Mechanics and Structures

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Mechanics and Structures
IENG 331, Safety Engineering Fall 2005
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Assignment

• Read Chapter 10 from Brauer Text
• Study the Review Questions

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Introduction Historical Events

• 4/27/78 West Virginia scaffold collapse
• 170 fall, 51 deaths
• Lack of bolts, inadequately cured, insufficient
  strength in concrete
• 5/30/79 DC-10 crash, Chicago
• 271 deaths
• 3/8 engine support bolt failed, engine broke
  away ripping 3 redundant hydraulic flight control
  lines

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Contact Stress

• S F / A
• S, stress, force per unit area (e.g., psi)
• F, force
• A, contact surface area

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Safety Factors

• A safety factor is often applied
• Makes an allowance for unknowns related to
  materials, assembly, use, age, corrosion, wear,
  etc.
• SF failure producing load / allowable stress

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Understand tension, compression, shear, torsion,
bending, bearing, punching shear, column buckling
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Other Structural Failure Considerations

• Static loading vs dynamic loading
• Instability of base or foundation
• Weather, e.g., Wind loading, snow on roofs

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Causes of Structural Failure

• Design Errors
• Faulty Materials
• Physical Damage
• Overloading and Inadequate Support
• Poor or Faulty Workmanship
• Poor Maintenance, Use and Inspection

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Poor or Faulty Workmanship

• Hyatt Regency Hotel Kansas City
• 1981 Walkway collapsed

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Applications - Friction

• Suppose someone is about to push a large box,
  assuming it will slide. It might also tip over.
  Which will occur, the sliding or the tipping?
  Assume the coefficient of friction between the
  box and floor is 0.6.

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Multiple Modes of Failure