Experimental testing and numerical modeling of steel frames under close-in detonations

Even though blast events in inhabited areas are characterized by a low probability of occurrence, they can present a high risk for buildings and their occupants. The means to reduce the vulnerability and prevent the progressive collapse of buildings includes large stand-offs, enhanced local strength of structural elements, and increased redistribution capacity after a local damage. Blasts are extremely complex events, especially when the charge is detonated at a small distance from the building. In such cases, the application of analytical methods may give inaccurate results. The paper presents the results of a combined experimental/numerical program, which focused on the response of steel frames to close-in detonations. Two identical specimens were tested inside a specialized bunker for different charge sizes and stand-off distances. Very similar behaviors and failure modes were observed for the two specimens. The numerical model, calibrated against test data, was able to accurately predict the deformations and failure mode of the specimens. The results of the parametric numerical study indicated that the local failure mechanism and resistance to progressive collapse of steel building frames depend very much on the blast load parameters but also on the level of gravity loads in columns.