The Reasonable Structure Of Long-span PC Continuous Rigid Frame And Web Crack Research

No matter structural or construction technology,long-span prestressed concrete girderbridge has very good adaptability and operability.So in the design of the highways and rail-roads,it is increasingly being used by enginneers.With upgrade of the bridge design softwa-re,progress of design engineer’s experience and level,make use of new materials and newtechnology,prestressed concrete continuous girder bridge tends to large-span.At the sametime,with the growing traffic demand,the box girder become more and more wide and lig-ht-weight,blazonry will cause vertical height decrease.The deformation of large-span prest-ressed concrete girder bridge under the operating period is generally lower than the designvalue. And the cracks of the prevalence diseases in the long-span prestressed concrete cotin-uous rigid frame.The main purpose of the paper is to study the parameters of the prestressed concrete co-ntinuous rigid frame, analyse the structure stress and the downwarping under the different pa-rameters.And to research the causes of the cracks in the box girder.Through the two parts rea-serch,presenting the reasonable structure of Long-span PC continuous rigid frame and the w-ed thickness,summarized a Long-span PC continuous rigid frame bridge design parameter ref-erence list for the designers.This paper deals with the structural aspects of the prestessed concrete continuous rigid f-rame how to alleviate the trend of downwarping and the body crack.In order to analyse this p-roblem,the paper collects both at home and abroad that the long span more than100m of pres-tressed concrete continuous rigid frame’s parameters.The main design parameters（the fulcru-m high-span ratio,mid span high-span ratio,power of the beam bottom parabolic curve,and rat-io between side span and main span）of prestressed concrete continuous box girder. Throughthe use of special birdgr design software,these parameters are being changed,combine withengineering example.The impact of changes in these parameters on stress of box bridge and d-ownwarping is calculated.Then the characteristic of web is studied.Especially analysed the re-ason of the web cracks——principal tensile stress of web.To analysis the changes of differentweb thickness in diffrernt form along with the longitudinal,the influencing of principal tensile stress and deflection of box girder bridge,the result that adopting relative alleviation form canimprove the principal tensile stress and downwarping.The web stress is considered under spe-cial unbalance loading condition and calculated using plane and space finite element program.Vertical prestressed also help to improve the web cracks，but the loss of the vertical prestresswill cause the problems of the increasing of principal tensile stress and the development of theweb inclined cracks.The improve suggestions are put forward in this paper.