ALL 136 roller bearings on the M6 Thelwall viaduct are to be replaced with spherical sliders just seven years after a US$42M refurbishment, the UK Highways Agency has said.
The 1.4km long, 36 span viaduct, which crosses the Manchester Ship Canal near Warrington in the north of England, was partially closed last year following routine inspection. This revealed that 17 bearings had cracked.
The viaduct was originally built in 1963, but was refurbished by contractor Amec in 1996, converting the jointed deck into a monolithic structure with four carriageways carrying northbound traffic only. Southbound traffic was switched to a new viaduct built alongside.
As well as the roller bearings, 178 rocker bearings were also installed, but these show no sign of stress.
Since the discovery of roller bearing failures on the refurbished structure, all but one lane of traffic has been switched to the new viaduct which has been adapted to take six lanes of traffic. The remaining lane remains open to provide junction access.
Italian manufacturer FIP supplied the roller bearings for the refurbishment, which included replacement of the concrete deck and supports. Consultant was Pell Frischmann.
So far 17 failed bearings have been recorded. Some of these failed after traffic had been diverted off the viaduct.
How many of the rest have already failed is uncertain, as the origins of the cracks are obscured until thermal movements cause the bearing to roll, exposing the cracks.