1. Structural Engineering

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

3. 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

4. Design Process

5. 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)

6. 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

7. Forces in Structures

8. 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

9. Forces Acting in Structures
Vertical: Gravity
Lateral: Wind, Earthquake

10. Forces in Structural Elements
100 lb
Compression
100 lb
Tension

11. Forces in Structural Elements
100 lb
Bending
Torsion

12. Structural Systems

13. Typical Structural Systems
Arch

14. Typical Structural Systems
Truss C T
Forces in Truss Members

15. Typical Structural Systems
Frame

16. Typical Structural Systems
Flat Plate

17. Typical Structural Systems
Folded Plate

18. Typical Structural Systems
Shells

19. Providing Stability for Lateral Loads
Racking Failure of Pinned Frame
Braced Frame
Infilled Frame
Rigid Joints

20. Materials Used in Civil Engineering
Metals
Cast Iron
Steel
Aluminum
Concrete
Wood
Fiber-Reinforced Plastics

21. 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

22. Concrete Components Sand (Fine Aggregate) Gravel (Coarse Aggregate)
Cement (Binder)
Water
Air

23. Fiber-Reinforced Composites
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

24. Properties of Materials (Why are they used)

25. Definition of Stress T Example (English Units): T = 1,000 lb (1 kip)
Section X 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 = N (Newton)
1 in = 25.4 mm
T = 1,000 lb x 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
Stress = Force/Area T

26. Definition of Strain T Strain = DL / Lo DL Example: Lo = 10 in.
DL = 0.12 in.
Strain = 0.12 / 10 = in./in.
Strain is dimensionless!!
(same in English or SI units)

27. 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

28. 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

29. Axial Stiffness T DL Stiffness = T / DL Example: T = 100 lbLo
Stiffness = T / DL
Example:
T = 100 lb
DL = 0.12 in.
Stiffness = 100 lb / 0.12 in. = 833 lb/in.

30. 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.

31. Stiffness of Different Structural Shapes
Stiffest
Stiffer

32. Types of Structural Elements – Bars and Cables
Bars can carry either tension
or compression
Cables can only carry tension

33. Types of Structural Elements – Beams
Loads
Tension
Compression

34. Triangles

35. Formulas
SOH, CAH, TOA
c2 = a2 + b2 H O A