Box Girders Of High Speed Railways And The Deflection Of Control Test Analysis

Prestressed concrete box girders of single box section have following advantages,good overall performance，convenience in construction, low material consumption,bearing loads in a simple and concise form, pleasing shape, enough twist rigidity andhigh construction efficiency, along with small maintenance cost and low noise inoperation. Consequently this type of structure has been widely used for bridges inrailway specialized for transporting passenger and high speed railway. It is obviousthat the quality control of prestressed concrete box girders become the matter ofcommon concern. The main problem is too larger deflection at middle-span andcracking on the bottom flange of beam. Over deformation in girders increase cracking,in turn, the cracks will cause more deformation due to the deterioration of flexuralrigidity. It is shown that both construction quality and the loss of pre-stress contributeto the over deflection at mid-span of beams.Based on the experience of precast construction from Beijing-Tianjin high-speedrailway and Wuhan-Guangzhou high-speed railway, along with experimental resultsof box girders in situ and information from long term observation, the paper presentsthe anti-arch theory、calculation and anti-arch design for box beam with double body,also the analysis of the factors to influence the construction quality in key process andthe quality control. Theoretical calculation and test in situ show that the deformationin the girder meets the requirement. The results given in the thesis are of referentialvalue and provide application experience to other domestic construction project of thesame type of structures. The research contents are summarized as follows. he studythe following four aspects.1) The calculation and design of pre-setting anti-arch.2) The detail examination of factors to affect the deformation of box girders inkey construction procedure including the profusion of high-performance concrete andstretch-drawing of girder body.3) Static experiment of box girder and deflection evaluation.4) Statistics of long term observation data in some box girders in service, and themodification of calculation approach of pre-setting anti-arch on the basis of testresults.By calculation and experiment, we get following results and conclusions,(1) the value of pre-setting anti-arch by post-tensioning method is17.85mm;(2) the ratio of deflectionto span length under static living test loading is0.9957/6811(<1.05/533), and passed thequalification check;(3)The statistics result from long term inspection of deformationis19.19mm, and it is close to the prediction value by theoretical estimation.