Dahlberg, Justin

One of the primary objectives of this project, Development of Cost-Effective Timber Bridge Repair Techniques for Minnesota, was to produce a timber bridge repair manual. This manual is comprised of some of the content from the final report for the project, along with an extended presentation of timber maintenance options. This final manual is a standalone document from which the maintenance and repair options can be implemented. A final report (2015-45A, "Development of Cost-effective Timber Bridge Repair Techniques for Minnesota") and a technical summary (Manual Gives Cost-Effective Techniques to Extend Timber Bridge Life Spans) were also developed.

The primary objective of this work is to provide formal guidance to county engineers throughout Minnesota for repairing timber bridge components. The benefit of having such a resource will be measured by improving the overall condition of the transportation system and reducing system failures through implementation by local officials. As is often the case, funds required to complete repairs are limited and, as a result, any method used must not only be structurally feasible but also economically feasible. This report provides bridge owners and caretakers several routine maintenance and repair options aimed to meet the goals of simplicity and affordability. The economic impact of repairing timber bridges was assessed for multiple scenarios: a comparison was made between the net present value of repair at varying repair costs over time and the net present value of varying reconstruction costs over time. Through this exercise, for each scenario, a point in time was identified when repair or reconstruction makes most economic sense. An additional assessment of overall costs (direct plus indirect) was completed, which included the increased user costs due to bridge posting or closure. This assessment made clear that when indirect costs are included, the benefits of maintaining or repairing a bridge to prevent posting or closure become great. A standalone manual, Cost-Effective Timber Bridge Repairs: Manual for Repairs of Timber Bridges in Minnesota, and a technical summary, Manual gives cost-effective techniques to extend timber bridge life spans, were also developed for this project.

Minnesota has over 2,000 bridges that contain structural timber in the superstructure or the substructure. Historically, inspections for timber bridges have been mostly limited to visual inspection, hammer sounding and probing. These techniques have proven appropriate for advanced decay detection, but are inadequate for early stage or internal deterioration. During this project, new advanced inspection techniques and equipment were identified that were capable of improving the quality of timber bridge inspection. This equipment and technologies were introduced into routine bridge inspections through the development of standard inspection protocols, integration of the results into bridge data management software, development of a customized inspection manual, outreach training for MnDOT districts and state counties, recommendation of equipment purchases, and completion of an economic assessment on the use of advanced inspection techniques. Implementation of these inspection techniques will support the long-term service life of Minnesota's timber bridges and will improve the safety and reliability of Minnesota's bridges.