Date of Award

5-2008

Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Civil Engineering

Advisor

Habib J. Dagher

Second Committee Member

Eric N. Landis

Third Committee Member

Roberto Lopez-Anido

Abstract

The resistance of conventionally constructed wood-framed structures to extreme pressures created by blasts, wind or earthquakes depends largely on the material’s strength, energy absorbing capacity and ductility. A fiber-reinforced polymer (FRP) coating that can be applied to structural wood members to increase its strength and energy absorption was developed at the University of Maine’s Advanced Engineered Wood Composites (AEWC) Center. This coating changes the failure mode of the wood: moving from a brittle tensile failure to a more ductile failure characterized by compression of the FRP and wood fibers in the compression zone followed by plastic hinge behavior. This led to substantial increases in displacement capacity, and ultimately, energy absorption.

The coated members are used primarily for blast resistance for force protection in a rapidly deployable modular building designed for the military. The components of the modular building will have high strength to weight ratios, be environmentally durable, and have the ability to host ballistic/fragmentation armoring materials.

Static bending tests of coated 2x4 studs, coated plywood sheathing (3/8”, 1/2" and 3/4" thicknesses) and modular assemblies were performed to obtain force-deformation relationships. From these tests, ultimate strength and energy absorption were calculated and then compared to conventional wood members. Several rounds of testing were conducted on both studs and sheathing with various amounts, layups, and orientations of coating. The results show that with very small reinforcement ratios (1-2%), the 5th percentile strength and energy absorption of the studs can be increased up to 399% and 880%, respectively. Similar increases were seen with the coated sheathing.

The 2x4 and plywood materials were then combined into 4ft x 8ft wall sections and tested in 3-point bending and under uniform load. Two different wall types were examined: T-panels (sheathed one side) and sandwich panels (sheathed on both sides). The results show that the 5th percentile moment capacity and energy absorption can be increased by more than 600% and 300%, respectively.

Two foot wide coated roof panels, initially constructed of 14ft 2x8 joists, were assembled and tested in 3-point bending and under a 90 day creep load. The roof joists were replaced with 18ft 2x10s, in order to have a 16ft clear span for the modular building. Strength and energy absorption increases were approximately 700% and 300%. Per ASTM D 6815, all roof panels passed the criteria with a 90psf dead load applied.

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