Seismic assessment approaches for mass‐dominant sliding contents: The case of storage racks

The typical view of seismic performance of structure‐content systems is one of segregation: Contents are assumed to be of low mass relative to the supporting structure, leading to a separate treatment of the two, whereby one first analyzes the structure and then subjects any contents to the resulting peak floor acceleration responses. Racking structures are of the exact opposite persuasion, having massive “palletized” contents that can slide on top of light cold‐formed steel frames, with Content‐Structure‐Sliding Interaction (CSSI) governing global and local response. In support of assessment and design, three approaches are investigated to capture CSSI: (i) introducing friction sliders per pallet and running nonlinear response‐history analysis, (ii) increasing the model viscous damping and using elastic response‐history analysis, and (iii) reducing the horizontal seismic loads in tandem with modal response spectrum analysis. Each comes with its own challenges and modelling/analysis needs, offering different levels of accuracy (or no appreciable capability at all) when assessing the actual sliding displacement of contents. Three case studies are employed to calibrate empirical relationships for damping amplification and seismic load reduction, largely removing the bias of simpler alternatives (ii) and (iii), respectively, to level the ground for future code applications.