Demolition of the US. Grant Suspension Bridge

The U.S. Grant suspension bridge, across the Ohio river at Portsmouth, Ohio, was built in 1927. The bridge superstructure was systematically removed in August 2001 as the first step in making way for a new cable- stayed bridge. This paper describes the old suspension bridge, the demolition constraints and the engineering required to safely de-construct the bridge. The bridge crossed two major shipping routes, the Ohio River and the CSX Railroad. Both of these transportation facilities permit only minimal disruption to services, which added to the complexity of the project. The engineering process for the contractor began by investigating the two proposed schemes shown in the contract documents. This assessment was conducted by Buckland & Taylor Ltd., using specialized bridge analysis and evaluation software developed in house. This assessment quickly identified critical construction issues. The Contractor’s equipment and preferred methods were taken into account to develop a scheme to satisfy the contract and Contractor’s requirements. The demolition scheme adopted by the Contractor differed significantly from both of the alternate demolition schemes proposed by the Owner’s Engineer. The procedure used for the demolition consisted of about 30 distinct stages, requiring less temporary works and equipment relocation yet still respecting all safety and transportation service requirements. The superstructure was removed by crane in both 17.5’ and 3.5’ sections. After the entire truss was removed, explosive charges were used to cut the main cables and cause a controlled collapse of the towers away from the shipping channel. This resulted in a faster and more economical scheme than originally suggested. The detailed engineering for the scheme was reviewed by the appropriate authorities, which included the Ohio Department of Transportation, the United States Coast Guard, CSX Transportation and the Corps of Engineers, with approval being received for the demolition plan as submitted. This paper discusses the sequential de-construction of the bridge deck and trusses, which was performed to satisfy strength and stability requirements due to self weight and wind loading during the entire demolition process. The modeling techniques and software used to study alternative de-construction sequences and to verify the selected sequence are presented, as well as high- lights of the de-construction work.