Different Early-age Strength Of Concrete Creep And Creep Under Load For Long-term Effects Of Prestressed Beam

The impact of creep on reinforced concrete structures especially long span prestressed bridge has been valued widely, but the creep nature was studied from the perspective of concrete material and mechanical model in past theoretical and experimental research, the deeper research and close combination are lacked in actual project structure. Most of existing concrete creep prediction models and theoretical calculations are based on above 28d of concrete standard curing specimen, while earlier creep nature and theory of concrete have not been studied systematically.This paper starts from actual project, the combination of laboratory tests and finite element calculation is adopted, four concrete specimens with strength grades ranging from C20 to C50 are designed, the creep characteristics of early-age concrete are summarized theoretically from test results, the creep model for early-age concrete is set up. The prestresss of early-age tension part on the basis of full understanding on creep theory of early-age concrete, and then take tensioning program of remaining prestress until the strength increases and meets design requirements, and good results of new tension program in reducing concrete creep is found by comparing it with traditional tension program. The main research results are as follows:1.The concrete specimens with four strength grades ranging from C20 to C50 to designed to take early-age creep test, the data recorded for 60 days are summarized, the creep characteristics and laws for C20 ~ C50 early-age concrete are derived. In order to understand the long-term creep trend, the relation curve between creep coefficient and time is set up, and the fitting is made, the formula for creep coefficient of early-age concrete is obtained, this is the first experiment & research for early-age concrete made at home and abroad.2.The prestress of early-age tension part is created through establishment of creep theory for early-age concrete, the tension program of remaining prestress is tensioned until the strength increases to meet requirements, and it is found that new program in reducing the creep of prestress component has a significant role by comparing it with traditional tension program. The tension program is the first measure firstly attempting to lower the creep, and the effectiveness of the program has been verified under the conditions of laboratory test and finite element calculation.3. Take construction parameters and conditions of actual works as reference, take simulative calculation on prestress bridge of reinforced concrete based on finite element analysis, take the bridge shrinkage creep in the following decades into consideration, and the internal force value and deformation value of this bridge were on this basis are obtained. The new construction method is firstly applied in actual construction by calculation, providing the basis of numerical calculation for promotion and application of this method in the future.