InTrans / Aug 14, 2018

Cold Temperature Effects on Stress-Laminated Timber Bridges: A Laboratory Study

Stress-laminated bridges perform well if adequate bar force is maintained to provide the interlaminar friction and load transfer between adjacent deck laminations. Stress-laminated decks are made of both wood and steel components; therefore, different material thermal properties may cause bar force to change as the temperature changes. In response to concerns about the performance of stress-laminated bridges in extremely cold climates, a cooperative research project between the University of Minnesota, the USDA Forest Service Forest Products Laboratory, and the Federal Highway Administration was initiated to evaluate system performance at temperatures ranging from 21.1å¡C to -34.4å¡C. Stress-laminated bridge deck sections, constructed of red pine lumber and high-strength steel stressing bars, were placed in cold temperature settings of -12.2å¡C, -17.8å¡C, -23.3å¡C, -28.9å¡C, and -34.4å¡C, while bar force measurements were collected. Testing was completed at three different moisture contents: >30%, 17%, and 7%. At -34.4å¡C, bar force losses were high when the deck moisture content was above fiber saturation and were moderate to low when the moisture content was below 18%. In all cases, bar force loss was fully recovered after temperatures rose to 21.1å¡C.