Composite-reinforced timber highway guardrail: Development and structural testing

For aesthetic reasons, various government agencies install timber guardrails on scenic highways and roads in place of conventional steel guardrails. Most acceptable timber guardrails rely on a continuous steel backing member to carry the large tensile forces caused by vehicle impact and transfer load to the posts. However, these guardrails are relatively expensive and heavy due to their use of large, solid-sawn timber sections with steel reinforcing. This study focuses on the development and structural testing of a novel timber guardrail that consists of a hardwood gluedlaminated member strengthened with a fiber-reinforced polymer (FRP). The FRP acts in place of steel to carry the impact-induced tension, and the guardrail is significantly shallower and lighter than conventional timber guardrails. Details regarding the analysis of the guardrail response under vehicle impact, the development and testing of a unique and easily installed rail-to-rail field splice connection capable of carrying the tensile forces caused by vehicle impact, and the evaluation of guardrail durability in exterior conditions are given. In addition, the structural behavior of the guardrail was assessed using experiments that produced the simultaneous tension and flexure forces expected during vehicle impact using a single hydraulic actuator and a three-point bending test apparatus. The performance of the guardrail exceeded expected demands, and based on the development and testing documented in this paper, the FRP-reinforced timber guardrail is expected to be capable of passing required vehicle crash tests. Future research should more thoroughly address bond durability, especially when preservative treatments are used.