Review of building design systems and problematic structural elements inhibiting progressive collapse

To design for blast or ballistic loadings a structure is or has been subjected to, a designer needs to be fully aware of all aspects of normal building design systems that will be confronted as well how the mechanism of collapse will or has occurred. Some structures, depending on how they are designed or constructed, possess inherent structural problems that can impede collapse. In the case of a controlled demolition (implosion) prior to the use of explosives RC stairwells should be removed, RC facia with windows removed, all internal cladding and ceilings removed and internal shear walls used to accommodate wind loadings demolished. RC floors should be weakened by removal of sections of the concrete floor matric thus allowing for the formation of plastic hinges when the tensile forces in the floors shift to the reinforcing steel causing it to yield. Everything possible must be done to facilitate collapse and allow gravity to assist in the process. With an uncontrolled demolition (implosion) many factors are unknown during the design process and assumptions must be made. In this case based on past events, explosives and charge weights used must be assumed in advance of an event but nevertheless the design engineer must produce a design that facilitates a delay in collapse long enough for those caught inside the structure to escape to safety. Understanding building design systems in relation to possible collapse and problematic structural elements that could possibly inhibit such collapse are imperatives in designing for and against explosive demolitions.