Plas y Nant Bridge
| Plas y Nant Bridge | |
| Previous Station | Waunfawr |
| Previous Location | Pont Cerrig y Rhyd |
| Bridge | Pont Plas y Nant |
| Construction | UB 64 |
| Operational | UB 33.65 |
| Status | In Use |
| Next Station | Plas y nant |
| Latitude | 53:05:02N |
| Longitude | 4:10:14W |
| Grid Reference | SH547562 |
Grid Reference :SH547562 Lat / Long :53.08376 / -4.17051
Pont Plas y Nant is the third of the three 50-ft humpback girder bridges across Afon Gwyrfai. It was inspected by Jim Wood, a distinguished BR bridge engineer (and author of Bridges for Modellers) who pointed out that the vertical stiffeners are not opposite one another and therefore that the bridge has been re-set - i.e. it is second-hand. It was probably a standard-gauge bridge sold off when its line was being upgraded in the 1870s. It was formerly possible to see the rust marks from deck beams some 6ins deep which were there prior to those we found when we took over. The bridge is reported in Boyd to have been rebuilt in 1894; this would be consistent with the beams we found. The bridge was entirely re-decked in 2001-2 and extra pieces were welded into the end sections of the humpbacks because we mistrusted their strength in shear at the ends. They have all been carefully coated in a paint which should last at least 20 years. As part of the work, a walkway was added to the outside of the western bridge beam; this is a mitigation measure carrying a private path replacing a previous route crossing the bridge on the trackbed itself. The former standard-gauge scantlings have allowed the narrow-gauge track on this bridge to be curved, which complicates the dynamic stresses, but fortunately the train is approaching Plas y Nant halt and is therefore going slowly. At the other two bridges the track is straight and the speed limit correspondingly higher.
