Experiment Study On Long-term Performance Of Concrete Cable-stayed Bridge

The structural behavior caused by shrinkage and creep effects of long span concrete bridge is a complicated problem which has not been resolved completely but needing resolved urgently in bridge engineering. In conjunction with a project "Concrete cable-stayed bridge model test" of Huizhou city, Guangdong province, a series of experimental and analytical research on the shrinkage and creep effects of the real and model bridges had been performed, in order to obtain structural behaviors of long span concrete bridges under non-loading actions. The main investigations are summarized as follows:(1) Design and fabrication of model bridgeIntroduced the theroy of model test, including model bridge design criteria and requirements; model bridge fabrication, testing content, et al. Based on the scheme design of Hesheng Bridge in Guangdong Province, a large prestressed concrete cable-stayed bridge model (1:15) was made on site. The beam and towers are made of concrete materials, and the cables using the same high-strength cable wires with the real bridge. The elastic moduli of concrete of different load ages have been tested in order to afford a reference for finite element analysis.(2) Creep and shrinkage tests and analysis of the model bridgeThe cable-stayed model bridge and prism specimens were made on site, with the same maintenance conditions. Long-term performance tests of cable-stayed model bridge and prism specimens were performed and porposed a conrete creep model of real and model bridge under the natural environment.Experimental observations of the cable-stayed model bridge showed that: time-related prestress loss of the main beam was3.6%, the upstream and downstream tower was respectively3.0%,2.0%. The side span support reaction was remain basically unchanged, the main span and auxiliary pier bearing reaction showed an increasing tendency over time. Creep strain was between55～85με. The main beam maximum displacement was3.0mm. the displacement caused by bridge tower shrinkage and creep occupies the total displacement30%～60%. Tension of the two pairs of cables near main span beam end had a large change, decreased by6.5%. As the measured creep curve of concrete prism specimens didn’t contain volume to surface ratio(V/S) parameter, so modified it according to the V/S considerable method of JTGD62model, GL2000model,respectively, obtained two concrete creep models:TEST-JTG model and TEST-GL model which can be applied to calculate long-term performance of concrete structure. JTGD62, ACI209R, GL2000, TEST-JTG, TEST-GL models are used to analyze creep effect of the model bridge, compared the calculated results with the measured data of strain, displacement and cable force, verify the applicability of TEST-GL model. The results also show that, the three kinds of models JTGD62, ACI209R, GL2000, the results of last model are closest to the measured data.(3) Test and long-term performance prediction of the real bridgeWe tracked the whole process of the construction monitoring, and conducted a number of test of the full bridge elevation and cable force on operational status. Compared the theoretical calculations and experimental results, and evaluated the results of three creep and shrinkage models, they are JTGD62, ACI209R and TEST-GL, in which; the results of TEST-GL model were in good agreement with the measured data. After the bridge had been operating for two years, the measured largest vertical displacement of the mid-span is about23mm, according to the TEST-GL model,5and10years later the predictive value is37mm.52mm. respectively. The transverse displacement of bridge tower is-1.41mm, so, it can be seen that the transverse displacement is almost zero.10years later, the tower will lean to the mid-span14.8mm.2years later, the measured biggest change in cable tension was3.8%,10years later, the predicted biggest change in cable tension was6.0%,7.7%after20years.(4) The initial equilibrium configuration determination method which can consider the creep and shrinkage effect of concrete cable-stayed bridgeIn order to predict the long-term performance of concrete cable-stayed bridge, the initial equilibrium configuration of cable-stayed bridge that considered the effects of shrinkage and creep was established. Based on the general iteration methods of cable force simulation, a method for accelerating iteration is obtained from the two aspects including the selection of initial values and over-relaxation iterative method. Modeling coordinate iteration method for bridge line-shape correction is given, and in company of accelerated iteration method are successfully applied in the modeling of initial equilibrium configuration of cable-stayed bridge, by collecting the construction records of the concrete cable-stayed bridge,creep and shrinkage effect can be considered in this model, so the initial equilibrium configuration of cable-stayed bridge established by these methods gives an adequate simulation of cable force distribution and bridge line-shape, and it can be used to several follow-up analysis, such as the long-term performance prediction of concrete cable-stayed bridge, the ultimate bearing capacity calculation etc..