Research On Crucial Technologies Of Cantilever Construction Of A 15-Span PC Continuous Box Girder Bridge Across Haizihu Lake

Because of the reduction of the number of expansion joints in the middle of multi-span Long-connected prestressed continuous girder bridges,the comfort and safety of driving are improved,and the durability of the bridge is increased as well.However,each pier provides a fulcrum for the beam in its multi-span and one-connection setting,which belongs to the multistatically indeterminate structure.When the cantilever casting method is used in construction,the longitudinal displacement of the support will be larger than that of the general span continuous beam under the action of external temperature change,concrete shrinkage and creep,and prestress.In addition,the multi-span Long-connected prestressed continuous girder bridge has a variety of spans,the height and cross-section of the main girder are different beacause of different spans,and it can design a variety of closure schemes for closure construction.Under different closing sequence,the construction difficulty and construction period of the bridge are different,and the secondary internal forces produced by the concrete shrinkage,creep and prestress of the beam are different,which casn affect the alignment of the bridge at completion state.What's more,the stress distribution of Block 0 during cantilever casting is complex under the action of temporary restraint and prestress,and it is easy to cause cracks and other diseases.Based on the background of 15-span concrete continuous box Girder Bridge across Haizihu Lake,this paper mainly researches the following important and difficult problems in the cantilever construction of Haizihu Bridge:(1)Six finite element models defining different closure sequence are established by using bridge calculation software Midas.The effects of different closure sequence on the stress,cumulative displacement and secondary internal force of the main girder after closure are compared and analyzed.At the same time,the stress,cumulative displacement and height difference of the main girders on both sides of the closure section in different closure sequence are studied by using mathematical statistics method.The optimal closure scheme is determined to provide useful reference for similar projects.(2)The finite element model of the bridge is established by using the general finite element software Midas,and defining the different stages of bridge cantilever construction in detail according to the design documents of construction drawings.The longitudinal offset of pier and abutment supports under prestress,shrinkage,creep and temperature is studied.The main factors causing the longitudinal offset are discussed.Finally,a reasonable method for setting the longitudinal offset of pier and abutment supports is put forward.(3)For the friction pendulum bearings commonly used in bridge seismic design,the prebias of the bearings are analyzed on the effects of prestress,shrinkage and creep,by comparing the friction pendulum bearings installed with the general types of bearings.(4)A three-dimensional finite element solid model of Block 0 is established by using finite element analysis software ANSYS.The longitudinal and transverse stresses of No.0 block of pier P2 and pier P3 of the Bridge across Haizi lake in 4 stages(the completion of pouring,block No.18 of pouring,maximum cantilever stage and closure stage of the whole bridge)are analyzed,which can provide useful reference for design and construction.