ce-252need of structural analysis

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Need of structural analysis

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Dr. Ashok K. JainProfessor of Civil Engineering

Indian Institute of Technology Roorkee

Jan 2010

Conceptual Structural System

STRUCTURE

EXCITATION RESPONSE

pv

EXCITATIONLoads

VibrationsSettlements

Thermal Changes

RESPONSEDisplacements

StrainsStress

Stress Resultants

Conceptual Structural SystemConceptual Structural System

EXCITATION RESPONSE

STRUCTURE

EXCITATION RESPONSEpv

Static Dynamic

Static Dynamic

Elastic Inelastic Elastic

Inelastic Linear

Nonlinear Linear

Nonlinear

This process of determining the response of a structure to the given

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excitation is known as structural analysis

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The study of solid mechanics helps in determining whether the material will be able to bear the different types of

stresses and strains

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This also depends upon the shape and size of the

structural element.

structural analysis

Why should I learn it ?

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Among all the civil engineering subjectsStructural engineering is the most difficult

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Among all the structural engineering analysis and design subjects,

Analysis subjects are the most difficultAnalysis subjects are the most difficult

Very difficultHighly mathematicalToo many calculations with too many chances of

structural analysis

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Too many calculations with too many chances of making mistakesToo monotonous

I am already afraid of STATICS

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Can I skip structural engineering subjects all together and still

become a civil i ?

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engineer ?

I put great amount of efforts in learning structural engineering subjectsStillI l k d

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I secure less marks as compared to the efforts put in other subjects

I know little of the structural analysis,So can I jump directly to

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j p ydesign ?

I have decided to go for IT job.

Do I still need to know Structural Engineering

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Structural Engineering ?

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How does it matter ?

If the forces are incorrectIf the nature of the forces is incorrectThat is

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Axial tension or compressionSagging or hogging bending moment


If the nature of stresses is incorrect tension or compressionIf there is confusion between normal

d h t

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and shear stress


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After all, Civil Engineers are known to work with a

big factor of safety

Myth

Factor of safety is meant to take care of Calculation errorsModeling errors

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gBad materials

Poor construction

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What is Civil Engineering ?

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Pure common sense

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Planning, design, execution and maintenance

of I f t t

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Infrastructure

Can you think of a facility which doesnt need

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c does t eedthe assistance of a civil engineer

?

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A structure

Must transfer all the loads ti it

GOAL

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acting on it safely to the soil below

Even in distress

Please Remember

A Civil Engineer, more specifically,

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p ya structural engineer

is responsible for the safety of lives of hundreds of people

Let us understand what is

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structural design ?

What do you mean by design ?

Creative

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Synthesis No Unique Solution/Open Ended Problem Collaboration in a Team

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What do you mean by design ?

Select appropriate materials Sh d i ( ti ) f b

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Shape and size (proportions) of membersDetailing of members and jointsDoes it satisfy functional requirements economically ?

A design must satisfy

Functional requirements - efficiencySafety against all loads, settlements, temperature fluctuations etc.Time effects and environmental impact

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Innovative

Time effects and environmental impactMust satisfy codal specificationsAestheticsFlexibility to meet future requirementsEconomical w.r.to time and money

Design Process

SYNTHESISANALYSIS

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PERFORMANCE ASSESSMENT

It is very difficult to satisfy so many design constraints

In view of limitations of material strength ductility

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material strength, ductilityand of course cost

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A large number of readymade software are now available in the marketwith very beautiful and powerful

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graphic interfaces.

Do I still have to learn analysis and strain myself?

many structures are known to have failed due to misuse

of the readymade packages

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Liability lies entirely with the designers

A good Designer has to be a good Analyst

However, A good Analyst may not be a good Designer

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good Designer

common sense is a must

A good Analyst has to begood in mathematics

Must be very careful with the sign convention

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Must be comfortable inlatest analytical tools

gincluding axes system

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Let us understand what is

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structural analysis ?

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Bending moment bending stressShear force shear stressAxial force axial stressin ario s members besides displacements

Analysis provides

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in various members besides displacements and rotations

Now design process is routine

To determine the relations betweenLoads applied on a body and the resulting deflections /deformationsLoads applied on a body and the

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Loads applied on a body and the resulting stresses

Stresses and strains for a wide variety of conditions and materials

You may use approximate methods to determine member forces

and their nature

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and their nature

for the understanding of structural analysis

Prerequisite

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Must know how tocompute support reactions in

simple beams and frames H = 0, V = 0, M = 0

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Prerequisite

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Must know how todraw free body diagrams

Free body diagrams

Cut a part of the structure that is of interest.Mark all the loads and internal member forces acting on the free body.

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Assume any direction for the internal forces. The correct direction will be known by satisfying the equations of equilibrium for the free body.

Free body diagram

Determinate Structures : Strength of Materials and Structural Analysis

S ti 11 5 T E 11 3 11 4 B E 12 11

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Section 11.5, Truss: Ex. 11.3, 11.4, Beam: Ex. 12.11, 12.13, 12.16,

Frame : Ex. 13.6 to 13.9

Indeterminate Structures : Advanced Structural AnalysisFrame : Ex. 3.11, 3.12, 5.6, 5.9, 7.2, 10.14 and 10.18Beam : Ex 11.3

M t k h t


Prerequisite

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Must know how tocompute and draw bending moment and shear force diagrams in simple

beams and frames

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Tension side

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Compression side

Sign Convention for BM Diagram

The Bending moment diagram is drawn on the tension side of the member. Thi id th f i f iti d

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This avoids the confusion of positive and negative BM.This helps visualize the deflected shape of the member.Moreover, the reinforcement in RCC members is always provided in the tension zone.


Prerequisite

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Must know how tocompute slope and deflection in simple beams and frames

Computing slope and deflection

Area moment theoremsConjugate beam method

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j gUnit load method

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Unit Load Method

Slope or deflection in beams or frames

EIMmdx

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Deflection in truss

EI AEuLF '

Must learn to apply cross-checks on all calculations

and interpretations

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interpretations

Symmetry / Anti symmetry

Let us play with

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form and support conditions

Truss

Pin endedmember

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Basic module

TRIANGLE

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Basic pin element

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Axial ForceCompression

Tension

Roof Truss

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Bridge Truss

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Bridge Truss

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Warren Truss

Warren Truss

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Bridge Truss

Pratt

57Howe

PIN CONNECTIONS RIVETTED OR WELDED

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Kuala Lumpur Airport, Malaysia


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Terminal 1D Delhi Airport

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Tokyo Inst Tech - Tokyo


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Pin ended column

Basic beam elementor

column element

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Axial ForceShear Force

Bending moment

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Statically determinate beams

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u = 0v = 0 = 0

u 0v = 0 0

u = 0v = 0 0

Continuous beams

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0

Arch

ParabolaEllipse

Any other

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Frames

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1

4

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Frames

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u = 0v = 0 0

u 0v = 0 0

1 4

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Frames

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Frames

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Loads

Static loadsDynamic loadsCyclic loads

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Deterministic loadsNon-deterministic loads

Loads

Concentrated loadUniformly distributed loadCouple or Bending moment

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Dead loadImposed loadLateral load

Permutation andCombinations

of

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FormSupport conditions

Loads

Sky is the limit

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Thank you

Suvarnabhumi Airport, Bangkok

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Ravana


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ce-252need of structural analysis

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