Recently, some photovoltaic (PV) equipment manufacturers have developed and implemented non-anchored or "isolated" PV array support on relatively flat rooftops on large commercial and institutional buildings. This technique saves significant time and expense over conventional PV array installation methods, and has the potential to decrease the risk of roof membrane failure. However, concerns regarding possible seismically-induced horizontal movement and wind uplift of PV arrays surround the introduction of this new technique, which currently is required to be considered as an "alternative means of compliance" for rooftop PV array implementation. The isolated approach explicitly relies upon friction between a PV array and its supporting roof membrane, which in principle is similar to the use of friction in a seismic isolation system. This paper describes the key seismic considerations related to this innovative method of PV installation on flat or near-flat building rooftops, and presents a rational approach for the evaluation of PV array seismic sliding displacements and determination of corresponding gaps for seismic movement.
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