Transcript Structural Engineering

Outline
• Introduction to Structural Engineering
• Design Process
• Forces in Structures
• Structural Systems
• Materials
• Definitions of Important Structural Properties
• Triangles
• UNITS (Dimensional Analysis)
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
Design Process
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)
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
Forces in Structures
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
Forces Acting in Structures
Vertical: Gravity
Lateral: Wind, Earthquake
Forces in Structural Elements
100
lb
100
lb
Tension
Compression
Forces in Structural Elements
100
lb
Bending
Torsion
Structural Systems
Typical Structural Systems
Arch
Typical Structural Systems
Truss
C
C
T
C
T
Forces in Truss Members
Typical Structural Systems
Frame
Typical Structural Systems
Flat Plate
Typical Structural Systems
Folded Plate
Typical Structural Systems
Shells
Providing Stability for Lateral Loads
Racking Failure of Pinned Frame
Braced Frame
Infilled Frame
Rigid Joints
Materials Used in Civil
Engineering
Metals
– Cast Iron
– Steel
– Aluminum
• Concrete
• Wood
• Fiber-Reinforced Plastics
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
• Wood
Values 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
Concrete Components
•
•
•
•
•
Sand (Fine Aggregate)
Gravel (Coarse Aggregate)
Cement (Binder)
Water
Air
Fiber-Reinforced Composites
Composite
Laminate
Polymer
Matrix
Glass
Fiber
Materials Aramid (Kevlar)
Carbon
Function of fibers:
•Provide stiffness
•Tensile strength
Polyester
Epoxy
Vinylester
Functions of matrix:
•Force transfer to fibers
•Compressive strength
•Chemical protection
Properties of Materials
(Why are they used)
Definition of Stress
T
Example (English Units):
Stress = Force/Area
Section X
T = 1,000 lb (1 kip)
A = 10 in2.
Stress = 1,000/10 = 100 lb/in2
Example (SI Units):
Section X
1 lb = 4.448 N (Newton)
1 in = 25.4 mm
T = 1,000 lb x 4.448 N/lb = 4448 N
A = 10 in2 x (25.4 mm)2 = 6450 mm2
(1 in)2
T
T
Stress = 4448/6450 = 0.69 N/mm2 (MPa)
Definition
of
Strain
T
Strain = DL / Lo
DL
Example:
Lo = 10 in.
DL = 0.12 in.
Strain = 0.12 / 10 = 0.012 in./in.
Lo
Strain is dimensionless!!
(same in English or SI units)
T
•
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
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
Axial Stiffness
T
DL
Stiffness = T / DL
Example:
T = 100 lb
DL = 0.12 in.
Lo
Stiffness = 100 lb / 0.12 in. = 833 lb/in.
T
Bending Stiffness
Displacement
Force
Stiffness = Force / Displacement
Example:
Force = 1,000 lb
Displacement = 0.5 in.
Stiffness = 1,000 lb / 0.5 in. = 2,000 lb/in.
Stiffness of Different Structural
Shapes
Stiff
Stiffer
Stiffest
Types of Structural Elements –
Bars and Cables
Bars can carry either tension
or compression
Cables can only carry tension
Types of Structural Elements –
Beams
Loads
Compression
Tension
Triangles
Formulas
• SOH, CAH, TOA
• c2 = a2 + b2
H
O
A