the 2nd phase of Delamination surveys at the Kingston Bridge Complex

Description

The Kingston Bridge is situated in a strategic and prominent location near Glasgow city centre, crossing the River Clyde between Kingston on the south and Anderston on the north. The design was intended to be a practical means of connecting both sides of the city, whilst being seen from near and far in all directions. Combined with its height, this gives the bridge a landmark quality. It is a strategically significant structure which acts as the primary crossing of the Clyde for both regional and local traffic networks, with some 150,000 commercial and private vehicles crossing the bridge daily. The bridge is a cantilevered design comprising two number three-cell post-tensioned concrete box girders with a separation gap. Each deck carries five lanes of traffic over a combined width of 42m. The main river span is 143m with balancing back spans of 62.5m. The design and construction took place between 1967and 1970. W. A. Fairhurst & Partners undertook the design. The contractors were Logan / Marples Ridgeway. Strengthening was undertaken by Balfour Beatty between 1996 and 2000. The main bridge is linked to a complex network of approach structures and ramps on the north and south side. These combine to form the Kingston Complex. The structural form of the approaches typically comprises standardised single and twin-cell concrete box girders with post-tensioned continuous table-top spans and reinforced concrete suspended spans. The deck widths vary to suit the lane requirements at carriageway level. This results in 1, 2, 3, 4, and 5 lane variations throughout the complex. The cantilevering sections of the table-top spans support the suspended spans via a stepped joint known as a half-joint. There are 156 half-joints within the complex. There are other sections within the complex which depart from the standard table-top and suspended span structural form. For example, there is a continuous multi-span section forming part of the North Approaches over Argyle Street which does not have half-joints. This is known as the Anderston Cross Continuous Span Section. Moreover, the Stobcross On and Off-Ramps originally comprised half-jointed sections, however, these were eliminated between 2003 and 2005 through strengthening and reconstruction (respectively). Variations of the table-top spans also exist where the North and South Approaches meet adjoining ramps. In some instances, the supporting column grid lines are set at considerable skews. Previous assessment work was carried out to the north and south approaches between 1992 and 2007. Extensive repairs were carried out between 1996 and 2003 and are now failing, leaving the structures in a similar or worse condition than in the early 2000’s. Inspections have identified significant defects, particularly around the half-joints, with issues such as cracking, spalling, exposed reinforcement and widespread water ingress accelerating deterioration. Construction defects have also historically been a factor together with the effects from chloride ingress and carbonation which has led to repeated concrete repairs over the years. Therefore, a programme of inspections has been proposed to identify further defects within the structure and proactively prevent incidents of further spalling and delamination. The consistent routine of inspections and monitoring will be carried out by prioritising critical areas and half-joints and creating a log of weekly reports, drawings and photographs. The immediate flagging of urgent defects will allow for reactive repair works and prioritisation of critical structures and their repairs in the future. The scope of the scheme is to complete full delamination surveys across 13 highway road bridge structures and 1 footbridge structure in the complex. This will include thorough delamination surveys of all areas with a focus on the half-joints. Additional monitoring will be required for existing defects such as crack gauges and quantifying any movem