Welcome  to  the  HOT  TOPIC  in  Architectural  Surety  No 3 !
  EARTHQUAKE / TERRORIST BLAST PROTECTIVE  STRUCTURAL  CIRCUIT  BREAKER
        The main lesson learned by structural engineers from the latest terrorist bombings of  U.S. government
  buildings (ASCE 1999) is a need to assure structures ability to sustain significant local damage and remain
  standing. To achieve this goal, it is not necessary to make significant sacrifice as to local damages provided
  the concept of the Blast Protective Structural System  ( BPSS)  is employed  (Shustov 1996).
  Despite some advantages of the building elevation configuration ( Topic 5 ), 
  it can neither eliminate nor mitigate a potentially destructive dynamic input. 
  For this reason, the structural circuit breaker shown on the left should be 
  included in the optimal design. Therefore, an architecturally secure building
  represents the following combination of innovative approaches: elevation
  configuration technique incorporating seismic shock and terrorist blast
  protective devices .
      The superstructure of this building is shaped in accordance with he elevation configuration technique in
  order to suppress resonant amplifications of the horizontal vibrations. 
       The substructure, occupying the first story and basement, is meant to mitigate horizontal components 
  of earthquake input or a terrorist blast.  It consists of two major components: a row of impact protective 
  bents , aligned with the building perimeter, and  shock evaders, positioned on each footing of the inner area. 
    The shock evader (on the left) partially interrupts and decreases the
  seismic waves penetrating into the superstructure  (Shustov 1994). 
  Developed from a fresh concept of an automatic passive control that 
  incorporates a  progressive frequency separation plus an ultimately 
  low damping , the  shock evader is a much more effective device than
  other known types of base isolators. The shock evader includes a
  slip-joint and a pedestal plate . The slip-joint consists of a housing, 
  attached to the superstructure, with a consumable-while-sliding 
  cylinder resting on the pedestal plate positioned on a footing.
       In order to facilitate a sliding, the cylinder is made of material with an adequate vertical  (axial) bearing 
  capacity and horizontal (shear) resistance but with a low friction coefficient and ability to wear away easily
  at the contact with the pedestal plate.  Since it is unlikely that a structure will experience more than some 
  hundred strong pulses during its lifetime, the abrasion of the cylinder will not cause any structural damage. 
      It is widely believed that a building subject to an explosive blast loading has a chance to remain standing
  only if it possesses an extraordinary resistive capacity. This belief rests on the assumption that the specific 
  impulse or the time integral of pressure, which is the dominant characteristic of the external blast load, is 
  fully beyond our control.  Fortunately, the last statement is only half-true.  We actually cannot control a 
  magnitude of a load itself but we can influence the timing of its application to structural elements as well 
  as the pattern of interaction of those elements, and this may make a difference. 
      This concept was used in the BPSS  presented as the impact protective bent in the top figure above. 
  When a blast impulse has developed, the vertical wall panel does not transfer its load share to the building
  frame immediately.  Instead, it  smoothly transforms its kinetic energy of translation into potential energy 
  of elevation.  Therefore, the horizontal component of the panel's induced pressure on the frame remains 
  relatively small.  The main advantages of BPSS are: 
  • It is simple and able to perform satisfactorily under severe conditions of spatial distortions.  
  • It can be operational  in both external and internal explosions.  
  • It will restore its initial, pre-explosion position after several excursions.  
       In contrast with the basic mode of  BPSS described above, the model building under the current project 
  can go even farther. The impact protective substructure  (the top figure above) combines BPSS elements
  with  shock evaders, which create a new level of blast protection.  Thus, in case of a powerful but a rather 
  distant blast, the building will have the ability to recall by means of sliding on its shock evading devices, 
  thus providing an additional blast impact mitigation. 
  Shustov, V., 1994, “Adaptive Systems: A New Application”, Proc. 1st World Conf. on Struct. Control,
   3: FP-32-FP-41, Pasadena, CA.
   Shustov, V., 1996, “Blast Protective Structural System”, Proc. 4th Int’l Conf. SUSI-96, pp.34-38, Udine, 
   Italy.
   Conrath, E.J., Krauthammer, T., Marchand, K.A., Mlakar, P.F.   (Task Committee), 1999, "Structural
   Design for Physical Security: State of the Practice", ASCE, Reston, VA.
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        This page was last updated on 04/19/00