This paper investigated the behavior of R/C beam-column joints in the plastic state subjected to repeated seismic load by static loading tests. The specimens were modeled on two types of structures constructed in recent years and 20 years ago.; i.e., tube structures , and moment-resisting-frame structures. The test results showed that at the story-drifts larger than yield deformation, (a) the stiffness deteriorated due to cyclic loads and the hysteresis loop changed to reversed-S shape, associated with concrete damage and the bond deterioration of the rebars in the beam-column joint, and (b) the ratio of energy dissipation by the beams decreased with increasing that of the beam-column joint.In order to simulate these observed relations, a new hysteresis model for R/C beams was proposed. This model can reflect performance deterioration by reduction of the peak responses and several stiffness-related parameters. In this paper, the authors discussed those parameters of the model based on the results, however, the authors are still making efforts to verify the parameters with previous studies for the future.
This study focuses on the vibration tests of concrete materials to evaluate their dynamic characteristics including damping property. The vibration tests are conducted based on the impact excitation using an impulse hammer. The vibration response of an object is measured by a laser Doppler vibrometer. Frequency spectra are analyzed by a spectrum analyzer from the measured time history responses. This vibration test approach is applied to several specimens with different dimensions and water-cement ratios. Damping ratio of each mode for a specimen is calculated by half-width method with the measured frequency responses. The vibration test results confirmed that it is possible to extract differences in natural frequencies and damping ratios due to differences in the dimensions and water-cement ratios of the specimens. The measured natural frequencies were compared to those calculated by finite element analysis, resulting in good agreement between them. It is verified from the experiments that the present vibration test approach for the concrete materials can evaluate their dynamic properties and is effective to develop concrete structures with a desired damping in future.
The authors proposed a new hysteresis model for R/C beams in order to investigate the remaining performance of the structures subjected to repeated seismic loads. The parameter settings included, (1) the degrading factor for loading stiffness based on the normalized dissipated energy, (2) the slipping hysteresis loop factor based on the maximum displacement and the normalized dissipated energy, and (3) the degrading factor for descending stiffness. This paper verified that the proposed model accurately simulated the test results with the parameters obtained by the experimental data. In addition, the tentative dynamic analysis incorporating the proposed model showed that the repeated seismic loads could increase seismic response.
'/%3e%3c/defs%3e%3cpath fill='%23012169' d='M0 0h10080v5040H0z'/%3e%3cpath stroke='%23fff' stroke-width='.6' d='m0 0 6 3m0-3L0 3' clip-path='url(%23b)' transform='scale(840)'/%3e%3cpath stroke='%23e4002b' stroke-width='.4' d='m0 0 6 3m0-3L0 3' clip-path='url(%23c)' transform='scale(840)'/%3e%3cpath stroke='%23fff' stroke-width='840' d='M2520 0v2520M0 1260h5040'/%3e%3cpath stroke='%23e4002b' stroke-width='504' d='M2520 0v2520M0 1260h5040'/%3e%3cg fill='%23fff'%3e%3cuse xlink:href='%23d' x='2520' y='3780'/%3e%3cuse xlink:href='%23a' x='7560' y='4200'/%3e%3cuse xlink:href='%23a' x='6300' y='2205'/%3e%3cuse xlink:href='%23a' x='7560' y='840'/%3e%3cuse xlink:href='%23a' x='8680' y='1869'/%3e%3cuse xlink:href='%23e' x='8064' y='2730'/%3e%3c/g%3e%3c/svg%3e)