Impact of embedded nut on the joint property of eccentric fittings.

The objective of this study was to explore the feasibility of two types of new insert nuts by taking inbuilt nut as the single variant. A series of experiments were conducted to analyze the influences of five types of commonly used inbuilt nuts and the two types of new insert nuts on the joint property of eccentric fittings under T and L-shape structures, and the breaking bending moment, rigid efficiency and failure characteristics of the two connection types were compared. Results are as follows: 1) the breaking bending moment of inbuilt nuts are ranked in the order of shim block ≈ cross dowel ＞ screw-in sleeve with flange ≈ screw-in sleeve with hexgon socket and flange ＞ screw-in sleeve with spine ＞ screw-in sleeve with four claws ＞ nylon spreading dowel; 2) the rigid efficiency of inbuilt nuts follows the order of screw-in sleeve with hexgon socket and flange ＞ shim block ≈ cross dowe l≈ screw-in sleeve with flange ＞ screw-in sleeve with four claws ＞ nylon spreading dowel＞ screw-in sleeve with spine; 3) the breaking bending moment and rigid coefficient of the seven types of T-shape inbuilt nuts are 26.7% and 26.8% higher than those of the L-shape, respectively; 4) the main failure characteristics of insert nuts are the deformation of trinity joint lever and eccentric wheel; while for the commonly used inbuilt nuts, the failure mainly includes timber tear and partial crushing triggered by pulling-out of inbuilt nut; and 5) in T-shape connection of cross dowel nuts, under the circumstance of only changing the destroyed joint lever and eccentric wheel, the breaking bending moment of the second time is reduced by 3.1% compared with that of the first time. Therefore, the types of inbuilt nut significantly affect the breaking bending moment of eccentric fittings; compared with commonly used inbuilt nuts, inserted inbuilt nuts are superior in stronger breaking bending moment, higher rigid efficiency and the availability of changing the destroyed hardware to realize the reutilization of plates, showing obvious advantages and feasibility.