Laser Scan and 3-D Model Aid Jefferson Avenue Bridge Repair
DETROIT, MI High tech surveying and 3-D modeling were used to evaluate repair methods for restoring operation of Wayne County's historic Jefferson Avenue Bridge that spans the Rouge River in Detroit, Michigan. Extensive damage to this drawbridge's north leaf and related mechanical features has kept it closed to vehicle traffic because of a freighter colliding into it in 2013. It has been closed for more than two years since the collision and has forced local traffic to find other ways to cross the Rouge River.
Damage was caused when a 45-year-old bridge operator, who had worked for the county for more than 17 years, closed the bridge as the 670-foot Herbert C. Jackson was passing underneath. The ship, an inter-lakes vessel registered in the United States, suffered a one-inch by six-inch gash to its hull above the waterline. It was able to be welded and moved shortly after the collision.
The Jefferson Avenue Bridge suffered extensive damage. The underside of the bridge suffered the most damage. Large pieces of steel had been sheered off and bolts and other mechanical pieces were broken off at the base. The bridge was insured which helped start the repairs needed for the historical bridge. Originally constructed in 1922, this is the first reported accident for the bridge. Wayne County has been working to acquire the resources necessary to do a complete repair by replacing the steel and fix the concrete base that was cracked as well which is why the repairs have taken longer than two years. Throughout that time, funding has been sourced and the bridge, which has been placed on the National Register of Historic Places, will be completed by late 2015.
Wade Trim, who was contracted to get an accurate assessment of the damage, completed a laser scan of the exterior of the bridge, interior machinery pits of the displaced north leaf, and the minor damaged sustained to the south leaf. After control and benchmarks were laid out, a Leica P-20 laser scanner was used to obtain more than 30 scan positions from both sides of the river. The scan positions were registered into a single point cloud that allowed engineers to obtain precise measurements and positions of all structural elements. It was determined that the north leaf has to be moved more than seven inches to properly align with the south leaf when the drawbridge is lowered into the horizontal position.
Bridge structures were modeled in 3-D to show the amount of warping in the steel girders and beams. The 3-D modeling also allowed measurements to be made on the center of the trunnion bearings' axle, used to raise and lower the bridge spans, to show how much the structure had been displaced. Wade Trim's design team is using the model to evaluate the stresses and displacements caused by the collision and will use that information to find the best methods to restore operation.