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Modern timber bridges have shown that timber is a durable option for primary structural members in highway bridges and can perform satisfactorily for 50 years or longer when properly designed; fabricated and maintained. However; various cost assumptions have indicated that timber bridges are more expensive than concrete bridges. This project was undertaken to better understand the benefits and costs of using timber bridges as a viable substitute for other bridge construction materials and designs. Two demonstration construction projects were completed to develop comparative information. A steel girder with a transverse glulam deck bridge with a curbless; crash-tested railing system was built; and a spike-laminated longitudinal deck bridge was constructed. Both projects were completed and allowed for a good comparison to be developed both in terms of project-specific cost and the time required for bridge construction completion. These projects showed that the main advantage of a timber bridge is the speed of superstructure construction with the other costs similar to that of other materials. It is clear from previous case studies; interviews with engineers; contractors; and suppliers; and the projects that timber superstructures can be installed within days to weeks; compared to months for other materials.

The appendices pertain to report 2020-16, Development of Cost-Competitive Timber Bridge Designs for Long-Term Performance. Appendix A: STEEL STRINGERS WITH A TRANSVERSE GLULAM DECK Appendix B: GLULAM STRINGERS AND A TRANSVERSE GLULAM DECK Appendix C: LONGITUDINAL SPIKE-LAMINATED TIMBER DECK Appendix D: ST. LOUIS COUNTY TIMBER BRIDGE DEMONSTRATION PROJECT Appendix E: HENNEPIN COUNTY TIMBER BRIDGE DEMONSTRATION PROJECT