Abstract Summary
On the 17th of October 2021 a grandstand of the Goffert stadium partially collapsed while a crowd was jumping on it. Forensic engineering concluded that the main reason of the collapse was that the load of a jumping crowd exceeded the design load of 4 kN/m2, as specified in the Eurocode. The actual collapse was due to the combination of dynamic non-linear response of the structure and a dynamic load of the jumping crowd. Both the response and the load were investigated, and ultimately combined in an equivalent non-linear single-degree-of-freedom (SDOF) system with a dynamic load. A geometrically and physically non-linear finite element (FEM) model was used to obtain the backbone curve of the response. This curve was obtained with a push-down analysis. The push-down analysis was force-controlled to allow the grandstand to rotate and deform freely, so that the failure mechanism could develop freely. The jumping load was modelled with a Fourier series based on how high the crowd was jumping and how well coordinated they jumped. Based on video footage during the col-lapse these parameters were estimated, and the number of people counted. It was conclud-ed that the mass of the people was roughly 3.5 kN/m2. An equivalent SDOF system was set up based on analytical formulae and the backbone curve obtained with the FEM model. With this model the non-linear dynamic behavior of the grandstand due to the jumping load of the crowd was assessed. Failure was found with the estimated jumping load after roughly the same number of jumps as was seen on video. Expressing this non-linear dynamic behavior as a quasi-static load leads to a value of 9.8 kN/m2, which implies a dynamic amplification factor of 2.7. This is an unusually high am-plification factor for crowds, which is the result of the combination of a dynamic load and non-linear behavior. For design purposes it is therefore advised to use only the linear-elastic capacity of the structure for controlling dynamic loads.
