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Structural Engineering

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Structural Engineering

- Introduction to Structural Engineering
- Design Process
- Forces in Structures
- Structural Systems
- Materials
- Definitions of Important Structural Properties
- Triangles
- UNITS (Dimensional Analysis)

- 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

- 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)

- 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

- Force induced by gravity (F=ma)
- Dead Loads (permanent): self-weight of structure and attachments
- Mass Vs. Weight
- Compression, Tension, bending, torsion

Vertical: Gravity

Lateral: Wind, Earthquake

100

lb

Compression

100

lb

Tension

100

lb

Bending

Torsion

Arch

C

T

C

C

T

Forces in Truss Members

Truss

Frame

Flat Plate

Folded Plate

Shells

Racking Failure of Pinned Frame

Infilled Frame

Rigid Joints

Braced Frame

Metals

- Cast Iron
- Steel
- Aluminum

- 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

- Sand (Fine Aggregate)
- Gravel (Coarse Aggregate)
- Cement (Binder)
- Water
- Air

Composite Laminate

Polyester

Polymer

Matrix

Epoxy

Vinylester

Glass

- Functions of matrix:
- Force transfer to fibers
- Compressive strength
- Chemical protection

Fiber Materials

Aramid (Kevlar)

Carbon

- Function of fibers:
- Provide stiffness
- Tensile strength

Properties of Materials(Why are they used)

T

Example (English Units):

T = 1,000 lb (1 kip)

A = 10 in2.

Stress = 1,000/10 = 100 lb/in2

Stress = Force/Area

Section X

Example (SI Units):

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

Stress = 4448/6450 = 0.69 N/mm2 (MPa)

Section X

T

T

T

DL

Lo

T

Strain = DL / Lo

Example:

Lo = 10 in.

DL = 0.12 in.

Strain = 0.12 / 10 = 0.012 in./in.

Strain is dimensionless!!

(same in English or SI units)

Compressive Failure

Tensile Failure

- Strength
- Ability to withstand a given stress without failure
- Depends on type of material and type of force (tension or compression)

- Ability to withstand a given stress without failure

- 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

T

DL

Lo

T

Stiffness = T / DL

Example:

T = 100 lb

DL = 0.12 in.

Stiffness = 100 lb / 0.12 in. = 833 lb/in.

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.

Stiffest

Stiff

Stiffer

Bars can carry either tension

or compression

Cables can only carry tension

Loads

Compression

Tension

Triangles

- SOH, CAH, TOA
- c2 = a2 + b2

H

O

A