Structures – Types & Loads

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10/25/20

CIVIL ENGINEERING DRAWING &

GRAPHICS CH (1+2)

Dr. Mohsin Siddique

Asst. Prof.

Dept. of Civil Engineering

FAST-NU

Lecture 10: Structures – types & Loads

24/10/2012

Structure

• Structure is a system of connected parts used tosupport a load

• Analysis of Structures

▫ - Strength

▫ - Rigidity

• Design of Structures

▫ - Safety

▫ - Esthetics▫ - Serviceability

▫ - Environment

▫ - Economy



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Structural Engineering

• What does a Structural Engineer do?

▫ A Structural Engineer designs the structuralsystems and structural elements in buildings,

bridges, stadiums, tunnels, and other civilengineering works (bones)

▫ Design: process of determining location, material,

and size of structural elements to resist forcesacting in a structure

Engineering Design Process

• Identify the problem (challenge)

• Explore alternative solutions▫ Research past experience

▫ Brainstorm

▫ Preliminary design of most promising solutions

• Analyze and design one or more viable solutions

• Testing and evaluation of solution▫ Experimental testing (prototype) or field tests

▫ Peer evaluation

• Build solution using available resources (materials,equipment, labor)



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Design Process in Structural Engineering

• Select material for construction

• Determine appropriate structural system for aparticular case

• Determine forces acting on a structure

• Calculate size of members and connections to

avoid failure (collapse) or excessive deformation

Examples of Typical Structures



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Classification of structureStructural supports

Classification of structure

Structural elements

• Tie member/ Tensionmember

• These are subjected to tensileforces

• Column

• The are generally subjected toaxial compressive forces



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Structural elements

• Beams/flexure members

• Subjected to bending moments

• Classification depends uponend/support conditions

• Beams column members

• Subjected to both axialcompression and bendingmoments


• As an engineer, you must be able to classify structuresaccording to their form and function and you must also beable to recognize various types of structural elements

• Structural System- compose of structural members joinedtogether by structural connections. Each structural systemmay be composed of one or more of the four basic types of structures

▫ 1. Trusses▫ 2. Cables and Arches

▫ 3. Frames

▫ 4. Surface structures



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Trusses

• Trusses consist of slender members, arranged in a triangular pattern

• Planar trusses are composed of members that lie in the same plane.They are frequently used to support bridges and roofs

• Space trusses have members extending in three dimensions and aresuitable for transmission line towers

All members are connectedtogether by PINS which arefree to rotate literally !!

Truss members are usually subjected to axial forces only (tension and compression)


Trusses

• Truss members use lessmaterial to support givenload. But they require a lotof fabrication

• Trusses can be used in the30-400 ft range.

• Trusses spanning greater

than 400 ft have also beendesigned.



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Cables and Arches

• Cables and arch type structures are used to span long distances

• Cables are usually flexible and carry their loads in tension

• The external load is usually applied vertically. As a result the cabledeforms with a sag

• Cables are commonly used to support bridges and building roofs

• Cables have an advantage over beams and trusses, especially forspans greater than 150 ft


Cables and Arches

Cable Bridge, Washington, USA. Golden gate bridge, San Francisco, USA.



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Cables and Arches

Hussaini Bridge (Passu, Pakistan)


Cables and Arches

• Arch has reverse curvature of a cable and it achieves its strength incompression

• The arch must be rigid in order to maintain its shape

• It is primarily subjected to compression

• Arches are used in bridge structures, doom roofs and opening inmasonary walls



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Cables and Arches

Arch Dam Arch Bridge


Frames• Frames are commonly used in building structures

• Frames are composed of beams and columns that are connectedtogether

• Planar (2D) fames with all members in one plane

• Space (3D) frame with all members in more than one plan

• Steel frames: structural elements made of steel

• RC frames: structural elements made of RC



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Frames

Flat Plate


Surface structures

• Membrane, plate or shell type structures with much lessthickness as compared to other dimensions

• The structures is subjected to in-plane (tension or compressionforces mainly)

• Surface structures may be made of rigid material such as reinforcedconcrete

• The structures may be shaped as folded plates of cylinders etc

• The are referred to as thin plates of shells



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Surface structures

Shells

Forces Acting in Structures

• Forces induced by gravity

▫ Dead Loads (permanent): self-weight of structure andattachments

▫ Live Loads (transient): moving loads (e.g. occupants, vehicles)

• Forces induced by wind

• Forces induced by earthquakes

• Forces induced by rain/snow

• Fluid pressures

• Others



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Forces Acting in Structures

Vertical: Gravity Lateral: Wind, Earthquake

Global Stability

Sliding Overturning



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Forces in Structural Elements

100lb

Compression

100

lb

Tension

Forces in Structural Elements (cont.)

100lb

Bending

Torsion



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Forces in Structural Systems

Arch


Truss

C

T

CC

T

Forces in Truss Members



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Frame


Snow load



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THANK YOU

• Questions….

• Feel free to contact:

[email protected]

Documents

Structures – Types & Loads