Quiz 1 review

The Nature of Blast Loading

• An explosion is a sudden expansion of gas in all directions.
• There is a wave of positive pressure at the front of the expanding gas, followed by a wave of negative pressure
  • An object is first pushed away from the blast source, and then pulled toward it.
  • The effects of the negative pressure are much less and can usually be neglected.

  

• The load an object experiences depends on several factors.
  • Charge size and type
    • Usually measured as pounds of TNT equivalent.
  • "Standoff distance" from charge to object.
  • Angle of incidence between surface orientation and charge location.
  • The simplified pressure for a given situation can be calculated using tables or the ATBLAST computer program.

The Physics of Structures Under Impulse Loading

• Structure has mass, stiffness, strength, and ductility.
• Impulse puts the mass in motion, giving it kinetic energy.
• The structure must convert this energy into some other form in order to bring the mass to a halt.
  • Keeping the structure elastic often produces either extremely large forces or displacements.
  • Example in window design [http://www.arpal.com/demo.asp]
  • [Demo]

Comparison of Elastic and Inelastic Curtain Wall Response

Design Issues

• Site planning
  • Standoff distance
• Building skin
  • The skin must be designed as a dynamic structural system.
  • [Demo]
• Structural frame
  • Redundancy
    • Remove column
      • Single member redundancy
    • Column effective length
      • Remove supporting beam
  • See DoD Standards section B-2.