Hardwood glued laminated timber bridges

Design standards and specifications for 5.5- to 27.4-m (18- to 90-ft) clear span hardwood glued-laminated (glulam) highway bridges have been developed and are available from the Pennsylvania Department of Transportation. Resin systems, preservative treatment processes, laminating procedures, and key structural properties have been determined and incorporated into the standards for three commercially important hardwood species: northern red oak, red maple, and yellow poplar. The keys to successfully bonding the hardwoods are proper open assembly time and clamping pressure. Pressure treatment cycles to attain 160.2 to 192.2 kg/m³ (10 to 12 pcf) retention of creosote in northern red oak, red maple, and yellow poplar glulam girders had no adverse effect on the flexural strength or stiffness.