Performance of stress-laminated timber highway bridges in cold climates

Abstract

This paper summarizes recent laboratory and field data studies on thermal performance of stress-laminated timber highway bridges. Concerns about the reliability of stress-laminated deck bridges when exposed to sub-freezing temperatures triggered several investigations. Two laboratory studies were conducted to study the effects of wood species, preservative, moisture content, and temperature variations on pre-stressing bar forces (critical factor) in stress-laminated decks. The field performance of several stress-laminated timber bridges were monitored within a Nationwide Timber Bridge Monitoring Program, a cooperative effort by the U.S. Forest Service, Forest Products Laboratory and Federal Highway Administration. Bar-force and temperature data from a subset of bridges were continuously monitored for a period of 2 to 5 years with remote data acquisition systems. Significant prestressing bar-force losses were observed in laboratory studies when the moisture content of deck laminations were at 30 percent and greater and the deck temperature reached 0°F (–18°C) and below. The field study concluded that the magnitude of cold-temperature induced bar-force losses were not significant enough to warrant special considerations in the U.S. bridge design code. However, it may warrant special considerations in cold weather regions outside the United States whenever deck lamination moisture contents exceeding 20 percent are combined with ambient temperatures remaining below 0°F (–18°C) for extended periods of time.

Citation

Wacker, James P. 2009. Performance of stress-laminated timber highway bridges in cold climates. Cold regions engineering 2009 : cold regions impact on research, design, and construction : proceedings of the 14th Conference on Cold Regions Engineering, August 31-September 2, 2009, Duluth, Minnesota. Reston, Va. : American Society of Civil Engineers, c2009 : pages 637-647. ISBN: 0784410720: 9780784410721.