Fatigue Performance of Saddle Connections in Aluminum Overhead Truss Sign Structures

Abstract

A newly developed saddle-type connection has been adopted for use at the joints of support-frame poles and truss chords in aluminum overhead truss sign structures (OHTSS) in Kansas since 2015. This paper describes a study aimed at evaluating the fatigue properties of the saddle connections using finite-element (FE) analysis methods. The study consisted of three parts: (1) analyses to capture global behavior of the sign structures under design-level fatigue loads; (2) analyses to quantify fatigue properties at weld toes using the hot-spot stress method; and (3) analyses to quantify fatigue properties at weld roots using the effective notch stress method. Four sign structures with spans of 18 m (60 ft), 25 m (83 ft), 34 m (110 ft), and 42 m (137 ft) were modeled. Fatigue loads representing natural wind gusts and truck-induced gusts were determined according to AASHTO provisions and applied to the OHTSS. The results indicated that the stiffener-to-pole welds in the bottom saddle connection are the most fatigue-sensitive welds and that the connection is expected to have satisfactory performance. This study could serve as an example for how to evaluate the fatigue properties of undocumented connections in sign structures without conducting costly experimental testing, and draws attention to key differences between common fatigue specifications and analysis methods.