anaisis estructural

8/12/2019 Anaisis estructural

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1. STRUCTURAL ANALYSIS -

FUNDAMENTALS


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1.1 INTRODUCTION

1.1 INTRODUCTION

What is a structure? - General Types: Based on deformation and type of

primary loadcarried [Axial (tensile, compressive), flexure, shear and

torsion]; combinationsof various types - How to determine? Strip it down toits basic skeleton

What does a structure do? - Carriesthe load - Loads actingon the structure:

Dead & Live (people, equipment, wind, wave, seismic)- Superposition

Principle- Keeps the structurein static and dynamic equilibrium-

Transfersthe load to contiguous structural components - Transfers the load

safely - Transfers the loads to the foundation


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Figure 1.2bThe spidersweb is

a good example

of a tension

structure. The

weight of the spider

and its prey is

supported by tensile

strength of the web


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Figures 4 and 5

All materials and structures deflect,

to greatly varying extents, when

they are loaded. The science of elasticity is about the interactions between forces and

deflections. The material of the bough is stretched near its upper surface and compressed

or contracted near its lower surface by the weight of the monkey

Fig.4

Fig.5


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Figure 1.1

A building structure safely transmits loads down to Earth


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1.1 INTRODUCTION (Contd)

Collapse or failure under applied extreme loads - Loads due to extremeenvironmental loads (acting, earthquake, wind) - Modes of failure: Plastic deformation(ductile, yielding), Brittle fracture, Buckling (elastic or inelastic), Fatigue, Vibration

(resonance), foundation settlement and failure.

Unserviceability:Excessive deformation, acoustic deformation

Unexpected load scenario or unwise design: Lack of or faulty sprinkler (firedamage), Inadequate sealing and paint protection (leakage and corrosion), Improper

anchorage of roof, reinforcement, etc. (Roof blown off or beam collapsing), Lack of sufficient

indeterminacy (collapse)


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1.2. DETERMINACY AND INDETERMINACY

What do we understand by determinate and indeterminate structures?Determinate:Forces and Moments are determined by statical equations of

equilibrium

Humbleys problem:Stool with three or four legs on irregular floor

Indeterminate structures:Less equations are available than the number of

unknown forces that constrain the body in space. Extra conditions of deformation

compatibility have to be introduced to solve the problem. These conditions will give

the extra number of equations required to solve the problem, which will indicate the

degree of indeterminacy

Determinacy and indeterminacy- Stable and unstable structures

Unstable:When more equations are available than the number of forces that

constrain the body in space, then the structure is unstable

.0,0 MF


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1.3 ASSESSING THE DEGREE OF INDETERMINACY

Easy to deal with by specifying simple types of structures - Truss structures:

2-D, 3-D, - Framed structures:2-D, 3-D Two-dimensional truss structures:m + r 2j, where m = number of

members, j = number of joints and r = number of external constrains.


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1.3 ASSESSING THE DEGREE OF INDETERMINACY (Contd)

Three dimensional truss structure:m + r 3j, where m = number of members,

j = number of joints, and r = number of external constraints


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1.3 ASSESSING THE DEGREE OF INDETERMINACY(Contd)

Two-dimensional framed structure:3m + r 3j +ec


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1.3 ASSESSING THE DEGREE OF INDETERMINACY(Contd)

Three-dimensional framed structure:6m + r 6j +ec


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ASSESSING THE

DEGREE OF

INDETERMINACY

(Contd)


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ASSESSING THE

THE DEGREE OF

INDETERMINACY

(Contd)

anaisis estructural

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