Bearing Tests of Glued Laminated Timbers with Drift-Pins

摘要

To investigate the accuracy of present designformulas for mechanical joints of glued laminated timbers(GLTs), dowel-bearing tests with a drift-pin were conducted inthis study. GLTs with four kinds of moduli of elasticity (5.9, 7.9,9.8, and 11.8 GPa) were prepared for the tests. These GLTs werecomposed of mechanically graded Japanese cedar and Japaneselarch laminae with uniform modulus of elasticity. Four types ofspecimens were cut from these GLTs; "Parallel type" in whichload was applied parallel to the grain, and "Perpendicular type"in which load was applied perpendicular to the grain. Five kindsof drift-pins with the diameter of 4, 8, 12, 16 and 20mm wereembedded into GLTs. Bearing stress was calculated by the ratioof a bearing load to the diameter and the length of a drift-pin.We investigated the relation of the diameter of a drift-pin to"five percent offset values" specified in ASTM-D5764, "initialstiffness" calculated by the ratio of a bearing stress to a unitbearing deformation, and "effective elastic foundation depth"(the ratio of modulus of elasticity of wood to the initial stiffness)based on the theory of a beam on elastic foundation.The results obtained were as follows.(1) Five percent offset values were constant regardless ofthe diameter for the "Parallel type" whereas they showed adeclining tendency with increasing of diameters for "Perpendicular type".(2) Initial stiffness decreased with increasing of diametersfor the "Perpendicular type", on the other hand, this tendencywas not clear for the "Parallel type".(3) Effective elastic foundation depth increased withincreasing of diameters for both types. Dr. Hirai's formulacommonly used to estimate the relationship between the depthand diameter of fasteners was applied to these results, howeverthe conformability was low. This discrepancy resulted from thefact that the formula was derived from experiments in whichfasteners of small diameters were used.