Seismic hazard mitigation of wine barrel stacks

Currently in California, typical stacking methods of 55 gallon Bordeaux wine storage barrels employ the use of portable steel cradle type racks to achieve stack heights upwards of six levels. Held in place by gravity alone, these stacks have no vertical connection between either the concrete warehouse supporting floor or any of the stacked barrels and racks. This current practice has been shown both in recent published research and recent earthquakes to not only violate the newly adopted California Building Code, 2007 [California Building Standards Commission, 2007], but also to pose a serious safety risk to the personnel working in wine storage facilities [Marrow, 2002; Chadwell et al., 2006; Brown, 2007; Chadwell et. al., 2008]. In an effort to mitigate hazard due to seismic excitation, research presented by Chadwell et. al, 2008 suggests the use of seismic isolation devices to change the effective response of wine barrel stacks during ground motion. These devices are in the form of steel ball bearings housed in a Teflon coated polynomial surface calibrated to maximize the protection of the stack against collapse during a seismic event. The research presented herein describes the state of an ongoing research program to provide wine barrel stack collapse hazard mitigation by use of seismic isolation bearings. What is unique to this particular application, unlike typical isolation where a balance between maximum displacements and force transmission is sought, is that seismic isolation of wine barrel stacks focuses only on collapse prevention. Excessive lateral displacements are not a main concern. The system is considered a success if after an earthquake, the stack remains standing without loss of property while maintaining life safety. This paper describes the development and details of the bearings used with emphasis on the general theoretical framework for housing of the ball bearings, the housing membrane to contain the ball bearings, and a proposed component model of the wine barrel stack Seismic Support System. With the component model parameterized from physical test data, an evaluation of the likelihood of success of an isolated wine barrel stackcan be found for various seismic demands.