construction
§ Easy repair
§ Recyclable -100% any number of times
§ Economy
Structural Steel and Its Applications contd..
6

Popular Steel Structures
HOWRAH BRIDGE (1943), Kolkota
Suspension type balanced cantilever bridge, with a central span
460 m between centers of main towers and a suspended span
of 172 m.
7

Popular Steel Structures contd..
WALT DISNEY CONCERT HALL (2003), LA
8

EMPIRE STATE BUILDING (1931), New York
9

Beijing National Stadium - It is also the world's largest steel structure with 26km of unwrapped
steel
BIRD’S NEST STADIUM (2008)
10

11
Light weight
What makes Steel Structures special?

12
Scope for Creativity
What makes Steel structures special contd..
Kauffman Center for the Performing Arts, Kansas City
Eiffel Tower - Paris
Tallest in the world from 1889 to 1930

13
Easy Extension
Easy Fixing of Facade
Faster repair and rehabilitation

14
Easy and Efficient Fabrication
Beijing National Stadium: Beijing, China

15
Larger Spans
Sydney Harbour Bridge: Australia- 500m
NASCAR Hall of Fame, North Carolina-
50m free span

16
Freedom for Architectural Design
Heydar Aliyev Center by Zaha in Baku Casey market town, Canberra

17
Sustainable and 100% Recycling is Possible

18
Slender Columns, More Space

19
Transparency (use of natural light)

20
Visible Connections

21
Weather Independent Construction

Advantages and Merits of Steel Structures
22

23
Reliability in material behaviour
o Material is homogeneous
o Manufactured in controlled conditions
o Variation in test results of sample material will be minimal
as compared to concrete or timber
o Assumption made for analysis are more realistic
Advantages and Merits of Steel Structures contd..

o Availability of manufactured and readymade sections in
the form of rolled sections as well as cold formed
sections.
o Fabrication of member sections are done in
factories/shops and assembling is partially completed in
the factory
o Site assembly of members are minimum and hence
errors will also be less.
o Time required to complete the construction of the steel
building is comparatively much lesser
o Handling will be easier since the sections are lighter 24
Faster Construction with minimum human errors

q Dead load will be less since the contribution from super
structure of steel structures will be much less
q These loads are the bigger part of the total load of the
structure.
q In large span bridges, tall buildings and structure having
poor foundation conditions, reduction in load will have a
positive effect
q Foundations can be better designed for earthquake/lateral
load conditions.
25
Higher Strength to Weight Ratio

v Steel is homogeneous and uniform material.
v Satisfies the basic assumptions of most of the analysis
and design formulas.
v The stress produced remains proportional to the strain
applied or the stress-strain diagram remains a straight line.
v If properly maintained (by painting, etc.) the properties of
steel do not change appreciably with time.
v Steel structures are more durable.
26
Elasticity, Uniformity, Durability and Performance

Ø percentage elongation is as high as 25 to 30% proving better
ductile property
Ø visible deflections or evidence of impending failure in case of
overloads
Ø ductile nature of the structural steel enable them to yield locally at
high stress points, to redistribute the stresses and hence help to
prevent premature failure.
Ø extra loads may be removed from the structure to prevent
collapse.
Ø M.I. of a steel structure can be calculated at any time since the
material do not crack or tear before ultimate load
27
Ductility and Warning before Failure

o Additions to existing steel structures are very easy to
be made.
o Connections between new and existing structures can
be employed very effectively.
o New bays or even entire new wings of buildings can be
added to existing steel frame buildings, and steel
bridges may often be widened.
28
Modifications/Additions to Existing Structures

q For temporary structures, steel construction is always
preferred.
q Army constructions during war are mostly made from
structural steel.
q The structures may be disassembled by opening few bolts
q Steel sections can be reused after a structure is
disassembled.
29
Temporary construction and possible reuse and recycle.

