INA Scores At New Wembley Stadium

Visible from across London, the steel arch above the new Wembley Stadium is being supported at each end by INA spherical plain maintenance-free thrust bearings. As well as being visually stunning, the 335m arch will also support most of the retractable roof that weighs about 7000 tonnes. The arch alone weighs some 1650 tonnes. INA was chosen by CBUK, the contractor responsible for the arch structure, to supply the bearings as housed, sealed units ready for installation. Weighing 3.5 tonnes apiece, the bearings proposed will meet the long-term operating requirements - the life expectancy for the units is one million movements and 100 years, with no maintenance requirements. The design of the arch required bearings with a maximum outside diameter of 1000mm, an inside diameter of at least 300mm and a maximum height of 250mm. To absorb thermal expansions and wind movements of the lattice arch, the bearings must support maximum swivel movements of +/-2.5deg under extreme conditions and +/- 0.7deg under normal conditions. A key factor in the bearing's ability to meet the specification is INA's Elgoglide low-friction, maintenance-free material. This is a PTFE, commonly known as Teflon, and fabric composite that has been developed by INA to meet the long-term, maintenance-free requirements of the architectural and construction industry. The low coefficient of friction and lack of stiction - even at extremes of temperature - ensure that structures move freely to take up structural movement caused by temperature fluctuations and wind loadings while, at the same time, reducing the stresses within the structure. A further advantage of the bearings is the lubrication in the contact zone even with the smallest level of swivel motion. Small swivel angles such as these are not possible with conventional spherical plain bearings requiring lubrication with grease or oil, because the swivel motion is not sufficient to form a hydrodynamic film that will reduce friction. To achieve the required life of 100 years and give protection against external influences, the spherical plain bearings were also coated with Corrotect, a thin electroplated protective coating that has proved effective for conventional rolling bearing arrangements over many years. A further problem in the bearing design was ensuring the linking of the bearings to the adjacent construction on site. Since the steel arch is assembled while horizontal and only fully erected after completion, the bearings must be fitted in the vertical plane. Axial spherical plain bearings are not self-retaining (the shaft locating washer is loose in the housing washer) so the bearing housing was provided with retaining clamps and transport eyebolts. These clamps are removed before initial use to allow movement of the bearings on the complete arch.