Research On Causes And Countermeasures Of PC Beam Bridges Deflection

Long Span Beam Bridges develop fast aroud the world.P.C. cntinuous rgid fame bidge has broken the record of 300m,and the longest prestressed concrete-steel cntinuous rgid fame bidge has a main span of 330m.Recently,deflection in the mid-span of P.C. cntinuous rgid fame bidge has been increasing,which troubles brdige engineers.This article is written about the study on the factors which influence bridge deflection.(1) Summarize the research on the courses of deflection in continuous rigid frame bridges,and point out the problem;(2) Summarize the requirements on temperature effect of prevailing domestic and overseas bridge specification, compare and analyse the total temperature gradient stress, primary stress and secondary stress through finite element software. Compare temperature gradient effect of three commonly used pavement according to JTG D60-2004. General Code for Design of Highway Bridges and Culverts[S].Appropriate temperature gradient and pavement should be chosen during the process of stucture analysis;(3) Comparation and analysis are executed to decide wether or not draped tendons in the webs are necessary. Draped tendons can decrease principal tensile stress of the concrete box girder and increase principal compress stress; They also provide the vertical shear forces in the opposite direction and offset some of the shear forces, enhance the the shear capacity. If the validity of vertical prestress can be guaranteed effectively, the principal tensile stress can also be inhibited;(4) Parametric analysis is taken on web thickness, beam height and the soffit curve of the main girder. Web thickness has significant effects on structure weight,but has less significant effects on improving the bearing capacity the structure; The actions caused by the height variation in the midspan is larger than that in the support;If the soffit take a larger exponentiation,it can suffer fewer radial forces; (5) During the design of long-span P.C beam bridges according to JTG D60-2004. General Code for Design of Highway Bridges and Culverts[S],crack resistance and maximum compressive stress should both be taken into sight,which is difficult;(6) Based on the analysis,countermeasures of deflction in P.C. beam bridges are put forward.