Aug 12, 2020Waterloo Truss Restoration
The Waterloo Bridge Restoration project is located on the Fauquier-Culpeper County Line in Virginia which is approximately 50 miles southwest of Washington D.C. The scope of work included with the 2019 restoration plans, prepared for the Virginia Department of Transportation (VDOT), includes the removal and member-by-member replacement of a historic 100-foot long wrought iron truss. ELR provided construction engineering services on behalf of the contractor, Corman-Kokosing.
The pinned truss that carries Route 613 over the Rappahannock River was designed and fabricated in 1878 by The Pittsburgh Bridge Co. for a cost of $1,498. The truss was designed to carry a 60 psf uniform load. By the early 2000’s, the truss was posted for 3 tons due to more than a century of corrosion and deterioration. The 2013 inspection report noted that the structure was in poor/serious condition because of the presence of widespread active corrosion and loose truss members in need of significant immediate repairs. In 2019, the Commonwealth of Virginia Department of Transportation released a set of restoration plans that included the replacement of the majority of the truss’ pins and structural members without entering the river, which the truss spanned.
Corman-Kokosing elected to lift the truss using a single crane and relocate it onto the adjacent bank to perform the restoration. ELR designed lifting beams in accordance with ASME BTH-1 standards to pick the truss at the top chords rather than at the original bearing points. The reasoning behind this was twofold:
- Rigging to the top chord of the truss provided a more stable lift. Loads are typically picked with the lift point above the center of gravity of the load when possible, because when the lift point is below the center of gravity, there is potential for the load to rotate around the lift points until the center of gravity of the load is centered below the lift point. When the lift point is above the center of gravity of the load, any out-of-plane rotation is resisted by gravity’s restoring force.
- Rigging to the top chord simplified the setup for dismantling. Since the truss was to be dismantled one pin at a time rather than all-at-once, each panel of the truss needed to be independently supported. Hanging the truss from above (what)during dismantling provided stability and flexibility for the contractor’s preferred dismantling sequence.
The restoration plans provided by VDOT required the contractor to submit detailed plans and calculations that verified truss stability during all phases of removal and dismantling. ELR created finite element models to not only verify the stability of the truss, but to verify the stresses in each member. Since the inspector had noted that some of the members were loose and that others had been previously rehabilitated, determining accurate member stresses posed a significant challenge. Similarly, the widespread corrosion noted in the 2013 inspection report was sure to affect the capacity of each member to a variable degree. Some of the members originally designed for tension when the truss is simply supported were required to be in compression when lifted from above, so ELR designed temporary bracing to resist all compressive forces in tension members.
This project was a collaborative effort between Hari Aamidala, P.E. and Grant Whittaker, P.E. to complete both the design and plans for Corman-Kokosing that were approved by VDOT.
About the ELR Project Team: Mr. Hari Aamidala is the Principal Engineer/Virginia Operations Manager. Hari is a licensed professional engineer who joined ELR in November 2019, and he has a Master of Science from Texas Tech University. Hari has completed similar truss rehabilitation projects for VDOT, including the John G. Lewis Truss Bridge in neighboring Loudoun County, Virginia. As the Project Manager and a Lead Engineer, he was responsible to coordinate with Corman-Kokosing and work with VDOT’s engineering staff and their consultants.
Mr. Grant Whittaker, based in ELR’s Columbus, Ohio office, is a licensed professional engineer in Virginia, West Virginia, and Ohio who has specialized in bridge and construction engineering for ELR since receiving his B.S. in Civil Engineering from The Ohio State University in 2013.
Development of the drawings for the detailing of the proposed lifting and dismantling/reassembly of the truss was provided by Mr. Chris Salter, based in the ELR’s Columbia, SC Office.