outline introduction to structural engineering design process forces in structures structural...
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Outline• Introduction to Structural Engineering
• Design Process
• Forces in Structures
• Structural Systems
• Materials
• Definitions of Important Structural Properties
• Triangles
• UNITS (Dimensional Analysis)
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Structural Engineering
• What does a Structural Engineer do?
– A Structural Engineer designs the structural systems and structural elements in buildings, bridges, stadiums, tunnels, and other civil engineering works (bones)
– Design: process of determining location, material, and size of structural elements to resist forces acting in a structure
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Design Process
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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, cost)
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Design Process in Structural Engineering
• Select material for construction
• Determine appropriate structural system for a particular case. Justify (tell me why) you used these particular structural systems.
• Determine forces acting on a structure
• Calculate size of members and connections to avoid failure (collapse) or excessive deformation
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Forces in Structures
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Forces Acting in Structures
• Force induced by gravity (F=ma)
– Dead Loads (permanent): self-weight of structure and attachments
– Mass Vs. Weight
– Compression, Tension, bending, torsion
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Forces Acting in Structures
Vertical: Gravity Lateral: Wind, Earthquake
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Forces in Structural Elements100
lb
Compression
100 lb
Tension
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Forces in Structural Elements 100
lb
Bending
Torsion
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Structural Systems
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Typical Structural Systems
Arch
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Typical Structural Systems
TrussC
T
CCT
Forces in Truss Members
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Typical Structural Systems
Frame
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Typical Structural Systems
Flat Plate
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Typical Structural Systems
Folded Plate
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Typical Structural Systems
Shells
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Providing Stability for Lateral Loads
Racking Failure of Pinned Frame
Braced Frame Infilled Frame Rigid Joints
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Materials Used in Civil Engineering
Metals– Cast Iron– Steel– Aluminum
• Concrete
• Wood
• Fiber-Reinforced Plastics
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Engineering Properties of Materials
• Steel– Maximum stress: 40,000 – 120,000 lb/in2
– Maximum strain: 0.2 – 0.4– Modulus of elasticity: 29,000,000 lb/in2
• Concrete– Maximum stress: 4,000 – 12,000 lb/in2
– Maximum strain: 0.004– Modulus of elasticity: 3,600,000 – 6,200,000 lb/in2
• WoodValues depend on wood grade. Below are some samples– Tension stress: 1300 lb/in2
– Compression stress: 1500 lb/in2
– Modulus of elasticity: 1,600,000 lb/in2
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Concrete Components
• Sand (Fine Aggregate)
• Gravel (Coarse Aggregate)
• Cement (Binder)
• Water
• Air
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Fiber-Reinforced Composites
PolymerMatrix
Polyester
Epoxy
Vinylester
Fiber Materials
Glass
Aramid (Kevlar)
CarbonFunction of fibers:
•Provide stiffness•Tensile strength
Functions of matrix:
•Force transfer to fibers•Compressive strength•Chemical protection
Composite
Laminate
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Properties of Materials
(Why are they used)
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Definition of Stress
Section X
T
T
Section X
Stress = Force/Area
T
Example (English Units):
T = 1,000 lb (1 kip)A = 10 in2.
Stress = 1,000/10 = 100 lb/in2
Example (SI Units):
1 lb = 4.448 N (Newton)1 in = 25.4 mm
T = 1,000 lb x 4.448 N/lb = 4448 NA = 10 in2 x (25.4 mm)2 = 6450 mm2
(1 in)2
Stress = 4448/6450 = 0.69 N/mm2
(MPa)
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Definition of Strain
L
T
T
Lo
Strain = L / Lo
Example:
Lo = 10 in.L = 0.12 in.
Strain = 0.12 / 10 = 0.012 in./in.
Strain is dimensionless!!(same in English or SI units)
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Engineering Properties of Structural Elements
• Strength– Ability to withstand a given stress without failure
• Depends on type of material and type of force (tension or compression)
Tensile Failure Compressive Failure
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Engineering Properties of Structural Elements
• Stiffness (Rigidity)
– Property related to deformation
– Stiffer structural elements deform less under the same applied load
– Stiffness depends on type of material (E), structural shape, and structural configuration
– Two main types
• Axial stiffness
• Bending stiffness
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Axial Stiffness
L
T
T
Lo
Stiffness = T / L
Example:
T = 100 lbL = 0.12 in.
Stiffness = 100 lb / 0.12 in. = 833 lb/in.
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Bending Stiffness
Stiffness = Force / Displacement
Example:
Force = 1,000 lbDisplacement = 0.5 in.
Stiffness = 1,000 lb / 0.5 in. = 2,000 lb/in.
Displacement
Force
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Stiffness of Different Structural Shapes
Stiffest
StifferStiff
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Types of Structural Elements – Bars and Cables
Bars can carry either tensionor compression Cables can only carry tension
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Types of Structural Elements – Beams
Tension
Compression
Loads
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Triangles
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Formulas
• SOH, CAH, TOA
• c2 = a2 + b2
H
A
O