Description
Swanley I/C East and West form part of the M25 Junction 3 interchange roundabout at Swanley in the UK. They are similar three span reinforced concrete beam and slab bridges with integral inclined piers. The soffits of the side spans of the structure started cracking soon after it opened in 1977 due to insufficient reinforcement in the deck. To remedy this, steel strengthening plates were bonded to the soffit of the side spans and to the top surface of the deck over the piers in the hogging regions.
The bridges have, in recent years been subject to Interim Measures Management following concerns over potential debonding to the steel plates bonded to the deck surface. When reflecting cracking has occurred in the surfacing, investigations have been undertaken including hammer tapping of exposed plates to map the debonding and manage the operation of the structure against a sensitivity study to plate debonding based on structural assessment.
During the management regime a strengthening rehabilitation / replacement scheme has been developed to replace the existing steel plates in the hogging regions with a new CFRP strengthening system composed on Near Surface Mounted Rods.
An extensive Early Contractor Involvement (ECI) and design development process has been undertaken to determine a solution that can be built in a sequence of existing plate removal that allows the existing structure to remain open to a lane of traffic during the works. This ECI included both procedural and laboratory trials on different materials and their properties to ensure buildability with the scheme constraints.
This paper presents the design, challenges and lessons learnt of Swanley I/C East bridge rehabilitation, which completed construction in November 2023.
