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.

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SYNOPSISThe out-of-plane buckling of a circular arch is studied. The arch is composed of two main ribs braced with transverse bars and is subjected to uniformly distributed radial forces (see Fig. 1) . The analysis is carried out by means of transfer matrix method and both the field matrix of arched rod and point matrix are presented. Attention isgiven to the influences of the flexural rigidity, the number and the location of bracing bars on the buckling strength of arches. Buckling coefficients for various types of arch are calculated by trial and error method. Useful suggestions about the bracing method are obtained from the results of computations.The theoretical analysis is followed by model tests in order to verify the results of computation.