Research On The Prestress Losses In The Vertical Pre-stressed Of PC Concrete Box Girder Bridge

With the development of science technology and traffic enterprise, The prestressed concrete (PC) box girder bridges ridge has been growing up rapidly in the recent years with it's unique predominance of handy construction, economical cost,Reasonable internal force and comfortable traveling.However, numerous investigations indicate that the representative cracks, especially skew cracks developin the bridge web. The skew cracks have effect on the appearance, bearing capacity, service life of the bridge and even the traffic safety. The causes of skew cracks in web are multiple. The losses of vertical prestressing is a very important reason which have not been resolved completely but needing resolved urgently in bridge engineering.This paper based on the program of transportation developments in west --"the research on cause and treatment technology of the contentious box girder bridge and continuous rigid frame box girder bridge", which program take on by ministry of communications highway research institution and participated by the Changsha University of Science and Technology, on the background of the Lin zi kou long-span bridge and lu shui long-span bridge in hunan province,a series of experimental and analytical research about the losses of vertical prestressing have been performed in this dissertation.The analysis indicated that the stress loss of vertical prestress caused by deformation of anchorage, the resilience of the tendon and the joint compression(σl2) is the largest reason of all and also the hardest to control;The elastic compression of the concrete(σl4) is more small .This thesis simulated the process of the constuction through establishing the local thress dimentional model ,and combined some method of the elasticity mechanics to advance the simplified calculation expression for elastic compressive loss of vertical prestressed reinforcement.Toword the loss of the concrete shrinkage and creepσl6.This paper make use of the software ANSYS which offered by the APDL to set up the local model of the girder beam model, and is applied the creep of the program to carry on the calculation of concrete shrinkage and creep of the girder beam model. On the base of the calculating results, the stress in the box girder webs and the stress loss in the vertical pre-stressed steel bar were researched. The rule of box girder webs stress and the vertical pre-stressed was effected by the concrete shrinkage and creep when it was working. And then the paper also predigest the calculation method of the nowadays criterion.Moreover this text even analyzed every representative factor influencing the stress loss in the vertical pre-stressed ,for example the incline of the anchoring plank ,the slippage and the seting excursion of the teinforcing steel bar and so on . The paper also sumed up the amelioration measures about the construction through consulting a great deal literatures and advanced some attitude and advice in myself .