MAterial course Ch3.ppt

8/13/2019 MAterial course Ch3.ppt

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Teaching Resource in Design of Steel Structures

IIT Madras, SERC Madras, Anna Univ., INSDAG 1

ROLE OF STRUCTURALENGINEER IN THE 21stCENTURY


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ROLE OF STRUCTURAL ENGINEER IN THE 21stCENTURYCONTENTS

INTRODUCTION

THE CHALLENGE FACING THE DESIGNER

DURABILITY AND LIFE CYCLE COSTISSUES

THE EVERYDAY LIFE OF STRUCTURAL

ENGINEER

DESIGN REQUIREMENTS CONCLUDING REMARKS


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INTRODUCTION

Engineers - Creators of artefacts, using their ingenuity

and capacity for original thinking within theconstraints of affordability and practicability

- Understand the role of financing, project

management and information technology inimproving the quality of designs

- Full and on-going interaction between other

members of the design team is essential tomaintain effective communication across

professional boundaries


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INTRODUCTION

Besides principal role as an innovator, the designer

of constructed facility has to ensure that his plan is

Fit for its purpose

Economical and durable

Safe, both for the users and for the environment

Buildable, without inconveniencing the community

Aesthetically pleasing.


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CHALLENGE FACING THE DESIGNER

There is no single correct solution to designproblem. There are many correct solutions due to

Designs are subjective to individual taste

Solutions are different according to specific

requirement

Designers own individual bias

Design problems are open ended


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Goals of the design project are

Safety of the structure and human beings

Timely completion of the project

Cost within the budgeted estimate

Engineering design:

A creative activity of building a new artefact which

provides an optimum solution to satisfy a definedrequirement or need without endangering the

environment.



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Herbert Hoover, a former President of the United

States of America - described the Engineeringprofession as follows (1961):

It is a great pro fession. There is the fasc inat ion o f

watching the f igment of th e imaginat ion emerge

thro ugh the aid o f Science to a plan on paper. Thenit moves to real isat ion in stone or metal or energy .

Then i t br ings jobs and homes to m en. Then i t

e levates th e standards of l iv ing and adds to the

comforts of l i fe. That is the Engineers high

privi lege. The great l iabi l i ty of the engineercom pared to men o f other profess ions is that h is

work s are ou t on the open, where al l can see them.



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His acts, step by s tep, are in hard subs tance. Hecannot bury his mistakes in the grave l ike

physic ians. He canno t argue them into th in air or

blame the judge l ike the lawyers. He cannot, l ike the

architects , cover his fai lures with tr ees and v ines.

He cannot, l ike the pol i t ic ians, screen his

sho r tcom ings by blam ing his opponents and hope

that the people wil l forget. The engineer simply

canno t deny that he did i t . If his works do not work,

he is damned forever.



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Onthe other hand , unl ike the docto r , his is not a

l i fe among the weak. Unl ike the soldier, destru ct ionis not h is purpose. Unl ike the lawyer, quarrels are

no t his dai ly bread. To the engineer fal ls th e job o f

cloth ing the bare bones of sc ience with l i fe com fort

and hope. No doub t, as the years go by, the people

forg et wh ich eng ineer did it , even if they ever knew.Or some pol i t ic ian puts his name on i t . Or they

credi t it to som e prom oter, who used other peoplesmoneyBut the engineer himself look s back at theunending stream of goodness which f lows from his

success with sat isfact ion that few otherprofess ions may know . And the verd ic t of h is

fel low professionals is all the accolade he wants.



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DURABILITY AND

LIFE CYCLE COST ISSUES Traditionally the Professional Structural Engineer is

responsible for the complete process from the

conceptual stages to the finished structure

Structural Engineer in the 21st century will not be

confined to immediate economic and environmental

impact and also responsible for the long-term

environmental effects on the community byconsidering the life cycle costs


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THE INFRASTRUCTURE CRISIS Advances in Science and Technology in last 50

years plunged the world into a number of crises,which have impacted directly on the construction

industry. Global effect of these dramatic changes

can be collectively termed the InfrastructureCrisis

Problem is enhanced by

Uncontrolled population growth

Industrialisation that resulted in global urbanisation


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THE INFRASTRUCTURE CRISIS

Housing sector Land contamination by sub-structures.

