Bolt-bearing strength parallel and perpendicular to the grain of four Indonesian hardwoods

Bearing strength is an important factor in determining the load-carrying capacity of a bolt-timber connection besides the bolt-bending yield strength. This study aims to determine the bolt-bearing strength parallel and perpendicular to the grain using three bolt diameters (6, 9 and 12 mm) in four hardwoods species with different specific gravities, namely terap (Artocarpus odoratissimus), durian (Durio zibethinus), mindi (Melia azedarach L) and rubberwood (Hevea brasiliensis Muell. Arg). The bolt-bearing strength was determined as described in ASTM D5764 using half-hole testing. The moisture contents ranged from 13.49–14.77% and specific gravities were 0.33–0.60. The higher the specific gravity, the higher the bearing strength. The bearing strength values parallel to the grain were higher than those perpendicular to the grain. The bearing strengths parallel to the grain were 3–18% and 2–24% lower than those based on the Indonesian National Standard (SNI) 7973 and National Design Specification (NDS) for Wood Construction 2015, respectively. In contrast, the experimental bearing strength of mindi was 8% higher than the SNI. Except for mindi, which was 22% exceed SNI and 9% above NDS, bearing strengths perpendicular to the grain were 3-32% and 14-41% less than values based on SNI and NDS, respectively.