Introduction to Structure

STRUCTURAL ANALYSISBFC23102

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Structure and Structural Analysis What is structure:

a system of connected/fabricated parts used to support a load orcreatures activities

Construction or framework of identifiable elements(components, entities, factors, members, parts, steps, etc.)which gives complete form and stability, and resists stressesand strain. Structures have defined boundaries within which:1. Each element is physically or functionally connected to

other elements, and2. The elements themselves and their interrelationships are

taken to be either fixed (permanent) or changing onlyoccasionally or slowly.

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Structure and Structural Analysis

Carry load of deck and pedestrian

Bridge structure

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Structure and Structural Analysis

Seismic Wave

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Connection

Behavior of a local region where the structural components are connected is very complicated

depends primarily on the type and details of the connection used.

To extensively investigate the behavior of the connection, a three dimensional model is necessarily used to gain accurate results.

For a standard, linear structural analysis, the connection is only modeled as a point called node or joint and the behavior of the node or joint depends mainly on the degree of force and moment transfer across the connection

Connection

Rigid joint

A rigid joint is a connection that allows the complete transfer of force and moment across the joint.

Both the displacement and rotation are continuous at the rigid joint.

Connection

Hinge joint

allow the transfer of the bending moment.

Thus, the displacement is continuous at the hinge joint while the rotation is not since each end of the member connecting at the hinge joint can rotate freely from each other

Connection Pin joint

A pin connection works essentially like a lapped joint.

It transfers vertical and horizontal shear loads and cannot resist any bending or moment (rotational) forces.

Many pin connections might look like they are designed to rotate but do not actually function as points of rotation for the structure.

Is used to simplify erection by allowing for some slight differences in angles of the members

Structure and Structural Analysis Structural engineering:

Planning

Analysis

Design

Construction

We are here

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Structure and Structural Analysis Designing a structure:

- Utility / Serviceability

- Durability

- Safety

- Economy / Cost

- Aesthetic / Architecture value

- Material

- Environmental constraints

Thus, structure can be defined as a part of construction which has one or more element is subjected to various loads that it must resist without either collapsing or deforming excessively

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Type of Structures Tension and compression structure

- Column (compression)

- Cable-supported structure (tension)

- Arch (compression)

- Truss (compression & tension)Column

Manchester city Stadium - Cable

structureSidney Harbour

bridge - Arch

London St.PancrasTrain Station -

Truss

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Type of Structures Flexural beam and frame

- Beam

- Frame

- Combination structure

(bridge, building)

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Concrete Beam Steel Beam

Frame

Type of Structures Structure surface

- Slab

- Folded plates shells

- Dome

- Skin-type structure

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Slabs

Folded plate shells Domes Skin type structure

Structural Analysis Structure analysis:

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Is a process determining the reaction of the structureunder the specified loads or actions.

Reaction can be measured by establishing the forcesand deformations throughout the structures.

Structure must be analyzed, once a preliminary design of structure is proposed

Objective to determined load, forces and displacement

In design internal forces, shear, moment

Results use to redesign the structure

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Type of Supportwww.uthm.edu.my With Wisdom, We Explore

Roller support

- 1 direction of translation constraint

- 1 component of support reactions in the direction of constrain

to accommodate local high value of negative bending moment

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Pinned support

- 2 directions of translation constraint

- 2 components of support reactions in the direction of constrain

mostly applied for simplify manner in building design

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Fixed support

- 2 directions of translation constraint

- 1 directions of rotational constraint

- 3 components of support reactions in the direction of constrain

fixed supports are rarely found in practice

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Link support

Ball and socket

Rigid support in space

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Structure

Stable

Determinate Indeterminate

External

Internal

Unstable

Static Geometry

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Stability

- Equilibrium principle

Type of structure instability

- Kinematics unstable (Partial constraint)

Number of reaction at the support or number of the member is less than the minimum requirement.

Some cases: one of the member have fewer reaction forces than equations of equilibrium than must be satisfied

- Geometry unstable (Improper constraint)

Location or the arrangement of the support or member are improper

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Classification

Classification Beam FramePlane truss

Space truss

Statistical unstable

r < n + 3 3m + r < 3j + n m < 2j - r m < 3j - r

Determinate (only if geometrically stable)

r = n + 3 3m + r = 3j + n m = 2j - r m = 3j - r

Indeterminate r > n + 3 3m + r > 3j + n m > 2j - r m > 3j - r

n = number of internal hinge; r = number of reaction; m=number of member; j = number of joint

Kinematics unstable

Geometry unstable

Stability & determinacy

Determinacy

The ability to compute support reactions using plan statics.

Determinate The equations of equilibrium are sufficient to find all

the forces

Indeterminate There are too many reactions to solve for

Principal statically equilibrium are insufficient to determined support reaction and/or internal distribution

Stability & determinacy classification

Classification Beam FramePlane truss

Space truss

Statistical unstable

r < n + 3 3m + r < 3j + n m < 2j - r m < 3j - r

Determinate (only if geometrically stable)

r = n + 33m + r = 3j + n m = 2j - r m = 3j - r

Indeterminate r > n + 33m + r > 3j + n m > 2j - r m > 3j - r

n = number of internal hinge; r = number of reaction; m=number of member; j = number of joint

Stability and determinacy of beam structure

Stability and determinacy of frame structure

Stability and determinacy of plane truss structures

* Geometrically unstable due to the hinge in one straight line

**Geometrically unstable due to parallel reactions (horizontally unrestrained)