Study On Mechanical Properties Of LBL Variable Angle Single Shear Nail Joints

In recent years,modern bamboo structure has gradually entered people’s vision.Compared with traditional structures,it has the advantages of light weight,good seismic performance and renewable.However,it is the note that the key point of the joints is the design and research stage.Modern bamboo structures are usually connected with various metal connectors,where the price and use of nail joints is lower and easier respectively.The existing research on LBL nail joints is mainly focused on the mechanical properties under the action of along grain direction and monotonic loading,but little research has been carried out on the mechanical properties of the grain under inter-directional clamping and cyclic loading.So,a kind of three-member single shear LBL nail joint specimen is designed in this paper.Considering the influence of the angle between the nail diameter and texture direction,the monotonic loading test and cyclic loading test are carried out,and the mechanical properties are studied by using finite element software.The main findings are summarised below:(1)The material properties of LBL and nail were tested,and the tensile,compression,bending,shear,pin groove bearing strength of LBL and the bending yield strength of nail were obtained;On the basis of various wood structure specifications,the formula suitable for calculating the bearing strength of LBL pin groove is derived.(2)The minimum requirement for the transverse stress edge distance of LBL with pre-opening is 8 times(8d)of the nail diameter.The LBL nail joint is shown a typical type IV yield mode under monotonic loading.The nail is bent and deformed,and plastic hinges are formed in the main material and side material,and the pin groove deformation at the contact between the main material and side material is obvious;The pin groove of main material and side material is deformed obviously;The fatigue fracture is occurred in the nail under cyclic loading.(3)Bearing capacity and initial stiffness of the LBL nail joint is gradually increased with the increase of nail diameter under monotonic loading.The nail joint had a decreasing trend with the increase of angle.The use of large-diameter nails had high initial stiffness,equivalent damping viscosity coefficient and cumulative energy consumption under cyclic loading;The equivalent damping viscosity coefficient decreased slightly with the increase of angle.(4)Smith’s formula and Branco’s formula are used to predict the yield load and initial stiffness of LBL nail joint specimens under monotonic loading.In the exponential function,the Floz and Hassenieh model formulations are applied to predict the load-displacement curve of LBL nail joint specimens under monotonic loading,and the modified Dolan model is applied to predict the hysteresis curve under cyclic loading.(5)Finite element software is used for modeling and analysis.The failure form and load-displacement curve of the model and test are compared and analyzed,it is found that the failure form of LBL nail joint is truly simulated and its load-displacement curve is generally consistent.Thus,the change of elastic-plastic stage is better simulated in this paper.