Connection Design And Bearing Performance Evaluati On For Larch Laminated Wood Beams And Columns

Laminated wood structure buildings are an important direction of wooden house in residential development with the properties of low-carbon,energy,seismic resistance and stability, so they are used widely gradually. In the laminated beams and columns connections, the metal connectors are used to connect beams and columns, such as dowels, bolts and steel plates. This research will combine domestic wooden structure industry, and do some series tests. Firstly, testing the half-hole dowel bearing properties of Larch glued-laminated timbers and Larch dimension lumbers, and analyzing the impact of density and diameter to the dowel bearing properties; Secondly, assembling with glued-laminated timber, steel, and bolts or dowels, then test lateral bearing capacity of connections with doweled wood-steel-wood which were loaded perpendicular to the gram (including dowled perpendicular to the layer dierection,θ=90°and dowled parallel to the layer dierection,θ=0°) and the bolted steel-wood-steel were loaded parallel to the gram(including bolted perpendicular to the layer dierection,θ=90°and bolted parallel to the layer dierection,θ=0°), from that, we could obtain the proportional limit load, yield load, yield strength and initial slope and other parameters and the failure modes; At last, glued-laminated beams and colums were assembled with special connectors, bolts and dowels and so on, to simulate the performance of beam and columns connections and evaluate the bearing capacity of U-plate and T-plate.Main results are summarized as follows:Reference to ASTM D5764-97a, half-hole dowel bearing capacity was tested with 47 Larch dimension lumbers, the results showed that the dowel bearing yield strength was about 39.93MPa which is a better agreement with theoretical value of 42.49MPa.The dimension lumbers were gourped by density and pressed into 50 glued-laminated timbers with two component polyisocyanate adhesive, results showed that connection capacity loaded parallel to grain was significantly greater than loaded perpendicular to grain, and the yield load is about 1.48times to 1.93 times than loaded perpendicular to grain; when loaded parallel to grain, the bearing strength of glued-laminated timber increased with density increasing, the coefficient of determination R2=0.7701; when loaded perpendicular to grain, R~2=0.6054, while, the strength decreased with dowel diameter increasing. the dowel bearing yield strength loaded parallel to grain of medium density glued-laminated timber with corresponding dowel diameter 10mm, 12mm, 18mm was 43.1MPa, 42.67MPa,41.9MPa; the strength loaded perpendicular was 25.56MPa, 25.12MPa, 21.89MPa, respectively.After samples damaged, the through split from the bolt hole to the end of glued-laminated timber could be abserved and bolt or dowel occured the plastic hinge. Bolt had been produced a plastic hinge with diameter 10mm and material grade 4.8, the two sides of hinge is remain upring; while bolt with diameter 12mm, two plastic hinges; the material of dowel is Q235, after test, there is a platic hinge clearly; when paralleled to the grain, and the bolts or dowels are parallel to the glue line(θ=0°),the proportional limit load, yield load, yield strength were closed to the direction of perpendicular to the glue line(θ=90°), so is the same to perpendicular to the grain, that is the direction between bolts (dowels) and glue line did not matter the bearing load; Foschi equation could simulate the joint's load-displacement curve well, which reflected the post-elastic region and the joint characteristics after yield, and represented the flexible and plastic transformation process.Glued-laminated beams and columns had been damaged mainly in the beam with a crack, The max bearing load of T-plate and U-plate is equal, while the displacement of the max load is not the same, T-plate for 35mm, and U-plate for 15mm, so U-plate is better and the beam damage is relatively smaller; the yield load of U-plate id 74.62kN, which was greater than the yield load 51.43kN, obtained by the same size glued-laminated beams and columns glued by Japan cedar, which had already passed the performance certification; the yield load of T-plate connectoris 45.94kN, so U-plate connector is better than T-plate.