Evaluation of Dual Support, Triangular Slip-Base Sign Installations (0-1792-8)

Large sign panels have long used extruded aluminum panels as a signage substrate. See Texas Department of Transportation (TxDOT) Sign Mounting Detail (SMD) (2-1) through SMD (2-4). The aluminum panels are extruded with wind beams integral to the sign panel and have typically been mounted on hot rolled W-shape supports with 4-bolt uni-directional slip bases. The supports incorporate fuse plates just below the sign panel that serve as hinge points when errant vehicles impact the supports. In addition, TxDOT uses 2.5-in (64 mm) diameter schedule 80 pipe with triangular slip bases to support a range of small signs (see TxDOT SMD [1-1] through SMD [1-5]). One of TxDOT's districts proposed mating the extruded aluminum panels with the schedule 80 pipe supports. Such a system would provide a cost-effective solution for dual support sign installations with sign panels up to 60 ft2 (5.6 m2). Since the pipe support does not have a hinge point, the impact performance of this type installation was unknown, and full-scale testing was deemed necessary. This report summarizes the results of an investigation of the performance of extruded aluminum sign panels up to 2.5-in (64 mm) mounted on dual schedule 80 pipe supports with triangular slip bases. Static testing of the pipe clamp/extruded aluminum panel connection was performed prior to full-scale crash testing to determine the strength of the connection and controlling failure mode. This information was used to select an appropriate number of connectors for sign panels up to 60 ft2 (5.6 m2), which is the maximum area permitted on two 2.5-in (64 mm) diameter schedule 80 pipe supports per TxDOT standards. Extruded aluminum sign panels up to 60 ft2 (5.6 m2) mounted on dual 2.5-in (64 mm) diameter schedule 80 pipe supports with triangular slip bases meet National Cooperative Highway Research Program (NCHRP) Report 350 requirements and are considered suitable for implementation. Four universal pipe clamps, two on each support, should be used in field installations.