Structural Vulnerability Assessment

Due to the nature of extreme loads resulting from blasts, impacts, seismic events and progressive collapse, large amounts of structural damage can usually be expected. This damage cannot be studied solely as the initial loading type; the user must also be able to additionally consider the secondary effects of the failing elements on other parts of the structure.

1. Initial Load: The initial load is the type of loading which may cause damage to a main supporting column and which can lead to a progressive collapse.
2. Secondary Effects: The secondary effects come from flying debris. This may cause another failure in other main supporting elements and can result in the structure loosing its ability to carry the increased loads, leading to a total failure.

Most structural analysis methods currently used to perform a structural vulnerability assessment depend on the Finite Element Method (FEM). Unfortunately FEM is not capable of automatically analyzing a structure up to element separation and collision which has a great effect on a structure’s performance during collapse. For example, a blast load can cause damage to a main supporting column in a structure, which will cause debris flying from the damaged column to be moving at a very high velocity. This debris can cause additional local failure in another column upon impact and can lead to the progressive collapse of the entire structure. While FEM can determine a point of failure, it cannot calculate crack propagation, separation of elements or secondary collision of structural elements.

The Applied Element Method (AEM) on the other hand has the ability to analyze a structure right down to element separation and secondary collision. This allows structural engineers to fully study the effects of such extreme loads, from the initial cracking until the all elements come to rest. AEM analysis was used by Applied Science International, LLC in the modeling and simulation of the collapse analysis of Oklahoma’s Murrah Building.