Comparison of Response from Combined Axial and Blast Loads Calculated with SDOF and Finite Element Methods

摘要

Single-degree-of-freedom (SDOF) analyses are used to design many blast-resistant structures, which is an important part of explosive safety. Typically, the SDOF analyses consider flexural component response, but they can also consider other response modes including compression and tension membrane, arching from axial loads, and component response that includes secondary moments from axial loads acting on deflections caused by flexure. This latter response is often called 'P-delta' response, since the axial load (i.e. P) acting on the component with a midspan deflection (i.e. delta) causes additional bending moment that adds to the bending moment from the applied blast load. It is typically unconservative to neglect the additional bending moments from P-delta response for blast design of exterior wall components that support significant axial load from the roof or floors above. This paper describes how P-delta response can be incorporated into the SDOF analyses in a simple manner and also summarizes a comparison study of P-delta response calculated using the SDOF methodology and dynamic finite element analyses for beam-columns and two-way spanning wall panels subjected to combined dynamic axial load and lateral blast loads. The comparison is based on maximum deflections calculated with each method since component blast damage is typically based on the maximum calculated deflections. Any eccentricity of the applied axial load, relative to the centroid of the component cross section, can also be incorporated into the SDOF analysis approach. This approach does not consider secondary moments from frame sway, or flexibility of the building lateral load system that allows the top of the axially loaded components to deflect relative to the bottom. Frame sway must be considered as part of an analysis of the lateral load resisting system of the whole building, rather than SDOF analyses of individual wall or column components with combined axial and lateral loads.