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STRUCTURAL ENGINEERING

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Title: STRUCTURAL ENGINEERING


1
STRUCTURAL ENGINEERING

2
What Does a Structural Engineer Do?
3
What Does a Structural Engineer Do?
4
Roles of a Structural Engineer
  • Lead engineer/Project engineer
  • Consultant for an architect
  • Consultant for another engineer, insurance
    companies, lawyers, etc.
  • As well as
  • Aerospace design.
  • Product design, etc. for industries.
  • Facilities engineer.

5
Lead or Project Engineer
  • Defines project goals
  • Costs
  • Performance requirements
  • Supervises design based on these requirements.
  • Outlines tasks
  • What needs to be done who will do it
  • Organizes Project
  • Calendar
  • Sequence

6
Palm Valley Interchange
7
Lower Granite Dam Lock Repair
8
Consulting for an Architect or Engineer
  • The architect works with the client to establish
    project requirements
  • space requirements and relationships
  • siting
  • aesthetics
  • lighting
  • finishes
  • budget

9
Consulting for an Architect or Engineer
  • The engineers job is to make the architect look
    good.
  • Ensure integrity of structure
  • Provide economical solutions.
  • Develop innovative ways to solve new problems and
    use new materials.

10
Boise Air Terminal
11
Design Process
  • Conceptual design
  • Layout (location, size, shape, spans)
  • Materials (steel, concrete, masonry, timber)
  • Performance requirements
  • Cost estimates

12
Design Process (cont.)
  • Preliminary Design
  • Layout framing
  • Rough sizing of members foundation
  • Interaction with mechanical, electrical, etc.

13
Design Process (cont.)
  • Final Design
  • Detailed analysis
  • Final member sizes
  • Preparation of bid documents
  • Inspect and review construction process.

14
Day-to-Day Tasks
  • Beginning
  • Quantity take -offs
  • Checking shop drawings
  • Inspecting construction
  • Repetitive simple designs

15
Day-to-Day Tasks
  • Intermediate
  • Developing complex computer models
  • Analyzing wind or earthquake loads
  • Creating complex designs

16
Day-to-Day Tasks
  • Advanced - Working directly with client
  • Establish project performance criteria
  • Select structural framing system and layout
  • Estimating costs

17
Design Loads
  • Design loads include
  • Dead loads
  • Self-weight,
  • Permanent contents.
  • Live loads
  • Occupants,
  • Transient contents
  • Environmental loads
  • Wind, snow, earthquake, etc.

18
Uncertainty
  • Dead loads can be predicted with some confidence.
  • Live load and environmental load predictions are
    much more uncertain.
  • E.g., it is nearly impossible to say what will be
    the exact maximum occupancy live load in a
    classroom.
  • It is also difficult to say how that load will be
    distributed in the room.

19
Uncertainty (cont.)
  • Structural codes account for this uncertainty two
    ways
  • We chose a conservative estimate (high-side
    estimate) for the load
  • E.g., a 50-year snow load, which is a snow load
    that occurs, on average, only once in 50 years.
  • We factor that estimate upwards just to be sure.

20
Load Factors
  • Newer codes have separate load and resistance
    factors
  • Load factors overestimate the load.
  • Resistance factors underestimate the strength
    of the structure.
  • Dead load factors range from 1.1 to 1.4
  • Smaller uncertainty.
  • Environmental and live load factors range from
    1.7 to 2.0 and higher.
  • Higher uncertainty

21
Design Loads
  • Since we cant predict exactly the maximum load a
    given structure will experience, the design codes
    provide
  • Rational procedures for estimating a reasonable
    maximum value
  • Procedures for arranging the loads on the
    structure.
  • Experience has shown that if the engineer follows
    these procedures he/she can expect the structure
    to perform properly (I.e., not collapse, etc.)

22
Wind Loads
  • What factors should the wind design loads
    consider?

23
Wind Loads
  • Current codes consider
  • Maximum wind speed expected at the location in
    question
  • Maximum speed in a 3-second gust with a 50-year
    return period.
  • This is based on historical data
  • Coastal regions, such as Florida, have higher
    design wind speeds than most inland areas.

24
Topography
  • Codes consider the effects of general topography.
  • E.g, inland vs. exposed coast.
  • They also consider local terrain
  • Exposure factors account for shelter provided by
    surrounding buildings and trees.
  • Standard wind speed measurements are based on
    moderate topography and terrain.

25
Building Height
  • Codes also account for the fact that wind speeds
    tend to increase with height.
  • Standard measurements are made 33 ft (30 m) above
    the ground.

26
Aerodynamics
  • Codes must also consider the drag forces
    generated by the wind.
  • The drag coefficient is based on
  • The shape of the building
  • Rectangular vs. rounded, etc.
  • Whether building is open or closed
  • Based on the number of windows and doors
  • Windward vs. leeward forces.

27
Importance Factor
  • Codes also consider how important the building
    is.
  • If the building is a hospital that must remain
    functional during a hurricane, the design wind
    loads must be increased.
  • If the building is an agricultural storage
    building that doesnt endanger anything nearby,
    the wind loads can be decreased.

28
Summary
  • Design loads used by engineers represent rational
    estimates of loads that we should consider in our
    design.
  • Experience has shown if we design for these
    loads, the building should survive for a
    reasonable amount of time (50 years or more).

29
Summary (cont.)
  • The models try to consider situations that will
    have a significant effect on the design load.
  • Max wind speed, topography and terrain, building
    height and shape, etc.
  • The maximum loads estimated by the design codes
    are then factored to add a safety margin to our
    calculations.
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