The Study Of Continuous Rigid-frame Structure Of Reinforced Concrete Box Girder Demolition Technology

With the sustainable and rapid development of the traffic circulation in China, parts of the built bridges couldn’t meet the functional requirements, thus need to be removed and reconstructed. At present, the most removing methods of bridges are blasting method and mechanical removal method. This thesis investigated the characteristics and the scope of the applications for these two methods. Nevertheless, there is neither theoretical guidance nor standardized norms to follow for removing such bridges; therefore the research on this domain is still in the range of preliminary exploratory stage. In the present study, the continuous rigid-frame structure of reinforced concrete box girder is studied. With engineering examples, the removal construction techniques and the structural analysis are carried out. Finally the specified removal plans are proposed.The continuous rigid-frame structure of reinforced concrete box girder investigated in this study is situated at the central road of the west third ring in Zhengzhou, belonging to the prosperous urban area. In terms of the current situation of this bridge and its structural characteristics, the mechanical removal method was used. Based on the static cutting and lifting techniques, the removal plan composed of full support, temporary backwater, cutting by segments, lifting one by one was used. The results show that this plan has many advantages such as:high security, easy for construction process control, low environmental impact and requirement of engineering equipment, thus the proposed demolition plan can be taken as a good example for the other similar bridges in the city.With the influences of the factors like design, construction, materials and overload, the carrying capacity of the bridges will decrease, and the original internal forces will change too. This reduction of the resistance or the variation of the internal forces may cause local instability or even the collapse of the whole structure. Therefore, before the demolition and during the removal period, it is necessary to analyze and calculate the internal forces for the structure, and to establish a monitoring or alarming system. In this study, the finite element method was used for internal force analysis and demolition system of the continuous reinforced concrete boxed beam, to clarify the variation of internal forces and realize the prediction of the structural state during the process of demolition. Based on the above internal force analysis and verification, the security assurance program and the measures for construction control were proposed.The studies show that, for the different project, using the finite element software for the structural analysis, proposing beneficial suggestions for the construction plan and structural design, and choosing the corresponding construction method and techniques, all these measures could ensure the safety of the removal of the bridges. The content of the present thesis can give practical guidance to the demolition of the boxed beam bridges in the city.