21 1月 英国论文代写：伦敦千禧旅桥结构研究
The millennium Brigade Bridge at London was first opened in 2000. This was Foot Bridge so thousands of people flocked to walk across it. This was suspension bridge so there are chances of some wobble in this bridge. Though this bridge did not cause harm as soon as people started to cross through this bridge, an expected effect began to emerge. The people were synchronizing their footsteps with the bridge movement which caused it wobble more and more (AASHTO, 1991).
This happened because with the small wobble in the bridge, the people who were crossing the bridge started to counterpart this wobble by changing their patterns of movement. However, instead of reducing the motion, the people were causing a feedback loop. In this case, the people as more tried to stop the motion, the wobble happened more. The lateral force exerted by people on this moving deck was found as the movement over the bridge.
This wobble led to resonance and vibration on the bridge. This was also found that this kind of phenomena on this bridge was not because of the technical issue but this kind of phenomena can be observed anywhere if the lateral frequency is below 1.3 GHz and loaded with sufficient number of people at a time. This was a steel structure failure for this bridge at the time because of the movements form the pedestrians was quite high for the bridge suddenly.
The bridge structure was shallow suspension bridge. In this case the bridge cables are as much as possible below the level of the bridge deck. This structure was shallower than the conventional suspension bridge structure. Fabricated steel box are used as transverse arms for the bridge. The cables are source of primary structure of the bridge. These cables have very shallow profile. This bridge follows some of the characteristics of the Ribbon Bridges but this bridge has multiple spans. The resulting total dead load cable tension is 22.5MN. The structural system of this bridge is in both horizontal and vertical direction.