Effect of top support span in four-point bending of wooden beams versus three-point bending

Abstract

This article investigates the influence of geometrical parameters in four-point bending of wood. The monitored factors affecting the bending characteristics were the bending method (three- and four-point bending) and the span of the top support mandrels ‘V’ in four-point bending of a beam (80, 90, 100, 110, 120 and 130 mm). Changes in the span of the top support mandrels ‘V’ in four-point bending result in a change in the distance of the upper beam mandrel from the supports of the test specimen ‘a’ (55, 60, 65, 70, 75 and 80 mm), which was another monitored parameter. Two wood species were selected for the experiments: oak ( Quercus robur L.) and spruce ( Picea abies L.). The investigated mechanical characteristics describe the behaviour of beams in both the elastic and plastic regions of the stress-strain diagram under bending load. The experimental data were processed using the MATESS software, which addresses limitations of current standards by applying novel mathematical approaches to accurately determine the boundary points of the stress-strain diagram. The results of this research deepen knowledge of wood loading and show the effect of the geometric parameters of bending on the overall bending characteristics, where the 4-point bending test with a longer loading span and the higher density wood species (oak) showed superior mechanical properties. Understanding these influences is essential for optimizing structural design and improving the accuracy of numerical models for wooden beams. The provided numerical modeling offered reliable and appropriate results compared to experimental properties.