Evaluation of Design and Retrofit Concepts for Slip-Base Sign Support Systems (7-3911-S)

In response to feedback obtained from field crews, TxDOT routinely assesses the performance of its breakaway sign support systems and identifies areas in which design improvements can result in reduced installation and maintenance costs or improved impact behavior. This project investigated several independent issues related to the performance of small sign supports. These issues include: the effect of keeper plate thickness on the impact performance of slip-base sign supports, an evaluation of methods for retrofitting slip-base stubs which incorporate a lifting ramp or cone, and investigation of a bolt-down anchor design for direct attachment of small signs to concrete pavement or median islands.|Tests determined that a 26-gauge keeper plate can be used in place of the standard 30-gauge keeper plate to help alleviate reported field problems with slip-base sign supports. Use of a 26-gauge keeper plate in a triangular slipbase small sign support system did not impede the breakaway performance and was determined to comply with National Cooperative Highway Research Program (NCHRP) Report 350 performance criteria.|A plastic spacer ring was determined to be the most cost-effective alternative for retrofitting existing slip-base foundations to permit their use with the new TxDOT slip-base system. The plastic spacer ring provides the required separation between the slip plates to accommodate an existing lifting cone and does not impede the breakaway performance of the small sign support.|Various configurations of a bolt-down base for small sign supports were tested in an attempt to achieve an anchor system that would accommodate design wind loads, be crashworthy in a vehicular collision, and have a high degree of reusability after an impact. Although the system met all NCHRP Report 350 performance criteria, further strengthening is needed to increase reusability and decrease maintenance after an impact.