原子力施設RC床スラブの面内せん断性状に関する実験研究

Abstract

A high degree of seismic safety is required in nuclear power plants. To evaluate accurately the seismic behavior of a nuclear reactor building, it is effective to use an analysis model that takes in-plane shear characteristics of the floor slab into consideration. However, few experimental studies of the in-plane elasto-plastic shear characteristics of the floor slab that is constantly subjected to out-of-plane dead and live loads have been reported. Therefore, fundamental data needed to decide on restoring force characteristics and shear strength to be used for an analysis model is insufficient. In this study, the static loading tests were carried out to identify the elasto-plastic behavior of a reinforced concrete floor slab subjected simultaneously to uniformly distributed out-of-plane load and in-plane shear force. Prior to test planning, as a first step, a fact-finding survey was conducted to collect data on representative nuclear power plants in Japan including the dimensions (length, width, thickness) of typical floor slabs, dead loads, live loads and the amount of reinforcement. The configuration of test specimens and test parameters were determined on the basis of the results thus obtained. A total of seven test specimens were prepared, and the amount of reinforcement and out-of-plane distributed load level of the floor slab were used as parameters. The configuration of the test specimens is basically the same as that of specimens for a typical sheer wall test. In the tests, first, distributed loads were applied to the specimen as out-of-plane forces and were kept constant, and, next, in-plane shear forces were applied. The results of the tests revealed that cracking patterns and the in-plane failure mode depends on parameter differences. The test results also clarified the effects of each parameter on the load－deformation relationship and in-plane shear strength. Using the experimental results thus obtained, the strain behavior of reinforcing bars, deformation components, a method of setting restoring force characteristics in analysis model were studied in detail. Also, a method of evaluating in-plane shear strength taking account of the influence of out-of-plane forces was proposed. From the results of this study, the following conclusions can be drawn: (1) Within the range of out-of-plane force acting on a floor slab of a typical nuclear power plant, the influence of out-of-plane force is small, and the failure mode due to in-plane shear is similar to shear failure of a wall. (2) In practicing the evaluation of the earthquake resistance of a nuclear power plant, the in-plane shear behavior of a floor slab can be evaluated by using the restoring force characteristics model for a shear wall shown in JEAC4601-2008. (3) In cases where out-of-plane force exceeds the limit considered in the standard design process, as out-of-plane force increases, the influence of punching shear failure due to out-of-plane force tends to increase and in-plane shear strength tends to decrease. (4) By referring to previous studies, a method of evaluating the in-plane shear strength of a plate member in the case where it is subjected to uniformly distributed out-of-plane loading has been proposed. The proposed method makes it possible to accurately evaluate the in-plane shear strength of a floor slab subjected to a large out-of-plane force exceeding the limit assumed in the design.