Seismic Performance Criteria for the Rocking and Overturning Behavior of Freestanding Contents in Buildings

During a severe earthquake, the violent shaking causes freestanding non-structural elements to sway and overturn, potentially injuring occupants or causing the elements themselves to break apart. This study investigates how freestanding contents (FSCs) in buildings respond to various earthquake intensities, detailing their movement through extensive analysis of dynamic performance. The stability of the FSCs on each floor varies depending on the earthquake’s intensity, the building’s structural mode shape, the FSCs’ geometry, and the chosen performance assessment method. A series of multi-level seismic excitation assessments of FSCs were conducted using 30 earthquake records, classified into 50%, 10%, and 2% probabilities of exceedance in 50 years. The floor’s responses, including absolute peak floor acceleration and relative peak floor velocity from both elastic and inelastic analyses, provided the seismic demand. The Ishiyama criterion made it difficult to evaluate FSCs’ seismic capacity because of the ambiguous distinction between rocking and overturning movements. A new criterion, specifically developed to differentiate between rocking and overturning of FSCs, has been proposed to address this issue. The results translate into practical guidance for design and protection: because the demand-to-capacity ratios for overturning are governed by the floor level, content slenderness, and the elastic-versus-inelastic modeling assumption, the proposed criterion identifies which floors and which content geometries are genuinely at risk, allowing anchorage, restraint, or relocation measures to be targeted where they are most needed rather than applied uniformly. This supports more reliable and economical seismic protection of non-structural building contents.