The project involved strengthening of an existing 5 span half through metal underbridge over the River Taw, in order to achieve a rating of RA5 at 35 mph.
The bridge has a maximum clear span of approximately 11.4m with a skew angle of approximately 300. Each span of the bridge comprises 2 simply supported longitudinal riveted wrought iron plate girders, with transverse wrought iron plate cross girders supporting longitudinal wheel timbers and a concrete slab decking.
The bridge was fully operational during the works and CASE Consultants assisted Dyer and Butler in developing a temporary works scheme for suspending the scaffold over the river. This was achieved by introducing independent temporary steel beams spanning between the existing bridge piers. The temporary steel beams were moved between adjacent spans as the works progresses and were removed once the strengthening works were completed.
The following main works were undertaken to strengthen the structure to the required rating;
- Installation of 20mm top and bottom flange strengthening plates to the main girders. The new connections were made using M20 Tension Control Bolts. Tension Control Bolts Grade S10T fasteners are high-strength (10.9), high ductility (14%) friction grip bolts for use in structural steelwork connections. Their primary advantage over other types of friction grip bolt is the ease or preloading.
- Installation of 171x178UKT29 stiffeners at each cross girder location.
- Installation of 150x75UKPFC18 cross bracing between main girders.
- Replacement of cross girder and main girder rivets with M20 Tension Control Bolts.
- Replacement of the damaged precast concrete deck panels with a GRP grating.
- Undertaking of steelwork repairs and infilling of gaps and voids to the faying surfaces.
- Paint protection to the proposed steelwork and existing wrought iron elements.
- Installation of a 810mm wide Type 1 Safe Cess Walkway.
- Masonry repairs above mean water level to the piers and abutments.
- Vegetation removal
CASE Consultants undertook the detailed design of the structural elements and worked closely with Dyer and Butler under a Design and Build Contract for the Client Network Rail.
Contract Value £1.4m
