Influence of gravity load trapezes in the seismic performance of suspended piping systems

Non-structural elements play a critical role in the post-earthquake functionality of code-compliant and emergency management facilities. Poor seismic performance of suspended piping systems has been documented in the aftermath of recent seismic events in urban regions, which hindered the continuous operation of several buildings and facilities. The seismic design of such systems usually consists of installing channel or rod braces to minimize the swaying of the suspended pipes and increase the lateral stiffness of the gravity load supports, which typically are channel or rod trapezes. One common assumption made when analysing and designing suspended piping systems, is that the lateral stiffness of the gravity load trapezes, often referred to as hangers, is negligible in comparison with that of the sway-braced trapezes, resulting in the sway-braced trapezes being designed to sustain the totality of the seismic loads. This paper presents the results of a numerical study that investigated the influence of the gravity load trapezes of seismically designed suspended piping systems on their seismic performance. Two different suspended piping layouts using channel trapezes installed in four different reinforced concrete moment-resisting frames were investigated under two conditions: i) neglecting the lateral stiffness of the gravity load trapezes, and ii) assuming an elastic-perfectly plastic behaviour for the gravity load trapezes consistent with the material and section properties provided by the manufacturer technical specifications. The results are compared by means of fragility curves for various performance objectives and recommendations are given.