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Transcript of 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.
CHALLENGE FACING THE DESIGNER
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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.
CHALLENGE FACING THE DESIGNER
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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.
CHALLENGE FACING THE DESIGNER
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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.
CHALLENGE FACING THE DESIGNER
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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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Examples of Steel Framed Structures
Saw tooth roof Space frame roof
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Examples of Steel Framed Structures
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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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.