Experimental And Theoretical Study On Mechanical Properties Of Screw Connection Of Laminated Bamboo Lumber

The application of engineered bamboo structure is of great significance for realizing low-cost and ecological village houses,promoting low-carbon energy-saving green buildings in my country.The price of wood screws is relatively low,and the construction and installation are simple to meet the requirements of simplified assembly construction.However,the current research on the wood screw connection of the laminated bamboo lumber(LBL)beam-column structure is relatively scarce,and there is a relatively lack of relevant engineering bamboo structure design specifications.This paper uses LBL as the material,focuses on the mechanical properties of the wood screw connection with LBL,conducts the experimental research on the withdrawal capacity of the wood screw connection with LBL,and the shear capacity of the wood screw connection with LBL and steel plate,Through theoretical analysis,establish a calculation formula for bearing capacity suitable for wood screw connection with LBL,The main research results are as follows:(1)The basic physical and mechanical properties of LBL and the basic material properties of wood screws were determined through investigation and experiment.(2)Completed the withdrawal test on 135 wood screw connection with LBL,the failure mode was obtained as the anchoring depth increased,from the withdrawal failure of the wood screw to the yield failure of the wood screw.The recommended critical anchoring depth was 7d.The effects of wood screw diameter,anchoring depth and connection texture direction on the withdrawal resistance of LBL with wood screw were analyzed,Based on the European wood structure design code,conducted a theoretical analysis of the connection,established the withdrawal capacity of the computational formula used in designing the wood screw connections with LBL.(3)Through the experimental research on 126 specimens of wood screw connection cross-grain and along-grain shear resistance of LBL and steel plate,the influence of wood screw diameter,anchoring depth,end distance,spacing,row distance and other factors on the failure mode and mechanical properties was analyzed.The results supported that when the anchoring depth of wood screws increases to 4d,the failure mode changes from the withdrawal failure of the wood screw to the shear failure of the wood screw.Through the influence of the end distance,spacing and row spacing on the failure mode and connection load-bearing performance.Proposed construction requirements of LBL and steel plate with screw were put forward.(4)The design method of connection in Chinese,American and European wood structure codes was analyzed,and the calculated results of the design method of wood structure codes were compared with the test results.By contrast,the error of the European code which considered "rope effect" was the smallest,but it was still more than 50%.Therefore,the mechanical principle of the wood screw connection with LBL joints was analyzed,and the theoretical calculation method for the bearing capacity of the wood screw connection with LBL was established by deducing the theoretical formula.