Foundation, Concrete and Earthquake Engineering

What Structural System Perform Best against Explosion?

In the wake of the Sept. 11, 2001 terrorist attacks in the U.S., safety to all buildings in regard of design and construction continue to be in great demand. Blast resistant concrete buildings subjected to external blast pressures are generally shear wall structures rather than rigid frame structures. Shear wall structures respond to lateral loads in a somewhat different manner than rigid frame structures; the basic difference being the manner in which the lateral loads are transferred to the foundation. In rigid frame structures the lateral loads are transmitted to the foundation through bending of the columns. In shear wall structures, the lateral forces are transmitted to the foundation through both bending and shearing action of the shear walls. Shear walls are inherently strong and will resist large lateral forces. Consequently, shear wall structures are inherently capable of resisting blast loads and can be designed to resist substantially large blast loads whereas rigid frame structures cannot be economically designed to resist significant blast loads. 

Exterior Shear Wall Construction
Exterior Shear Wall Construction
In shear wall structures, beams and columns are usually provided between shear walls to carry the vertical loads including blast loads on the roof and not to transmit lateral loads to the foundation. For example, blast loads applied to the front wall of a two-story shear wall structure are transmitted through the roof and intermediate floor slabs to the shear walls (perpendicular walls) and thus to the foundation. The front wall spans vertically between the foundation, the floor, and the roof slab. The upper floor and roof slabs act as deep beams, and, in turn, transmit the front wall reactions to the shear walls. The roof and floor beams are not subjected to significant axial loads due to the diaphragm action of the slabs. The interior columns are usually not subjected to significant bending moments since there is no sidesway due to the extreme stiffness of the shear walls. However, significant moments can result from unsymmetrical loading conditions. Columns which are monolithic with the exterior walls may be required for severe load conditions. These exterior columns are subjected to both significant axial load and moment. The axial load results from the direct transfer of the roof and floor beam reactions while the moments are caused by the lateral blast load acting on the exterior wall.

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