30
Watertight and Airtight Construction
n Steel structures provide completely impervious
construction.
n Structures like reservoirs, oil pipes, gas pipes, etc.,
are preferably made from structural steel.

v High-rise buildings, long span bridges and tall
transmission towers are made up of structural steel.
v Industrial buildings up to a span of 90 m can be designed
by plate girders or trusses.
v Bridge spans up to 1000m are made with steel arches.
v Longest suspension bridge is around 1990m (in Japan).
31
Long Span Construction

Forces and Effects
32
• Forces induced by gravity
• DL(permanent): self-weight of structure and attachments
• LL (transient): moving loads (e.g. occupants, vehicles)
• Forces induced by wind and earthquakes
• Forces induced by rain/snow
• Fluid pressures
• Others
Behaviour of Structural steel systems under loading

Forces and Effects contd..
33
Vertical: Gravity Lateral: Wind, Earthquake
Behaviour/Failure of Structural steel systems under loading contd..

34
Sliding Overturning

35
Truss
Frame
Arch

36
Typical Structural Systems
Arch

37
Typical Structural Systems contd..
C
T
C
C
T
Forces in Truss Members
Truss

38
Typical Structural Systems contd..

39
Shear yielding near support
Web crippling
Web buckling

40

41
a point of bifurcation was reached during concrete
placement on the torsionally flexible steel tub girder
Pedestrian Bridge at New York (2008)
Lateral Torsional Buckling
and Slenderness

42
Full depth fatigue crack
Behaviour/Failure of Structural sections under loading contd..

43
Buckled steel girders during erection for a bridge

44
Web crippling of the I-girder over the column
support (no web stiffeners given)
Trusses collapsed during erection of roof
Web
crippling

45
1.4m high welded I-girder which initiated the
structural collapse of a commercial centre
Weld fractures at the exterior fin beam-to-
column connection

46
Buckled X-brace of the steel gymnasium
Column base anchor bolt fracture due to overturning.

47
• 300-foot telescope in Green Bank , W. Virginia collapsed in 1988. In 1962 when commissioned
it was the largest astronomy telescope on earth.
• The collapse was due to the sudden failure of a key structural element -- a large gusset plate
in the box girder assembly that formed the main support for the antenna.

• Steel is an alloy, of iron & carbon
•The small percentage of manganese, sulphur, phosphorous,
copper & nickel added to steel, improve the properties of
structural steel.
• Carbon & manganese - high tensile strength but lower
ductility
• Welding is easier in the case of ductile steel and ductile
steel performs better in lateral load combinations.
• Chrome & nickel impart corrosion resistance property to
steel.
•It also resist high temperature
48
Structural Steel Sections –An Overview

Ø Steel structures are assembly of structural steel shapes joined together by
means of riveted / bolted or welded connections.
Ø Concrete structures are easily joined together by monolithic construction.
Ø Special methods are required to join individual members for steel
structures.
49
Welded Connection
Bolted Connection
Structural steel sections – an overview contd..

Properties of Structural Steel
q The structural steel is classified as mild steel and high tensile
steel.
q Standard quality steel is classified under grade E250 & E350
and where, 250 & 350 are the yield stress of steel.
q High tensile steel (Weldable quality Steel) is designated as
E410 & E450. where 410&450 are yield stress of steel as given
in IS2062
q The carbon equivalent of E250 and E 450 varies between 0.42
to 0.52
50

Mechanical Properties (Table 1 of IS 800 -2007 )
■ All structural steel used shall conform to IS 2062
■ The Mechanical properties of structural steel, with respect to,
the yield stress, ultimate stress and elongation of structural
steel shall be as per Table 1 of IS 800 -2007
■ Grade denoted by
– E250 - yield stress 250 N/mm2. (also depends on the
thickness of the plate)
– Fe 410 W - Ultimate strength 410 N/mm2
51

Structural Steel – Mechanical Properties
■ Steel is an alloy of iron and carbon. By adding manganese, sulphur, phosphorous,
nickel, chromium and copper different varieties of steel can be made.(Ref : IS800-2007)
52

