The influence of various seismic parameters on the seismic performance of rectangular reinforced recycled concrete columns was comprehensively revealed through collecting and screening experimental data from 53 rectangular recycled aggregate concrete columns. The research results showed that the bearing capacity of the specimens decreased and the ductility performance increased, which were attributed to the following factors. a. The increase in the replacement ratio and slenderness ratio of recycled coarse aggregate, and b. the reduction in the axial compression ratio and the strength of recycled aggregate concrete. The seismic design limitations and boundary conditions of this study are γ ∈ [0, 100%], n₀ ∈ [0, 0.9], λ₀ ∈ [5.06, 18.479], λ ∈ [1.09, 3.93], ρ_sl ∈ [1.01%, 2.45%], ρ_sv ∈ [1.4%, 5.33%], and f ∈ [C30, C50]. Thus, it is recommended that for the seismic design value of rectangular recycled aggregate concrete columns, the optimal longitudinal reinforcement rate be set at 1.59%.

In order to analyze the axial compressive properties of ultra-high-toughness cementitious composite (UHTCC)-confined recycled aggregate concrete (RAC), a batch of UHTCC-confined RAC components was designed and manufactured according to the requirements of GB/T50081-2002 specifications. After analyzing the surface failure phenomenon, load-displacement curves, scanning electron microscope (SEM), and parameter analysis of the specimen, the result shows that UHTCC-confined RAC is an effective confinement method, which can effectively improve the mechanical properties and control the degree of surface failure of RAC structures. Compared with the unconfined specimen, the maximum peak load of the UHTCC confinement layer with a thickness of 10 mm and 20 mm increased by 44.61% and 79.27%, respectively, meeting the requirements of engineering practice. Different fiber mixing amounts have different effects on improving the mechanical performance of RAC structural. The specific rule was steel fiber (SF) > polyvinyl alcohol fiber (PVAF) > polyvinyl alcohol fiber (PEF) > no fiber mixture, and the SF improves the axial compression properties of UHTCC most significantly. When there are strict requirements for improving the mechanical properties of the structure, SF should be added to UHTCC. On the contrary, PVAF should be added to UHTCC.

Conventional slope stability analyses often rely on two-dimensional models, which neglect local geological heterogeneity and spatial distribution of materials. This simplification can lead to inaccuracies in evaluating slope safety. Additionally, traditional strength reduction methods (SRMs) uniformly reduce the parameters of rock and soil, failing to represent the actual degradation process during progressive failure. This study aims to improve the accuracy of slope stability analysis by developing a method that better captures the spatial variability of geological conditions and the nonsynchronous degradation of shear strength. A three-dimensional (3D) geological model was constructed to restore the actual stratigraphic structure of the slope. Based on the shear strength degradation mechanism, a nonsynchronous coordinated reduction (NSCR) method was proposed, incorporating advanced reduction steps (n) and a correlation factor (λ). This method simulates progressive slope failure more realistically. An engineering case study demonstrated that the 3D NSCR method obtained a safety factor of Fs = 1.265, which is very close to that of the most critical two-dimensional limit equilibrium method section (with a difference of about 1%), whereas the traditional SRM and the two-dimensional coordinated reduction method show relatively larger errors. The 3D analysis revealed the overall dangerous slip surface, providing enhanced insight into slope instability mechanisms. The proposed NSCR method, supported by 3D geological modeling, improves the accuracy of slope stability analysis by better representing progressive failure. It is a feasible and effective tool for engineering applications involving complex slope conditions.