Shape optimization of U-shaped damper for improving its bi-directional performance under cyclic loading

• The bi-directional performance of U-shaped damper was investigated by physical tests.
• U-shaped damper presented evident strength degradation under bi-directional loading.
• FE model built in ABAQUS well simulated the behavior of U-shaped damper.
• The RS method was adopted in the shape optimization of U-shaped damper.
• The optimization significantly improved the performance of U-shaped damper.

A U-shaped damper typically has a stable and saturated hysteretic performance along the in-plane direction and is usually installed in the isolation layer. However experimental study shows that the conventional U-shaped damper presents an unstable hysteretic performance when it sustains bi-directional deformations. Therefore, shape optimization is needed to improve the hysteretic performance of the U-shaped damper. To obtain an optimal shape for the U-shaped damper, a finite element (FE) model was built using a general FE analysis software called ABAQUS. Comparisons of results obtained from FE models with those obtained from experimental studies demonstrated the effectiveness of the FE models. Optimization of a U-shaped damper was carried out using the FE model. The length and shape of the straight part of the U-shaped damper were treated as optimization parameters and the enlarging the end of the straight part was adopted as the improved approach. The formula for the ratio of the energy dissipated by rate-independent and rate-dependent plastic deformation (ALLPD) to the maximum cumulative equivalent plastic strain (PEEQ) was derived though regression analysis. After four levels of optimization processes the optimal shape of the improved U-shaped damper was obtained, and the bi-directional performance was significantly improved compared to that of a conventional U-shaped damper.