THE STRENGTH PROPERTIES OF DRIFT-PINNED, BOLTED, OR/AND LAG-SCREWED TIMBER JOINTS WITH STEEL GUSSET PLATES

To investigate the strength and stiffness of drift-pinned, bolted, or/and lag-screwed timber joints with steel-gusset plates, this study was conducted with tension-type lateral-strength tests. Specimens were glulam lumber of Douglas-fir (Pseudotsuga menziesii (Mirb.) France). Four kinds of joint types (Table 1) used consisted of inserted steel plates or steel side plates with single fasteners. Fourteen series of tests were conducted with combinations of two loading directions (parallel to the grain (0 degree) and perpendicular to the grain (90 degree)), three diameters of fasteners (d=12 mm, 16 mm, and 20 mm), and two thicknesses of specimens (75 mm and 150 mm). The results obtained were as follows: 1) Generally speaking, great strengths were observed in 0-degree loadings. On the other hand, relatively small strengths always were observed in 90-degree loadings. 2) In 0-degree loadings, the joint strengths of the bolted joints with steel side plates were the greatest of the four joint types. Those of the drift-pinned joints with inserted steel plates and the bolted joints with inserted steel plates were about the same. In the case of d=12 mm, the lag-screwed joints with steel side plates when the slenderness ratio (L/d, L: effective lengths of fastener)=5.9 had about the same strengths as the drift-pinned joints with inserted steel plates when the slenderness ratio=11.6. 3) The bolted joint and lag-screwed joint with steel side plates had remarkably tough characteristics. This properties also could be estimated from the failure or ultimate phenomena to some extent. 4) The ratio of maximum load to the yield load (P-max/P-y5%), which was determined by the so-called ''5% offset method(1))'', was very large particulary in the bolted and lag-screwed joints with steel side plates loaded in the 0-degree direction. This trend became more remarkable as the slenderness ratio increased.