SUMMARYA real-time hybrid experimental method, in which output from an actuator-excited vibration experiment and response calculation are combined on-line and conducted simultaneously in real time, is being developed as a new seismic experimental method for structural systems. In real-time hybrid experiments, however, there is an inevitable actuator-response delay, which has an e!ect equivalent to negative damping. To solve this problem, a real-time hybrid experimental system (including an actuator-delay compensation method) was developed. And seismic experiments were conducted in order to demonstrate the advantages of this system. Experimental results obtained using the developed hybrid experimental system were compared with exact results obtained using shaking-table experiments, and it was found that the two experimental methods gave almost identical results. It can therefore be concluded that the structural response can be obtained precisely by using the developed hybrid experimental system. Comparison of these experiments showed the advantages of the hybrid experiments; that is, they are simple and economical. This is because the hybrid experiment requires only a small structure as the excitation model, while a shaking-table experiment must consider the whole structural system.

We developed an on-line experimental system for conducting hybrid experiments in real time. It combines a computer, which conducts vibration simulation and generates a control signal, and a hydraulic actuator, which conducts a vibration experiment driven by the control signal. This system compensates for actuator delay and thus enables experiments to be carried out in real time. We evaluated the stability of the experiments with respect to the mass of the structure under excitation, and we developed a new method for compensating actuator delay in order to increase the stability condition. In this method, the compensated control signal is generated from the simulation results by using not only displacement but also velocity and acceleration. This method provides a stability criterion (allowable ratio of mass of the structure under excitation to that of a numerical model) about three times larger than that from the current method.

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An improved shaking-table control method has been developed. This method compensates the reaction force caused by a nonlinear specimen in real time, and thus maintains a desired table acceleration. To do so, it identifies the difference between the desired and the actual transfer characteristics of the shaking table, then compensates for the difference. Because the required time for this combination of identification and compensation is less than one second, the method can compensate, in real time, for the disturbance caused by a nonlinear specimen. By means of a series of experiments, it is confirmed that the method can maintain a desired table acceleration even when a nonlinear specimen is under excitation.

As a countermeasure against high residual stress, we have developed some residual stress improvement methods, as Water Jet Peening (WJP) [1] [2] for components installed in water, Shot Peening by Ultrasonic-wave vibration (USP) for components installed in air, and outer surface irradiated Laser Stress Improvement Process (L-SIP) [3] for components being able to approach from outer surface only. WJP is applied to Reactor Vessel (RV) outlet/inlet nozzle safe-end joints (Alloy600 weld metal), RV Bottom Mounted Instrument (BMI) inner surface and J-weld. Especially, it is difficult to apply BMI because BMI inner surface is very narrow space (inner diameter; approximately 10–15mm) and BMI J-weld is complicated 3-dimensional form. On the occasion of actual application, we carry out the verification tests and check that a stress improvement was effective as one of PWSCC mitigation. And the compressive stress induced by WJP is verified to continue to exist under actual plant operation conditions. Thus, in addition to replacing the material with Alloy 690, converting the residual stress to the compressive can prevent the occurrence of PWSCC.