Abstract
Enunciation of the principle of strong columns and weak girders is a recent worldwide trend in earthquake-resistant design of R/C frames. However not much is yet clarified on the sufficiently reliable requirements of column-to-girder relative strength for realizing the target of girder-yielding failure. The effects of multi-dof dynamic loading influence significantly their yielding and hysteretic performance, and are not so simple as to permit a straightforward use of dynamic modification factors toward the peak stress produced at unyielding sections. Actually the latter exhibits markedly erratic nature in the increasing order of story shearing forces, member shearing forces and bending moments. The associated higher-order effects become particularly noticeable at side columns of moment-resisting frames and at coupled shear walls. In the present quantitative study for practical purposes, the peak stress is resolved into the SRSS pair of reference and residual components. The residual component is designed to stand for the dynamic effects, and examined advantageously in two separate steps of its relative distribution and a single absolute factor in acceleration. Contrary to an ordinary understanding, this proves unbounded even after the formation of kinematic sway mechanism. Rather this tends to increase in proportion to ground acceleration, which allows to identify the absolute factor in a form of amplification ratio. Thus the current problem is reduced to the relative distribution and the amplification ratio, both of which are then characterized with relation to the contribution of higher-order oscillation in ideally elastic system or pseudo-elastic system accounting for the partially differing reduction of secant stiffness.
