Live-Load Testing and Long-Term Monitoring of the Varina-Enon Bridge: Investigating Thermal Distress

Abstract

During detailed visual inspections, inspectors on the Varina-Enon Bridge noticed a significant flexural crack opening, visually estimated at 1.5 mm under traffic, on the last span of the approach structure among other significant cracks on June 29, 212. To investigate the causes of the observed cracking, live-load testing, long-term monitoring, and structural analysis were used including 77 total strain, crack displacement, deflection, and temperature sensors. The live-load test produced a crack opening of approximately .5 mm when under a less-severe thermal gradient. The collected data indicated the crack opening was greatly influenced by interaction of vehicular loads and thermal gradient magnitude. There were 389 crack openings larger than .625 mm over the 17 months of the long-term monitoring, with a maximum measured crack opening of approximately .76 mm. Maximum measured thermal gradients were found to be in excess of the as-built design thermal gradient but similar to the current design thermal gradient. This may indicate potential underestimation of the maximum design thermal gradient, but would require a more robust study.