I'm looking for a justification for the use of cotton duck bearing pads without a sole plate. I'm specifically considering their use with precast I-girders.
Say I have a two span bridge, simply supported for dead load, with expansion bearings at the abutments and fixed bearings at the piers.
The configuration for the expansion bearings that I'm familiar with is:
(bearing plate embedded in girder - welded to sole plate - which is attached to stainless steel sliding plate - that rests on a PTFE sheet - which is attached to the cotton duck pad)
The configuration that the Nebraska Department of Roads specifies for a "fixed" bearing is:
(bearing plate embedded in girder - sitting on cotton duck pad)
How can this be justified as a fixed girder? Are there studies that support the reliability of counting on friction between the bearing and a steel plate?
If it's not truly a fixed girder, do I have a "floating" bridge? What design considerations/concerns does this raise? If you've encountered this consideration what is your design approach?