British Motorists Deal With Major Roadway Bearing Failures

Motorists in Britain are facing miles of gridlock and travel difficulties in the northwest, due to a massive number of bearing failures in the M6 Thelwall Viaduct spanning the Manchester ship canal, River Mersey, and Warrington Road. The M6 is Britain's busiest and longest motorway, and this section in Warrington, Cheshire is the second-busiest stretch of road in Britain -- often carrying 180,000 vehicles every day.

In 1963, the original six-lane Thelwall Viaduct was constructed. By 1996, traffic volume and safety issues (the original viaduct had no berm, for example) required building a second, parallel, viaduct. The second viaduct, at 1.5km (4,500 feet) in length, is the world's longest continuously-welded plate girder deck bridge. The 1963 viaduct was then refurbished and rededicated to four lanes of northbound traffic while the new viaduct took four lanes of southbound traffic.
The 1963 Thelwall Viaduct is 1.4km (4,417 feet) long. Its 36 spans, weighing 11,000 tons, rest on 136 roller bearings on steel pads. Each bearing is approximately 350mm in diameter and 500mm long.

The bearings are needed to allow the span to expand and contract without buckling. At temperature extremes, it can expand and contract by more than 24 inches.

In July 2002, one failed bearing was discovered in the 1963 Thelwall Viaduct; it was immediately closed to all but one lane necessary to maintain a local exit, running on the shoulder.

Engineers for the Highways Agency quickly determined that virtually all of the 136 roller bearings supporting the spans either have failed or are on the verge of failure. Seven were found to have failed completely; one found sheared completely in half had been replaced only six years earlier. Twelve of the bearing support plates were also found to have cracks. Corrosion and vibration damage are the apparent culprits, even though the bearings and pads are protected by skirts and stainless steel.

The bearings have now been equipped with acoustic monitoring equipment, backed by in-person around-the-clock inspections.

Meanwhile, the Southbound viaduct has been reoriented from four lanes so that it now carries six narrow lanes of traffic, three lanes each direction and no berms. This has caused miles-long backups, not only because of the congestion and low speed limits, but also because a broken down vehicle anywhere along the span brings traffic to a virtual standstill. In addition, very low speed limits are required on the northbound lanes due to their running severely off-camber in places.

Rural towns and narrow roads are the only alternatives for drivers attempting to avoid the viaducts. However, these towns and roads were quickly overwhelmed and residents have been complaining loudly.

The cost of replacing all of the bearings is estimated at between £30 million and £70 million, but experts put the true costs, including damage to local roads and economies, at more than £150 million.

Recently, the Highways Agency told the House of Commons they now believe the bearing replacement project will not be completed until at least March 2005.

The Highways Agency also said, "Laboratory testing and investigations into how the roller bearings have failed is substantially complete," but refused to comment further about its findings or who it believes should bear financial liability for those failures.


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