In order to reveal the damage mechanism of ancient timber structures and to make a reasonable evaluation of the damage degree under earthquakes, this paper proposes a multi-scale seismic damage evolution analysis method for the ancient timber structure. Based on the generalized force-deformation relationship and performance-based seismic design, the generalized damage index is established through test data fitting analysis, thus multi-scale consistency damage indices are proposed. According to the multiple point constraint method (MPC), a multiple-scale model is developed for ancient timber structures, which can reveal macro mechanical properties and local failure details. The proposed damage evolution analysis method is validated by a cyclic loading test of mortise-tenon joint and a shaking table test of the multi-story timber framework, and the evolution process and results are also shown. The proposed multi-scale analysis method provides evaluation results of seismic appraisal for existing ancient timber structures, including assessments at the local material, component to overall structural levels. Furthermore, it elucidates the evolutionary relationships between each level of the whole structure, providing a scientific basis for reinforcement and repair work.

The current seismic design codes for bridges primarily rely on design response spectra derived from far-field observational records, which fail to accurately reflect the ground motion characteristics and structural seismic response characteristics in near-fault regions. As a result, the seismic design for bridges in near-fault regions may be unsafe. To address the issue, near-fault ground motion time histories are selected from the Pacific Earthquake Engineering Research Center (PEER) database based on principles including source distance, moment magnitude, and peak ground acceleration(PGA). Average spectra are calculated using site foundation conditions and PGA as grouping principles, and then calibrated using a least-squares piecewise fitting method. This process yields statistical recommendations for three key parameters of the near-fault horizontal design gauge response spectrum: amplification factor, attenuation index, and characteristic period. Finally, adjustments were made to propose a gauge response spectrum that considers near-fault earthquake characteristics, providing a basis for incorporating near-fault ground motion effects into China's seismic design codes for bridges.

The dynamic response of compacted coarse-grained soil as a filling material for the surface layer of railway subgrade bedding is crucial for the overall performance of the subgrade structure under long-term cyclic train loads. This study conducted a series of cyclic triaxial tests to investigate the effects of fine content, confining pressure, and cyclic stress amplitude on the accumulated behavior of coarse-grained soils. The test results indicate that under the same cyclic loading conditions, specimens with higher fine content exhibit less accumulated axial strain. Furthermore, coarse-grained soil specimens exhibit less accumulated axial strain under higher confining pressure or lower cyclic stress amplitudes. Subsequently, the plastic shakedown limit of coarse-grained soils with different fine contents was determined based on a universal shakedown criterion. The results demonstrate that the plastic shakedown limit of coarse-grained soil specimens gradually increases with an increase in fine content. Under higher confining pressure, the corresponding plastic shakedown limit of coarse-grained soil is also higher. Additionally, by plotting the stress state corresponding to the plastic shakedown limit of coarse-grained soil on the plane of p-q, a relationship was established between the coefficient of fine content (FC) and the model parameters in the existing shakedown criterion. A united plastic shakedown criterion is then proposed for coarse-grained soils with different fine contents. The conclusions can provide a theoretical foundation for the design and stability assessment of railway subgrades.

In this paper, it is proposed that the frame structure of glulam pillar and steel beam can address the issues of complex joint structure, limited beam stiffness and low lateral stiffness of long span glulam beam and column structure joints. Three joint specimens without planted bar and three joint specimens with the diameter of planting reinforcement as a variable were designed. Monotonic loading experiment were conducted on two joint specimens without reinforcement, while other joint specimens underwent low-cycle repeated loading to obtain their seismic performance, including failure mode, hysteresis curve, skeleton curve and energy dissipation capacity. The experimental results show that the measure of reinforced with planted bar can effectively improve the local bearing capacity of the transverse grain, the flexural stiffness and ultimate bearing capacity of the joints, but the increase in the diameter of the reinforcing bar has little impact. The energy dissipation capacity of the joint can be significantly improved by the measure of reinforced with planted bar, and the seismic performance of the joint can be improved. The failure modes of flexible end plate and rigid end plate are different, the members of the flexible end plates are S-shaped deformation and failure mode, the joint angle deformation is large, the bending stiffness is small, and the rigid end plate members are the transverse compression deformation and failure of the wooden column, and the bending stiffness and bearing capacity of the joint are strong. The formulas for the ultimate flexural bearing capacity of the joints are derived, and the theoretical values agree well with the measured ones.

A semi-active impact damper (SAID) with controllable timing is presented based on vibro-impact mechanism, aiming to control the multi-modal vibration of civil structures under earthquake excitations. The proper impact actuating force can interfere with the accumulation of structural vibration amplitude without additional controllable elements. In this paper, a device construction with adjustable collision clearance was proposed based on the SAID mechanical model and corresponding semi-active control strategy. The damping performance of the SAID system in a five-story frame structure is studied through shaking table tests. The results showed that the SAID system could effectively reduce the acceleration at the top floor of the structure and the inter-story drift. Time-frequency energy analysis revealed that the SAID system can transfer the structural vibration energy from low-order modes to high-order modes to accelerate the energy dissipation during the controlled impact process and suppress the structural response caused by dominant modes. An enhanced semi-active impact damper (ESAID) is further proposed to reduce the adverse effect of the acceleration sudden change caused by the impacts while improving the damping performance of the SAID system.