WITHDRAWAL PROPERTIES OF HARDWOOD DOWELS IN END JOINTS II - EFFECTS OF DOWEL DIAMETERS, YOUNGS MODULI OF ADHERENDS, DOWEL SPACINGS AND NUMBERS OF DOWELS

A series of pull-out tests of dowels glued parallel to the grain of th e wood was made to determine the effects of some variables of adherend s on withdrawal properties. Considered variables were dowel diameter, modulus of elasticity (MOE), dowel spacing, and number of dowels. With drawal strengths calculated from theory(3)) increases with increases o f dowel diameters. The theoretical predictions were consistent with th e results of bond-line-failed specimens for 8, 12, and 16 mm dowels. H owever, more than half of the specimens of 16 mm dowels failed by dowe l fractures at considerably less loads than those failed by bond line fractures. The tensile stress at ultimate loads calculated on a Volker sen model might reach the tensile strengths of dowels for all diameter s tested. Withdrawal strength might be sensitive to the variation in t ensile strength of dowels. Steel dowels were tested to study the effec ts of dowel MOE. Withdrawal strength for steel dowels did not level of f at long embedded-dowel length. These results were predicted qualitat ively from the theory. The effects of MOE of the wood member on withdr awal strength were found to be negligible provided that stiffness rati os of the wood member to a dowel were large enough as perdicted from t he theory. A test series was conducted to study the effects of dowel s pacing and number of dowels. The results suggested that doubling of th e diameter is a sufficient dowel spacing. Withdrawal strength for mult iple dowels was found to be about 80% of that for single dowels. This reduction in strength might be caused for the following two reasons: ( 1) Bonding was performed by inserting dowels into lead holes filled wi th adhesives. Some glue starving might occur for multiple dowels, whic h led to insufficient adhesion. (2) Same cross-sectional eccentricity of the dowels in lead holes would be induced by misalignments of lead holes. The section of the thinner bond line would cause greater sheer stress and failure.