The Mechanical Properties and Sustainable Conservation of Traditional Brick Arches: A Study of Residential and Official Buildings in Jinzhong, China

Traditional Chinese brick-and-stone archways are not merely architectural products shaped by geographical constraints; they also embody a highly rational structural logic. Drawing on the unique earthen environment of the Loess Plateau and the region’s traditions of brick-and-stone construction, the Jinzhong region of China has developed a distinct system of archways. Consequently, to deconstruct the mechanical wisdom inherent in the traditional building techniques of the Jinzhong region, this study selected residential buildings in Qi County and Pingyao, as well as Qing Dynasty (1636–1912 AD) official architecture, as case studies. Through field investigations into the masonry techniques of three typical vault forms—the single-centre arch, the double-centre arch, and the four-centre arch—the study revealed their evolutionary characteristics in terms of geometric form. Static numerical simulation analysis was conducted using the Abaqus CAE 2025 (Dassault Systèmes, Vélizy-Villacoublay, France) platform. The study found that, under a simulated surface load of 0.027 N/mm², different arch profiles exhibited significant quantitative mechanical differences, and their stress distributions and deformation thresholds showed distinct scenario-specific tendencies. The results show that, compared to a semicircular arch, the official double-centred arch reduces maximum displacement by approximately 20%, and the maximum principal stress decreased from 1.35 MPa to 1.215 MPa, effectively mitigating the risk of cracking at the arch crown. With this high sectional stiffness and displacement-constraining capability, it supports the high load requirements of defensive city fortifications. Compared to the Pingyao gentle-type four-centre arch, its maximum displacement increased by only about 10%, and the maximum principal stress rose by only about 8%. Therefore, given similar mechanical performance but considering construction feasibility, the official double-centred arch was selected for the construction of defensive city fortifications. Furthermore, although the stress concentration at the corners (arch feet) of the Pingyao gentle-curved four-centred arch is approximately 4.8% higher than that of the pointed four-centred arch, its spatial utilization is improved by 15–20%; This geometric trade-off achieved through composite curvature maximizes interior clear space while maintaining structural stability, aligning with the functional requirements of guyao architecture for large-span living spaces. Meanwhile, the semicircular vaults of Qi County demonstrate universal value in low-load residential door and window components due to their low construction threshold. These quantitative data and qualitative observations indicate that the evolution of traditional forms is not merely an esthetic pursuit, but rather a precise optimization of structural performance within the constraints of material strength. This coupled relationship between “geometric form, load-bearing mechanism and usage context” confirms the inherent principles of resource efficiency and performance balance within traditional building systems. The quantitative assessment framework established in this study provides scientific guidance, grounded in construction logic, for the preventive conservation and precise reinforcement strategies of historic masonry structures.