Structural Design of Frames Able to Prevent Element Buckling

Two formulations of a special multicriterion optimal design problem devoted to elastic perfectly plastic steel frame structures subjected to different combinations of static and dynamic loads are presented. In particular, two minimum volume design problem formulations are proposed: in the first one the structure is designed so as to be able to elastically behave for the assigned fixed loads, to elastically shakedown for serviceability seismic load conditions and to prevent the instantaneous collapse for suitably chosen combinations of fixed and ultimate seismic loadings; in the second one the structure must also satisfy further appropriate constraints related to element buckling. The actions that the structure must suffer are evaluated by making reference to the actual Italian seismic code and the dynamic response of the structure is performed by utilizing a modal technique. The applications are devoted to flexural steel frames, the different designs obtained are compared and the sensitivity of the structural response has been investigated on the grounds of the determination and interpretation of the Bree diagrams of the obtained optimal structures.