PSI - Issue 78

Alessandro Contento et al. / Procedia Structural Integrity 78 (2026) 1975–1982

1976

1. Introduction Nonstructural elements (NSEs) encompass a wide range of components within buildings, such as mechanical equipment, ventilation systems, electrical installations, medical devices, architectural panels, furnishings, and historical monuments. While these elements do not directly contribute to the structural strength of a building, they are essential for its functionality, safety, and economic and cultural value. During seismic events, the vulnerability of NSEs can lead to severe damage, compromising building operability, and—most importantly—posing a risk to the safety of occupants and workers. Seismic protection of NSEs is of growing importance, particularly in critical buildings where operational continuity is essential. For instance, the damage or loss of medical equipment during an earthquake can severely hinder emergency and healthcare operations. Similarly, the overturning or damage of industrial machinery can cause long-term production stoppages, resulting in significant economic losses. Despite the relevance of these issues, the protection of NSEs has often been considered secondary to structural aspects of buildings, historically leading to gaps in regulations and design practices, which only recently have begun to be addressed. Current research focuses on developing more effective methods for evaluating the seismic response of NSEs and designing appropriate protective devices, also considering the complexity and variety of possible configurations. NSEs can be classified into different categories depending on their function, location, and behavior during an earthquake. This classification is fundamental to properly guide protection strategies and isolation or restraint techniques. An initial distinction can be made based on the nature and function of the elements: • Architectural elements: include facades, suspended ceilings, decorative panels, and glazing. These components are often vulnerable to displacements and vibrations induced by earthquakes. • Mechanical, electrical, and plumbing (MEP) elements: include HVAC systems, electrical equipment, piping, ducts, switchboards, and communication systems. Their integrity is critical to maintain the building's functionality during and after a seismic event. • Special and movable equipment: industrial machinery, hospital equipment, IT systems, and heavy furnishings. These elements require specific protection to prevent overturning, sliding, or functional damage. Another useful classification is based on the type of dynamic behavior during an earthquake: • Elements rigidly attached to the structure, which more or less follow the building's motion and may experience high levels of stress. • Freestanding or movable elements (such as statues or pedestal-mounted machinery), which are subject to rocking and independent shaking. Their response can be highly nonlinear and complex. • Isolated or damped elements, equipped with seismic isolation or damping devices that reduce transmitted forces and limit damage. This multifaceted classification is essential for developing differentiated design approaches and for more accurately assessing seismic risk. Recent research has particularly focused on freestanding and isolated elements, due to the complexity of their dynamic behavior and the growing adoption of isolation and damping technologies. The present paper summarizes and discusses the critical review assessment carried out by the authors in D’Angela et al. (2025). For more detail regarding literature review, limit of research, and future perspective, the readers are kindly referred to the abovementioned extensive study. 2. NSEs subject to rocking 2.1. Seismic response mechanisms of NSEs The seismic response of NSEs is influenced by multiple factors, including their geometry, mass, anchorage methods, and interaction with the supporting structure. Understanding these response mechanisms is crucial for developing accurate predictive models and effective protection solutions. For example, rigid and freestanding elements, such as statues or heavy machinery, tend to respond primarily through rocking motion. This behavior can result in large angular displacements, increasing the risk of overturning and causing damage to both the element itself and nearby objects. The rocking phenomenon is affected by the element’s geometry (height, width, base dimensions), mass distribution, and the stiffness of the supporting surface (Fig. 1).