Page 17

NSCJuly2016digi

NSC 17 July/Aug 16 to the use of plan bracing to provide the required stability,” says Mr Robinson. To install this structure Cleveland Bridge delivered six braced pairs of girders, each measuring 2.5m deep, to site and assembled them into units, each measuring 15m wide by 23.75m long. This assembly work was carried out using 500t-capacity mobile cranes and done on the temporarily closed northbound carriageway of the A1. “We then painted the bolted connections and the main contractor was given access to fit the permanent formwork to the assembled girders. This reduced the need for additional road closures to install the formwork when the girders were in position,” says Cleveland Bridge Construction Manager Ian Brierley. The 500t crane was then replaced with a 1,000t-capacity crane, which lifted the four sections into place during two consecutive overnight road closures, with the heaviest lift weighing 170t. A similar procedure for a near identical bridge was carried out at the southern end of the scheme near the village of Leeming. Known as the Low Street Overbridge, this structure over the A1 is slightly lighter requiring 378t of structural steelwork. A slightly different approach was needed for the Agricola Underbridge that carries the A1 across the River Swale, just south of Brompton. Agricola is an existing three-span steel composite semi-integral structure, which has been widened to accommodate the new three-lane highway plus its hard shoulder. After the abutments and centrallypositioned pier had been extended on either side, the southbound and northbound elements of the bridge each required 87t of steel that equated to four new 1m-deep girders each with an overall length of 57m. Each side of the Agricola Underbridge was installed in a single visit using a 200t-capacity mobile crane positioned on the existing and temporarily closed A1 bridge over the River Swale. As New Steel Construction went to press (early July) Cleveland Bridge still had one more bridge to install. This is Fort Overbridge, a two span continuous steel composite bridge supported on conventional abutments with inspection galleries. The structure replaces the existing Fort Overbridge, which had insufficient spans for the widened road. As the structure is near the Roman site of Cataractonium some archaeological works were undertaken prior to the work starting on the new bridge. According to Aecom the requirement to include a number of large services proved to be a challenge during the design of this bridge. “Working closely with Cleveland Bridge and the various utility companies a solution was found to locate the services within steel ducts beneath the deck slab supported on the cross bracing. The bridge steelwork will be installed with the ducts already in place reducing the number of lifting operations on site,” explains Mr Robinson. Summing up the steel bridgeworks, Mr Brierley says: “All of our bridge beam installations have been required to take place during a temporary closure of the A1 or its service roads. This required careful planning of the works to allow the programme to be achieved and avoid delaying the reopening of the A1 and the associated disruption to national traffic.” The other four bridges are Brompton North Underbridge, Brompton South Underbridge, Sowber Hill Accommodation Overbridge and Kneeton Hall Accommodation Overbridge (see map). Left and below: Kneeton Lane Overbridge being installed Kneeton Lane Overbridge Agricola Underbridge is widened with new steel girders Fort Overbridge will be the last steel bridge to be installed Bridges


NSCJuly2016digi
To see the actual publication please follow the link above