The Portsmouth Gateway Bridge

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Year 3 Civil Engineering
Pedestrian, Cycle and Public Transport Bridge between Horsea Island and Tipner, Portsmouth, UK
Group Members
Adam Curranw, Aidan Brown, Cashel Cahill, Paul Bryans, Robert Gaskins-Rogers, Yashraj Dhawan

Supervisors
Dr. Joel Smethurst, Dr. Alan Bloodworth

Portsmouth City Council proposed the development of a pedestrian, cycle and bus rapid transit (BRT) bridge that also contributes to achieving the Council’s vision of a sustainable and modern city. The bridge was required to be a ‘gateway structure’, providing a future proof link between Horsea Island and West Tipner, which has been earmarked for urban development. The final design was required to meet all of the functional requirements of the client’s brief, including; enabling efficient public transport links, enhancing key viewpoints, and minimising damage to the SSSI at Tipner Lake. The budget for the design was £25 million. The proposed bridge is a single pylon cable-stayed structure with a single span of 120m. A single clear span was driven by the need to provide a clear navigable channel. Furthermore, this design requires no pile caps within the intertidal zone and makes use of the existing earthwork supporting the M275. The design makes use of an orthotropic bridge deck solution, highlighted for its efficiency and ease of prefabrication. The deck is 12m wide; with a central trapezoid steel spine beam connected to the locked coil strand cables. Cantilevered beams are attached perpendicularly to the spine to support the deck plates and deck stiffeners. The tapered concrete pylon is 50m tall and angled at 200 vertically, it also requires no back-stays; but instead relies on the weight-balance relationship between the pylon and deck. As a landmark structure, the bridge is designed to reflect the industrial and maritime history of Portsmouth through its semi-fan cable arrangement. The design is large and imposing, yet aesthetically pleasing in form and stature, providing a complimentary landmark to the existing Spinnaker Tower.

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