State-of-the-Art Review of Approaches for the Design of Timber Beams with Notches

Abstract

change in different ways: elastic -decreases, and plastic -remains at the same marks with slight deviations in one direction or another. The initial modulus of elasticity of the studied samples is greater by 23-55%.It was found that the strength of deeply modified materials by the polymer composition "Silor" increases in the range of 17-21%, deformability (critical relative deformation) is reduced by 7-20%, and the initial modulus of elasticity increases significantly by 26-35% compared with wood of the same breeds modified superficially.The sixth section describes the scope of valid (complete) and optimized (with a limit at the point of boundary deformation) diagrams of "stress -strain". Using such diagrams, the mathematical apparatus of calculation of various elements and constructions on the basis of continuous, glued and modified wood is improved.

Impact of knots on the fracture propagating along grain in timber beams

“…Starting from the well-known weakest link model by Weibull, a strongest link model recently developed and published shows the potential of being an efficient tool in modelling the positive impact of knots and local grain deviations on the strength of wood when subjected to shear stresses and stresses perpendicular to the grain. 9 Example of the FE-Model of an end-notched glulam beam during progressive crack growth with a realisation of the randomly distributed clear wood and knot sections (Jockwer 2014). The light grey dots along the crack path represent nodes assigned to clear wood material properties, whereas the black dots represent nodes assigned to higher fracture energy values of knot sections 10 Examples of load deflection curves from FE-Models of end-notched glulam beams with knots along the crack path (Jockwer 2014)…”

“…9 Example of the FE-Model of an end-notched glulam beam during progressive crack growth with a realisation of the randomly distributed clear wood and knot sections (Jockwer 2014). The light grey dots along the crack path represent nodes assigned to clear wood material properties, whereas the black dots represent nodes assigned to higher fracture energy values of knot sections 10 Examples of load deflection curves from FE-Models of end-notched glulam beams with knots along the crack path (Jockwer 2014)…”

“…2 Spatial distribution of fracture energy within a lamella derived from 27 tests (Jockwer 2014). The right specimen at position 1 contains a knot in the crack plane Möhler and Mistler (1978) performed tests on notched beams with different notch depths.…”

“…Jockwer ( 2014) studied the load-carrying capacity of end-notched beams and suggested optimised reinforcement methods. In a test series on unreinforced glulam beams, the crack opening and crack shearing Riberholt (1972) 5 Mean values and standard deviations of the average shear stress at failure V ult /(bαh) from end-notched beam tests on solid timber beams reported in Möhler and Mistler (1978) 6 Crack path with a clear wood and b a knot in the vicinity of the notch corner from tests on notched glulam beams (Jockwer 2014) displacements were measured in the notch corner. addition, the surface deformations were recorded and analysed by means of digital image correlation (DIC).…”

“…The distribution parameters of the knot factor can be determined by fitting the results of the simulation to 7 Average shear stresses (V/(bαh)) in dependency of the deflection at the load introduction point. Comparison between a specimen with a knot along the crack path and a specimen with clear wood along the entire crack path (Jockwer 2014) 8 Crack opening δ at the notch corner of notched beam specimens with and without knots along the crack path (Jockwer 2014) test results from the literature. Fitting the results of the simulation to from the literature yields to a knot factor with a mean value of approximately 2 and a coefficient of variation of 40%.…”