| Technological innovation and industrial upgrading of bridge demolition and replacement have gradually become research hotspots in the field of bridge engineering in recent years.Urban bridges in normal operation are inevitably damaged due to their material properties and the dynamic or static loads of surrounding environments.The accelerating demolition construction of urban bridges has extremely safety requirements in the construction stage because of problems such as tight schedule,great social influence,and great difficulty in construction.In this paper,according to the widely used prestressed concrete girder bridge applied in urban bridges,the accelerating demolition construction process based on SPMT was introduced,and the beam at various stages of the accelerating demolition construction was analyzed.Finally,a calculation method for accelerating demolition of bridges was established to evaluate the safety of the construction scheme.Based on the engineering example of the Beizhai Road Viaduct BDLK1-3 Demolition Project which is a(33+33+33)m prestressed concrete curved slope beam bridge,the main achievements are as follows:(1)Based on the accelerating demolition method of SPMT module car,and the analysis of the accelerating demolition process and key technical problems of existing prestressed concrete girder bridges,the demolished beam body may be reused(such as the displacement of the upper structure of the bridge,the bridge body needs to be accelerating),also may be removed temporarily and processed for other reasons.So the beam is required transport safely to bracket for storage.In order to ensure the safety of the construction,it is necessary to evaluate the bearing capacity of the box girder before the removal of the load without considering the live load,but considering the prestress loss.Based on this,the cutting segment is determined.In order to ensure the safety of each segmented beam body,this paper studies the analysis method of box girder structure before accelerating demolition,which is based on the analysis principle of single-box and three-room curved girder bridge structure.Through the state analysis of the bridge before cutting,the laws of the bearing capacity of each beam before cutting are obtained.Through the analysis of the bridge state after the system transformation,the displacement and stress characteristics of each section of the beam after the system transformation are obtained.These results also provide a basis for the subsequent refinement analysis to obtain the corresponding warning values and limits for the safety of the structure during the removal.(2)In order to monitor the stability and structural safety of the continuous beam during the overall transportation in the actual demolition construction,the relative vertical displacement of each monitoring point in the moving process is monitored in real time to ensure that beam doesn’t slip or overturn due to the failure of the local support system,and doesn’t damage due to stress of the partial section is too high.In this paper,the refined analysis method of beam structure in dangerous working condition is studied,and the characteristic and law of spatial displacement and stress of beams in each section of demolition are obtained.Through these results,it can be used not only to study the structural safety of the beam during the removal,but also to be used for the corresponding warning value and limit of the beam structure safety during the removal for the actual demolition construction monitoring. |
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