| In recent years,modern bamboo and timber structures have become a key development direction in China’s construction industry due to their green,lightweight,high strength and humanistic characteristics.Structural failure often begins with the destruction of the nodes,nail nodes as a common form of connection,with simple construction,easy installation,low price and other characteristics,in domestic and foreign wood structure connection is used.Southern pine has become an excellent building material due to its excellent structural properties,but the research on its nail nodes is not enough.In this paper,the nail nodes of southern pine were tested for pullout and shear resistance in accordance with the load bearing direction,and compared with the nail nodes of LBL to investigate the influence of factors such as cut surface,nail diameter,nail entry depth,nail type and the angle between load and grain direction on the performance of the nail nodes.The main research results are as follows:(1)The flexural yield strength of light round steel nails,galvanised twist nails and cement nails,the compressive strength of southern pine and LBL and the pin groove bearing strength were obtained from southern pine,LBL and nail material properties tests.(2)Pull-out tests on Southern Pine nail nodes were carried out to investigate the nail grip performance of Southern Pine end faces and chord faces under the influence of parameters such as nail diameter,nail entry depth and nail type.The results show that there are some differences in the damage patterns of the specimens,with the form of damage being related to the roughness of the nail body,but not to the nail diameter or nail entry depth.The damage pattern of the galvanised twist nail specimens was mainly in the form of circumferential shear damage of the wood,accompanied by the removal of wood chips.(3)The nail pull-out load-displacement curve mainly consists of an elastic section,a slip section and a drop section,which show obvious non-linear characteristics.The displacement in the elastic rise section grows very slowly but the load grows very rapidly,and when the embedded force and friction between the nail and the wood are overcome,the nail starts to slip and then the load starts to fall slowly.(4)Southern pine end grip force is less than the chord surface grip force,grip force and nail diameter is a linear positive relationship;grip force increases with nailing depth,galvanised twist nails grip force is better than light round steel and cement nails.(5)A variable angle shear test jig was developed and a single nail shear test was carried out on a three-wood member to investigate the effects of nail diameter,nail type and angle between grain directions on the shear load capacity and initial stiffness of nail nodes.The results show that the shear load capacity and initial stiffness of southern pine are positively correlated with nail diameter and negatively correlated with the angle between grain directions;the shear resistance of galvanised twist nails is better than that of bare round steel nails.(6)The mechanical properties of LBL and southern pine nail nodes were compared and analysed by means of pull-out and shear tests on LBL nail nodes.The results show that the grip strength of LBL is better than that of southern pine,with the former being more than three times the grip strength of the latter.the shear load capacity of LBL nail node specimens is about two to four times that of southern pine;the Blass formula is more suitable for calculating the shear load capacity of southern pine,while the Hassenieh model is more suitable for predicting the shear test curve of LBL. |
