Factors Triggering Combined Analysis of Coupled Industrial Structures Subjected to Seismic Loading

Coupled structural systems are commonly found in either vertical (i.e., “stacked”) or horizontal (i.e., “adjacent”) configurations. Stacked industrial structures typically consist of elevated equipment supported by a primary nonbuilding structure. Adjacent industrial structures are often linked structurally by piping, electrical trays, struts, and mechanical equipment components. Regardless of the interaction between structures, they are often analyzed independently because it is the simplest and most cost effective method for completing the engineering and design. There are key factors which determine when a combined analysis of coupled industrial structures subjected to seismic loading is more appropriate to accurately capture the overall structural system behavior. The mass of the supported equipment and pipe is one of these factors since the added component mass can become the driver of the system’s natural frequencies and affect the overall seismic response. Another factor affecting the seismic response of coupled industrial structures is the relative natural frequencies of the interconnecting components. Currently, there is limited guidance within the codes and standards that specifies whether a combined analysis of coupled structures is necessary to accurately model the seismic behavior of the structural system. Parametric studies have been performed on analysis models of both stacked and adjacent coupled structures; the studies evaluate the effects of mass and natural frequency of the structures on the overall structural system response. A set of decoupling criteria or “triggers” for combined analysis are obtained by means of this study. The proposed triggers provide guidance to practicing engineers regarding the conditions in which a combined analysis of industrial structures is required in order to appropriately capture the behavior of coupled structural systems subjected to seismic loading.