Date of Award

5-2001

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Civil Engineering

Advisor

Habib J. Dagher

Second Committee Member

Stephen M. Shaler

Third Committee Member

Beckry Abdel-Magid

Abstract

Glued-laminated timber (glulam) is a wood product formed by face bonding lumber laminations in a prearranged order to create larger structural members. Capable of spanning greater lengths and carrying greater loads, glulam has advanced wood as a building material. Although glulam timber offers significant improvement over sawn timber, its ultimate bending strength often remains limited by strength reducing flaws, such as knots and finger joints, in the tension zone.

Tensile reinforcement of glulam has been researched in the past, most commonly using metal reinforcement, without commercial success. Recent advances in high strength composites, such as pultruded glass fiber reinforced polymers (FRP), offer new opportunity to further engineer glulam.

This project developed a pultruded, phenolic, E-glass FRP to be compatible with two of the most widely used glulam species, Douglas-fir (DF) and western hemlock (WH), using conventional wood laminating methods and materials. Since glulam is defined by gluing laminations together to form a larger structural member, one objective was to develop a set of laminating parameters between FRP and wood laminations that achieve the required bond strength and durability required for use as a structural member. Wood is subjected to hygro-thermal strains; this presented challenges in laminating to the more dimensionally stable FRP.

The bond between the FRP and wood was required to exceed the minimum strength and durability requirements established by the American Institute of Timber Construction (AITC 200-92). A large matrix of independent variables was evaluated in 1,533 bond strength tests (ASTM D905), and 218 bond durability tests (AITC T110).

Satisfied with a set of laminating parameters, a total of 102, 22-0" long full size glulam test beams were fabricated in a glulam manufacturing plant, with three FRP reinforcement ratios: 0% (controls), 1% and 3%. The laminating parameters developed in the laboratory were successfully incorporated into the full-scale glulam manufacturing process.

Four-point bending tests to failure were conducted according to ASTM D198 on 90 of the beams. Performance gains of up to 17% in stiffness, 95% in ultimate bending strength, 108% in allowable bending strength and 117% in ductility were produced over the unreinforced control specimens, on average. For adequately reinforced beams, failure mechanisms were also reversed from tension to compression. These studies indicate that FRP reinforcement technology is mechanically feasible, structurally beneficial and immediately producible.

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