A Parametric Investigation of the Influence of Knots on the Flexural Behavior of Timber Beams

Abstract

The presence of knots significantly influences the mechanical behavior of timber. This research presents a parametric finite element analysis of the effect of knot characteristics on the flexural capacity of timber beams. Parameters include knot radius, longitudinal and vertical positions, length, and diving angle. The generation of the FE model is based on a technique developed in a previous research stage. The validation of the model is done via bending tests on a set of beams as well as a number of independent research studies. The numerical model accurately recreates the three-dimensional geometry of the knot and related fiber deviations. The capacity of the beams under bending is evaluated via the Tsai–Wu failure criterion. Findings reveal that the presence of knots in the tension zone leads to an early tensile failure and insufficient utilization of compression capacity, the decrease of bending capacity may rise significantly (up to 39% in this investigation), the knot inclination may positively or negatively influence the behavior depending on the diving angle, and moderate knot length can be detrimental to flexural capacity.

Evaluation of the tensile strength of Korean yellow poplar lumber

“…Therefore, it is necessary to study and experiment to identify the factors that affect its strength. In addition to the grade of sawn timber, several studies have reported the influence of factors on strength, such as drying temperature, density, knots, and slope of grain (Gerhards 1983;Nagai et al 2011;Saad and Lengyel 2023). Typical types of defects in wood that cause failure of structural lumber mainly include ring failure, checks, wane, knots, and grain angle.…”

Experimental Research and FE Model of a Bolted Steel-CLT Composite Connection

“…Their research is based on the analysis of an elastic and plastic orthotropic material (biaxial anisotropic), and the conclusion is that Hill's criterion can be applied for modelling of those materials. The same authors show that material model can be successfully used for modelling of timber with discontinuities -knots [8]. The main disadvantage of the continuum models is the lack of material models that are ready to use in contemporary engineering software.…”