Bearings span the Thames

Plain spherical bearings supplied by INA Bearing Company have fulfilled a pivotal role in ensuring the success of the latest footbridge to cross the River Thames.

Plain spherical bearings supplied by INA Bearing Company have fulfilled a pivotal role in ensuring the success of the latest footbridge to cross the River Thames.

The Hungerford Bridge Millennium Project constitutes a replacement for the Hungerford Bridge walkway, which has, for some years, provided a pedestrian link from the Embankment to the South Bank.

INA has supplied a dozen Elges GE 260 UK 2RS spherical plain bearings for the footbridge, which is being constructed as two walkways, one on each side of the existing railway bridge carrying the line between Charing Cross and Waterloo stations.

Although the footbridge is an independent structure with its own foundations, the designers have developed a scheme that gives the appearance of its being supported on the existing caissons.

This is achieved by suspending each walkway on a set of pylon structures 'angel wing' profiles attached through the pylon tip by a spherical bearing.

The bearings, which are PTFE lined, provide a flexible suspension point at the attachment point of the support derrick, and were sourced from INA by Butterley Engineering.

Derbyshire-based Butterley is the steelworks contractor for the bridge, which is being constructed with a reinforced concrete deck.

The spherical bearing format provides a means of taking up shrinkage and creep in the structure over the months following installation.

The reinforced concrete used for the deck structure cures over a period of time during which its dimensions alter.

Although the movement is very small - a few millimetres over the entire span - there is a need to make allowance for the movement to prevent induced stresses in the rigid steel support structure.

Spherical plain bearings provide an elegant solution to what is, essentially, a short-term requirement during and immediately after the build.

Once the structure has fully settled the self-aligning properties of the bearing will be redundant, though the load bearing requirement will continue indefinitely.

Selection of the INA Elges bearing was based on a combination of fitness for purpose, cost and delivery.

The bearings supplied have an outer ring diameter of 400mm and a 260mm through bore, and feature a maintenance-free PTFE lining to the outer ring, within which the spherical form of the inner ring is able to move.

In bearing terms the bridge application is one combining a high load bearing capability with very restricted movement.

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