The Construction Of Information System For Disaster Prevention And Reduction Of Urban Bridges And The Analysis On The Cause Of Cracks

With the development of society and economy and the increase in urbanism, thedisaster prevention and reduction becomes more and more important. Thisdissertation expounds the importance of disaster prevention and reduction of urbanbridges, the necessity of information system construction, and content and method forthat system. The analysis of the cause of cracks is the main part of the information systembecause the cause of cracks is various and complicated. Without the analysis of bridgecracks, it is difficult to discover the cause and principle of them, and thus difficult tomake the project for disaster prevention. The cause of cracks is always a hot issue inthe disaster prevention and reduction research and needs to be solved urgently. This dissertation starts with the investigation of all cracks on bridges being usedin Fuzhou, then analyses the usual place of cracks and the common form of them, anddiscovers that the main causes leading to cracks are loading, temperature, shrinkage,construction and so on. Through vehicle loads test, the finite element method with the software ANSYSto establish the entire space models and calculation analysis, checking crack width byhand, it is discovered that transverse stress in box girder exceeding tensile strength ofconcrete is the main cause of longitudinal cracks in prestress concrete continuous boxgirder bridge. Besides early form removal, short concrete age, great constructionalloading, downward movement of steel on the bridge deck, the use of earlystrengthening agent and pumpcrete can also lead to longitudinal cracks in this kind ofbridges. At present there is no evident influence of these cracks on the wholemechanic behaviors. But as traffic volume is increasing rapidly and the loading in thefuture should still increase, it is necessary to observe the cracks for a long time, so asto investigate whether the strength performance and durability structure are affected.In order to prevent from the appearance of these two kinds of cracks, it is suggestedthat the horizontal prestressing steel wire should be designed in prestress concrete IIcontinuous box girder bridge, which is an effective way to prevent longitudinal cracks.To avoid constructional cracks, we should strictly control form removal time andconstructional loading time in the course of construction, avoiding early removal andconstructional overloading. The crack problems discussed in this dissertation are common, but often don'tattract enough attention, which is very disadvantageous to preventing the appearanceof bridge cracks. So, we should pay more attention to bridge cracks, strengthen andperfect the digital information system for disaster prevention and reduction of urbanbridges and establish the foundation for the scheme of disaster prevention of the mainbridges in Fuzhou.