Numerical Simulation and Experimental Validation of Masonry Walls Strengthened with Stiff-Type Polyurea Under Seismic Loads

The deterioration of aging masonry structures poses significant challenges to structural safety, particularly under seismic loading. In response to the growing need for effective retrofitting solutions, stiff-type polyurea (STPU) has emerged as a promising material due to its high tensile strength, durability, and rapid application characteristics. This study investigates the seismic performance of masonry walls retrofitted with STPU through both shaking table tests and finite element analysis (FEA). Three types of specimens (non-strengthened, STPU-strengthened, and STPU + GFRP-strengthened walls) were subjected to out-of-plane seismic loading with additional mass loading to simulate real-world conditions. Experimental results demonstrated that STPU significantly improved the ductility and seismic resistance of masonry walls, with the STPU + GFRP hybrid system showing the highest performance. A simplified micro-model using ABAQUS successfully captured the primary failure modes and load-bearing behavior observed in the experiments. Furthermore, a parametric study on STPU thickness identified 2 mm as the most efficient thickness considering both strengthening effect and material economy. These findings confirm the effectiveness of STPU as a retrofitting material and demonstrate the reliability of the proposed numerical modeling approach in predicting the seismic response of retrofitted masonry structures.