MODERNISATION OF INDIAN STEEL DESIGN CODES A …indiainfrastructure.com/presentations/pdf_download.php?file=PDF... · adopted based on recently revised code IRC: 112 ... Explanatory

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


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.


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.


INTRODUCTION

IS: 800 – 2007

The basic Code for Steel Design and Construction in India



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.


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


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


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.


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.


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)



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.


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.


LIMIT STATE DESIGN


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).


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



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



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


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.


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.


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


FATIGUE


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.



Major Components of Composite Construction

Composite Beams:--


Fig. 4 Typical Composite Girder


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.




Composite Slabs:--




Composite Columns:-- (Two Types)

1. Fully or Partially steel encased concrete sections (Fig. 6)




Composite Columns:-- (Two Types)

2. Concrete in-field Steel Hollow Steel Columns (fig. 7)

Fig. 7 Concrete in-filled Steel Hollow Sections


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



General Structures


Fig. 8 Construction Stage of Indira Pariyabaran Bhawan


General Structures


Fig. 9 Indira Pariyabaran Bhawan

Fig. 10 New Office of INSDAG


General Structures


Fig. 11 Handloom House


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



Bridges



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



Box Girder Bridges


Fig. 13 Components of Box Girder Superstructure


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



Box Girder Bridges


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.



Thank You

Documents

MODERNISATION OF INDIAN STEEL DESIGN CODES A …indiainfrastructure.com/presentations/pdf_download.php?file=PDF... · adopted based on recently revised code IRC: 112 ... Explanatory