•Modulus of elasticity , E = 2 x 105 N/mm2
•Modulus of rigidity, G = 0.769 x 105 N/mm2
•Coefficient of thermal expansion, α = 12 x 10-6/◦C
•Poisson’s ratio
Ø Elastic range = 0.3
ØPlastic range = 0.5
•Unit mass of steel = 7850 kg/m3
Physical Properties of Steel (CL. 2.2.4.1, IS 800- 2007)
53

Structural Steel Sections - Types
54
• Hot rolled Sections
• Cold Formed Sections
• Built-up Sections

ISMC/JC/LC
ISA
ISNT/ LT/JT/HT
Solid Bars
Flats and Plates
ISHB/WB/MB/LB/JB
Hot Rolled Sections
55
Structural pipe and tube Section

(a) Channels (b) Zed (c) I-shaped double channels
(d) Angles (e) Hat sections
Cold Formed Sections IS811-1987(2004)
56

Built-up (I) shapes.
Built-up (C) Channels.
Built-up (L) Angles.
Built-up Sections
57

Round and rectangular bars Cables composed
of many small wires.
Single and double angles.
Structural tee. Built-up box sections.
Tension Members
58
Rolled Beam
sections.

(a) Rolled Beam
sections.
(c) Structural
tee.
(b) Double
angles.
(e) Pipe
section
(d) Structural
tubing
Compression Members
59
(f) Built-up section

(a) Rolled Beam-and
other I-shaped
sections.
(c) open web joist.
(b) Built-up
Sections.
(f) Built-up members
(d) Angle
(e) Channel (g) Composite steel-Concrete
Flexural Members
60

Building Frames - Timber, Concrete and Structural Steel
Steel Building Design
61

62
The principal criteria influencing the choice of structural
material are
ØStrength
ØDurability
ØArchitectural Requirements
ØVersatility
ØSafety
ØSpeed of Construction/Erection
Ø Maintenance
ØCost
Steel Building Design contd..

63
Design of any building structure depends on (in addition to
budget)
• need to provide more usable floor space and choice of
cladding system
• special requirements like floor height, maximum height of
building etc.
• site location and site conditions
• local design codes and exposure conditions
• speed of construction

• depth of the floor zone
• requirement of natural lighting, ventilation and services
• need for special structural arrangement for public or
circulation areas
• benefit of using longer span at a reasonable cost
• provision for future expansion
Hierarchy of Design Decisions
64

■ Steel construction is being used for almost every type of
structure including multi-storey buildings, bridges,
industrial buildings, towers, etc.
■ There are two main categories of steel structures:-
65
Structural System
1. Framework or Skeletal System
2. Shell System

■ The main load carrying elements in this type are one-
dimensional or line elements (such as beams, columns, etc.)
forming two-dimensional or three-dimensional frames.
– Examples are:-
66
Framework or Skeletal System
n The frameworks of industrial buildings with their internal
members such as crane girders, platforms, etc.
n Highway and railways large span bridges.
n Multi-storey buildings, large halls, domes etc.
n Towers, poles, structural components of hydraulic works
n All other trusses and rigidly connected framed structures.

■ The main load carrying elements in this category of
structures are plates and sheets besides some skeletal
members.
– Examples are:-
67
Shell System
n Storage Tanks and reservoirs for the storage of liquids and
gases.
n Bins and bunkers for the storage of loose material.
n Special structures such as blast furnaces, air heaters, etc.
n Large diameter pipes.
n All other plate and shell structures.

IS 800 – 2007 Key Changes
68
IS : 800 – 1984
Working Stress Method
•Factor of safely for yield stress
•Allowable stresses are less than
‘fy’.
•Pure elastic approach for analysis
of structures under working loads.
•Yielding or buckling never occurs
at working loads
•Deformations are evaluated at
working loads.
IS : 800 – 2007
Limit State Method
• Partial safety factor for material (γm) for
yield and ultimate stress.
• Working loads are factored (increased) as
per partial safely factor (γf) causing Limit
State of strength.
• Post buckling and post yielding plays
important role in estimating capacity of
structural elements at Limit State.
• Deformations are evaluated at working
loads.