Water pollution

Environmental degradation , for instance in the form

of climate change, ozone depletion, deforestation

and acid rain


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THE DURABILITY CRISIS Is it better to spend (say) 40% more initially, in order

that the life of a structure could be doubled? Whatis better value to the client? Spend less initially or

opt for a longer life?

Total neglect of durability considerations in all the

infrastructure projects undertaken so far combinedwith primitive construction practices have resulted

in a durabilitycrisis

It is costing billions of rupees annually for repair

and rehabilitation of structures all over the world.

Hence, life cycle costing is now a mandatory

requirement in the planning process in West


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TIME WASTED IS MONEY WASTED AND

OPPORTUNITIES LOST When a constructed facility is completed early, it will

result in an early return on the capital employed

Delays in the completion of a project would

therefore represent a delay in the return on capitalinvested, besides the loss of interest, which thatsum would have earned otherwise

This essential relationship between time and moneyis well understood in the Western world butunfortunately this is not the case in India


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COST COMPETETIVENESS BY USING

ALTERNATIVE MATERIALS In India, the designs are invariably limited to

concrete-intensivestructures

Often the best optimal design solution will be a

sensible combination of reinforced and/orprestressed concrete elements with structural steel

elements

There is a direct link between GNP per capita andthe per capita consumption of steel


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LIFE CYCLE COST ISSUES

ASTM E917- 83 (1983) describes standard practices

for evaluating LCC of buildings and building systems

Motivation for LCC is that on any investment

decision, all costs arising from decision, both

immediate and in future are potentially important

Fast track methods in construction in western world

triggered the wide spread implementation of LCCstudy that ensure enhanced productivity and efficient

utilisation of the capital.


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LIFE CYCLE COST ISSUESLife cycle cost of a structure can be regarded as

being made up of

INITIAL COST

PERIODIC MAINTENANCE COST

COST OF DISMANTLING THE STRUCTURE

LESS THE SALVAGE VALUE


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Flyover construction - The Indian way


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Flyover construction - The Indian way


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Do the business need roads?


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Do the business need roads?


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Where else do we store junk?


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Where else do we store junk?


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PERIODIC MAINTENANCE COST

Contributes to the longevity of structure

Economising this cost results in increased

expenditure later date

Most neglected activity in India

Problem is compounded by several mythsprevailing in Engineers and Architects


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Myths

Concrete lasts forever without maintenance

Concrete bridges outlast steel bridges

Concrete bridges last forever without

maintenance

Structural steel can not be adequately protected

from corrosion

A steel structure is less safe in a fire than other

types of structures

Maintenance of Concrete intensive structures issignificantly cheaper than that of Steel

intensive Structures


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COST OF DISMANTLING THE STRUCTURE

AT THE END OF ITS LIFE

Cost of dismantling steel structure is well below

R.C. structure

SALVAGE VALUE OF CONSTRUCTION

PRODUCTS

Cost of material recovered from steel-intensiveconstruction is almost equal to the original cost


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EVERYDAY LIFE OF A

STRUCTURAL ENGINEER

Structural engineer designs structural systems forbuildings, bridges, dams, offshore platforms etc.

System - An assemblage of components withspecific objectives and goals and subject to certainconstraints.

Any constructed facility is a system; Structuralsystem is one of its major sub systems.

Components of the structural system have to meetdesign requirements of strength and stiffness whilesatisfying economy, buildability and durabilitycriteria.


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Examples of Steel Framed Structures

Braced frame Moment resisting

frame Core and suspendedfloors


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Saw tooth roof Space frame roof


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Pylon Lattice girderTapered portal


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GOALS

Every system will have goals and specify whatthe system is to accomplish and how it will effect

the environment and other systems

They are made in statements of specific designobjectives such as

purpose

time limitation

cost limitation

environmental constraints


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SYSTEM OBJECTIVES

Objectives explain in detail the requirements that thesystem must satisfy to attain the goals.

