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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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Classification of structure
Structural elements
• Beams/flexure members
• Subjected to bending moments
• Classification depends uponend/support conditions
• Beams column members
• Subjected to both axialcompression and bendingmoments
Classification of structure
• 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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Classification of structure
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)
Classification of structure
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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Classification of structure
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
Classification of structure
Cables and Arches
Cable Bridge, Washington, USA. Golden gate bridge, San Francisco, USA.
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Classification of structure
Cables and Arches
Hussaini Bridge (Passu, Pakistan)
Classification of structure
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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Classification of structure
Cables and Arches
Arch Dam Arch Bridge
Classification of structure
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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Classification of structure
Frames
Flat Plate
Classification of structure
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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Classification of structure
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
Forces in Structural Systems
Truss
C
T
CC
T
Forces in Truss Members
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Forces in Structural Systems
Frame
Forces in Structural Systems
Snow load
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THANK YOU
• Questions….
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