69
Axes of sections
IS800-2007
Along the
member
X Parallel to length of the member
Major
Axis
Z Parallel to flange/perpendicular to smaller leg of
an angle
Minor
Axis
Y Perpendicular to flange/parallel to smaller leg of
an angle
Axes Convention (Clause 1.8, IS 800-2007)

Classification of Sections as per IS 800-2007
70
All structural steel sections are thin walled, either open web
or closed sections
■ Made up of plate elements, joined together
■ Phenomenon of local buckling imposes limitations to the
thickness of each element of the section
– Lead to overall failure of the structure
– Lead to redistribution of the stresses, reducing the design
capacity

Classification of Sections contd..
Elastic-plastic moment rotation curve
Ideal condition
71

Classification of sections contd..
Elastic-plastic moment rotation curve (assuming no local buckling)
Based on moment rotation characteristics
Clause 3.7 IS 800-2007
72

Plastification of Beam under pure flexure
1
Plastic Hinge
2 3
4
W
73

Plastification of Beam under pure flexure contd..
74

Strength – slenderness ratio relationship
75

Method of Structural Analysis
Section 4-IS 800-2007
76
Frames are
1. Sway Frames
2. Non- sway Frames
Forms of Construction for
analysis
1. Rigid Construction
2. Semi-rigid Construction
3. Simple Construction
Methods of Analysis
1. Elastic Analysis
2. Plastic Analysis
3. Advanced Analysis
4. Dynamic Analysis

Design Philosophies
■ Working Stress Method (WSM)
Ø Considers linearly elastic behaviour.
Ø Stresses caused by characteristic loads are
checked against allowable stress.
Allowable stress = Yield stress/F.O.S
77

■ Limit State Method (LSM) – Section 5, IS 800-2007
Ø Probabilistic method
Ø Considers safety at ultimate loads and serviceability at working
loads.
Ø Multiple safety factors.(for Load & Material)
ü Ref Cl 5.3 and Cl 5.4
ü Table 4 and Table 5 IS 800-2007
Ø Two limit states
ü limit state of strength
ü limit state of serviceability
78

Limit State of Strength Limit State of Serviceability
Yielding, Crushing and Rupture Deflection
Stability against buckling,
overturning and sway
Vibration
Fracture due to fatigue Repairable damage, Fatigue cracks
Brittle Fracture Corrosion, durability, fire
Multiple safety factor: Table 4 and Table 5 IS 800(2007)
• Partial safety factor for loads, γf
• Partial safety factor for materials, γm
Clause 5.2 IS800-2007
79

According to IS 800:2007
Cl.5.3.3. Design actions (loads) is expressed as:
where,
γfk = partial safety factor for different loads k (Table 4)
Qck = characteristic loads
Cl.5.4.1. Design strength is expressed as:
where,
γm = partial safety factor for material (Table 5)
Su = ultimate strength
Qd = Σ γfk Qck
Sd = Su/ γm
80

γf (Partial safety factor for loads), Table 4 IS 800-2007
81

γm(Partial safety factor for materials), Table 5 IS 800-2007
82

Optimization of Design
Objective of any design is to
achieve
§ Safety for the planned lifetime
§ Serviceability
§ Durability
§ Economy
83
The optimal solution for economy
should be based on
§ Functional requirement
§ Strength and serviceability
§ Aesthetic satisfaction
§ Capital and Maintenance

§ Selection of framing system
§ Design of individual members
§ Design and detailing of connections
§ Fabrication process adopted
§ Erection methodology used
§ Specification and documentation
§ Corrosion protection and fire protection
§ Extent of digital integration
§ Form of contractual relationship implemented
84
Optimization of design contd..

