The UEL subroutine of the bio-inspired isolation system is used in the real 3D structural model to demonstrate the relative advantage compared to the traditional linear isolation system. Take a teaching building of a certain primary school as an example, where the linear vibration isolation system is applied in this model in contrast to the bio-inspired isolation system. To make it comparable, the stiffness and damping coefficient of the bio-inspire isolation system and linear isolation system should be kept the same.
The teaching building is a frame structure with a total of four floors and an altitude of 14.4 m. At the view of the plane figure, the structure is 64.4 m in the EW direction and 27.2 m in the NS direction. The 3D view is shown in Figure 12
. The local seismic fortification intensity is 8 degrees, with a PGA of 0.2 g. The site classification for construction belongs to class II and the third group.
The selection of strong motion records for nonlinear dynamic analysis is not a straightforward process. Subjected to the excitation of near-fault long-periodic pulsed seismic motion, the displacement of the isolated layer of the structure is more likely to be much larger than the structure under regular seismic motion. Bio-inspired isolation bearing can simultaneously reduce the displacement of the isolation layer and the acceleration response of the superstructure. Twenty-eight near-fault seismic waves with the same PGA of 0.4 g are selected in this part to be applied to the teaching building to study its response under rare earthquakes.
The information of 28 seismic motions is shown in Table 5
. All selected seismic waves are near-fault pulsed seismic waves with an epicenter distance of 10 km or less.
The parameters of the isolators are shown in Table 6
. The traditional linear isolation system adopts the combination of LRB700 and LNR600, while the bio-inspired isolation system employs the combination of NSB700 and LNR600, of which NSB take the place of LRB700. The NSB isolator has one more parameter to express the BIO force than the LRB isolator. The total peak value of the BIO force in the isolation layer occupies approximately 1% of the self-weight of the upper structure. Each NSB700 isolator contributes a value of 37.9 KN.
The plane layout of isolation bearing is shown in Figure 13
. NSB700 should always be arranged as close as possible to the edges of the structure to be conducive to the eccentricity and enhance the torsional capacity, since NSB can provide a larger restoring force than LNR like LRB.
A dynamic response of the bio-inspired isolation system and linear isolation system can be obtained by direct time history analysis. To evaluate the effect of the bio-inspired isolation system superior to the linear isolation system, a reducing rate is introduced. The reducing rate is defined as (RBIO
, of which RBIO
represent the response of the bio-inspired isolation system and linear isolation system, respectively. The reducing rate of base displacement, acceleration of the superstructure, and interlaminar shear force are shown as Figure 14
, Figure 15
and Figure 16
The displacement of the bio-inspired isolation layer is at most 44.5% and on average, 20.4% less than that of the linear isolation system under the excitation of the seismic wave in the X-direction.
In the Y direction, as a result of the larger height-width ratio of the building, the acceleration responses in the upper structure of the bio-inspired isolation system are larger than those of the linear isolation system.
shows the interlaminar shear force reducing ratio of the superstructure of the bio-inspired isolated system relative to the linear isolation system.
In the X direction, the maximum reduction ratios are 32.8%, 37.9%, 37.9%, and 38.4%, respectively, and the average reduction ratios are 12%, 13.8%, 16.5%, and 20%, respectively. In the Y direction, the shear forces of the bio-inspired isolation system in floor I and floor II are smaller than those of the linear isolation system and are much larger in floor III and floor IV. The possible reason for this is that the aspect ratio in the Y direction is relatively larger than that in the X direction. Shear forces in floor I and floor II are more liable to be controlled since the isolation layer is much closer to floor I and floor II. These results show that the bio-inspired isolation system may be sensitive to the aspect ratio. In the process of designing the system, it is necessary to take more consideration of the applicability.
According to the Seismic design code for Buildings in China, the shear force of the isolated model should be less than 40% of the shear force of the non-isolated model. As for the bio-inspired model in this case, the shear force ratio in the X and Y direction is 0.234 and 0.285, which means that the shear force is still acceptable.
The bio-inspired isolated structure performs much better than the traditional linear isolated structure in the acceleration of the superstructure in both the X direction and Y direction. In the X direction, base displacement of the bio-inspired isolated structure is, at most, 21.6% less than that of the traditional linear isolated structure under certain seismic waves. The mean reducing ratio reaches 5.1%. In the Y direction, base displacement of the bio-inspired isolated structure is, at most, 34.7% less and 7.1% on average.