Date of Award

2003

Level of Access

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

Advisor

William G. Davids

Second Committee Member

Donald A. Grant

Third Committee Member

Richard C. Hill

Abstract

This study focuses on the development of an aesthetically pleasing, cost effective, timber guardrail system, which utilizes low-grade New England hardwoods such as red maple and beech. This required that several issues be addressed, including structural modeling, rail section design, rail fabrication, evaluation of durability, rail-to-rail field splice connection design, and the evaluation of guardrail system performance under impact loading. The use of glulam beams in infrastructure is increasing rapidly with the reduced availability and increase in cost of high grade solid sawn timber. New techniques allow for increased material usage while maintaining a high strength product. Selective stacking of laminates, using finger jointed lumber, and using a brickwork layup were all techniques which were used to increase utilization of lower grade lumber. To enhance the system performance, the glulams are reinforced with fiber reinforced polymer (FRP). Using these techniques a glulam guardrail was developed, which is relatively light, durable, and should be capable of passing the NCHEW Report 350, Test Level 3 crash test. The guardrail was evaluated through modeling and quasi static bending and tension testing. To evaluate the effectiveness of the design under the Test Level 3 crash test, the test and rail system was modeled using the Barrier VII dynamic impact program. This demonstrated that the guardrail system is not only under large bending loads, but also encounters large tensile forces. This tension force will need to be transferred between rail sections by use of a splice connection, if the rail is to perform effectively. Glulam beams are not traditionally used for applications where it is necessary to transfer large tensile forces between members. Designing a highstrength bolted connection between both wood and composite members is inherently difficult due to their tendency to fracture. A solution was developed where steel connection plates were bonded to the ends of the rail sections during fabrication so that the field connection only requires bolting the rail to a steel splice plate. The reinforced glulam maple guardrail system was tested in four ways to assess its performance. The first was an eccentrically loaded tension test, which was designed to test the rail splice connection. The second test was a simply supported three point bending test. From this test the modulus and section properties for the guardrail beams were determined. The third test which was performed was a combined bending and tension test to determine the response of the rail under actual impact loading conditions. Using the experimentally determined modulus, a model of the beam under combined bending-tension was used to design a reaction frame. This reaction frame induced tension in the rail by restraining the shortening of the rail due to bending. The durability of the rail and splice design was evaluated for exterior exposure using the ASTM Dl 101-A delamination test. The major conclusions of the study are that the FRP-reinforced hardwood glulam guardrail appears to be capable of passing an actual crash test, and that the rail is a cost effective alternative to existing timber guardrail systems.

Share