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August 30, 2016 Institute for Steel Development & Growth 1
ARIJIT GUHA
Assistant Manager (Civil & Structural)
Institute for Steel Development & Growth
Kolkata
MODERNISATION OF INDIAN
STEEL DESIGN CODES – A BOON
TO THE CONSRUCTION INDUSTRY
INCLUDING BRIDGES
TOPICS COVERED
Introduction
IS: 800 – General Introduction
Design Philosophies
Allowable Stress Design method
Evolution of Limit States method
Discussion on Latest Steel Codes
Revision of Codes in Bridge Construction
Revision in the concept of Fatigue
Steel-Concrete Composite Construction
Codes for Steel-Concrete Composite Construction
General Structures
Bridges
Composite Box Girders
Future Actions in Codes
August 30, 2016 Institute for Steel Development & Growth 2
INTRODUCTION
The Construction Industry ----- most often guided and
controlled by steel, cement as the prime material of
construction.
Cement ----- Requires a healthy partnership with
aggregates and steel to form the structural element
called concrete.
Steel -----
a) It not only has an advantage of partnering with
concrete but
b) Also it can go alone as an individual structural
element.
August 30, 2016 Institute for Steel Development & Growth 3
INTRODUCTION
DESIGN CODES
Structural steel ---- Use as preferred material by
designers and builders increases with modern rational
codes.
Codes -----
a) Should be updated with the scientific researches.
b) The codes should and also be user friendly.
c) The design engineers will only then be inclined in
deciding on using steel.
Modern codes at par with other international codes ----
Automatically increase the steel consumption in the
country which plays a direct role in the country’s
economy.
August 30, 2016 Institute for Steel Development & Growth 4
INTRODUCTION
IS: 800 – 2007
The basic Code for Steel Design and Construction in India
August 30, 2016 Institute for Steel Development & Growth 5
August 30, 2016 Institute for Steel Development & Growth 6
IS: 800 – EVOLUTION IN LAST 15 YEARS
The earlier edition of IS: 800 prepared in 1984 and reaffirmed in
1991 was out-dated.
This code was based on Allowable Stress Design, which was in
vogue till the 1960’s all over the world.
The modern Limit State Method had been developed and adapted
in advanced countries in the early 1970’s
This method is technologically improved and results in a more
rational design.
The general practice all over the world is based on Limit State
Method (LSM) or Load and Resistance Factor Design (LRFD)
Method.
It was found essential during the year 2002 – 2003 that this code
should be modified to LSM similar to what had been done for
reinforced concrete structure codes back in 1984.
The code was thus prepared and published by the Bureau of Indian
Standards (BIS) in 2007.
August 30, 2016 Institute for Steel Development & Growth 7
IS: 800 – EVOLUTION IN LAST 15 YEARS
Countries and their design format:
Australia, Canada,
China, Europe, U.
K., Japan
Limit State Method (LSM)
U S A
Load and Resistance Factor Design (LRFD)
and Allowable Stress Design Method (ASD)
India Limit State Method (LSM) [Adopted in 2007]
Table 1: Countries and their Design Format.
DESIGN PHILOSPHIES
Major change in design philosophy in India -----
With the introduction of Limit States Method (LSM)
Attributing the existing Allowable Stress Method ofdesign gradually redundant.
This LSM was introduced for all type of construction----
reinforced concrete construction
steel construction
steel-concrete composite construction.
However, it is important to understand the differingphilosophies of Allowable Stress Method of Design andLimit State Method / LRFD as they apply to design ofsteel structures
August 30, 2016 Institute for Steel Development & Growth 8
ALLOWABLE STRESS DESIGN
Linear Elastic Theory of Steel developed in 19th Century
It enabled stress-strain behaviour of new materials like wrought iron& mild steel to be accurately represented.
It also enabled indeterminate structures to be analyzed.
The distribution of bending and shear stresses could now becomputed correctly.
The first attainment of yield stress of steel was generally taken to bethe onset of failure.
The basic condition to be satisfied in design is factual < fallowable
factual = Actual Maximum Stress in a Section
fallowable = Allowable Stress in the Section
August 30, 2016 Institute for Steel Development & Growth 9
ALLOWABLE STRESS DESIGN (ASD)
Allowable stress has been defined in terms of a “factorof safety“ (Fs),
Fs represents a margin for overload and other unknownfactors which could be tolerated by the structure.
The factor of safety (Fs) in ASD, is fixed, Ignoring variability of loads are, in terms of either frequency or
magnitude.
Ignoring inconsistency of material and construction practices
Fixed Fs makes the design rigid. It takes away the advantage of flexibility and more optimised
aspects of design.
