Date of Graduation

12-2025

Document Type

Thesis

Degree Name

Master of Science in Civil Engineering (MSCE)

Degree Level

Graduate

Department

Civil Engineering

Advisor/Mentor

Heymsfield, Ernie

Committee Member

Murray, Cameron

Second Committee Member

Fernstrom, Eric

Keywords

Bridge; Parallel Chord Truss; Stress Lamination; Timber; Truss

Abstract

This thesis examines multiple design options for constructing short span crossings for the military using indigenous timbers. Using indigenous timbers allows for a significant reduction in resources that must be brought into a site for construction. Construction time is minimized by optimizing the steps to convert indigenous timber into structural members for use as timbers in a short gap crossing. A major objective during this thesis study was to examine approaches for maximizing timber strength for design purposes and reduce timber weight for handling purposes. Wood strength and wood weight are highly dependent on moisture content. Decreasing moisture content addresses both issues. Drying timber reduces weight and increases strength when moisture content levels fall below 30%. Consequently, methods for wood drying were studied. A kiln chamber was designed and constructed during this thesis to evaluate approaches for quickly reducing moisture content with the objective of generating structural members for use in a short gap crossing. Given the nature of a typical short gap crossing site, construction was limited to light construction equipment. To evaluate member behavior, the modulus of elasticity is used as a metric for comparison between green and dry timber. A higher modulus of elasticity corresponds to a stiffer structural member. Two bridge options are evaluated in this thesis using softwood and hardwood timbers indigenous to the northwest Arkansas area. Both bridge options were tested to determine their capability to carry an MLC-40 design vehicle load over a 16-ft short gap crossing. Option one is a stress laminated parallel chord truss bridge consisting of built-up truss modules transversely secured with post-tensioning rods to form the bridge deck. The second option evaluated is a stress laminated timber short gap crossing with underdeck post-tensioning cables. This option allows for simpler construction; however, is limited to hardwood species due to the high modulus of elasticity required.

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