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.