Floor response of yielding structures

Abstract

The New Zealand loading code, NZS 4203:1976, specifies design
forces for parts and portions determined on the assumption that maximum floor accelerations are related to the yield level for ordinary structures. The code committee were aware that there was a scarcity of factual information on the subject and suggested that studies be carried out.
The work described in this paper is aimed at investigating floor motions
in buildings responding elastically and inelastically to earthquake
motions and thus obtaining a basis for the design of parts and portions
and also ancillary services. Twelve structures ranging in height from one to eight storeys and of varying structural type were analysed using a dynamic computer program for elastic response and for two different levels of structure yield strength. Time histories of floor acceleration were obtained at each floor level and from these the maximum absolute values were obtained. To derive loadings on flexible and flexibly mounted components, response spectra were calculated for upper floors and thus the amplification factors relating floor spectra to ground spectra were derived. The basic dynamic parameters used were the El Centro 1940 N-S earthquake record, with constant damping and material strain hardening ratios. The effect of variations in these parameters was studied on a limited number of the structures. From results obtained, tentative equations have been formulated for
the design of both rigid and flexible components. For flexible components the floor amplification function was found to be very complex and due allowance must be made for uncertainties in dynamic parameters such as component damping and for factors such as higher mode effects influencing the response.