Study On Temperature Gradient Patterns Of Concrete Rectangular Aqueduct Under Large Temperature Difference Natural Environment

Aqueduct is a kind of important crossing structure to transport water across rivers,roads and valleys.The nonlinear temperature distribution is always generated inside the aqueduct subjected to complex ambient environments during operation.Due to the specific structure of aqueduct it is easy to form excessive thermal stress,which is bound to result in the deterioration of aqueduct surface.For thin-walled structures such as aqueduct,it is easy to develop into concrete penetrating cracks.And it can threaten the normal operation of aqueduct and reduce the operating life.However,there is no specific design-code for aqueduct design,and other relevant design-code don’t give clear guidance on how to consider thermal effect.The temperature difference and temperature gradient of rectangular aqueduct in the large temperature difference natural environment were analyzed based on the finite element numerical simulation.The applicability of the bridge design specification in the aqueduct design was discussed.The effect of structural parameters and water temperature on the temperature gradient were analyzed by finite element method.Through the extreme value analysis,the meteorological parameters under different guarantee rates were gained,and the boundary conditions under different return periods are obtained.The boundary conditions were brought into the finite element model of aqueduct,and the vertical temperature gradient in Xinjiang was obtained by the finite element method.Through the above method,it was extended to different regions of China.The temperature gradient patterns suitable for rectangular aqueduct in different regions of China had been presented.Finally,the influence of surface insulation on temperature gradient of aqueduct is explored.It hopes the present research can contribute to further theoretical support for aqueduct design and safety assessment during operation period.The main work and conclusions of this paper are as follows:(1)The research on the aqueduct heat conduction model considering natural environment temperature is carried out.Taking the rectangular aqueduct in Xinjiang as an example.Based on the finite-element method,the temperature field of aqueduct cross-section was calculated and temperature distribution law was analyzed.Rectangular aqueduct temperature gradient and the applicability of different bridge design-codes in aqueduct design was discussed.The research shows that the rectangular aqueduct will produce a large temperature gradient on its inner and outer surfaces during the operation period(especially when aqueduct is filled with water).Larger temperature stress may be generated on the aqueduct,which can have great impact on the service life of aqueduct.The adverse effect of temperature gradient need be considered in the design.The vertical temperature gradient distribution of rectangular aqueduct is similar to that of box girder stipulated by various bridge design-codes.Nevertheless,there exists certain difference in the characteristic values.The vertical temperature gradient profiles of box girder in bridge design-code are not suitable for direct application.(2)The effect of rectangular aqueduct structure parameters and water temperature on the vertical temperature gradient was studied by finite element method.The results show there is linear change stood out in between water temperature and the vertical maximum temperature difference.Under positive temperature gradient,aqueduct orientation has little effect on the vertical maximum temperature difference(almost no effect under negative temperature gradient).The plate thickness and depth-width ratio of aqueduct have a certain influence on the vertical temperature distribution.However,there have little effect on the vertical maximum temperature difference and vertical temperature distribution trend.(3)The vertical positive and negative temperature gradients of aqueduct were calculated by the meteorological data from June to August and December to February.The meteorological parameters under different guarantee rates were presented by extremum analysis and set as the boundary conditions of aqueduct finite element model.The vertical temperature gradient of rectangular aqueduct in Xinjiang area was calculated by finite element method.In order to facilitate engineering application,the double broken line form was recommended.Based on the division of climate regions in China,through the above method,the vertical temperature gradient patterns of rectangular aqueduct suitable for different regions of China was proposed.The patterns is convenient to be used in conjunction with the current structural design load code.Through theoretical calculation,it was found that rectangular aqueduct will produce large thermal stress under vertical temperature gradient patterns,especially in the case of temperature drop.Thus,the effects of temperature gradient should be considered in the aqueduct design.(4)The finite element simulation of temperature field and stress field of rectangular aqueduct with surface insulation(laying surface insulation board)was carried out.The influence of laying surface insulation board on aqueduct was analyzed.The results show that maximum temperature difference and maximum tensile stress are greatly reduced for aqueduct with roof after laying surface insulation board.In addition,when the thickness of surface insulation board is larger,the surface insulation effect is more efficient.The temperature gradient of aqueduct without roof still exists after surface insulation.However,after surface insulation,the maximum tensile stress is greatly reduced.