Plastic design of dissipative truss moment frames

In this paper, a new design approach for Ductile Truss Moment Frames (DTMFs) able to guarantee, under seismic forces, the development of a collapse mechanism of global type is presented and applied. In particular, DTMFs consist in a special Truss Moment Frame where the energy dissipation is provided by means of special devices located at the ends of truss girders at the bottom chord level. The proposed design methodology is based on the kinematic theorem of plastic collapse. The method is based on the assumption that sections of truss elements and the yield threshold of dissipative parts (i.e. special devices) are known, so that the column sections are the unknowns of the design problem which are obtained by imposing that the equilibrium curve corresponding to the global mechanism has to lie below those corresponding to all the undesired mechanisms within a displacement range compatible with local ductility supply of dissipative elements. The design methodology has been implemented in a computer program and applied to the design of some DTMFs. Aiming to demonstrate the effectiveness of the proposed approach, some push over analyses have been carried out to compare the obtained pattern of yielding with the design goal, i.e. the development of a collapse mechanism of global type.