The Effect of Circular Arc Tapers on Strength of Timber Beams End-Notched on the Tension Face

Abstract

Timber beams such as joists and rafters are often end-notched on the tension face to enable flush and secure seating. Circular arc tapers cut at the notch corners to reduce shear stress concentration and increase fracture toughness have received less attention in the literature and construction standards than the cases of linear, fillet, and no taper. A design standard for the circular arc taper is suggested based on FE and physical three-point bending tests for six taper geometries as well as ASTM Standards D245 and D1990. The physical tests use thirty total specimens of 2✕6 nominal no. 2 kiln-dried Douglas-Fir four feet in length; every specimen exhibits a shear initial failure mode.