A pedestrian crowd walking on a footbridge causes the footbridge to vibrate. These vibrations become an issue of serviceability and can give rise to discomfort for the pedestrians, whereby they should, to as large extent as possible, be prevented. Currently, there is a lack of reliable models to describe a dynamic load on a footbridge, due to a walking crowd. Therefore, there is a need for such models. Lately, a great amount of research has been carried out on the subject pedestrian-induced vibrations of footbridges, though most of it with focus on lateral vibrations. Conversely, this project has been performed aiming to accurately model pedestrian-induced vertical vibrations of a general footbridge. For that purpose, starting from an existing model, a somewhat improved model, comprising three sub-model, has been developed. The sub-models are: one model of the pedestrian crowd walking along the footbridge, one model describing the load from the pedestrian footstep and one model describing the interaction between the pedestrians and the footbridge. In order to get statistically reliable results, numerous simulations of the pedestrian-induced vertical vibrations of a specific footbridge have been performed, using the developed model. Averaging the results over the simulations, we could conclude that the model gives an average error of 7 %, compared to experimental data. The measured quantity giving these results was the absolute maximum value of the acceleration at the midpoint of the footbridge. The achieved dynamical response of the footbridge is qualitatively satisfying, while the quantitative error is larger than we hoped for, whereby we conclude that further improvement of the model is needed before we are able to accurately model pedestrian-induced vertical vibrations of footbridges. / När en folksamling går över en gångbro uppstår vibrationer i gångbron. Dessa vibrationer påverkar brons användbarhet och kan ge upphov till obehagskänsla hos fotgängarna, vilket gör att vibrationerna i största möjliga utsträckning bör motverkas. I nuläget saknas pålitliga modeller för att beskriva den dynamiska last en gångbro utsätts för när en folksamling går över den. Således föreligger ett behov att utveckla en sådan modell. Under de senaste decennierna har mycket forskning utförts inom området människoinducerade vibrationer i gångbroar. Dock har merparten av denna forskning berört endast laterala vibrationer. Detta projekt däremot, har genomförts med syftet att, med ett noggrant resultat, modellera människoinducerade vertikala vibrationer i en generell gångbro. För att uppnå detta har jag utgått från en befintlig modell och från den utvecklat en ny modell bestående av tre delmodeller. De tre delmodellerna är: en modell som beskriver hur folksamlingen rör sig över gångbron, en modell som beskriver den kraft det mänskliga fotsteget uträttar på gångbron och en modell som beskriver interaktionen mellan fotgängarna och gångbron. För att uppnå statistiskt tillförlitliga resultat har modellen som utvecklats i detta projekt använts för att utföra åtskilliga simuleringar av människoinducerade vertikala vibrationer i en specifik gångbro. Om vi medelvärdesbildar resultaten över simuleringarna framgår det att modellen som utvecklats ger ett resultat som avviker med 7 % från experimentellt data. Detta gäller för den maximala accelerationen vid gångbrons mittpunkt. Den resulterande dynamiska responsen ser kvalitativt sett bra ut, medan den kvantitativa avvikelsen är större än vi hoppats på. Därför drar vi slutsatsen att vidare förbättringar av modellen behövs för att den ska kunna användas till att på ett noggrant sätt modellera människoinducerade vertikala vibrationer i gångbroar.

Vibration serviceability in the design of footbridges is gathering enormous prominence as comfort restrictions get enhanced. Comfort verifications are often becoming critical when considering human induced dynamic loading on lightweight structures, which are increasing in slenderness and flexibility. The aim of this work was to build up understanding about the running load effects on the response of footbridges and proving that it could imply a critical load case that would require verification. Additionally, the accuracy of potential models to estimate the structural response was evaluated. Finally, aiming for a practical application, this work provides a step forward towards the possibility of adopting a simplified design methodology to be included in the future guidelines and an insight into the potential effects of a marathon event. While the walking load case is a well-studied phenomenon, not much attention has been paid to the running induced excitation. Guidelines motivate that there is no need for verification and exceptionally, some get to suggest a time domain load model definition. The interaction phenomena as well as the effects of groups of runners in the dynamic response of the structure remain still unknown. Limiting the work to the vertical component of the response and force and based on a large set of additional assumptions, experimental and numerical analyses were performed. Three footbridges were tested and subjected to tests involving different motion forms; jumping, walking and running. On the other hand, the time domain load models available in the literature were applied accounting for the spatial displacement of each of the pedestrians along the footbridge. In the most advanced of the models, aiming to account for interaction effects, the subjects were modelled as independent mechanical systems. The results derived from the experimental study helped characterizing the running load effect on the footbridge's response and proved that there may be structures in which running could comprise a critical load case. Furthermore, the numerical analyses allowed to verify the accuracy of the suggested models and the improvement that the human structure interaction effects involve. The analyses resulted in complementary sets of conclusions that built up understanding about the running load effects on footbridges; such as the sensitivity of the estimated response to the structure's modal properties and the influence of the parameters that characterize the running motion. Finally, the suggested simplified design methodology was able to estimate, with a very reasonable error for the current case study, the calculated response by the most accurate of the models. To sum up, this work serves as a motivation to include the running load case in the guidelines and establishes a starting point for further research and simplified design methodologies based on the strategy and models suggested in this work.