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Evaluation of Retrofit Procedures for Nail-Laminated and Stringer Bridges

https://research.thinkwood.com/en/permalink/catalogue1434
Year of Publication
2002
Topic
Mechanical Properties
Material
NLT (Nail-Laminated Timber)
Application
Bridges and Spans
Author
Larson, Timothy
Seavey, Robert
Organization
University of Minnesota
Year of Publication
2002
Format
Report
Material
NLT (Nail-Laminated Timber)
Application
Bridges and Spans
Topic
Mechanical Properties
Keywords
Retrofit
Static Load Tests
Dynamic Load Tests
Deflection
Research Status
Complete
Summary
Many of the 1,400 timber bridges in Minnesota do not meet present day standards. Some of these bridges can be improved rather than replaced. When the desired service level can be attained by widening a bridge six feet or less, the bridge can be retrofitted by placing a second, wider, transverse deck onto the existing deck and substructure. Bridge components must be carefully inspected prior to a retrofit project. The retrofit of Bridge #6641 in Sibley County is a good example. First, the bituminous surface was removed. A longitudinal beam supported the extended deck. Grout was poured and leveled and then nail-laminated panels were laid transversely. A bituminous surface was laid over the full width of the new deck. The cost of the project was $51,632. (Replacing the bridge was estimated to take 2-3 years and cost $215,000.) The county quantified the strength change and load distribution characteristics by performing static and dynamic load tests before and after the retrofit. Adding a second deck effectively decreased the static deflections and improved the transverse load distribution. Nail-laminated timber bridge #2642, also in Sibley County, was retrofitted in 1992 and load-tested again in 1995. All dynamic deflections were lower than those of the post-retrofit tests in 1992. This improvement can be explained in part by the drying of the moisture that was introduced into the bridge deck during grouting. A retrofitted timber bridge is expected to last an additional 20-40 years.
Online Access
Free
Resource Link
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2311 records – page 1 of 2311.