Creep Model And Application Of Fiber Reinforced Concrete Under Cyclic Load And Varied Temperature And Humidity

Creep is the inherent time-dependent property of concrete,and how to accurately analyze the influence of creep on the long-term behavior of concrete bridge is a major problem.At present,a lot of research work has been carried out on concrete creep at home and abroad.Various creep models for analyzing the long-term performance of concrete structures have been proposed.However,theoretical analysis and engineering practice show that the error of long-term behavior of bridge structures can often reach more than 20%?60%when the current creep models were used for analyzing.The main reason is that the cyclic loading of traffic and varied temperature and humidity are not taken into account.Therefore,it is of great theoretical significance and engineering application value to study the creep model of concrete under cyclic load and varied temperature and humidity.Based on the research background of Hong Kong-Zhuhai-Macao Bridge and supported by the major research projects of Hong Kong-Zhuhai-Macao Bridge,this paper systematically studies the creep effect of Fiber Reinforced High Performance Concrete(FRHPC)of Hong Kong-Zhuhai-Macao Bridge.Considering the cyclic effects of traffic loads and the actual varied temperature and humidity in natural environment,the CEB-FIP(1990)model adopted by China's bridge code is revised.The creep model of FRHPC of Hong Kong-Zhuhai-Macao Bridge under cyclic load and varied temperature and humidity was proposed.The creep behavior of steel-concrete composite continuous girder bridge of Hong Kong-Zhuhai-Macao Bridge is analyzed.The research results provide theoretical basis and technical support for the long-term performance prediction of Hong Kong-Zhuhai-Macao Bridge,and also have important reference for the long-term performance study of similar offshore bridges.The main innovative achievements are as follows:(1)A creep model of Fiber Reinforced High Performance Concrete for Hong Kong-Zhuhai-Macao Bridge is established(FRHPC Model).In order to improve the crack resistance and durability of the steel-concrete composite continuous girder bridge of Hong Kong-Zhuhai-Macao Bridge,the Fiber Reinforced High Performance Concrete developed by our research group is adopted.Unfortunately,the existing creep models are not suitable for creep performance analysis of FRHPC,therefore,the creep test of FRHPC for 180 days was carried out,and the creep properties was obtained.Based on the CEB-FIP(1990)model and the experimental data collected,a creep model named FRHPC Model,considering the influence of fiber content on the creep properties of high performance concrete,was established by modifying nominal creep coefficient and creep time development coefficient by?_fc and?_fc,respectively.The error between the predicted value and the experimental result was3.3%at 180 days of loading,which provides support for accurate prediction of long-term creep behavior of steel-concrete composite continuous girder bridges of Hong Kong-Zhuhai-Macao Bridge.(2)A creep model of Fiber Reinforced High Performance Concrete under cyclic load is proposed(CFRHPC Model).Cyclic loading can significantly increase the creep effect of concrete,however,the effect of cyclic load on creep are not taken into account by current creep models.In this paper,creep tests of Fiber Reinforced High Performance Concrete specimens under cyclic load were carried out.According to the most disadvantageous stress state of bridge structure,the average loading stress is 0.4f_{c p} and the stress amplitude is 0.2f_{c p}(f_cp is the axial compressive strength).The cumulative times of cyclic loads are 120,000,300,000 and 540,000.Consequently,the creep development law of fiber reinforced high performance concrete under different times of repeated loading is obtained,and the non-linear relationship between the times of repeated loading and creep coefficient is established.Based on the FRHPC Model,the creep model of FRHPC under cyclic load,namely,CFRHPC Model,is proposed by introducing the influence factor?_cyc=1.095×(N N₀)^0.075of cyclic load.In addition,on the basis of specimen test and the CFRHPC Model,a set of three-point creep loading device was designed to carry out creep test of Fiber Reinforced High Performance Concrete beams under cyclic load.The results show that the predicted value of CFRHPC Model is in good agreement with the measured value at 180 days,and the maximum error is 4.3%,and the CFRHPC Model is verified.(3)A creep model of Fiber Reinforced High Performance Concrete under varied temperature and humidity is established(TFRHPC Model).The effect of temperature and humidity on concrete creep is significant.At present,the fixed annual average temperature and relative humidity are used to analyze the long-term performance of bridge structure,which is seriously inconsistent with the actual varied temperature and humidity in natural environment.Based on the least square method,the time-varying functions T(t?)and RH(t?)of temperature and relative humidity are proposed through statistical analysis of the actual climate data of temperature and humidity,and the relationship between the time-varying functions of temperature and humidity and CEB-FIP(1990)Model is established,and the feasibility of the method is verified by experiments.Based on this,a creep model,TFRHPC Model,of Fiber Reinforced High Performance Concrete under varied temperature and humidity is established,which provides a theoretical basis for the analysis of long-term creep of bridge structures considering the environmental actual temperature and humidity.(4)The creep behavior of steel-concrete composite continuous girder bridge of Hong Kong-Zhuhai-Macao Bridge is obtained.Based on the forecast traffic volume of steel-concrete composite continuous girder of Hong Kong-Zhuhai-Macao Bridge,the influence coefficient of cyclic load?_cyc is determined.According to the meteorological data of actual temperature and humidity at the bridge site,the time-varying functions of varied temperature and humidityT_{HZ M}(t?)and RH_{HZ M}(t?)are proposed,and four creep models for long-term performance analysis of steel-concrete composite continuous girder bridge of Hong Kong-Zhuhai-Macao Bridge are established,namely FRHPC Model,CFRHPC Model,TFRHPC Model and TCFRHPC Model.Based on that,a refined finite element model is established to simulate the construction process according to the actual whole process,and four creep models are embedded into the finite element program.The stress and deflection of the main girder in the positive and negative moment zone of the steel-concrete composite continuous beam bridge of Hong Kong-Zhuhai-Macao Bridge in 30 years are analyzed.The results show that the creep effect of TCFRHPC Model considering the effects of cyclic load and varied temperature and humidity is the greatest.The maximum creep deflection of side span reaches 12.21 mm in 30 years,and the Fiber Reinforced High Performance Concrete slabs in negative moment zone of 2#?6#pier are still in compression state.