The value of factor of safety in most cases is taken to bearound 1.67. Variability of loads with time like seismic load or wind load Fs is
sometimes modified by a fixed amount depending on loadcondition and combination.
August 30, 2016 Institute for Steel Development & Growth 10
ALLOWABLE STRESS DESIGN (ASD)
Deficiencies of ASD
1. Consequences of material non-linearity,
2. Non-linear behaviour of elements in the post-buckledstate.
3. Rigid factor of safety,
4. Ability of the steel components to tolerate hightheoretical elastic stresses by yielding locally andredistributing the loads.
These deficiencies as well as advanced knowledge ofstrength of material beyond yield point and its plasticplateau led to the development of an alternative to theASD based on the limit states of a material. Thus themodern Limit States Method was evolved.
August 30, 2016 Institute for Steel Development & Growth 11
EVOLUTION OF LIMIT STATE DESIGN
Limit State Method (LSM) Design ---- Developed to address thedrawbacks of the existing ASD.
ASD suffers from the inability of the factor of safety to adequatelyaddress the variable nature of loading conditions.
LSM has separate Factor of Safety both for
the applied load
the permissible loads/moments/shears etc.
LSM makes use of the plastic range of material for the design ofstructural members
LSM considers the good performance of steel in tension comparedto compression and specifies variable factors
The main advantage of the limit state method is that it takes intoaccount this variance by defining limit states, which addressstrength and serviceability
Concept of Limit State Design can be covered broadly under
Ultimate Limit State Design (ULS)
Serviceability Limit State Design (SLS)
August 30, 2016 Institute for Steel Development & Growth 12
August 30, 2016 Institute for Steel Development & Growth 13
Curvature
MY
Rotational Capacity
Flexural member performance using section classification
Slender
Semi-Compact
Compact
Yield moment
MP
Moment ‘M’
Plastic momentfy
fy
fy
fy
<fy
<fy
ALLOWABLE STRESS DESIGN
LIMIT STATE DESIGN
Design requirements are expressed as follows:
Sd Rd
Sd = Design value of internal forces and moments caused by the
design loads,
Fd = f * Characteristic Loads.
f = a load factor which is determined on probabilistic basis
Rd = Characteristic Value of Resistance
m
m & f = Factors , which is also determined on a ‘probabilistic basis’.
f makes allowance for possible deviation of loads and thereduced possibility of all loads acting together.
m allows for uncertainties of element behaviour and possiblestrength reduction due to manufacturing tolerances andimperfections in the material.
August 30, 2016 Institute for Steel Development & Growth 14
LIMIT STATE DESIGN
A Civil Engineering Designer has to ensure that the structures and
facilities he designs are (i) fit for their purpose (ii) safe and (iii)
economical and durable.
Thus safety is one of the paramount responsibilities of the
designer.
The uncertainties affecting the safety of a structure are due to
Uncertainty about loading
Uncertainty about material strength and
Uncertainty about structural dimensions and behaviour.
These uncertainties together make it impossible for a designer to
guarantee that a structure will be absolutely safe.
Designer can only ensure that the risk of failure is extremely small,
despite the uncertainties.
An illustration of the statistical meaning of safety is given in Fig. 1.
August 30, 2016 Institute for Steel Development & Growth 15
LIMIT STATE DESIGN
August 30, 2016 Institute for Steel Development & Growth 16
DISCUSSION ON LATEST STEEL CODES
IS: 800 – 2007 :---- The basic code for design and construction for
all steel structures This code has been prepared based on stipulations laid down in the
corresponding Euro Codes
Modifications have been made based on
• Geographical parameters
• Indian construction practices
• resources available in India
Few other codes have been revised or formulated in the recent past
under BIS and IRC and few are under preparation,
BIS Codes
Revision of IS: 801:--- Cold Formed Sections ---- Under Preparation
Revision of IS: 11384:--- Composite Construction --- Under Preparation
Revision of IS: 806:---- Tubular structure ----- Under Preparation
Revision of IS: 808:---- Sectional Properties --- Under Preparation ( It will
include parallel Flange Sections and thus IS: 12778 will get merged with
it).
August 30, 2016 Institute for Steel Development & Growth 17
REVISION OF CODES IN BRIDGES
Major Codes that have been revised or formulated in the recent past
or under preparation for Indian Roads congress (IRC)
IRC: 24–2010 ---- Basic Steel Code for Construction of Steel Bridges
This code deals with steel Bridges and has been prepared in line with
IS: 800 – 2007.
The basic design philosophy is the LSM.
Design against Fatigue has been introduced based on stipulations laid
down in IS: 800 and the existing design procedure using IS: 1024 – 1979
has been discarded.
IRC: 22–2015 ---- Basic Steel Code for Construction of Steel Bridges
This code deals with Steel-Concrete Composite Bridges and has been
prepared in line with IS: 800 – 2007.
