STRUCTURAL ENGINEERING

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STRUCTURAL ENGINEERING

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What Does a Structural Engineer Do?
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What Does a Structural Engineer Do?
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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.

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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

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Palm Valley Interchange
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Lower Granite Dam Lock Repair Jarrod Milligan
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Consulting for an Architect or Engineer

• The architect works with the client to establish
  project requirements
• space requirements and relationships
• siting
• aesthetics
• lighting
• budget

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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.

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Boise Air Terminal
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Forensic Engineering

• Finding out what went wrong.
• Insurance companies
• Lawyers

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Design Loads

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

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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, say, a
  classroom.
• It is also difficult to say how that load will be
  distributed in the room.

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Uncertainty (cont.)

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

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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

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Simplified Wind Loads

• Since we cant predict exactly the maximum load a
  given structure will experience, the code
  provides
• 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.)

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Wind Loads

• What factors should the wind design loads
  consider?

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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).

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Summary (cont.)

• The models try to consider situations that will
  have a significant effect on the design load.
• Max wind speed, 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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Example Building
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Design Methods

• Method 1 Simplified Procedure
• Simple diaphragm building,
• Low-rise,
• Enclosed,
• Regular geometry, symmetric,
• Not flexible, prone to flutter/vortex shedding,
  torsion etc.
• Method 2 Analytic Procedure.
• Method 3 Wind Tunnel Procedure.

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Wind Loads on Structures
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Gust Factor, G

• G 0.85 for rigid, low rise buildings

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Wall Pressure Coefficients, Cp
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Wind Velocity Pressure
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Importance Factor

• Agriculture Buildings Category I
• Typical Buildings Category II
• Hazardous Buildings Category III
• Essential Facilities Category IV

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Wind Load Map Western US
Wind speeds in MPH (kph)
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Velocity Pressure Exposure Coefficients
Exposure B, Case 2
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Velocity Pressure Exposure Coefficients Notes

• Case 1
• a. All components and cladding.
• b. Main wind force resisting system in low-rise
  structure designed using Figure 6-10 Method 2.
• Case 2
• a. All main force wind resisting systems in
  buildings except those in low-rise buildings
  designed using Figure 6-10.
• b. All main wind force resisting systems in other
  structures.
• We will use Case 2.

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Velocity Pressure Exposure Coefficients (cont.)
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Exposure Categories

• Exposure B
• Urban and suburban areas, wooded areas Exposure
  B shall be assumed unless the site meets the
  definition of another type of exposure.
• Exposure C
• Open terrain with scattered obstructions
• Exposure D
• Flat unobstructed areas exposed to wind flowing
  over open water for a distance of at least one
  mile

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Directionality Factor Kd
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Topographic Factor Kzt
If flat terrain Kzt 1
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Wind Loads

• Calculate Wind Loads
• Wind From East
• Wind From West

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