Selection of framing system
§ greater economy can be achieved through
§ a repetition of similarly fabricated components.
§ A regular column grid is less expensive than a non-
regular grid for a given floor area.
§ greater economies can be achieved when the
column grids in plan are rectangular with
§ the secondary beams should span in the
longer direction
§ the primary beams in the shorter
85

Design of individual members
Important design criteria to remember
§ Lighter is not always better
§ design of connection, its detailing and cost of fabrication
§ dynamic response of lighter structure may become critical
§ Use of standard products
§ avoid built up sections
§ Repetition/Standardization
§ minimize chances of errors
§ Prefabrication and modularization
§ quality, speed of construction, safety
86

Design of individual members
Before finalizing the members
§ Select available rolled sections
§ Compare economy of using larger section size with that
of local strengthening of sections with plates
§ Avoid using stiffeners indiscriminately
§ Do not design full strength splices (to develop full section
strength) unless it is required
§ Use high strength steel appropriately
§ Where fully rigid joints are adopted, they shall generally
be confined to the major axis of the column member.
87

Design of column sections
1. Calculate the effective length as per Table 11 IS 800-2007
2. Assume the slenderness ratio Table 3 IS 800-2007
§ 40 for columns carrying heavy loads
§ 70-90 for rolled steel beam sections
§ 110-130 for struts
3. Find the stress using the appropriate Table 8 (a), (b), (c) or (d)
(IS 800-2007) based on the column buckling curves given in
Fig 8 (IS 800-2007) and Table 10
4. Select the section from SP 6(1) and check the suitability as per
Table 2(IS 800-2007)
5. Calculate the design strength as per clause 7.1.2 (IS 800-2007)
88

Design of beam sections (laterally supported)
1. Calculate the design moment with appropriate load combination
as per Table 4 (IS 800-2007)
2. Calculate plastic section modulus as per clause 8.2.1.2 (IS 800-
2007)
3. Select the section from Annex H (IS 800-2007)
4. Check suitability of the section as per Table 2 (IS 800-2007)
5. Calculate the design strength as per clause 8.2.1 (IS 800-2007)
89

Think, before finalizing the members
§ Is the deflected shape consistent with what was expected?
§ Is the beam depth consistent with standard rules-of-thumb?
§ Do connection details match the assumptions used in the
analysis?
§ Are the primary structural member sizes similar to members
in similar projects?
§ Do beams deflect more than permitted?
§ Intuitively and instinctively, would you want to walk under
it, live above it, and climb on it?
90
Some questions we can ask ourselves

Former USA President Herbert Hoover, an engineer turned politician, said:
The great liability of the engineer …compared to men of other professions……is
that his works are out in the open where all can see them ….His acts …..step by
step …are in hard substances.
He cannot bury his mistakes in the grave like the DOCTORS.
He cannot argue them into thin air…..or blame the judge…..like the LAWYERS.
He cannot, like the ARCHITECT, cover his figures with trees and vines.
He cannot, like the POLITICIANS, screen his shortcomings by blaming his
opponents….and hope that people will forget.
The ENGINEER simply cannot deny his actions.
If his works do not work.., he is damned.
91
To conclude..

References
• Bureau of Indian Standards (BIS) 2007, General Construction In Steel - Code of Practice (Third
Revision) IS 800-2007
• Bureau of Indian Standards (BIS) 1989, Dimensions for Hot Rolled Steel Beam, Column,
Channel and Angle Sections (Reaffirmed 2004) IS 808-1989
• https://www.steel.org.au/focus-areas/steel-and-design/design-for-economy accessed on 02-
08-2020
• http://learningfromearthquakes.org/2011-03-11-tohoku-japan/ accessed 0n 03-08-2020
• https://www.steelconstruction.info/Concept_design#Multi-storey_buildings accessed 0n 03-
08-2020
• http://www.iitk.ac.in/nicee/RP/2005_Indian_Hot-Rolled_SERC.pdf accessed on 03-08-2020
92

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