| Popis: |
After the widely known cases of human induced vibrations that affected the Millenium Bridge, London and the Passerelle Solférino, Paris, several and important studies were conducted on this kind of dynamic load. This is still today the cause of discomfort problems, sometimes not negligible, because of the increased slenderness of footbridges required to reach some standards of beauty. Although many steps further in the field of walking pedestrian induced loads have been done, today’s engineers are starting to ask themselves how structures may react when subjected to the action of running pedestrians. In fact, because of the increasing number of running competitions in urban environment, they would know if the current dynamic load models, barely and superficially provided by literature or by the most used design guidelines, are adequate to realize structures where expected comfort levels are satisfied. So, after the description of fundamental elements concerning the nature of human induced loads and the possible human-structure interaction, a case study is developed. Three numerical models are developed, using the software Ansys Mechanical APDL, for a steel footbridge at the design stage in the engineering office McCarré (Belgium) and that will be built in few months in Louvain-La-Neuve (Belgium). The models differ in the arch geometry, whose effect on the modal properties is investigated. The results of two different dynamic analyses on the footbridge under a running pedestrian are then compared. The first is a harmonic analysis exploiting the running pedestrian load model provided by a well-known European guideline for footbridges design (HiVoSS guidelines, Human induced Vibrations on Steel Structures guidelines). The second is a transient analysis under a moving and time varying load based on the running pedestrian load model proposed by Racic and Morin [47]. The load time history produced by their numerical generator and made available for this thesis has been at the base of the work. Since in general the pedestrian will not move only on the nodes of the finite element mesh, a Matlab code named RealRun1 was developed during this thesis to solve the problem. This post-processes the time-history to provide the equivalent nodal loads on the structure as a function of time and position of the runner on the footbridge. Finally, clear differences of results are obtained from the two analyses. Being the footbridge still at the design stage, the need of some structural adjustment of the footbridge to ensure expected comfort levels was pointed out. The results also showed that more research is necessary to develop a robust load model for running pedestrians, improving the one provided in HiVoSS. Master [120] : ingénieur civil des constructions, Université catholique de Louvain, 2017 |
