Feasibility and Consequences of Moving Beam Plastic Hinging Zones for Earthquake Resistant Design of R/C Buildings.

Abstract

In this analytical investigation, the feasibility and consequences of moving the potential location of beam plastic hinging zones a proper distance away from the column face during an earthquake-resistant design of reinforced concrete buildings have been studied. A new beam analytical model which allows the user to specify lower member yield flexural capacity at a location away from the beam end has been developed and incorporated in the DRAIN-2D inelastic dynamic analysis program used at the University of Michigan. Three study frames with varying beam spans and number of stories were used in the study. The dynamic response of each frame under two different earthquake records was studied for two design cases. In one case for each frame, the beam hinging zone was assumed to occur at the column face and in the other case the beam hinging zone was analytically moved one beam depth away from the column face. Another variable for the case of the moved hinging zone was the relative moment strength at the column face to that in the hinging zone. The results indicated that seismic response of reinforced concrete buildings was sensitive to moving the beam hinging zone away from the column face. The degree of sensitivity, however, was not uniform and varied widely depending on the response parameter, beam span length, the beam flexural strength at the moved plastic hinging zone, and the input earthquake record. Based on a theoretical assessment of the results, the salient conclusions are that moving the beam hinging zone should not be a problem for beams with normal span to depth ratios if an appropriate value is selected for the ratio of the beam flexural capacity in the proposed plastic hinge location to that at the column face. For beams with relatively small span to depth ratios (less than 7.0), special reinforcement detailing would be required at the moved plastic hinging zones to resist significant increases in the beam rotational ductility dem and , in the beam shear forces and in the number of the inelastic deformation reversals.