Study On Vibration Characteristics Of Footbridge Under Pedestrian (Group) Walking Loads

With the rapid development of China’s city construction, the number of footbridges inthe city is growing. Due to the utility of modern new building materials and structure,newly constructed modern footbridges tend to have larger spans, less mass and lowerdamping, causing that these ones are more sensitive to the pedestrian walking loads.Especially when the flow and density of pedestrian is large, the bridge’s vibration responseis more obvious. Consequently, the dynamic safety and applicability problems of modernfootbridges are more prominent than in the past. Actually, in recent years, there have beenmany problems of applicability of footbridge caused by the large amplitude vibration morethan the accidents caused by the collaps at home and abroad. So, it is necessary to study thevibration characteristics of crowd load for footbridge.Focusing on this problem, the characteristics of crowd loads, dynamic structuralproperty of footbridges and vibration response induced by crowd loads were studied in thisthesis. The main content of this thesis is as follows:1. The experiments for measuring pedestrian vertical forces were carried out by usingwalkway test. Then, the step length and frequency were analyzed statistically. Consideringthe relationship between the dynamic load factor and frequency, the pedestrian load modelwas fitted out accordding with Chinese actual situation by using the fourier series model.Finally, taking advantage of the previously fitted single pedestrian load model, the crowdloads model was introduced by Monte-Carlo method, based on the principle ofsuperposition.2. A multi-span uniform beam vibration model was built by segmenting multiple spanbridges. The exact frequency equation and mode shapes were derived by using Laplacetransform accurately. Taking a three span footbridge in Beijing as an example, the first fourmodal frequencies and the corresponding vibration mode are obtained through thetheoretical model and the ANSYS simulation.3. Based on forced vibration theory, the analytical solution of vibration responseinduced by singal walking load is derived accurately utilizing mode superposition method.And, the multi-span beam vibration response was studied under the different step lengthand step frequency. Meanwhile, the theoretical solution and the ANSYS simulation resultswere compared. 4. Taking a three span footbridge in Beijing for example, the vertical acceleration timehistory of midspan induced by single person was analyzed, which verified the theoreticalmodel and the simulations. Based on the ANSYS software, the vibration response offootbridges induced by random people (group) walking load are calculated and analyzed,which lays a foundation for further analysis and evaluation of the footbridge comfort andsafety.