This was first published in 2008 and later revised in 2015
The basic design philosophy is the LSM.
The properties and stipulations corresponding to Concrete has been
adopted based on recently revised code IRC: 112 - 2011.
Earlier code dealt with only composite Beams. New construction
technology pertaining to columns and beams have been adopted for the
first time in this code
August 30, 2016 Institute for Steel Development & Growth 18
REVISION OF CODES IN BRIDGES
Other Codes / Guidebooks that have been revised or
formulated in the recent past or under preparation for Indian
Roads Congress (IRC)
Explanatory handbook to IRC: 22
Design Handbook to Steel-Concrete Composite Box Girder
Bridges
Guidelines for Cable Supported Bridges
Guidelines for fabrication and erection of Steel Bridges
Guidelines for Condition Monitoring of bridges
Guidelines for Connection Design
Other important and Relevant Codes revised in the recent
past.
IRC: 112 – 2011 --- Concrete Bridges
IRC: 6 – 2014 --- Loads on Road Bridges
August 30, 2016 Institute for Steel Development & Growth 19
REVISION OF CODES IN BRIDGES
NEW REVISION/MODIFICATION OR INTRODUCTION
The most important introduction in the latest Limit
States Codes, IS: 800 – 2007 or IRC: 22 – 2015 & IS: 24 –
2010 is the
STRESS RANGE Concept in FATIGUE DESIGN
August 30, 2016 Institute for Steel Development & Growth 20
FATIGUE
FATIGUE ---- It applies to changes in properties which occur in
a material (Quite Prominent in Steel) due to the repeated
application of stresses or strains.
Fatigue Stress ---- The additional stress in a structure or
structural member due to the intermittently occurring variable
(Cyclic) load.
In effect, anything subjected to repeated loading, arising, for
example, from waves, wind, live loading, pressure or
temperature fluctuations, vibration, etc., is potentially at risk
from fatigue
These fatigue problems are extremely critical in terms of safety
and cost.
August 30, 2016 Institute for Steel Development & Growth 21
FATIGUE
Before IS: 800 -2007, Fatigue Assessment was done
based on IS: 1024 – 1979.
IS: 800 -2007, for the first time introduced a complete
chapter on Design against Fatigue
IRC: 24 – 2010 and IRC: 22 – 2015 introduced the
same concept for steel and composite road bridges.
August 30, 2016 Institute for Steel Development & Growth 22
FATIGUE
Stress Ratio Concept
The two parameters on which permissible fatigue stress is
dependent is Stress Ratio (fmin / fmax) and number of stressCycles during the design life “N” (IS: 1024 – 1979) .
Hence Dead Load plays an important role in determiningfatigue strength
Stress Range Concept
The two parameters on which permissible fatigue stress is
dependent is Stress Range (fmax – fmin) and number of stress
Cycles during the design life “N” .
Hence Transient Load plays an important role in determining
fatigue strength
August 30, 2016 Institute for Steel Development & Growth 23
FATIGUE
August 30, 2016 Institute for Steel Development & Growth 24
Range, R = fmin / fmax
fe
One load cycle
fm
fmin
fmax
fmax =Maximum stress
fmin =Minimum stress
fr = Stress range
fe = Alternating stress amplitude
fr
fm =Mean stress
S
t
r
e
s
s
Time
Fig - 3
STEEL-CONCRETE COMPOSITE CONSTRUCTION
Steel-concrete composite construction combines the
compressive strength of Concrete with the tensile strength of
Steel
It evolves an effective and economic structural system.
Over the years this specialized field of construction has become
more and more popular in the western world
It has developed into a multifaceted design and construction
technique.
It is only recently getting popularized in India in the last few years
Still limited to commercial structures like multiplexes, some
industrial structures and a few multi-storied constructions.
More recently gained popularity in the bridge sector in India,
mostly in the eastern region in Kolkata and in the northern sector
in New Delhi in the form of flyovers and ROB’s.
August 30, 2016 Institute for Steel Development & Growth 25
STEEL-CONCRETE COMPOSITE CONSTRUCTION
Major Components of Composite Construction
Composite Beams:--
August 30, 2016 Institute for Steel Development & Growth 26
Fig. 4 Typical Composite Girder
STEEL-CONCRETE COMPOSITE CONSTRUCTION
Major Advantages Composite Beams (General construction in
Buildings and Structures) :--
1. Considerable savings in weight of steel components over
non-composite construction.
2. Greater stiffness of composite beams results in shallower
depths for the same span.
3. Thus, lower storey heights are adequate resulting in
a) Savings in cladding costs
b) Reduction in wind loading
c) Savings in foundation costs.
