Methods of Enhancing the Performance of Timber Beams

  • Benjamin Brown

Student thesis: Doctoral ThesisPhD


The use of timber in the construction industry is increasing as a sustainable alternative structural material to steel and concrete. However, timber beam design is often limited by the serviceability requirements of the structure. To investigate this limitation, two novel methods of enhancing the mechanical performance of glued laminated timber (Glulam) beams were explored: curve laminated beams and curve reinforced beams.
The stiffness of timber in the grain direction is around 40 times greater than the perpendicular direction. Therefore, the timber’s grain was aligned to the curved principal stress path by curving the laminations of the Glulam beam. This builds on an idea from 1903 by Otto Hetzer who reinforced a low-value wood beam with a curved tension member of high-strength wood. Experimental tests on nine 80 x 32 mm curve laminated beams spanning 1440 mm showed an improvement in stiffness of 9% compared to equivalent straight laminated Glulam beams.
Previous research has shown that improvements in the strength and stiffness of Glulam beams can be obtained through the introduction of reinforcing materials such as steel or FRP into the cross section. Introducing a curve to the reinforcement that followed a principal stress path was used to improve the shear stiffness of the beam and to help understand the curve laminating technique. In this study an analytical model for a curve reinforced beam was established based on Timoshenko beam theory. The model predicted a Glulam beam reinforced with 5% cross sectional area of curved steel would improve stiffness by 12% compared to a straight reinforced Glulam beam.
The analytical model was validated by both a finite element model and by experimental testing on straight and curve reinforced beams. Four-point bending tests were carried out on three straight and three curve reinforced beams with 405 x 90 mm sections spanning three metres. The curve reinforced beams with a 2.2% area of steel showed stiffness improvements of 7% compared to the straight reinforced beams and 79% compared to the unreinforced Glulam beams. However, a parametric study using the validated analytical model showed that the inclusion of the steel and resin reinforcing materials increased the total embodied carbon of the reinforced beams despite achieving a reduction in cross sectional area of 14% for the curve reinforced beams compared to the unreinforced beams. This suggests that the curve laminated technique has the greatest potential as a low carbon beam as it is a whole timber system.
Date of Award28 Jun 2023
Original languageEnglish
Awarding Institution
  • University of Bath
SupervisorPete Walker (Supervisor) & Mark Evernden (Supervisor)

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