PSI - Issue 78

Alessandra Marino et al. / Procedia Structural Integrity 78 (2026) 1753–1758

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pipe-tank connection resulting in a continuous release of the content. On the contrary, the elastic (diamond shape) buckling produces less severe deformations generating small fractures in the tank wall. Moreover, tank sliding or uplifting could generate the failure of pipes or pipe joints with a continuous release of the content. Excessive overturning moments could instead generate an instantaneous release of the content. This latter is typical of slender unanchored tanks. Slender and squat equipment supported by steel or concrete columns are also typical units of process plants. For example, slender storage (broad and slender) tanks are often used to storage liquefied gas or as liquid/gas separators. They typically suffer excessive displacements of the support structures with the consequent detachment of the pipes from the vessel or in extreme cases with the collapse of the entire structure. Finally, piping systems and support structures are not generally extremely vulnerable to earthquakes. Problems could arise in the pipes for excessive displacements between adjacent structures that moving reciprocally could generate excessive stresses in the pipes and their rupture. The seismic vulnerability of process plant components can be investigated using different tools. Because risk and resilience analysis often requires a probabilistic approach, fragility curves need to be employed, which represents the probability of exceeding a given limit state. In this respect an intense activity has been performed in the last years to derive fragility curves for process plant units, in more particular for storage tanks. Fragility curves can be derived using approaches of increasing complexity as judgmental, empirical (or observational) and numerical. A reference document for fragility and risk analysis is the well known HAZUS manual which provided, for most of the structural and nonstructural constructions, including oil & gas installations, proper fragility curves. It easily recognizable the highest vulnerability of the columns as well as of vertical and horizontal storage tanks. Less problematic are the piping systems and the stacks. Consequently, it is clear the necessity to adopt mitigation measures. In this respect passive and active strategies could be adopted. For example, seismic passive control systems could represent a quite simple and effective tools to reduce the seismic response of the structures. In this paper the use of active solutions that is “Integrated SMART sensors” for the seismic risk management of major-hazard industrial plants, which includes early warning systems and active protection systems as Safety interlock systems (SIS) based on different typologies of sensors. 3. Earthquake Early Warning Systems Early warnings systems are recognized as a focal point for the prevention of nuclear accidents, whereas poor attention has been given to the seismic safety management of chemical process plants, where a large amount of hazardous chemicals is usually stored. On the other hand, providing a reliable warning from few seconds to minute before the ground motion arrives is now possible. Thus, specific actions addressed to significantly reduce damage and loss of containment in storage tanks, pipelines and reactors, and prevent accidental scenarios, which may affect the surrounding area and population, should be specifically designed.

Fig. 1. Earthquake Early Warning System

The main characteristic of an EWS, for the development of effective mitigation actions in case of earthquake, is the arrival time of the seismic waves. The estimated warning times for locations at different distances from the earthquake epicenter is essential. Locations within 20 miles of the fault will likely not receive any warning as, on average, it will take 10 seconds to detect and locate the earthquake. The time required to detect and issue the warning for an earthquake depends on the distance between the earthquake source and the closest measurement station. It takes a short time (2 miles per second) for seismic waves to travel from the source (e.g. the point on a fault