Displacement Based Seismic Design of Steel Moment Resisting Frames

Modern design methods described in the current Italian or European Technical Standards are generally based on the comparison between the demand calculated in terms of forces or base shear associated with the design earthquake, and the corresponding capacity. This design philosophy can be seen as the natural result of the historical evolution of the study of structural dynamics and strictly related to how buildings are usually designed for other actions, such as dead and live loads: if the strength capacity of the structure and of its elements does not exceed the applied loads, the collapse will occur. For applied loads this approach has a strong physical basis. In fact, usual not-seismic load such as dead, live, snow and, with some approximations, wind load, can be considered as statically applied to the building or to some structural elements and the load does not suddenly change neither in intensity or in direction. So, once the strength capacity is exceeded, the element is not longer able to resist to the applied loads and collapse occurs. However, several limitations have been recognized to the force-based design, as detailed described in Chapter 2, and with the intent of overcoming these deficiencies and recognizing that the most suitable parameter to evaluate the response of buildings to the action of the earthquake is represented by the displacements and the deformations induced in the building itself, many different displacement-based design (DBD) methods have been proposed and developed during the last decade (Calvi, 2003). In order to develop an actually applicable Direct DBD method also for steel MRF structures, recommendations that account for different joint typologies would be needed, including the effects that different joint components have on non-linearity, hardening, damage of mechanical properties, pinching’ and so the global behavior of the whole structure. Within this thesis work, the influence of joint hysteretic behavior, detailing, non-linearity, hardening, cyclic damaging on the displacement and dissipative capacity of steel MRFs is studied from a DBD point of view.