4. Faster rate of construction.
August 30, 2016 Institute for Steel Development & Growth 27
STEEL-CONCRETE COMPOSITE CONSTRUCTION
Major Components of Composite Construction
Composite Slabs:--
August 30, 2016 Institute for Steel Development & Growth 28
STEEL-CONCRETE COMPOSITE CONSTRUCTION
Major Components of Composite Construction
Composite Columns:-- (Two Types)
1. Fully or Partially steel encased concrete sections (Fig. 6)
August 30, 2016 Institute for Steel Development & Growth 29
STEEL-CONCRETE COMPOSITE CONSTRUCTION
Major Components of Composite Construction
Composite Columns:-- (Two Types)
2. Concrete in-field Steel Hollow Steel Columns (fig. 7)
Fig. 7 Concrete in-filled Steel Hollow Sections
August 30, 2016 Institute for Steel Development & Growth 30
CODES FOR COMPOSITE CONSTRUCTION
General Structures
IS: 11384 – 1985:
Code for General Construction in Steel-Concrete Composite
Structures.
This code was prepared using LSM philosophy
It catered to only Composite Beams
This code is presently under revision under the purview of
CED – 38 committee of Bureau of Indian standards (BIS)
Major revision would include latest provisions and design
techniques for Composite Beams
New introduction would include Composite Slab and
Composite Columns
August 30, 2016 Institute for Steel Development & Growth 31
CODES FOR COMPOSITE CONSTRUCTION
General Structures
August 30, 2016 Institute for Steel Development & Growth 32
Fig. 8 Construction Stage of Indira Pariyabaran Bhawan
CODES FOR COMPOSITE CONSTRUCTION
General Structures
August 30, 2016 Institute for Steel Development & Growth 33
Fig. 9 Indira Pariyabaran Bhawan
Fig. 10 New Office of INSDAG
CODES FOR COMPOSITE CONSTRUCTION
General Structures
August 30, 2016 Institute for Steel Development & Growth 34
Fig. 11 Handloom House
CODES FOR COMPOSITE CONSTRUCTION
Bridges
IRC: 22 – 2015:
Code for Construction in Steel-Concrete Composite Structures
for Road Bridges
The last edition of the code was in ASD philosophy
This code has been recently revised to LSM philosophy
It caters to Composite Beams and Columns
August 30, 2016 Institute for Steel Development & Growth 35
CODES FOR COMPOSITE CONSTRUCTION
Bridges
August 30, 2016 Institute for Steel Development & Growth 36
CODES FOR COMPOSITE CONSTRUCTION
Box Girder Bridges
Obligatory spans of a grade separator is generally to the tune
of 40-50 metres.
Steel-concrete composite box girder system suits best for
these spans.
A very old practice as far as the developed countries are
concerned.
Typical cross section include concrete deck on steel box
section.
Used aplenty in grade separators and flyovers in Kolkata
They have been found to be better than standard PSC box
girder in terms of performance and reduced Dead weight
Load on Foundation
Seismic Action
August 30, 2016 Institute for Steel Development & Growth 37
CODES FOR COMPOSITE CONSTRUCTION
Box Girder Bridges
August 30, 2016 Institute for Steel Development & Growth 38
Fig. 13 Components of Box Girder Superstructure
CODES FOR COMPOSITE CONSTRUCTION
Box Girder Bridges
1. IRC: 22 – 2015:
2. Guidebook For Design and Construction of Composite Box
Girder Bridges
This Guidebook is presently under preparation
Major provisions of IRC:22 – 2015 is utilized to prepare this
guidebook
A worked-out Example as guideline is being included in this
guidebook for the benefit of the designers
August 30, 2016 Institute for Steel Development & Growth 39
CODES FOR COMPOSITE CONSTRUCTION
Box Girder Bridges
August 30, 2016 Institute for Steel Development & Growth 40
Fig. 14 Box Girder for Gariahat Flyover in Kolkata
FUTURE ACTIONS ON CODES
Codes and standards are the backbone for design and
construction.
The code stipulations covers
The basic fundamentals based on which the design has to be made
The guidelines and limitations for a particular design or
construction based on various conditions associated with the
geographical location of the structure and the function of the
structure itself.
The codes have been revised or prepared mostly to make them at
par with other international codes.
There are still some grey area in the codes which may be improved
in the near future after proper feedback from users as well as from
research and experimental data.
The codes developed in the last 10 to 15 years or that are under
preparation are mostly a synergy of research findings both in India
and abroad
These codes are illustratively and accurately conducive for Indian
design and construction spectrum.
August 30, 2016 Institute for Steel Development & Growth 41
August 30, 2016 Institute for Steel Development & Growth 42
Thank You