Feasibility And Factors Of Windening A Prestressed Concrete Frame Bridge With Rigid Connection

Widening of the existing bridge is becoming to be a very urgent problem as the transportation in our country improving rapiedly nowadays. When coming to the relationship of the new bridge and the existing one, alertnative methods are keeping them disconnected or connecting whit joint which have defferent rigidity, in which connecting with completely rigid joint is proved to be best considering the travelling performance and maintenance problems. At the same time, connecting with completely rigid joint may be up against much problems which mainly caused by the shrinkage and creep of the concrete. After roundly realizing the basic theroy of shrinkage and creep of concrete, the feasibility of widening a prestrssed concrete frame bridge using rigid connecting and the main factors are studied. Conclusions of this thesis are followed.1) Mechanism of shrinkage and creep of concrete is discussed, in which moving of the water between crystals of the concrete and destroying of the microstructure in the concrete under stress are generally accepted. GL2000 model is considered to have the best precision of predicting the shrinkage and creep of concrete. Practical model can be obtained from experimental datum using the GL2000 model as well.2) Comparing with the disconnected beam, the internal force of the rigidly connected beam caused by the dead load and live load are bigger, while that caused by temperature and settlement of the widening bridge are less markedness. Influnce of connecting with rigid joint to the intensity and crack resistance of the existing bridge are limited. Considering the monolithic performance, it's feasible to connect the bridges with rigid joint at one time.3) Analysis of the performance in the closure belt using finite element method identifies that the closure belt is very important to a successful connecting. It tend to crack under the compresion of the wheel and deformation of the beam caused by shrinkage and creep. What's more, the influnce of the settlement of the widening bridge is even bigger, which should be restrictly controlled.4) Analysis of the main factors influncing the connection indicates that the time closure pour placed and the character of shrinkage and creep of the concrete are the most notable. Delay the time closure pour placed and reduce the shrinkage and creep of concrete can improve the performance of the widening bridge, especially that of the closure belt, while has inapparence influnce to the intensity and crack resistance of the existing bridge.5) Making sure the rigid connection to be successful, several methods can be applied. Such as reducing the prestress degree in the design, adjusting the time closure pore placed, adopting reduced shrinkage and creep concrete, and improving the construction method.Conclusion hereinbefore is useful not only to the widening of the analysed bridge, but also to similar bridges in our coutry aflerword.