Case Studies

This project, involving the complete restoration of the 1923 Scherzer style Inchinnan Bascule Bridge over the White Cart Water in Renfrew, was completed in August 2004 at a cost in excess of £1 million. This major civil engineering project by Renfrewshire Council has saved this important road link from imminent closure, allowed removal of a long standing weight restriction and, by re-establishing the opening facility, has secured the use of the river for freight and pleasure craft.

The restoration of the structure was executed over several phases and, due to the complexity and historical significance of this moveable bridge, detailed planning was required at every stage involving a high level of co-operation between designers and contractors.

The renovation of the mechanical and electrical opening mechanism was carried out first. This involved dismantling the motors, gearboxes, drivers drum controller and rack and pinion mechanism with repair or replacement of any defective parts. Other components repaired or replaced in keeping with the original design included the slate insulated switchboard, the limit switch mechanism, brake solenoids and brake linings.

The structural repair and strengthening of the bridge was then undertaken in a phased manner as required by this form of bridge.

The east approach span, that is the span on to which the opening span rolls during bridge opening, was strengthened by carrying out extensive repairs to the original bridge steelwork and introducing two additional cross beams into the existing steelwork grillage to assist in supporting modern highway loading.

The ribbed slab deck of the reinforced concrete west abutment span was replaced in its entirety due to its poor condition. The deterioration had been caused by the ingress of salt laden run off water over many years. The new deck was designed to accommodate modern highway loadings. The concrete deck was integral with the existing reinforced concrete piled substructure which itself was subject to extensive repairs during this phase of the project. As the deck of the west abutment span incorporates a landing edge on to which the opening span of the bridge bears when in its closed position, the opening span was propped open for the duration of this phase.

The steel panel deck of the opening span and its supporting members were replaced with a similar but greatly improved arrangement designed to modern loading standards and with a view to less onerous future maintenance operations. Among the design constraints associated with this phase of the work was the need for the overall mass of the new arrangement to match the original in order to safeguard the fine balance of the structure. Additionally the overall depth of the new components had to be the same as the original in order to tie in to the bridge approaches and not encroach upon the available headroom to the opening span elevated transverse members.

During the last phase of the project a new protective system of vibrant colours was applied to the bridge steelwork and a major new architectural lighting system in complimentary tones was installed to highlight this unusual structure. The result is that the fully restored bridge has now become a major feature on the main approach to Renfrew town centre from Glasgow Airport and is one of the attractions included in Renfrewshire's annual Doors Open day. This national event encourages members of the public and especially children to visit various sites highlighting the built heritage of the area.

As a Grade A listed structure planning approval, including detailed consultations with Historic Scotland, was required for each stage of this project.