Mechanical Engineering, bridge bearings, structural engineering Specialists In Structural Movement Control
Mechanical Engineers Specialising In Structural Movement Control
Welsh box girder gets ready to roll again
New bearings were installed on the Cleddau Bridge in south Wales during a seven¬day operation late last month (April). The bridge, which is owned and operated by Pembrokeshire County Council is an 800m-long box girder which carries the highway some 40m above Milford Haven estuary. All thermal movement is concentrated at a pair of bearings near the middle of the bridge which are in a half joint within the main span.
The rollers that were installed when the bridge was built in 1971 had deteriorated as a result of corrosion and misalignment to the point where they were generating considerable resistance to movement and suffering further mechanical damage (Bd&e issue no 67).
Finding a suitable replacement was very difficult since the steel used in the original bearings is no longer manufactured, and potential alternatives were not suitable to be used in such an aggressive environment. Some manufacturers misunderstood the constraints and suggested a simple replacement with sliding bearings.
After the article in Bd&e, consultant Bill Harvey was contacted by manufacturer Maurer Söhne with details of a sliding bearing specif cally designed as a replacement for rollers. The bearing has two sliding faces and a central curved slider to accommodate change of tilt. It will also be able to tolerate the plan rotations caused by thermal bending experienced by the bridge at dawn and dusk.
To jack the bridge in order to replace the bearings, extended and strengthened wings at the half joint were designed by Flint & Neill.
The bearings were installed by Ekspan during a seven-day operation; the bridge was jacked on to temporary slides, providing enough clearance without over-stressing the Demag joints above or interrupting the traffic. The old bearings were removed in turn and new base plates were bedded on epoxy mortar before the new bearings were assembled in pieces because of the very restricted working space. At one point the temperature rose and the gap closed to the point where the working space was lost temporarily.
There will be a full article about the project in the next issue of Bd&e.
All copyright for this article is the property of Bridge Design & Engineering published by the Hemmingway Group, thanks acknowledged to Helena Russell, editor of Bd&e, for kindly giving us permission to use this feature.