Abstract:

Objective: In the paper, testing in the full size structural beam connected with a dowel (drift pin) to the slotted-in steel plates in the loading direction of perpendicular to the grain of the beam was done to study the failure mechanisms and load-bearing performances of the dowel joint of Japanese cedar beam. The research was conducted to provide basic data for the design of dowel joint at the end of the beam in the post and beam structure. Method: After slotting and drilling at the end of the beam, a single dowel was connected to the slotted-in steel plates. The bending shear testing under load perpendicular to the grain was carried out on the Japanese cedar beam of sawn timber and glued laminated timber (glulam) in the same size, respectively. According to the general analysis method in Japan, standard percentile values of load-bearing in the short term of dowel joint in the beam were determined, and compared with the calculated values based on the yield load specified in 5 different national standards. Result: In the initial loading, the load-displacement curve had a linear relationship in a linear elastic stage. As the displacement increased, the curve became nonlinear and entered the elastoplastic stage. When the displacement increased to a certain value, initial brittle cracking occurred at the end of the beam, and the load was suddenly reduced rapidly, and then the load rose again. When loaded to the limit state, the beam member split and lost its bearing capacity. Cracks along the horizontal shear plane of the pin hole in the beam component happened with yield mode Ⅲ in the final failure. The standard percentile value in the short-term bearing capacity of the single dowel joint in the slotted-in steel plates at the end of beam of the sawn timber and glulam beams with a cross section of 120 mm×240 mm depended on the yield load, which was 8.6 kN and 13.7 kN, and the average load value corresponding to the initial cracking was 15.0 kN and 21.1 kN, the average yield load was 14.50 kN and 15.00 kN, and the average maximum load was 27.0 kN and 30.8 kN, respectively. Conclusion: The average value of maximum load and the yield load of a single dowel connection of glulam beams was greater than that of the sawn timber beams, and the coefficient of variation was significantly smaller than that of the sawn timber. The moisture content of glulam beams was relatively low and less variation. The above reasons resulted in the standard value of pin joint load of glulam timber a little higher than that of sawn timber, i.e. a higher connection bearing capacity. When the dowels were used as the main type of connectors for post and beam components, glulam with certificated strength grades as the wood component might be preferable to sawn timber. The bearing capacity of the pin connection in the beam end had a good correlation with the bearing capacity of the single pin connection and the number of pins, which could be used as the design basis of the beam-column joints with metal connectors. The cracking of the wood after pin yielding occurred. The initial cracking depended on the shear strength or perpendicular tension strength of the wood and the pin hole position at the end of beam. After the initial cracking, the dowel could still play a supporting role, which kept the joint a good ductility. The standard percentile values of bearing capacity of sawn timber and glulam beam by test data had a good correspondence with the calculated value of the yield load formula specified in the several standards. The calculation formulas of brittle failure in the standards from various countries could predict the brittle failure of the pin connection. Compared with the testing values, the calculation values of the cleavage failure in the Japanese standard were closer, and the calculation results of the European and Canadian standards were more conservative. The brittle failure in the design of the wood connection in our current standard had not been considered fully. In the future, further research should be done related to the calculation formula and parameters of the dowel connection to better ensure the safety and reliability of the wood components connection.

Key words: Japanese cedar, wood structural component, dowel(drift pin) connection with slotted-in steel plates, bearing performance under load perpendicular to grain, yield modes, brittle failure