Study On Temperature Field And Temperature Stress Of Hydration Heat In Bridge Massive Concrete Cushion Cap

The problems related to massive concrete were first proposed in the construction of water conservancy projects.With the rapid development of bridge construction in China in recent decades,the requirement for bridges with large span is getting higher and higher.More and more massive concrete cushion caps,abutments,bridge piers,zero blocks,anchorages and other components appear in the construction of bridges.To reach the strength standard,ordinary strength concrete or high strength concrete is normally used in massive concrete components of bridges,which is different from large hydraulic structures that often use roller compacted concrete with low hydration heat.During the construction process,the hydration reaction of cement in large volume components of bridges will produce a huge amount of hydration heat.Due to the poor thermal conductivity of concrete,the hydration heat accumulates continuously inside the components,causing large temperature differences between internal concrete and outer surfaces,which may bring about large tensile stress on the surfaces of concrete components.Temperature cracks will appear if the tensile stress exceeds the allowable tensile strength,leading to serious impacts on the working performance and service time of structures.Thus it is of vital importance to research the temperature field and temperature stress of hydration heat in bridge massive concrete.This paper takes the Fu River Bridge,which is a part of the fourth ring road in northern Wuhan,as the research object.On the basis of computational theories of temperature field and temperature stress,a computing program is compiled using the APDL language of ANSYS finite element software to simulate and analyze the temperature field and temperature stress of massive concrete cushion cap which takes the cooling effect of water pipe into consideration.The main contents of this paper are as follows:(1)The development history and research status of many aspects relevant to massive concrete and cooling pipe are systematically reviewed,such as theoretical researches,experimental researches,numerical simulation studies.etc.This provides a useful reference for the research in this paper.(2)According to the computational theories of concrete temperature field considering the cooling effect of water pipe,this paper applies heat flow coupling method to simulating the convective heat transfer between concrete and water pipe and elaborates on the realization process of transient thermal analysis in ANSYS.According to the FEM calculation results of temperature and temperature time history curves of characteristic points in the cushion cap,this paper concludes the features of temperature field of hydration heat in massive concrete and analyzes the impacts of some changes on the concrete temperature field.These changes include layered pouring,dismantling thermal insulation material,and stop water in water pipe.This paper also introduced the temperature monitoring process of cushion cap.A comparison is made between temperature monitoring results and FEM calculation results to analyze the sources of the error and verify the accuracy of the finite element model.(3)On the basis of FEM computational theories of temperature stress,this paper applies the indirect method of thermal stress analysis to calculating the temperature stress of cushion cap and elaborates on the realization process of the transition from transient thermal analysis to structural analysis.This paper uses the equivalent stress calculated according to the fourth strength theory to research the development of maximum tensile stress of elements on the cushion cap surfaces and elements near the water inlet.The development of the concrete stress inside the cushion cap is studied according to the positive stress in the direction of X.The distribution features of temperature stress in the cushion cap is obtained and the cracking of concrete on the surfaces of the cap and near the water pipe is estimated.(4)The influence of four variables on the cushion cap's temperature distribution,temperature differences between the internal concrete and outer surfaces,and occurrence time of maximum temperature is studied respectively.The four variables are concrete pouring temperature,water inlet temperature,velocity of water flow,and the duration of water cooling.This paper also proposes some suggestions on temperature control from the perspectives of the concrete raw material selection,pouring temperature control,cooling pipe,and insulation measures on the cap surfaces.