Muir Rd & Bedwin St Cable Bridges
Bedwin Street Cable Bridge
Concept design, detail design and documentation of a single 30m span, 3m wide plank girder cable bridge carrying 2 phase, 330kV cables over the railway line at Muir Road. Concept design, independent proof checking design and documentation of a three span (23m, 32m, 28m), 3m wide plank girder cable bridge carrying 2 phase, 330kV cables over the main Illawarra railway lines, Sydney Metro line and Sydney Metro tunnels at Bedwin Road.as part of Transgrid’s “Powering Sydney’s Future” project. The bridge is also designed for pedestrian and cyclist use.
Vince Scolaro was instrumental in developing a design of cable bridges (in lieu of deep under-crossings) for Transgrid to cross the railway lines at Granville, Regents Park and Potts Hill as well as crossing some minor waterways as part of the original Holroyd to Rookwood section of this project. Based on this previous involvement, CSS was engaged to adopt similar designs for this project.
The team were very proud to be part of this project, allowing HV cables to be buried underground (in lieu of overhead lines) as well as integrating multi-use design for these bridge structures.
Technical innovations achieved
Having multi-use function, these bridges have specific and complex electrical / structure interaction requirements including earthing and bonding issues such as bridge isolation requirements and electrical continuity of reinforcement to ensure no step and touch potentials or electrolysis corrosion exist. This requirement was conflicting with not being allowed to have closed ties in the girders as this causes Electro-magnetic loop inductions to be developed. Our solution was to split the ties into two sections with the top section comprising FRP reinforcement with is non-conductive thus eliminating the potential for electro-magnetic loop inductions to be developed.
The Bedwin Road north abutment is sited directly above the Sydney Metro tunnels with limited bearing capacity. The bridge was made continuous over the piers and released both longitudinally and transversely at the northern abutment to enable closely spaced Micro piles to be adopted at this location. The use of these micro piles together with no lateral load transfer ensured that the limiting vertical allowable bearing pressure could be achieved.
Benefits to the client
Benefits included the construction of a shorter length bridge structure with associated lower costs, lower impacts to the local road network, lower impacts to both pedestrian and cyclists with shorter tie-ins at the northern end as well as shorter cable length because of a shorter bridge structure at the northern end.
Bedwin Street Cable Bridge in progress
Bedwin Street Cable Bridge Digital design
