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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?

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Outline
Outline

  • Introduction to Structural Engineering

  • Design Process

  • Forces in Structures

  • Structural Systems

  • Materials

  • Definitions of Important Structural Properties

  • Triangles

  • UNITS (Dimensional Analysis)


Structural engineering
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



Engineering 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
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 acting 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 structures1
Forces Acting in Structures

Vertical: Gravity

Lateral: Wind, Earthquake


Forces in structural elements

100

lb

Compression

Forces in Structural Elements

100

lb

Tension


Forces in structural elements1

100

lb

Bending

Forces in Structural Elements

Torsion



Typical structural systems

Arch

Typical Structural Systems


Typical structural systems1

C

T

C

C

T

Forces in Truss Members

Typical Structural Systems

Truss


Typical structural systems2

Frame

Typical Structural Systems





Providing stability for lateral loads

Racking Failure of Pinned Frame

Infilled Frame

Rigid Joints

Braced Frame

Providing Stability for Lateral Loads


Materials used in civil engineering
Materials Used in Civil Engineering

Metals

  • Cast Iron

  • Steel

  • Aluminum

  • Concrete

  • Wood

  • Fiber-Reinforced Plastics


  • Engineering properties of materials
    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
    Concrete Components

    • Sand (Fine Aggregate)

    • Gravel (Coarse Aggregate)

    • Cement (Binder)

    • Water

    • Air


    Fiber reinforced composites
    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


    Properties of materials why are they used

    Properties of Materials(Why are they used)


    Definition of stress

    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

    Definition of Stress


    Definition of strain

    T

    DL

    Lo

    T

    Definition of Strain

    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)


    Engineering properties of structural elements

    Compressive Failure

    Tensile Failure

    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)


    Engineering properties of structural elements1
    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

    Lo

    T

    Axial Stiffness

    Stiffness = T / DL

    Example:

    T = 100 lb

    DL = 0.12 in.

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


    Bending stiffness
    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

    Stiffest

    Stiffness of Different Structural Shapes

    Stiff

    Stiffer


    Types of structural elements bars and cables
    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

    Types of Structural Elements – Beams



    Formulas
    Formulas

    • SOH, CAH, TOA

    • c2 = a2 + b2

    H

    O

    A


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