Predicting Blast-Induced Body Motions of a Buried Structure with Footings

摘要

An approximate theory is presented for predicting the absolute and relative body deflections of shallow-buried shelters in order to provide the designer with a rational approach for selecting footing dimensions. The theory consists of two coupled parts, one that describes the motion of the free field and another that defines the motion of a model of the structure, its foundation, and the covering soil. The soil characteristics are represented by straight-line approximations to the loading and unloading portions of the stress-strain diagram from a one-dimensional compression test. Incremental strains are integrated as the stress wave propagates downward to obtain the absolute free-field displacement at the elevation of the footings. Motion of the structure is represented by a single-degree-of-freedom analog. Empirical functions are used to represent footing reaction and arching in the model of the structure. These functions are incorporated in the differential equation of motion, which is solved with the aid of a digital computer. The results are compared with available test data; velocities and deflections agree reasonably well but the magnitude of the peak accelerations from the theory are larger than the corresponding measurements. Computations performed with the computer code indicate that surface loads above about 100 psi cannot be resisted if the maximum relative deflection between the footing and the floor slab is limited to 2 inches. (Author)