Monte Carlo Analysis of the Intensification Factor of Design Response Spectra for Hoisted Loads

Seismic requirements play a crucial role in the design of mechanical systems for infrastructures located in earthquake-prone regions. This process becomes significantly more complex when non-linearities are present, making system-specific analyses necessary. The evaluation of earthquake effects, as mandated by national regulations, is typically based on linear response spectra, which describe the peak response of a harmonic oscillator with a given natural frequency to external vibrations. However, for non-linear systems, computationally intensive transient simulations are required. Developing simplified methods to extend design loads without relying on such complex simulations would be highly beneficial, particularly for commonly encountered non-linear systems. One such system is a hoisted load manipulated by an overhead crane. Strong earthquakes can induce oscillations that cause periodic slack rope conditions—where the rope loses tension and the load temporarily enters free fall—resulting in peak accelerations that exceed those predicted by linear models. This study focuses on quantifying these amplified accelerations in hoisted loads subjected to non-linear dynamics. Using a Monte Carlo approach, it establishes intensification factors—expressed as a function of key physical parameters—relative to a given design response spectrum.