Bedding cushion cracking in concrete dam is widespread, and has not been completely prevented [1,2]. There are many cracking causes of bedding cushion, including construction difficulty and structure requirements for concrete dam. Based on the method of FEM simulative calculation of temperature and stress fields of mass concrete using water cooling pipes, this paper makes relatively in-depth study on crack mechanism for concrete bedding cushion on rock. It is revealed that all three factors of uneven thickness of bedding cushion, thickness of new dam concrete placed on cushion after off period and foundation gallery upon bedding cushion have great influence on the tensile stress of bedding cushion and should be paid special attention during construction. The calculation results show that the tensile stress of thinner concrete cushion layer is much greater than the thicker one, and the thinner upon new concrete will also make greater tensile stress in cushion. As a result, both the thinner cushion layer and the cushion with thinner new concrete on it would have a bigger chance to crack than others. The mechanism is used to explain reasonably a dam crack in construction. Then some cracking prevention measures, which should have reference value for the construction of bedding cushion, are put forward in this paper.
Based on the real construction process and field environment of large sluice pier for Caojie Project, considering the factors of surface insulation, internal cooling, the strength of the foundation and environmental climate, the basic theories of temperature field and stress field of concrete and 3D FEM combining with cooling pipe discrete model and iteration method are used to carry out the study of cracking mechanism. According to the 3D dynamic simulation of the temperature filed and stress field for the pier, reasonable temperature control measures are put forward for reference during construction period. The result of the simulation shows that the concept of the exterior thermal insulation and interior pipe cooling measures are of great useful in practice, and the methods should have great reference signification in future.
Using low placement temperature and proper water pipe cooling water, the cracks are rarely appears in the interior of the dam, but the surface of the dam is prone to cracking. During the construction, the surface of the dam may be wet due to several factors such as creep, maintenance and so on, so the effect of the heat preservation is always been over-estimated. For those concrete blocks constructed in cold season, without proper heat preservation, the cracks are easy to appear soon after construction. For those concrete blocks constructed in hot period, under the influence of air temperature, the temperature of those concrete within about 5.0m of the dam surface are hard to control. So the key point to prevent the dam surface constructed in cold period is to take heat preservation measure suiting the on-the-spot situation. And for those dam blocks constructed in hot period, water cure on the surface of the dam can greatly reduce the risk of dam surface cracking.
Finite element simulations are widely used in the analysis of bird strike events in the literatures. While the shapes of the artificial birds used in the simulations are not indentical. In order to investigate the effects of artificial bird shapes on the response of laminated aircraft windshield, the often used shapes including hemispherical-ended cylinder, straight-ended cylinder and ellipsoid are modeled in this work. The striking velocity is 80.6 m/s and the SPH method is adopted. Based on the calculation results, the impact force, dissipated energy and major principle stress in the glass are analyzed. The analysis shows that the initial contact area would affect the values of these results. The shapes and aspect ratios affect the results through the initial contact area.
The shear modulus of PVB and SGP interlayer is analyzed. With the same conditions of load duration and temperature, the shear modulus of SGP interlayer is about fifteen times than that of PVB interlayer. A finite element model of laminated glass is established in this paper. The simulation results show that the maximum principal stress contours of PVB laminated glass change from a circular to a petal-shaped one and those of SGP laminated glass change form a quadrangular to a square-shaped one when the temperature rises from 20 degrees Celsius to 50 degrees Celsius.
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