Nonlinear dynamic failure analysis of truss structures at normal and elevated temperatures: Fid-Bau Portal

Nonlinear dynamic failure analysis of truss structures at normal and elevated temperatures

Agarwal, Puneet / Malla, Ramesh B.

Truss-and frame like structures are very commonly used for space and terrestrial applications. If a truss structure is subjected to a static or dynamic overload, one or more members of the truss may exceed their capacity. The load carrying capacity of the compression members decreases suddenly during postbuckling. This and other unexpected defects and conditions may give rise to sudden failure or reduction in member capacity of a single member in a truss structure, which may cause dynamic force redistribution in the remaining members, leading to progressive collapse of the entire structure. Under dynamic conditions, truss members may undergo inelastic cyclic behavior (including buckling, postbuckling in compression and yielding in tension) that may not have existed in the static loading conditions. A truss structure may also be subjected to an overload induced by elevated temperatures, e.g., in the event of a fire and high temperature service environment such as in space. The inelastic cyclic member behavior, and subsequently the dynamic response of truss structures, is affected by the presence of high temperatures. In this study, a numerical scheme has been developed to track and generate the force-deformation characteristics of every member (both at normal and elevated temperatures) of the truss at each iteration step of the solution scheme. Only the steady state condition at various temperature levels is considered. The member behavior for various temperature conditions is first derived, and is included in the dynamic analysis methodology developed for the normal temperature. The continuous change in the load-carrying capacity and the stiffness of members during the nonlinear force-deformation history has been incorporated in the analysis scheme using the Pseudo force approach. The solution methodology for obtaining the dynamic response of the structure is based on finite element technique and considers elasto-plastic material and large deformation geometric nonlinearities. To illustrate the behavior of a truss under overload, the methodology is applied to a two-dimensional three-member toggle redundant truss subjected to external static and quasi-static overloads. Results delineating the inelastic cyclic axial force- deformation relation of each member and the time variation of joint displacement and member force are presented. It is seen that the qualitative nature of the member force-deformation behavior at constant higher temperature is similar to that at normal temperature. However, the results show that even at a moderate elevated temperature of 50 degree C, at which material properties remain almost same as those at room temperature, leads to the buckling of a member and gives more severe effects. In general, therefore, the results from this work suggests that the complete inelastic cyclic member force-deformation behavior should be considered in analyzing failure of truss structures, especially when the structure is subjected to dynamic and other unusual loading at normal temperatures. Furthermore, the inelastic cyclic member behavior at elevated temperature should be considered in the failure/ progressive collapse analysis of truss structures to account for events/environments that give rise to high temperature.