Experimental research on mechanical performance of damaged bracket set joints

ObjectiveThe bracket set is an important component of the wooden structure in Chinese ancient architecture system, which plays a vital role in maintaining the mechanical properties of the whole structure reliable. There are different degrees of damage of bracket set joints in existing ancient structures. While at present, most of the researches on the mechanical properties of bracket set joints are based on intact bracket sets, and little consideration is given to the mechanical properties and deformation rule of damaged bracket sets, especially under the condition of decaying and volume loss caused by worm moths. Therefore, it is of great practical significance to study the effect of damage on the mechanical properties of bracket set joints or even the whole structure, which can also help provide scientific basis for the repair and protection of ancient timber structures.

MethodThis research took a typical second-story bucket arch on columns in supporting platform of Yingxian Wooden Tower, Shanxi Province of the northern China as the object, and made four groups of bracket set models with the 1/3.5 scale. One group of model kept in perfect condition, while the remaining three groups were drilled with holes in different positions artificially to weaken the stress-bearing section of components of the bracket set joints, so as to simulate the real damage to them. By adopting the vertical loading test, the load-displacement curves of four groups of bracket set joints were obtained, and the mechanical characteristics and deformation performances of bracket set joints were clarified combining the test result.

ResultThe test result and data analysis showed that under certain vertical loads, the failure of bracket joints was mainly reflected in the fracture, bending deformation of the second-story Hua-Gong and cracks on the connection block. The failure mode of damaged bracket set joints was similar to that of the intact one. While pre-drilled groups sufferred from worse damage as their ultimate load and stiffness decreased, and the negative effect caused by the former damage was more obvious on the stiffness of bracket set joints.

ConclusionWhen the damage type is the same and the overall damage condition of the structure is similar, the damage on the first story of a bracket set joint would exert greater influence on stiffness, which means it is easier to deform when bearing vertical loads.