Experimental analysis of warping torsion and bending in timber box beams

Abstract

In order to solve the problem in the analysis and design of timber box beams, this work applied the principle of minimum potential energy theorem in fabricating and testing timber box beams. This was achieved by applying an experimental approach in minimization of the potential energy of timber (an anisotropic material) which has variations in its intrinsic materials properties. A procedural testing of natural warping, and bending was done by carrying out investigation of pure bending of box beams using a compressive strength testing machine of maximum designed strength of 2500kN and carrying out investigation of pure bending of box beams using a flexural testing machine of maximum designed strength of 100kN. Consequently, a fabrication of box beams was done.. A comparative analysis was done to compare values obtain from the analytical method and the experimental values. It was observed that the test results from different species were in correlation with the analytical method.. The following deductions were made: In the longitudinal warping rates, the range of rate of warping are Danta ( 0.33 % to 1.67%) , Okan ( 0.5% to 1.22% ), Agba ( 0.33% to 0.83% ) and Afara (0.05% to 0.83%) in their descending order .In the lateral warping rate, the ranges of rate of warping are Okan ( 0.03 % to 2.33%), Danta (0.11% to1.0%), Agba ( 0.11% to 1.0%) and Afara ( 0.06 to 0.11%) in their descending order. In the radial warping rate, the ranges of rate of warping are Danta (0.5% to 1.34%),Agba (0.11% to 1.33%), Okan ( 0.03% to 1.33%), and Afara ( 0.06 % to 1,33%) also in their descending order. The racking forces in the flexural box beams tests are Okan(95kN), Danta (74kN), Afara( 45kN),and Agba ( 31kN) in their descending order. The racking forces in the compressive box beams tests are Okan (107kN), Danta (60kN), Agba ( 50kN), and Afara( 12kN) in their descending order. The jagged effect experienced by the box beam towards failure being caused by the progressive splitting of the extreme tension fibres shows that before the ultimate racking force, the box beam has been acting as a monolithic system, thus it resists the maximum force before failure occurs. The renewed increase in strength which tends towards the near maximum, but not the ultimate, occurs due to the resistance offered by the fibrous material of the timber species. This is an indirect method of accessing the resistibility of individual species fibrous material, it can be stated therefore that for the four species tested their fibrous resistibility are given in their descending order Okan, Agba, Danta and Afara. This study has confirmed that distortion of timber equally varies with different species.