Seismic Mitigation Performance and Damage of Prefabricated Base Isolation Structure Based on the Shaking Table Test

ObjectiveImproving the seismic performance of prefabricated reinforced concrete frame structure system has always been a research focus. At present, strengthening the design of beam-column assembly joints and adopting seismic isolation techniques are two different ways to achieve this goal. As an effective means to prevent earthquakes, the seismic isolation technology can effectively reduce the seismic action of the prefabricated reinforced concrete frame structure system. In order to verify the damping effect of the technical means in the prefabricated frame structure system, this paper carried out the research on the seismic mitigation performance and damage assessment of the fully prefabricated base-isolated structure, and clarified its seismic mitigation performance and damage mode.MethodsFirstly, A 1 : 4 scale model of three-story fully prefabricated base isolation structure was designed. Meantime, The dimensions, reinforcement configurations and assembly methods of precast reinforced concrete beams, slabs and columns are given. Then the beam-to-column assembly joint adopts dry rigid connection, the column end adopts double-constrained steel tube, and is confined by high-strength bolts. Secondly, Shaking table tests were conducted on the prefabricated base isolation structural model. And acceleration sensors and laser displacement transducers were installed on the test specimen to collect dynamic response data. The shaking table tests employed four sets (totaling eight records) of natural ground motions as seismic inputs, which were from CHY028 station of the 1999 Chi-Chi earthquake and El Centro Array #9 station of the 1940 Imperial Valley earthquake, respectively. Additionally, some main parameters and time history curves and acceleration spectra (5% damping) of seismic waves were provided in the paper. According to the purpose of the test, 19 sets of shaking table test conditions were designed for prefabricated base isolation structures, with seismic wave amplitude as the primary variable. At the same time, two groups of sweep frequency tests were carried out on the test model with white noise. Finally, the horizontal cyclic load was applied to 8 groups of lead rubber bearings by the compression-shear testing machine, including the basic performance test at 100 % shear deformation and the sampling test at 250 % shear deformation of 2 groups of lead rubber bearings.Results and Discussions Firstly, according to the basic performance test and sampling test results of 8 groups of lead rubber bearings, it can be seen the errors of the post-yield stiffness <italic>k</italic>_d, the equivalent stiffness <italic>k</italic>_{eq100 %} and the equivalent damping ratio <italic>ζ</italic> of the lead rubber bearing were 1.7 %, 2.7 % and 11.3 % at 100 % shear deformation, respectively, indicating that its basic parameters of mechanical properties were relatively stable. In the sampling test, the hysteresis curve of the lead rubber bearing was relative full when the shear deformation were 50 %, 100 % and 250 %, indicating that it had good energy dissipation capacity. When the shear deformation was 100 % to 250 %, the lead rubber bearing had a strengthening phenomenon.The observed behavior can be attributed to two primary mechanisms: First, the cyclic hardening and constraint enhancement of the lead core increased the stiffness of the lead core. Second, the strain hardening and geometric nonlinearity of rubber leaded to an increase in its shear stiffness. Secondly, the shaking table test of the prefabricated base isolation structure showed that there was no obvious cracking phenomenon in the precast reinforced concrete column under the action of large earthquakes, while the beam-column double steel tube assembly joint had obvious friction slip phenomenon, indicating the assembly beam-to-column joint can not meet the requirements of rigid joints. Thirdly, the seismic mitigation performance of the prefabricated base isolation structure is analyzed by using the acceleration Arias strength <italic>I</italic>_a and the reduced seismic ration <italic>β</italic>. From the acceleration Arias intensity <italic>I</italic>_a ratio of each layer of the structure and the shaking table, the acceleration Arias intensity <italic>I</italic>_a ratio is mainly distributed in 0.4-0.5 under the far-field ground motion, and the acceleration Arias intensity Ia ratio is mainly distributed between 0.5-0.8 under the near-field ground motion, and the acceleration Arias intensity <italic>I</italic>_a ratio decreases with the increase of the amplitude of the seismic wave. Meantime, from the change of reduced seismic ration <italic>β</italic>, the reduced seismic ration <italic>β</italic> under far-field earthquake is mainly distributed between 0.4-0.6, and the reduced seismic ration <italic>β</italic> under near-field earthquake is mainly distributed between 0.2-0.4, and with the increase of seismic wave amplitude, the reduced seismic ration <italic>β</italic> increases. Overall, the results of the two analysis indicators are basically the same. Finally, a comprehensive damage assessment of the prefabricated base isolation structure was conducted using three key parameters: natural vibration period, lateral displacement, and isolation layer stiffness degradation. From the perspective of the natural vibration period of the structure, the first three periods increased by 8.9 %, 13.3 % and 10.3 %, respectively, and the error was about 10 %, indicating that the structure had certain damage. However, from the perspective of the lateral displacement of the structure, the lateral displacement of the lower part of the structure has increased, and the lateral displacement of the upper part of the structure has decreased slightly. The overall increase has not exceeded 5 %, demonstrating that the overall damage of the upper structure is relatively small. Additionally, from the stiffness degradation of the isolation layer, the equivalent stiffness of the isolation layer before and after the test was 2.83 kN / mm and 2.42 kN / mm, respectively. And the equivalent stiffness of the isolation layer is reduced by 14.5 %, indicating that the isolation layer has certain damage.ConclusionsThis study investigates the seismic mitigation performance and damage characteristics of prefabricated base isolation structures through shaking table tests, validating the reliability of its overall seismic mitigation performance and analyzing its damage mode. The results provide theoretical and technical support for promoting the application of such structures.The results shows that the two indexes of Arias strength <italic>I</italic>_a and reduced seismic ration <italic>β</italic> indicate that the prefabricated base isolation structure has good seismic mitigation performance. And compared to the near-field ground motion, its seismic mitigation effect is better under the far-field ground motion. After more than 20 earthquakes, by comparing the three damage indexes of natural vibration period, lateral displacement of structure and stiffness degradation of isolation layer, the maximum values of each damage evaluation index are all within 15 %. The damage of lead rubber bearing is the main structural damage mode. The damage of the upper structure is relatively light, further verifying its overall seismic mitigation performance is relatively stable.