Neoprene Bearing Pad Slippage at Louisiana Bridges

Abstract

Elastomeric bearing pads provide a medium to transfer girder loads to the supporting substructure. Low cost and low maintenance, in comparison with mechanical-type bearings, make elastomeric bearing pads attractive to use. However, some problems have developed with their use. Failure modes for bearing pads include crushing, delamination, and slippage. The most notable of these failure modes is slippage or “walking” out of position. The objective in this paper is to determine the cause of neoprene bearing pad slippage and recommend practical guidelines to remedy the problem. The Louisiana Department of Transportation and Development has experienced bearing pad slippage at some of their prestressed concrete beam bridges. The methods used to investigate this phenomenon included measuring thermal movements and erecting video equipment to monitor bearing pads and traffic simultaneously. In addition, material testing was performed to determine the composition of problematic elastomeric bearing pads. By using time-lapse video equipment, bearing slippage was found to occur on a daily basis. Other findings include that a major number of bearing manufacturers add wax to their neoprene bearings to satisfy AASHTO specifications. As a result of this investigation, the conclusion is that the primary cause of neoprene bearing pad slippage is due to wax materials that are added during pad manufacturing.