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Iowa State University--Becoming the Best

Field Testing and Evaluation of a Demonstration Timber Bridge

Profile view of timber bridge

Completed timber demonstration bridge


Principal investigators:

Co-principal investigators:

Project status


Start date: 11/15/08
End date: 12/31/11


Report: Field Testing and Evaluation of a Demonstration Timber Bridge (2.64 mb pdf) February 2012

Tech transfer summary: Field Testing and Evaluation of a Demonstration Timber Bridge (2.18 mb pdf) Feb 2012



About the research


Asphalt wearing surfaces are commonly used on timber bridges with transverse glued-laminated deck panel systems to help protect the timber components. However, poor performance of these asphalt wearing surfacesin the past has resulted in repeated repair and increased maintenance costs.

This report describes the field demonstration and testing of a newly-constructed, glued-laminated timber girder bridge. Previous field work revealed that differential panel deflections in the glued-laminated deck were one significant factor resulting in the premature failure of the asphalt wearing surfaces on these bridges. In addition, laboratory work subsequent to the field testing attempted to address the problematic asphalt cracking common in transverse glued-laminated panel decks by testing several deck joint connection alternatives.

The field demonstration project described in this report showcases the retrofit detail that was determined to provide the best field performance. The project was a cooperative effort between the Bridge Engineering Center (BEC) at Iowa State University and the United States Department of Agriculture (USDA) Forest Service Forest Products Laboratory (FPL).