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Bridge strengthening increases load capacity

Client: Neath Port Talbot County Borough Council
Location: Baran Road Bridge, Rhyd-y-fro, Neath
Approved Installer: Goldhawk Bridge Restoration Ltd.

Carrying the Baran Road over the Upper Clydach River, the semi-circular arch has a 7.34m span with a 3.45m central rise. The arch barrel, abutments and spandrels are all of natural stone construction while the parapet walls are of continuous masonry construction.

Problem

Following a recent assessment the bridge had been restricted to a gross vehicle weight of 7.5 tonnes so did not meet the current standards for highway bridges. Although the general structure was in a fairly good condition some 10% - 20% of the stonework joints had loose mortar and mortar jointing absent at the arch springing level. In addition, the spandrels and parapet walls were partially covered in ivy while the arch soffit had a coating of leached calcite deposits.

Helifix Solution

Test Caption

- Analysis using ASSARC masonry arch assessment program 
- Repair scheme devised using MARSYS computer package
- All vegetation was removed and leached deposits blasted away using a fine glass powder. 

Stainless steel helical reinforcing bars were bonded into longitudinal radial and transverse rebates cut into the underside of the arch with interlocking helical ties installed at right angles to the bars, at the grid intersections, and the entire system encapsulated with structural adhesive.

Missing mortar joints were established by raking out and re-pointed to a depth of 75mm-100mm and the whole structure was also re-pointed using an approved lime/sand mix.

The concealed repairs and strengthening caused minimal disturbance to the bridge fabric, maintained normal structural movement and left the visual appearance of the bridge virtually unaltered. They also enabled the weight restrictions to be lifted by increasing the load carrying capacity from 7.5 tonnes to 40 tonnes to meet current requirements.