Asymmetric base-isolated structures subjected to severe torsion may suffer further aggravation of their torsional and translational responses under pulse-type earthquakes. To counteract these detrimental impacts, this study introduces a two-stage optimal design method. The first stage involved the application of the NSGA-II algorithm for determining an optimal isolator arrangement—namely, position and category—with the objective of reducing both the maximum interstory rotation of the superstructure and the isolation layer. In the second stage, the inclusion of viscous dampers served to minimize the excessive translational response triggered by pulse-type earthquakes. The influence of these dampers’ positions on the structural response was carefully evaluated. The final application of this optimal design method was demonstrated on an asymmetric base-isolated structure. The results indicated a significant reduction in the translational and torsional responses of the asymmetric base-isolated structure when the two-stage optimal design method was utilized, compared to those of structures designed using traditional conceptual methods. It was found that by installing viscous dampers in the isolation layer along both the x and the y directions—specifically, underneath the mass center of the superstructure (CMS)—the effectiveness of the torsional resistance from the first stage could be effectively maintained.

The shear pin of the friction pendulum bearing (FPB) can be made of 40Cr steel. In conceptual design, the optimal cut-off point of the shear pin is predetermined, guiding the design of bridges isolated by FPBs to maximize their isolation performance. Current researches on the shear pins are mainly based on linear elastic models, neglecting their plasticity, damage, and fracture mechanical properties. To accurately predict its cutoff behavior, the elastic-plastic degradation model of 40Cr steel is indeed calibrated. For this purpose, the Ramberg-Osgood model, the Bao-Wierzbicki damage initiation criterion, and the linear damage evolution criterion were selected to develop the elastic-plastic degradation model of 40Cr. Subsequently, parameter calibration of this model was performed through uniaxial tensile tests on two sets of six smooth, round bars with different diameters. Following this, finite element simulations were conducted for the pure shear test of grade 10.9 high-strength bolts made of 40Cr steel, aiming to verify the elastic-plastic degradation model. The results showed that the failure modes and force-displacement curves simulated by the finite element method were in good agreement with the test results. Moreover, the error between the primary characteristic parameters (initial stiffness, peak load, fracture displacement, and absorbed energy) obtained by finite element calculation and the test values was within 15%. These results demonstrated that the calibration elastic-plastic degradation model of 40Cr steel can predict the cutoff of the shear pin.

Lubricated curved surface sliders (L‐CSSs) with modified ultrahigh‐molecular‐weight polyethylene (M‐UHMWPE) are highlighted in the prevention of bearing failure due to the high‐temperature degradation of friction materials during high‐speed operation. This is vital for seismic isolation in large‐span bridges; however, their hysteretic behavior under the variable contact pressure induced by seismic vertical actions is underexplored. For this reason, a theoretical model of the CSS under variable contact pressure was developed. It is evident that variable contact pressure primarily affects the hysteretic performance of the bearing by altering the restoring force and friction force in real‐time. Dynamic cyclic tests were conducted at contact pressures ranging from 30 to 90 MPa and frequencies from 0.01 to 0.03 Hz. Test results demonstrated stable hysteretic behavior, with breakaway and average friction coefficients exhibiting minimal fluctuations. The accumulative dissipated energy increased significantly with contact pressure, achieving a maximum gain of 362.25%, while the equivalent damping ratio exhibited a maximum change of 14.6%, initially decreasing and then increasing. Loading frequency had a minor effect, with accumulated dissipated energy decreasing by up to 7.5% and the equivalent damping ratio varying by up to 6.7%. Finally, a validated finite element model further analyzed the influence of the amplitude, frequency, and time phase of variable contact pressure, revealing an irregular parallelogram‐shaped hysteresis curve. The shape of hysteretic curves and energy dissipation capacity were significantly affected by these parameters. These findings enhance the understanding of L‐CSS performance in bridge seismic isolation, providing critical insights for design under dynamic loading conditions.