Fragility analysis of floor micro vibrations induced by internal vehicles in high technology factories

This study explores the micro vibrations in long span floors induced by internal moving vehicles or automated guided vehicles (AGVs) in high technology fabrication factories (or fabs) by using a bivariate fragility assessment model that considers both the vehicle weight and moving speed. Dynamic time history analyses of an equivalent sub-structural multiple span continuous beam model with moving forces generated by a modified Kanai-Tajimi power spectral density function are performed. The maximum root-mean-square (RMS) floor velocity response of each pair of AGV weight and speed are obtained and in turn used to determine their best fitting median plane and standard deviation for constructing the graphical fragility surface. Probabilistic assessments of floor micro vibrations that exceed a specific vibration level for various vehicle weights and speeds can be directly determined from the fragility surfaces. Instead of using a deterministic approach, probability-based surfaces are a promising alternative for assessing floor micro vibrations that exceed a specific vibration level for various random AGV movements. Moreover, the fragility surfaces can be used to determine the appropriate weight and speed of the AGV or assist in the conceptual design of vibration-sensitive production floor systems based on a given exceedance probability of the desired vibration level.