Proposition of New Method for Quick Assessment of Maximum Beam Ductility in Steel Moment Frame under Higher Mode Effects

Abstract

A simple equation to estimate beam maximum ductility (µθb) of regular steel structures under ordinary (i.e., without near fault effect) earthquakes is proposed. This equation is a function of period, number of span and global ductility. The proposed procedure enables the rapid assessment of beam plastic rotation of existing buildings and direct deformation-controlled seismic design of new ones. To prepare rational databank, a considerable number of steel MRF with different geometric configuration were analyzed using nonlinear static and dynamic procedure (NSP and NDP). The NSP is used to evaluate the plastic hinge sequencing, force and deformation demands over the height of frames. However, the NDP is applied to prepare databank of demands. The proposed relation is based on nonlinear regression of the results of thousands of NDP. The result of study shows that the µθb is significantly higher than interstory and global ductility. Furthermore, the higher modes effect is completely sensible on increase of rotation ductility in upper stories of high-rise buildings. Finally, the ability of calculating µθb with acceptable precision is the advantage of proposed relation. The result of the proposed relation then could be compared with acceptance criteria of FEMA356 and therefore the performance level would be indicated.