Some essential objectives are

Health, safety and welfare of occupants of the structure

Minimization of initial cost Life cycle cost

Construction time

One criterion must be associated with each objective;

it helps to evaluate alternative systems for thestructure.


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CONSTRAINTS AND STANDARDS

Constra ints:Restrictions on the values of designvariables that represent properties of the system,

which are under the control of the designer. (For

example, an I-beam section of 200 mmdepth may

be desirable, but not available.)

Standard: Value or range of values associated

with each constraint


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CODES AND SPECIFICATIONS

Structural engineer uses relevant codes and

specifications in design of structures

A detailed set of rules and suggestions for design

of a class of structures is called an engineering

specif icat ion. Interested party prepares these

specifications and they have no legal or official

sanction.

Codesare frequently formulated by a group of

professionals with a view to their adoption by theprofession as a whole. Revised at regular

intervals.


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DESIGN REQUIREMENTS

Principal design requirement of a structure isthat it should be both buildable and fit for its

purpose.

Fitness for purpose requirement of theconstructed facility depends on the satisfaction

of its structural and other requirements.

Other design requirements include those ofeconomy and harmony.


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MULTI - DISCIPLINE PROJECT ORGANISATIONOwners

representative

Design Team

Management

Lead disciplines

Principaldisciplines

Support

disciplines

THE PROJECT MANAGER Engineer or Architect

DESIGN PROFESSIONAL Engineer or Architect

Lead design team leaderEngineer or Architect

Struct.

Engg

Electrical

Engg.Architecture Mech

Engg.

Civil

Engg.

Geotech.

.Engg

Survey-

ing

Space

planning

Land

Scaping

Scheduling,

EstimatingUrban

planning

D fi iti f th


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Teaching Resource in Design of Steel StructuresIIT Madras, SERC Madras, Anna Univ., INSDAG

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THE OVERALL

DESIGN PROCESS

Definition of the

problem

Use

Consideration of

alternative designs

Primary design

Selection

Modification

Final design

Final evaluation

Documentation

Execution


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The structural design process

Design CriteriaDesign Codes

Design criteria

Design codes

Knowledge

Experience

Imagination

Intuition

Creativity

Invention or modification of

structural systemPreliminary analysis Approximation

Loads

Behaviour

Proportioning Members and Joints

AnalysisLoadsBehaviour

Evaluation

Final Design


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DESIGN VERSUS ANALYSIS

In an analysis problem, all the parameters

are known - a unique solution can be

arrived.

Designer has to make several decisions,

each of which could affect the final result.

As a consequence, no unique solution can

be offered


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DESIGN ALTERNATIVES

Design for strength

Specifies that the design resistance of a structural

component is greater than the required strength to

transmit the loads safely

Design for serviceability

In the serviceability design criteria for structures, the

designer seeks to make the structure sufficiently stiff sothat its deflections under the most adverse working

loads will not affect its serviceability


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FACTORS CONSIDERED IN THE

DESIGN COMPARISON

Materials to be used Arrangement and structural system and flooring

system to be adopted

Fabrication and type of jointing

Method of erection of the framework to be used

Type of construction for floor, walls, cladding andfinishes

Installation of ventilating/ heating plant, lifts,water supply, power etc.

Corrosion protection required Fire protection required

Operating and maintenance costs


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MAJOR BUILDING STRUCTURAL SYSTEMS

Wall-bearing construction Beam and column construction

Trusses

Rigid frames

Arches

Suspension cables and cable-stayed systems

Steel lamella roof

Dome


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Beam and column construction


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Single Bay, SingleStorey Structures

Knee brace 3pin portal Flat


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Cable stayed structures


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CONCLUDING REMARKS

Role of a structural engineer in designing

constructed facilities in 21stcentury is discussed.

Importance of life cycle costing and a rational

selection of appropriate materials for construction

is stressed .

A strong case is made to account for durability

and environmental considerations in the design

process.

Structural design process and structural systemsare described.

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