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Challenges of high dam construction to computational mechanics
ZHANG Chuhan
Front. Struct. Civ. Eng.. 2007, 1 (1): 12-33.
https://doi.org/10.1007/s11709-007-0002-6
The current situations and growing prospects of China s hydro-power development and high dam construction are reviewed, giving emphasis to key issues for safety evaluation of large dams and hydro-power plants, especially those associated with application of state-of-the-art computational mechanics. These include but are not limited to: stress and stability analysis of dam foundations under external loads; earthquake behavior of dam-foundation-reservoir systems, mechanical properties of mass concrete for dams, high velocity flow and energy dissipation for high dams, scientific and technical problems of hydro-power plants and underground structures, and newly developed types of dam-Roll Com pacted Concrete (RCC) dams and Concrete Face Rock-fill (CFR) dams. Some examples demonstrating successful utilizations of computational mechanics in high dam engineering are given, including seismic nonlinear analysis for arch dam foundations, nonlinear fracture analysis of arch dams under reservoir loads, and failure analysis of arch dam-foundations. To make more use of the computational mechanics in high dam engineering, it is pointed out that much research including different computational methods, numerical models and solution schemes, and verifications through experimental tests and filed measurements is necessary in the future.
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Fracture resistance on aggregate bridging crack in concrete
ZHANG Xiufang, XU Shilang
Front. Struct. Civ. Eng.. 2007, 1 (1): 63-70.
https://doi.org/10.1007/s11709-007-0006-2
Fracture toughening exhibited in quasi-brittle materials such as concrete is often mainly related to the action of aggregate bridging, which leads to the presence of a fracture process zone ahead of stress-free cracks in such materials. In this investigation, the fracture resistance induced by aggregate bridging, denoted by GI-bridging, is the primary focus. In order to quantitatively determine it, a general analytical formula is firstly developed, based on the definition of fracture energy by Hillerborg. After this, we further present the calculated procedures of determining this fracture resistance from the recorded load vs. crack opening displacement curve. Then, both numerical simulations and fracture experiments are performed on concrete three-point bending beams. Utilizing the obtained load against crack opening displacement curve, the value of GI-bridging at any crack extension as well as the change of GI-bridging with the crack extension is examined. It is found that GI-bridging will firstly increase with the development of crack and then stay constant once the initial crack tip opening displacement reaches the characteristic crack opening displacement w0. The effects of material strength and specimen depth on this fracture resistance are also investigated. The results reveal that the values of GI-bridging of different specimens at any crack propagation are strongly associated with the values of fracture energy of specimens. If the values of fracture energy between different specimens are comparable, the differences between GI-bridging are ignored. Instead, if values of fracture energy are different, the GI-bridging will be different. This shows that for specimens with different strengths, GI-bridging will change greatly whereas for specimens that are different in depth, whether GI-bridging exhibits size effect depends on whether the fracture energy of specimens considered in the calculation of GI-bridging is assumed to be a size-dependent material parameter.
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Biaxial tensile-compressive experiment of concrete at high temperatures
SONG Yupu, ZHANG Zhong, QING Likun, YU Changjiang
Front. Struct. Civ. Eng.. 2007, 1 (1): 94-98.
https://doi.org/10.1007/s11709-007-0009-z
Biaxial tension-compression experiments of concrete of five stress ratios at high temperatures were carried out using the large static-dynamic triaxial test system in the State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology. The stress ratios s1/s3 are 0, 0.1, 0.25, 0.50, and 0.75. The temperatures are 20vH, 200vH, 300vH, 500vH, 600vH. The mechanical behavior of concrete under biaxial tension-compression at high temperatures is analyzed. It is found that both the tensile strength and strain diminished with the increase in temperature under each stress ratio. Based on the test results, the relationship between tensile strengths and stress ratios and temperature is proposed. In addition, the failure criterion of concrete under biaxial stress state of tension-compression at high temperatures is established.
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Effects of fiber curvature on the microstructure of the interfacial transition zone in fresh concrete
CHEN Huisu, SUN Wei, ZHAO Qingxin, L. J. Sluys, P. Stroeven
Front. Struct. Civ. Eng.. 2007, 1 (1): 99-106.
https://doi.org/10.1007/s11709-007-0010-6
The study on the interfacial transition zone (ITZ) of concrete has received lots of attention in the last decade. However, no information is available on the influence of the curvature of a rigid surface on the microstructure of ITZ. This paper employed computer simulation technology to study the influence of fiber curvature on the initial microstructure of ITZ in concrete. For the sake of simplification, the investigation was first focused on the mono-size spherical particle packing system around a cylindrical fiber with different diameters. An algorithm of serial cylindrical sectioning was developed. The curve of the solid volume fraction versus the distance to the surface of the fiber was used as a parameter to characterize the microstructure of the ITZ. Then, the influence of the ratio of fiber diameter to particle diameter on the initial ITZ s microstructure was studied. These curves were compared with the ones from flat aggregate surface on which mono-size spherical particles were packed. Furthermore, the multi-size spherical particles system was further investigated. The simulation results demonstrate that no matter whether the spherical particles system is mono-size or multi-size, the fresh ITZ s microstructure is irrelevant to the curvature of the fiber. The shape of the curve of solid volume fraction versus the distance from the surface of the fiber is similar to that around a flat aggregate surface. In all cases, the horizontal coordinates of the first peak of the curves are located at around half the mean weight diameter of the particles. The thickness of ITZ reduces slightly with the decrease in water/cement ratio. Therefore, one may use the ITZ s microstructure around a flat aggregate surface to represent the ITZ s microstructure around a cylindrical fiber in the fresh state, and vice versa.
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