Analytical Fatigue Evaluation and Test Specimen Design for Cantilevered Overhead Sign Structure Box Connections

Abstract

Cantilevered overhead sign structures (COSS) are susceptible to fatigue at many of their connection details, in particular the connection between the pole and mast-arm, due to stresses caused by natural wind gusts, truck-induced wind gusts, and galloping. There have been cases of structures within the Kansas Department of Transportation (KDOT) inventory, failing at the gusseted box connection, which is the connection detail utilized by KDOT to connect the pole and mast-arm. Behavior and fatigue life of these connection details are not well understood, which limits the ability to identify which structures should be considered for repair, retrofit, or replacement. This research was focused on analyzing behavior of the box connection used in COSS. A finite element analysis investigation was conducted on 21 different COSS based on KDOT designs to investigate the effects of changing geometry of the structure and the impact of switching from a gusseted box connection to a ring-stiffened box connection. Findings from the finite element analyses included: 1) thickening the mast-arm and pole aids in decreasing stresses experienced by the box connection, 2) as pole thickness increases, peak demands shift to the mast-arm socket connection for out-of-plane loading and to the baseplate socket connection for in-plane loading, and 3) utilization of the ring-stiffened box connection decreased stresses at the box connection for both out-of-plane and in-plane loading.