Experimental and numerical study on eccentric compression performance of Dou-Gong brackets at column tops

Abstract

The Dou-Gong bracket at column tops is the main force-transmitting member that connects the structural column and the roof in ancient timber buildings. The misalignment of the column or roof deviates the transmitted vertical load from the central axis of the Dou-Gong bracket, which adversely affects the vertical load-bearing performance of Dou-Gong brackets by the eccentric load. To quantitatively study the influence of the vertical eccentric load on the mechanical performance of Dou-Gong brackets at column tops, the vertical loading tests with different eccentricities were carried out on three Dou-Gong brackets. The eccentricity is defined as the ratio of the distance between the central axis of Dou-Gong brackets and the vertical load point to the side length of the top surface of Da-dou. The failure mode, vertical strength, compressive stiffness and deformability of Dou-Gong brackets at column tops under the axial compression and eccentric compression (eccentricity of 0.15 and 0.3) were obtained. The Dou-Gong bracket produces irreversible overall compressive plastic deformation under axial compressive loading. Different constitutive components of the Dou-Gong bracket squeeze significantly and compact into a whole part that is hard to separate. The final damage is the compressive collapse of Da-dou (a constitutive component of the Dou-Gong bracket) under compressive loading. However, tilting and rotation deformation of Pingban-fang and Da-dou were clearly observed under eccentric compressive loading, which results in a more brittle failure pattern. On this basis, a finite element parametric analysis on the vertical compressive performance of Dou-Gong on column tops was carried out. The results showed that a larger vertical eccentricity causes more notable tilting damage of the Dou-Gong bracket, which reduces its ultimate strength as well. When the eccentricity of vertical loading reaches 0.3, the ultimate strength of Dou-Gong brackets at column tops is reduced by 42% compared with the axial compression one.