Cold temperature effects on stress laminated bridge decks


Robert Seavey, Robert Erickson

December 1997

Report no. Mn/DOT 1998-03

This study evaluated the thermodynamics of stress-laminated bridges under laboratory conditions.

After assembling three timber laminated bridge deck panels of 120" x 43" x 12", high tension rods were used to form "stress-laminated" panels. Researchers placed the panels in a laboratory freezer, with cold temperature settings of 10?, 0?, -10?, -20?, and -30? Fahrenheit and repeated the process three times, each with the wood at a different moisture content--a "green" moisture content greater than 30 percent, a 17 percent moisture content, and a 7 percent moisture content (mc).

The results showed that the bar force reduction in the green moisture content sample was significantly greater than in either the 17 percent or 7 percent me tests. The study concluded that the moisture content levels and temperature fluctuations cause variations in rod stressing levels; that the tensioning losses occur within a few hours of the temperature drop; that the green moisture content levels have a severe adverse effect on the stressing levels; and that tensioning levels somewhat stabilize with moisture contents below 17 percent.

Based on this study, it would appear that any existing stressed bridge decks should be closely monitored until the moisture content of the members is less than 19 percent. Further study may be needed to determine the behavior of bridge decks with a moisture content above 17 percent and below the fiber saturation point.

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