Three of the steel plate girder bridges on the Dulles Metro Line Project featured Disktron Bearings which ranged from 225 kips to 900 kips in vertical load capacity. The rotational capacity of these bearings was 0.025 radians and the displacements on the expansion bearings ranged from 3 to 6 inches. One of the bridges also required uplift restraint, which was easily accommodated with the Disktron design.
Disktron Bearings can be easily modified for uplift restraint which is common in seismic zones. Uplift forces are also seen on some curved girder bridges and in flood prone regions where high water can result in the bridge becoming buoyant. The standard central pin or SRM on the Disktron Bearing is modified so that the upper and lower bearing plates cannot separate. This SRM acts like a trailer hitch on an automobile. For expansion bearings the upper slide plate is modified so that it lips under the upper bearing plate to resist the uplift force. Fully assembled the modified Disktron Bearing can accommodate uplift load, movement and rotation simultaneously which is a feature unique to this type of bearing.
Polytron Disc – By utilizing a polyether urethane disc, the POD Bearing accommodates vertical design loads of 10 to 10,000 kips while maintaining its ability to provide rotation in both longitudinal and transverse directions.
SRM (Shear Resisting Mechanism) – A large diameter high strength steel pin transfers horizontal loads from the upper bearing plate to the baseplate and isolates shear loads from Polytron Disc.
PTFE – The PTFE to stainless steel sliding interface results in a very low coefficient of friction.
Polished Stainless Steel – Stainless steel with a mirror finish provides a low friction sliding interface for the PTFE.
- Rotation capacity in excess of 0.08 radians
- Low vertical deflection for single and multi-span structures
- Ability to handle ultra high braking and traction forces
- Can accommodate all live to dead load ratios
- Accommodates high vertical and horizontal loads
- Maintains tight control of horizontal displacement of structure