Experimental Fatigue Evaluation of Welded Connections in Cantilevered Steel Sign Structures

Cantilevered steel sign structures, commonly used to support freestanding signs, are flexible, have low damping, and can be prone to fatigue-type failure as a result of wind-induced vibration. A sleeve connection, involving horizontal ring plates with two-sided fillet welds welded to the upper pipe and slot welds to connect the lower ring plates to the lower pipe, is commonly used to splice the upper and lower pipes of different diameters. Although the majority of these structures have performed well in long-term use, some structures have been damaged or destroyed as a result of cracking at the weld toe of the sleeve connections. A testing program was developed to evaluate the relative fatigue life of conventional and alternative connection details. Testing demonstrated that conventional welded connections had a short fatigue life. A revised sleeve connection detail incorporating a one-sided fillet weld detail at the critical joint was effective in enhancing the fatigue performance. Replacing slot welds by cement grouting the gap between two pipes significantly increased the fatigue life. Using a welded cone to provide a smooth transition between the pipes also showed improved performance. A tapered slip-joint connection that required no welded joints between the pipe sections provided the best fatigue performance.