EFFECTS OF STRESS-CONCENTRATION ON THE BENDING STRENGTH PROPERTIES AND ACOUSTIC EMISSIONS OF LAMINATED WOOD BEAMS HAVING END JOINTS

We report our studies of the bending strength properties and acoustic emissions (AEs) of 3-ply laminated wood beams whose tension side layer s (lower layers) were composed of one middle lamina with a steep scarf joint or a finger joint and two side laminae side-jointed (Figs. 1 an d 2). Furthermore, we investigated the effects of stress concentration on their bending strength properties and AEs. The bending Young's mod uli of 3-ply laminated wood beams having a steep scarf joint or a fing er joint in the middle lamina of the tension side layer were greater t han those having a butt joint. However, their bending strengths were n ot increased by the use of a steep scarf joint or a finger joint inste ad of the butt joint. They had AE generations from low loading levels and a great many AE cumulative event counts compared with the no joint type. With increasing slope of steep scarf joint, the distinction of fringe order of stress concentration in the side laminae around the ti ps of joint decreased, but the distribution area of stress concentrati on became wider. It also was observed that stress concentration occurr ed in the side laminae around the tips of finger joint. Hence, the abo ve results of their bending strengths and AEs can be explained by the occurrences of stress concentrations which were observed in the side l aminae around the tips of steep scarf joint and finger joint by the ph otoelasticity method.