Analysis of structures subjected to crowd loads

Abstract

The movement of people on any structure induces dynamic crowd load. The enthusiastic potential behavior of people from overwhelming happiness in concert, shows etc. on structures such as stadiums, auditorium, grandstands, bridges, malls and convention centers causes synchronized rhythmic movements. Resonance between forcing frequency and one or more natural frequencies of the structure resulting from human-structure synchronization leads to strong vibrations. Such vibrations not only affect structural stability, but also create discomfort among people. Pedestrian induced lateral vibration of Millennium Bridge, London is a classic example for the same. Crowd loads impose vertical as well as horizontal loads on the structure. Both these loads induce vibrations in corresponding directions. Beyond an acceptable limit of vibration level, people may feel uncomfortable. If there is a mode of low natural frequency, even a significantly low forcing frequency can lead to strong vibrations, which in turn may cause panic. The present research focuses on analysis of a simply supported slab strip subjected to crowd load. The crowd-structure interaction is analytically modelled and the modal parameters and the response of the occupied structure are determined. Furthermore, the effect of various parameters such as crowd size, crowd location and crowd activity on the behavior of occupied structure is studied. The comfort level of the people on the structure is also estimated. It is observed that crowd parameters affect the behavior of the system as well as the comfort level of the occupants. It is further seen that the trend of variation of natural frequency of the occupied structure with variation in crowd properties changes with change in the empty structure properties.