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On the dynamics of footbridges

A theoretical approach and a comparison between running and walking loads

Time: Mon 2021-05-31 13.00

Location: Videolänk, Du som saknar dator /datorvana kontakta Raied Karoumi / Use the e-mail address if you need technical assistance, Stockholm (English)

Subject area: Civil and Architectural Engineering, Structural Engineering and Bridges

Doctoral student: Daniel Colmenares , Bro- och stålbyggnad

Opponent: Professor Titular Pedro Museros Romero, Universitat Politècnica de València

Supervisor: Professor Raid Karoumi, Bro- och stålbyggnad (byte av engelskt namn 20110630), Bro- och stålbyggnad, Järnvägsgruppen, JVG, Byggkonstruktion; PhD Andreas Andersson, Bro- och stålbyggnad; Dr Mahir Ülker Kaustell, Tyrens

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The dynamic behaviour of lightweight footbridges is often susceptible to HumanInduced Loads (HILs). Generally HILs are taken into account as moving harmonicfunctions in which the loading frequency represents the step frequency of the pedestrians.In this way, there may be resonance if the loading frequencies fall within therange of the natural frequencies of the bridge, potentially compromising the serviceabilitylimit state of the structure. Therefore, it is important to understand how toaddress and model HILs in the context of lightweight and slender structures. Furthermore,interesting effects can be considered in the field of footbridge dynamics,such as the Human Structure Interaction (HSI) effect. The HSI effect can be understoodwithin a framework in which pedestrians behave as Tuned Mass Dampers(TMDs), possibly modifying the dynamic behaviour of the footbridge. In addition,the evaluation of the dynamic response of a footbridge is usually made through atime consuming dynamic analysis using the Finite Element Method (FEM). Mostof the analysis of this type of slender structures rely on a prescribed stationary harmonicloading scenario, and this is usually done in the context of a walking crowdevent and not much attention is given to running load events.The aims of this research project are to study the influence of running and walkingloads on the dynamic response of footbridges as well as to investigate and developa closed-form method in order to simulate the dynamic behaviour of footbridgessubjected to HILs. This has been achieved by comparing different approachesin order to simulate running load events for a small number of pedestrians withrespect to experimental results (Paper I). In addition, the simply supported beamand the clamped-clamped beam (Paper II) are studied when subjected to a movingharmonic load in a closed-form framework. Then, a comparison between normalwalking and normal running conditions is made. Finally, a general closed-formsolution for the moving harmonic load problem (Paper III) is developed using the2D Bernoulli–Euler beam theory for a continuous beam system on elastic supports.The results from the study indicate that running is more critical than walking fora single pedestrian crossing, despite the fact that it is easier to achieve a steadystate condition in a normal walking event than in a normal running event. Finally,the general solution of the moving harmonic load problem is found and it can beused to solve any load spectra in the time domain, with its static component, for ageneral multi-span beam system.