Strengthening the Hammersmith Flyover

Completed in 1961, Hammersmith Flyover is one of the first examples of an elevated road using reinforced concrete. it is built in segments held together with prestress which is described as “external” but runs in grouted ducts for part of its length. In 2011 the prestress was found to be deteriorating seriously and emergency strengthening to critical sections was installed in early 2012 in time for the London Olympics.

This talk will concentrate on phase II of the strengthening work which started in 2013. In Phase II, a completely new prestress was installed. It is believed to be the first time full replacement prestress has been installed in a bridge where it was not possible to remove the original. The bearings, which are unusually located at the bottom of the piers in pits, were also replaced.

The sub-title of this talk is “New structures are easy!” Many of the difficulties carrying out the work resulted from the form of the bridge which left very little space for the new prestress and from the requirement to keep the bridge open and minimise disruption to traffic below as well as on the bridge. The project included use of innovative ultra-high performance fibre reinforced concrete prestress anchors (some precast, some cast in situ using a novel syringe) and bespoke design approaches based on EN 1992.