Dynamic shakedown design of structures under repeated seismic loads

The paper is devoted to the formulation of an optimal design (minimum volume) problem of elastic perfectly plastic structures subjected to suitable combinations of static (fixed) and dynamic (seismic) loads. The structure is constrained to simultaneously respect two different safety criteria; actually, it must exhibit an elastic shakedown behaviour for the combination of loads characterizing the serviceability conditions and it must prevent the instantaneous collapse for the highest expected load condition (combination of loads characterized by the presence of fixed loads and maximum expected intensity of seismic action). The shakedown limit behaviour for the optimal structure will be imposed according with the unrestricted dynamic shakedown approach. The numerical application is devoted to the optimal design of a simple six floor plane steel frame and the solution is reached by utilizing a suitable harmony search algorithm.