Fatigue Performance of Overhead Truss Sign Structure Coupler Connections

Nearly all aluminum overhead truss sign structures (OHTSSs) in Kansas constructed before 2015 use an identical type of hot-riveted coupling assembly to provide connections between vertical poles and horizontal truss members. Although many of the connections have been in service for 30 to 40 years, no research has been conducted to determine their fatigue performance. This paper presents a study aimed at characterizing the fatigue performance of the coupler connections. The study includes a series of finite-element (FE) analyses and 24 experimental fatigue tests. The FE analyses were used to determine design-level fatigue demands on the coupler connections and to provide information for designing the experimental setups used in this test program. Four sign structures with three connection properties and six loading modes were modeled. The experimental tests were conducted to characterize the fatigue performance of the connection. Tests were conducted for three loading modes with respect to the load on the rivet connecting the two interior half-couplers: (1) tension, (2) vertical shear, and (3) horizontal shear. Results indicated that when loaded below 10 Ksi (68.9 MPa), the connection can be classified as a Category E′ based on stress in the rivet. The FE analyses and test results indicated that fatigue failures are unlikely to occur in the coupler connections used in OHTSSs. In addition, two used coupler assemblies from OHTSSs taken out of service were also tested and the failure surfaces were examined under a microscope. No reliable evidence of preexisting cracks was found.