| Deadweight of dam, hydraulic pressure, temperature and concrete creep can result in high local tensile stress near the orifice in arch dams, which lead to concrete cracking. It can affect the safety of the arch dam, so steel bars are needed near the orifice.By traditional method of design, the elastic theory is adopted to calculate stress distribution, and the amount of reinforcing bars for the orifice is determined according to the diagram of tensile stress. By this means, nonlinear properties of concrete and steel bars, as well as stress redistribution near the orifice caused by concrete cracking, are not taken into account. Furthermore, concrete cracking could not be well controlled by reinforcing bars. It is shown that the amount of steel bars is overestimated.In this thesis, stress distribution, concrete cracking and its propagating, and failure mechanism of the orifice of the Xiao Wan Arch Dam, as well as the influence of reinforcing bars are studied by both experimental tests and nonlinear analysis. Also, the improvement of the performance of the orifice in cracking control by using steel fiber reinforced concrete is studied. These works are useful for the design of the orifice in arch dams. The details are as following:1) Through the experiments of seventeen reinforced concrete plates with round openings, stress distributions of concrete and steel bars, concrete cracking, failure mechanism, and the influence of reinforcing bars with different amount and layouts on cracking and failure mechanism of the specimens are studied. The experimental study provides data not only for the validation of FEA model and nonlinear FEM program, but also for the research on new methodology of design for orifices.2) Nonlinear finite element analysis on the specimens is performed. The FE model and the FE program are validated by experimental results. The mechanism of concrete cracking and crack propagating is also studied by using finite element method.3) Based on the bond stress distribution function at the concrete-steel interface, a stress-strain relationship for cracked reinforced concrete tensile members is derived, and thereby an analytical model is proposed. By introducing a crack strength expression, the influence of non-uniform distribution of concrete stress in transverse and longitudinal directions in a reinforced concrete tensile member on concrete cracking is taken into account. A two-dimensional model, which is derived from the one for tensile members, is applied to the analysis of the experimental specimens. It is shown that the proposed model can not only take the ratio of reinforcement, the material properties of reinforcement and concrete and the crack spacing into account, but also be easily incorporated in finite element programs.4) Three-dimensional nonlinear analysis of the bottom outlet of the Xiao Wan Arch Dam is presented using sub-model techniques. The structural characteristics and failure mechanism of the bottom outlet, under loading of concrete deadweight, hydraulic pressure, internal water pressure and temperature are studied. It is shown that the meshing of the structure becomes easy and the computing time is reduced by using sub-modeling method.Ill5) Two-dimensional analysis on different sections of the orifice with reinforcing bars in variety of amount and layouts is carried out. A new formula for the calculation of reinforcing bars of the orifice is proposed, based on experimental and two and three dimensional analysis. The proposed formula is in accordance with the old one, and the affect of nonlinear material properties of concrete and steel bars is considered by an adjusting coefficient.6) Based on theoretical and experimental research on material characters of steel fibered reinforced concrete, a finite element model for nonlinear analysis of steel fiber reinforced (SFRC) structures is presented. Two-dimensional analysis on various sections of the orifice in the Xiao Wan Arch Dam is carried out. The influence of SFR...
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