 |
  |
|
|
|
|
| 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: |
|
| 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. |
|
You may also visit Dr.Shustov's Home Page or CME research Web Page or "HOT TOPICS ". Our address is: CME , 18111 Nordhoff Street, Northridge, California 91330-8347 |