Flexural Behavior Of Prestressed RPC-NC Composite Girder

With the rapid development of high-speed railway,the requirements for the behavior of bridge structure have exigent.The proper application of high performance material is an effective way to improve the performance of structures.In order to promote the application of high performance concrete in modern bridge structures,this paper proposes to apply reactive power concrete at the lower part of prestressed normal concrete girder,thus forms a kind of prestressed reactive powder concrete and normal concrete composite girder.This composite girder makes full use of the ultra-high mechanical performance and good durability of reactive powder concrete as well as the adequate compressive strength and low cost of normal cocrete.A theoretical and experimental research on the flexural behavior of prestressed reactive powder concrete and normal concrete composite girder was conducted.Based on the similarity theory and the railway standard girder No.2101,the static loading tests on the flexural behavior of prestressed reactive powder concrete and normal concrete composite model girders were performed.The experimental results show that the ductility of the composite girder increased with increasing RPC height,under the same prestress level;the first cracking load increased significantly with increasing prestress level,under the same height of reactive powder concrete;these prestressed reactive powder concrete composite girders exhibited typical flexural failure pattern in which the concrete crushing occurred as well as the rebar yielding at the peak load;the progress of mid-span deflection-load curves of prestressed reactive powder concrete and normal concrete composite girder could be divided into four stages,namely,the elastic stage before cracking,inelastic stage with cracking developement,hardening stage after the yielding of steel bars and descending stage after peak failure;the development of strains at the mid-span of composite girders basically agreed with the assumption of plane section;no sliding occurred at the interface between reactive powder concrete and normal concrete during the test,which indicated that the reactive powder concrete and normal concrete can work well in composite girder.Depends on the constitutive relations of materials and sectional analysis method,a nonlinear full-range analysis of prestressed reactive powder concrete and normal concrete composite girder under bending loads were conducted,the calculation results agreed well with the test results;on this basis,a comprehensive analysis of influencing factors on flexural behavior of prestressed composite girders were performed;based on the calculation of first cracking load,a reasonable range of reactive powder concrete height was determined to be 22%?53%of the total sectional height for prestressed composite girder.Based on the results of test and full-range analysis,the formulas and method for predicting the first cracking load,yielding load and ultimate load of prestressed reactive powder concrete and normal concrete composite girder were proposed,which considered the tesile strength and heights of reactive powder concrete.The code formulas for the crack width and the short-term stiffness of composite girder were modified on the basis of test results to consider the high performance of reactive powder concrete;the influencing factors on the ductility of composite girder were analyzed,the formula for predicting ductility was fitted based on the test results.The crack damage process of prestressed reactive powder concrete and normal concrete composite girder under bending loads was analyzed based on the acoustic emission technique.Reactive powder concrete material had a facility of dispersion crack,and numerous micro cracks occurred under loads.The results show that the accumulate hits number of prestressed composite girder is much larger than that of prestressed normal concrete girder under the same load when the number of steel strands is identical;Before loading,the average wave velocity of reactive powder concrete is 4342.8 mm/s,while the velocity of normal concrete is 2337.7 mm/s;the acoustic emission Ib value was calculated and compared with the test process of prestressed reactive powder concrete composite girder.The comparative results indicate that there is an obvious correlation between the Ib value and damage fracture process of prestressed composite girder.And the lb value could predict the final failure in some extent.The lb value intervals corresponding to different fracture stages were provided,this found an experimental basis for the application of acoustic emission in practical engineering and damage identification.