The Failure Mechanism Of Aluminum-Glulam Joints In Reticulated Shell Structure

With the implementation of carbon reduction policies in the construction industry,the number of timber structures in China is gradually increasing.The timber grid-shell structure,widely used by professionals in the domestic and international construction industry,is valued for its beautiful appearance,environmental friendliness,thermal insulation,and ability to span large distances.Among them,the large-span timber gridshell structure connected by bolted splint is easy to construct,highly prefabricated,and well-suited to the trend of prefabrication and assembly in China’s construction industry.The material properties of glued laminated timber exhibit anisotropy,with lower tensile strength in the transverse grain of the wood component,which can lead to transverse splitting failure of the wood component.On one hand,transverse splitting failure of wood is a brittle failure mode,characterized by suddenness and unpredictability;on the other hand,splitting failure of wood can lead to premature failure of bolted splint connections,preventing the splint from fully exerting its performance.Welding steel nails into the splint can limit the development of longitudinal cracks in the wooden beam,but the high density of steel results in heavy splint quality,which increased the seismic response of the structure.In this paper,an aluminum alloy splint connection is designed based on the nailed steel splint connection,and numerical analysis using finite element software ABAQUS is performed on this connection.The research content and results are presented as follows:1.This paper summarizes the application examples of large-span timber structures in China and abroad,analyzes the current research status of glued laminated timber structures and aluminum-timber joints.Addressing the problem of excessive self-weight of the connection zone in a k6 type glulam shell structure with bolted splint and wooden beams,which sets a hub at the connection,the design proposes the use of lightweight and high-strength aluminum alloy to replace steel,and studies its mechanical properties and failure mechanism.2.In order to select the most suitable aluminum alloy material for the connection,the mechanical properties of the splint and hub are adjusted by changing the aluminum alloy grades of the splint and hub,and their stress performance is studied under lowcycle reciprocating loads.The research results show that the bearing capacity and deformation performance of the splint significantly affect the failure mode of the connection.The poorer the deformation performance of the splint,the more obvious the "pinching" phenomenon in the hysteresis curve of the connection,and the more likely the failure mode tends to be the crushing failure of the steel nails holes and bolt holes of the wooden beam.3.To investigate the force transmission mechanism of steel nails and the failure mechanism of aluminum alloy nailed splint joints,aluminum alloy nailed splint joints with and without nails were designed to study the differences in their stress performance and failure modes.It was found that the addition of steel nails on the inner surface of the nailed splint significantly enhanced the initial stiffness and load-bearing capacity of the joint.The embedded steel nails prevented the development of longitudinal cracks in the wood beam and limited the occurrence of transverse cracking failure.4.The parameter analysis of the nailed splint connection was carried out to investigate the influence of the number of steel nails,the length of steel nails,and the aspect ratio of steel nails on the ultimate bearing capacity and failure mode of the connection,and to study the force transfer mechanism of steel nails.It was found that the ability of steel nails to participate in force transfer is positively correlated with the number of steel nails,the diameter of steel nails,and the length of steel nails in a nonlinear manner.5.To simplify the connection design,the formulas for calculating the ultimate load and stiffness of the connection,as well as the theoretical model for the momentdeflection curve,based on the Johanson yield model were derived.By comparing with the simulation results,it was found that the theoretical values had an error of less than10% compared to the simulation values,and the theoretical values tended to be more conservative.