Influence of the seismic shear proportioning factor on steel MRFs seismic performances

The work herein present has the purpose of investigating the influence of the shear proportioning factor for the design of Moment Resisting Frames where the most severe condition for the design of dissipative zones is the seismic action. This situation often happens when the frames are arranged parallel to the warping of secondary beams, i.e. when vertical loads are not relevant for the dimensioning of the beam sections. The shear proportioning factor is used to distribute the base shear among all the storeys of steel moment-resisting frames to design the beam sections according to the required storey seismic action. To this scope, reference is made to several MR-Frame structures designed by Theory of Plastic Mechanism Control design approach and Eurocode 8 where shear proportioning factors variable along with the structure height and equal to 1 are assumed. A shear proportioning factor variable has the scope of promoting the simultaneous activation of dissipative zones in plastic range while the constant one should time-spread the yielding of dissipative zones. The seismic performances of these frames are investigated using both push-over and dynamic non-linear analyses