Structural Load Testing and Flexure Analysis of the Route 701 Bridge in Louisa County, Virginia: Supplemental Report

A continuous slab bridge in Louisa County, Virginia, on Route 701 developed a planar horizontal crack along the length of all three spans. This project was designed to determine if the current 12-ton posted load restriction of the bridge (instituted in January 2002) could be raised and to determine if the horizontal crack causes degradation in the structural integrity, specifically stiffness, over time. These objectives were accomplished through field tests performed in November 2003 and October 2004. One truck (loaded to three different weights) was used to perform static and dynamic tests on the bridge, and the truck was oriented in three test lanes. Vertical displacement sensors, or deflectometers, attached to the underside of the bridge slab were used to measure deflections during truck passes. The recorded deflections were analyzed and normalized to document the current behavior of the bridge. The 2003 values were compared to estimated design values in accordance with the AASHTO Standard Specifications for Highway Bridges. Under the testing loads, the bridge behaved elastically, and thus raising the load rating of the bridge to 27 tons was considered safe. Normalized deflections from both years were compared to determine if there was progressive damage to the bridge attributable to crack growth. The researchers concluded that no degradation of the stiffness of the bridge occurred over the last year of service. Carrying out the recommendation of this report to remove the posting that restricts loading of the structure will not incur any significant cost. The benefit of removing the posting would be that trucks weighing more than 12 tons, but not exceeding the legal limit, could cross the structure. This would allow the Virginia Department of Transportation to defer superstructure replacement, at an estimated cost of $350,000, thus freeing up funds to address more pressing needs.