LOCATION:
The 115m long structure is divided into four ambitiously slender spans that hug the shoreline, touching down on discrete piers to provide a minimal footprint within the tidal zone.
Design and build of a low-carbon, pedestrian footbridge, positioned beneath the Grade-II listed Barnes Bridge, connecting the Thames Path which was previously broken by a 500m detour.
Early works included temporary causeway sheet piling and CFA piled pier foundations within the river to support the new bridge – with structural, vibration and crack monitoring in place throughout.
The bridge itself was manufactured offsite in four sections, or “spans”. These were subsequently installed from the river via a floating pontoon, using the rising tide to first manoeuvre them into position, then land them on the supporting piers as the tide receded, with millimeter critical precision under obvious time constraints.
Span 2 in particular was installed within just a 30-minute working window as the tide fell. Original plans intended to lift it into place with a dual crane lift, however this would have required possessions of the railway, increasing disruption and operational risks.
Floating span 2 into position on the tide
Challenge
The marine installation of the bridge sections required meticulous planning and attention to detail, to ensure “right first time” delivery.
Prior to transportation from Tilbury Docks, we designed and built the pontoon trestles for the bridge spans, undertook calculations for sea fasteners, buoyancy and stability calculations for the pontoons, and negotiated arrangements with Tilbury Docks and the Port of London Authority (PLA) for access/egress and river passage. Finally, we completed a cradle design to lift span 2 onto the pontoon.
Solution
Activities carried out to facilitate successful installation included the design and installation of:
- Impact protection columns in front of pier foundations 2 and 3 (P2 & P3).
- Temporary works either side of P2 & P3 as contingency, should span 2 not land correctly.
- Locating pins to ensure span 2 was positioned exactly above the bridge supports.
- Internal cage, ensuring post-tensioned bars and locating sockets were correctly aligned within P2 & P3 to receive the bridge span.
We sourced material for the locating pins and laboratory testing of the materials to ensure they met the specifications, followed by the manufacturing of the pins themselves. We undertook a 3D scan of both the bridge supports and bridge sections to ensure all components were within acceptable tolerances.
Outcome
The bridge was successfully constructed without affecting any of the 2M annual passengers that ride on the stretch of railway.
It has been nominated for and won a multitude of awards including a Civic Trust Award, a New London Award for Transport and Infrastructure, and was highly commended at the International Association of Bridge and Structural Engineering Awards.
