In-structure shock of underground structures: A theoretical approach

When an underground structure is subjected to a subsurface explosion, an in-structure shock occurs. The in-structure shock can be a major cause of disruption and even damage to the instruments and equipment contained in the structure if the detonation is relatively distant. For this reason, an appropriate analysis and prediction of explosion-induced in-structure shock is an important topic in the area of protective design of underground structures. In this paper, a detailed analysis is conducted on a representative buried structural element subjected to soil-transmitted blast. The soil–structure interaction is considered by introducing an interfacial damping between the structural element and the surrounding soil. Two phases of the structural response to the blast load, i.e., a blast loading phase and a free-vibration phase, are analyzed. Based on the analytically derived time histories of the structural response, which represent the in-structure shock, the response spectra concerning the equipment (sub-structures) attached to the main structure are constructed. Besides providing a theoretical approach for the evaluation of the in-structure shock and its subsequent effects, the present analysis is supplementary to the relevant provisions in TM5-855-1 and TM5-1300, in which only rough predictions of in-structure shock for buried structures are specified.