| Creep is an inherent time-varying property inherent in concrete materials,and its effects run through the construction of concrete structures and throughout their service life.Creep has a significant impact on the linear shape of long-span concrete bridges,which is one of the core technical difficulties of large-span concrete bridges.Using the creep prediction model to simulate the bridge is the mainstream method to analyze the creep deformation of the bridge.However,the existing prediction models are derived based on the regression results of the experimental results,which are inevitably different from the actual situation.In addition,most predictive models do not adequately consider the ambient temperature and humidity,which increasingly affects the accuracy of model prediction.Therefore,in order to accurately analyze the shrinkage and creep effect of actual engineering concrete and to study the method of reducing the shrinkage and creep of concrete,this paper adopts the research idea of combination of creep test and finite element simulation.The main research contents are as follows:1)The engineering concrete material was used to test the compression and creep of concrete test blocks,and the difference between the measured data and the prediction results of different prediction models was compared and analyzed.The results show that there are great differences between the prediction results and the measured values of different creep prediction models.The early creep prediction models JTJ 023-85 and CEB-FIP78 models overestimate the shrinkage and creep of concrete,and the deviation reaches 37.5%,and this difference will continue to expand over time.The predicted values of JTG D62-04 and CEB-FIP90 models are close to the measured values,and the deviation values are 6.3% and 5%,respectively.Aiming at the short-term holding time of indoor creep test,based on the creep prediction experience established by Borox and Neville,the long-term creep development of the concrete is presumed.The speculative process further validates the phenomenon of “increasing the time of shortterm creep test,which can effectively improve the prediction accuracy”.Finally,a short-term and long-term creep prediction model suitable for C55 concrete is obtained.2)The bending and creep tests of concrete beams were carried out under the two conditions of “constant temperature and humidity” and “temperature and humidity”,and the development law of concrete shrinkage and creep under two environments was compared and analyzed.The test results show that: The creep development under the environment of “temperature and humidity” is extremely significant due to the influence of ambient temperature and humidity,while the shrinkage and creep of concrete in the “constant temperature and humidity” environment has been a steady upward trend.Within 60 days,the shrinkage and creep development was extremely rapid,about 70% of the total shrinkage and creep,and the later development gradually slowed down.In addition,the test proves that when a certain critical temperature and humidity are reached,the increase of creep is much lower than the influence of the environment.The overall performance is that the concrete creep is positively correlated with the temperature,negatively correlated with the humidity,and the concrete creep is affected.The effect of ambient humidity is greater than the impact of ambient temperature.3)The creep test of the concrete mix ratio optimization design was carried out.The method of reducing the shrinkage and creep of high performance concrete was studied by adjusting the proportion and total amount of mineral powder and fly ash.The design of the ratio of mineral powder and fly ash is 1:1,1:2 and 2:1.There are 6 sets of test pieces,of which the total content of mineral admixture is 10%,22 of cementitious material.%,30%.The test results show that the mineral admixture has a great influence on the shrinkage and creep properties of high performance concrete.After 180 days of age,the maximum difference of shrinkage strain of the six specimens is 43με,and the creep strain is the largest.The difference is 126 με.When the total amount of mineral admixture is constant,the larger the proportion of mineral powder and fly ash is,the larger the concrete shrinks and the smaller the creep.When the proportion of mineral admixture is constant,the effect of the increase of total blending on shrinkage is firstly increased and then decreased,and the creep increases with the increase of total blending.When controlling a single variable,the amount of mineral powder is inversely proportional to the shrinkage and creep of high-performance concrete,and the amount of fly ash is inversely proportional to the shrinkage of highperformance concrete,which is proportional to the creep.Combined with the actual engineering situation,a better set of concrete mix ratios was selected,and the concrete creep was prepared for the finite element simulation to set the creep effect.4)The simulation analysis of the creep deformation of cable-stayed bridges was carried out using Midas Civil software,and the differences between the short-term and long-term deformation results of different creep prediction models were compared.The simulation results show that the simulation results using JTG2004 model and CEB-FIP90 model are close to the simulation results of this paper.The deviation from CEBFIP90 model is 6.4%,and the deviation from CEB-FIP78 model is the largest.69.9%.In addition,the existing creep prediction model simulation results overestimate the deformation performance of the bridge,and the difference will increase with time.Taking the CEB-FIP90 model as an example,the deviation value of the first year is 0.98 cm,and in the fifth year,the deviation value is 1.37 cm,but after the 10 th year,the difference is increased to 1.91 cm.By comparing and analyzing the temperature and humidity effects and simulating the deformation values of the bridge before and after considering the effect of temperature and humidity,it is found that the simulated difference caused by the two environments reaches 1.92 cm,which indicates that the ambient temperature and humidity have a great influence on the concrete creep. |
PDF Full Text Request