Fatigue Strength and Evaluation of Double–Mast Arm Cantilevered Sign Structures

Abstract

Double–mast arm cantilevered sign structures are widely used in Indiana and in many other states. Because of the large sign area and relatively high flexibility, wind loading on these sign structures occasionally produces significant stress cycles. Cracking caused by fatigue damage may occur at several critical spots on the sign structures. An analytical investigation of the fatigue lives of the critical details in double–mast arm sign structures is discussed in this paper. An analytical procedure is introduced, and wind load selection and simulation are explained. Finite element models based on a prototype double–mast arm sign structure are described, and dynamic analyses and fatigue life results are presented. It was found that the post-to–base plate socket weld connection was the most critical detail and that variations in the fatigue life occurred because of differences in the wind environment at various sites.