Research On Cracking Of Bridge Deck In Cable-girder Anchorage Zone Of Cable-stayed Bridge With Cantilever Assembling Construction

With the application and development of composite beam cable-stayed bridge,its construction methods are constantly improving.Investigations show that during the cantilever construction of composite beam cable-stayed bridges,cracking of the bridge deck in the anchorage area often occurs,which affects the durability of the main beam.In this paper,the cracking mechanism of deck in anchorage zone of composite beam cable-stayed bridge is put forward based on the science and technology plan project of Zhejiang Provincial Department of Transportation,"Research on construction mechanical properties of main girder and anticracking technology of deck".Then,the key issues in the construction process of the "prefabricated cantilever assembly of the main girder of the composite beam cable-stayed bridge" and the "deformation and matching measures of the main girder section of the composite beam cable-stayed bridge" and their effects on the main girder,especially the bridge deck are studied.Affected by the force,finally,reasonable and feasible crack control measures are proposed according to the cracking mechanism of the bridge deck in the anchorage zone and related research content.The main research contents and conclusions are as follows.(1)Summarize the crack characteristics of the anchorage area of the cable and beam of the Taizhou Bay Bridge,the Yueqing Bay Bridge and the Tongminghai Bridge,analyze the stress state of the deck of the composite girder cable-stayed bridge and the cause of the cracking of the deck in the cable-girder anchorage area,and point out the dead weight of the lifting girder and the cable force are the root causes of the diagonal cracking of the bridge deck in the anchorage area.(2)Due to the rapid construction requirements,the current composite girder cable-stayed bridges mostly adopt the construction technology of integral segment prefabrication and wet joint multi-segment cyclic pouring.Precast construction can greatly reduce the impact of concrete shrinkage on composite beams.However,the multi-segment cyclic pouring construction of wet joints will be unfavorable to the force of the main girder,and will also cause deviations in the cable force of the completed bridge.A small secondary cable adjustment is required to achieve the designed bridge state.(3)Through the theoretical analysis and refined finite element simulation of the construction process of suspension splicing of composite girder,the reasons for misalignment and the influence of matching measures are analyzed.The calculation results show that the difference of vertical deformation of the spliced section is mainly due to the weight of the hoisting beam segement being transferred to the cantilever beam segement through the bridge deck crane,which causes the relative vertical deformation of the cantilever beam to be much larger than that of the hoisting beam.According to the reason of section deformation and the influence law of construction factors such as lifting weight and crane station position,the crosssection deformation matching technology such as crane unloading,side web hoisting and reaction frame pre-tensioning is proposed.The above construction technology can greatly reduce the vertical deformation difference of the cross section,but it will adversely affect the force of the main beam and increase the risk of cracking of the bridge deck.(4)According to the cracking reason and location of the bridge deck,starting from the two ideas of "resisting" and "releasing",some technical measures such as local reinforcement,partial combination,local lagging pouring and control of hanging weight in the anchorage zone of cable beam are put forward from two aspects of design and construction.Through calculation,the crack control effect from high to low is lifting weight control technology,local delayed pouring technology,configuration of anti-cracking steel bars and partial combination technology.It is recommended to use the scattered assembly of components when the construction conditions permit to control the maximum lifting weight.When adopting the overall hoisting technology,it can be considered according to the difficulty and influence of each technology from small to large,according to the delayed pouring technology,anti-crack reinforcement technology and partial combination technology,and can also be used in coordination.