ABSTRACT
A new definition of the q-factor is presented briefly relating this factor to the maximum inelastic base shear force of the structure during its time-history. Such a definition is well applicable to steel frames with semi-rigid and partial-strength joints. In this case, assuming a design elastic response spectrum to characterize the seismic action, an elastic-plastic static global analysis should be used to check the structural resistance of frames which generally are partially dissipative. Then, adopting an elastic-perfectly plastic cyclic behaviour of the beam-to-column joints and considering different limited rotation capacities of these joints, a parametric investigation of the q-factor by means of non-linear dynamic analysis is performed for different types of multi-bays multi-storeys frames subject to severe ground accelerograms. In addition to the instructive conclusions deduced from this investigation, conservative values of the q-factor are proposed in low seismicity zones as a function of both the joint rotation capacity and the nominal ground acceleration. Finally, a design example is given to illustrate the new concepts and results of this paper.
