rubber pad 2 truss connection

huangyhg

"rubber" pad @ truss connection?
i am looking at an existing metal building with a 3'-6" deep steel truss clear spanning 64'.  the top and bottom chords of the truss frame into the flange of vertical columns (not tapered)at each end.  however, the bottom cord connection has a "rubber" pad shim between the column flange and the truss cord connection plate (this is not the case at the top cord, the connection is steel to steel)  i do know the buildings manufacturer and will contact them to get a response.
has anyone seen this type of connection before and what is the purpose of the "rubber" shim?
i have seen many elastomeric pads used beneath the bottom flange of bridge girders, maybe a bearing?
jheidt2543,
i think the purpose of the rubber pad is to make the truss-to-column connection a simple connection, and avoid a moment in the column due to the gravity loads.
i assume the stability of the building for lateral loads is provided by other structural elements.
welding (or providing fixity) at the bottom chord in the connection to the column has resulted in a number of connection-induced failures, hence some have devised to set them free along the plane of the columns-truss plane. this is more or less tantamount to what dlew says, support through diagonal being brought to the top corner.
so, the pad prevents a moment connection, yet allows the bolted connection to brace the bottom chord of the truss?
yes, there are other bracing systems in the building.
several posters have nailed the purpose of the pad ... to avoid an end moment connection to the column.
i've investigated several failures where the end connection was designed as simply connected but erected with hard connections on top and bottom chords.  
i've made it a practice to stop the bottom chord prior to reaching the end region.
i finally found some information regarding the rubber pad from the building manufacturer.  this is a metal building built around 1975, so it has taken some time to find the info., and with that in hand i thought i would pass it along.  it pretty much confirms the above responses
"the sidewall columns are welded "h" sections, non-tapered, and pinned base.  the columns are framed into the roof truss for lateral load resistance by means of a knee brace, creating an indeterminate frame.  a rubber deflection pad is also used with the knee brace to reduce the effects of roof live load upon the sidewall column"
thanks you all for your comments!