Research On Temperature Effect Of Fiber Reinforced Concrete Of A Cable-stayed Bridge

Fiber reinforced concrete box girders of extradosed cable-stayed bridges are subjected to various temperature effects from pouring to operation,including hydration heat of cement,sunshine temperature and annual temperature caused by environmental changes.The temperature effect of box girder is very important to control because of the large temperature stress which may lead to the cracking of fiber reinforced concrete and affect the long-term durability of bridge structure under the temperature effect and certain constraints.Especially for extradosed cable-stayed bridges with fiber reinforced concrete,the problem of temperature effect is more complex,and the mechanical and thermal properties of fiber reinforced concrete are different from those of ordinary concrete.There are few studies on the temperature effect of extradosed cable-stayed bridges with fiber reinforced concrete,so it is necessary to conduct in-depth research.Taking the South-to-North Water Transfer Bridge as the background project,this paper studies hydration heat temperature effect and long-term temperature effect of fiber reinforced concrete extradosed cable-stayed bridge,and puts forward some design suggestions for temperature control and crack prevention of the fiber reinforced concrete for the background bridge.The main work includes:(1)Through microcalorimetric test,the change rule of hydration exothermic rate and total amount of hydration exothermic heat with time is obtained.The results show that polypropylene fiber can reduce the increase of hydration exothermic heat caused by adding additives in concrete.Then,combined with literature,other relevant thermal and mechanical properties parameters of block zero fiber concrete are determined.(2)The temperature field and stress field of null block under hydration heat after pouring were analyzed by means of thermal-structural coupling method(indirect sequential coupling).By comparing the calculation results of the hydration heat release characteristics of the background bridge fiber concrete with that of the ordinary concrete,it is found that the background bridge fiber concrete is more disadvantageous to the temperature control and crack prevention of block zero.(3)In order to understand the influence of different influencing factors on the hydration heat effect of fiber reinforced concrete null block,the effect of ordinary steel bars,possible changes of thermodynamic and mechanical parameters and other construction measures and methods in the background bridge fiber reinforced concrete null block are analyzed.It is found that reducing the surface heat exchange coefficient,reducing the heat release of concrete and lowering the molding temperature play an obvious role in reducing the temperature difference between the center and the surface of the structure.(4)In order to study the long-term temperature effect of fiber reinforced concrete,the whole temperature change and sunshine temperature effect of the background extradosed cable-stayed bridge under completed condition are calculated and analyzed.Considering the change of sunshine temperature effect in one year,the fatigue load spectrum of the background bridge under temperature action is established,and the damage model based on continuum damage mechanics is determined.The fatigue of fiber reinforced concrete on the top of box girder under long-term temperature load is studied.Damage calculation shows that the existing fatigue damage of fiber reinforced concrete caused by long-term temperature load is far from the critical value of fatigue damage.Then the load coefficient of fatigue design for long-term temperature load is put forward.(5)Based on the analysis results of the influence of various factors on the temperature and stress fields of fiber concrete box girders and the existing literature,the temperature control and crack prevention suggestions for the fiber reinforced concrete of background bridge are put forward.