Using renewable plantation timber as a replacement option for unrenewable hardwood girders in bridges

Abstract

This project investigates the possibility of integrating reinforcement with softwood glulam (glue laminated) timber beams to provide an economic alternative to hardwood timber girders. The resources of hardwood timbers are dwindling due to a reduction in tree felling, and hardwood timber plantations are unable to keep up with demand. Due to this growing shortage, there is an increased need to find a suitable replacement for deteriorating hardwood timber girders on rural bridges throughout Queensland. This project analyses a possible alternative. From a design stand point, the beams should cater for the requirements specified by the Department of Main Roads. An experimental approach has been taken to study the effect of the integration of steel reinforcing within the laminates of a glulam timber beam. This design will be tested for strength using a four-point bending arrangement with two hydraulic jacks providing force on the member. The results of the test showed the beam catered for the requirements and specifications outlined by the Department of Main Roads up to 660kN. However, while the beam supported the load, the tested Modulus of Elasticity (MoE) fell outside the range of these specifications. It is considered that this could be easily rectified following minor changes to the design.