| In recent years, a large number of long-distance water projects have been constructed in our country, especially aqueduct, to overcome the very uneven water resource distribution of China. Among them there is Gansu Tao Diversion Project, which is located in high altitude area with large temperature difference and strong solar radiation. In the process of summer watering, concrete box aqueducts prone to produce temperature stress, and this needs to be given adequate attention. With the gradual increase of the scale of various types of aqueduct, its research is slightly lagging behind, especially the study about box body temperature effect on sunlight and its crack control measures. To this end, regarding the Liulin ditch aqueduct of Tao Diversion Project as an example, this paper has studied the process of box aqueduct temperature effect on sunlight and conducted a preliminary discuss of its surface insulation, to provide a reference for engineering practice.This paper has analyzed the reason why the sunlight temperature difference of box aqueduct could be caused, and calculated the initial conditions and boundary conditions of it on sunlight temperature field. The plane analysis model has been established by using finite element theory, to carry out the process of concrete box aqueduct temperature effect on sunlight with the finite element software ANSYS. It is shown that the box aqueduct’s sunlight temperature distribution is very complicated, and the roof temperature changes most intensely, followed by sternum, the sole plate minimum. When the box aqueduct is directly exposed to the nature, there is a high-outside and low- inside trend of temperature distribution in the body, and the temperature difference between inside and outside is large, thus tensile stress appears in the external and compressive stress appears in the internal. With the change of the weather conditions in summer day, the maximum tensile stresses that the structure bear are beyond the concrete design value of tensile strength(1.43 MPa) at most times, which is easy to make the aqueduct cracks. Therefore, appropriate insulation measures needs to be taken in the surface of the aqueduct to prevent cracks.This paper has comparatively analyzed the temperature field and thermal stress distribution of aqueduct body, which is laid polystyrene board or polyurethane insulation layer whose thicknesses are respectively 20 mm, 35 mm and 50 mm. After insulation, the maximum temperature of the aqueduct structure has been significantly reduced, and the maximum temperature difference between its inner and outer surfaces has also decreased, thus the temperature stress has been effectively reduced. The temperature stress can be in the range of the tensile and compressive strength of concrete. With the increase of the thickness of the insulation material, the outer surface temperature decreases gradually. This study has shown that insulation effect of the same material increases along with the increase of thickness, and the thicker the insulating layer is, the better the insulation effect is. But the reducing process of the aqueduct temperature stress is showing the tendency of intense at first and then slowly. The insulation effect of insulation materials with same thickness only depends on its thermal conductivity, and is inversely proportional to it.This study has compared the temperature field and thermal stress of box aqueduct on sunlight in summer, which is with insulation measures or not. One can see the influence effect of surface insulation on the temperature field and stress of box aqueduct, and come to a series of conclusions to provide theoretical basis and technical support with reference value for the design and construction of box aqueduct. |
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