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Introduction to Structural

Engineering

12-100 Introduction to Civil and

Environmental Engineering

Fall 1999

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Outline

Objective of Structural Engineering

Structural Engineering Process Types of loads

Types of structures

Load paths in structures Summary

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Civil Engineering Subdisciplines

structural

geotechnical environmental

transportation

construction

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Objectives of Structural

Engineering

Structural engineering is the science and art of designing

and making, with economy and elegance, buildings,

bridges, frameworks, and other structures so that they can

safely resist the forces to which they may be subjected.

The Structural Engineer,

Official Journal of the British Institute of

Structural Engineers

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Structural Engineering Process

Determine types magnitudes of loads

Determine structural context geometric and geological information

cost / schedule / height/ etc. limitations

Generate alternative structural systems Analyze one or more alternatives

Select and perform detailed design

Implement (usually done by contractor)

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Types of loads

Dead loads

Live loads Dynamic loads (e.g., trains, equipment)

Wind loads

Earthquake loads Thermal loads

Settlement loads

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Dead Loads

weight of the structure itself

floors, beams, roofs, decks, beams/stringers,superstructure

loads that are always there

Photos courtesy of Corel, Inc.

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Live Loads

People, furniture, equipment

Loads that may move orchange mass or weight

Minimum design loadings

are usually specified in

the building code

Photo courtesy of Corel, Inc.

Photo courtesy of Prof. P. Steif

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Load Example: Live Load in Ballroom

Live Load = 100 lb/ft^2Ballroom

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Dynamic Loads

Moving loads (e.g. traffic)

Impact loads Gusts of wind

Loads due to cycling

machinery

Photo courtesy of Corel, Inc.

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Load Example: Dynamic Load

HVAC

F

t

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Load Example: Water in a dam

Water,= density

hp = gh

Photo courtesy of Corel, Inc.

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Earthquake Loads

Structure loaded when base is shaken

Response of structure is dependent on thefrequency of motion

When frequencies match with natural

frequency of structure - resonance

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Load Example: Earthquake Load

Base Motion

Earthquake Load

Earthquake Load

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Structural Engineering International, Vol 5, No 1, 1995, pp.13

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Photo courtesy of Corel, Inc.

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Settlement

Structural Engineering International, Vol 7, No 3, 1997, pp.202J. Garrett

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Some Types of Structures

Arch

Planar Truss Beam/Girder

Braced Frame

Rigid Frame Space Truss

Cable Suspended Structure

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Arch

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Photos courtesy of Corel, Inc.

J. Garrett

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Planar Truss

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Photos courtesy of Corel, Inc.

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Beam/Girder

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Photos courtesy of Corel, Inc. Photo courtesy of Prof. P. Steif

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FramesBraced Rigid

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Cable Suspended Structure

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Cable Stayed Bridge

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Load Paths in Structures

Load Path is the term used to describe the

path by which loads are transmitted to thefoundations

Different structures have different load

paths

Some structures have only one path

Some have several (redundancy good)

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Load Path in Framed Structure

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Load Path in a Tied Arch

Courtesy of Pennsylvania Department of Transportation

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Summary

Structural Engineering:

identifies loads to be resisted identifies alternatives for providing load paths

(arch, truss, frame, ...)

designs structure to provide safe and

economical load paths (material, size,connections)

to be economical and safe, we must be able to

predict what forces are in structure.