Welded Sleeve Connection Design of Cantilevered Steel Sign Structures

Cantilevered steel sign structures are widely used for on-premises freestanding signs. A welded sleeve connection detail is commonly used to splice pipes of different diameters. This type of structure can be flexible and the connections are vulnerable to fatigue cracking attributable to wind-induced vibration. Fatigue has not been considered in design, although the connection has an inherently low fatigue resistance. To investigate the cause of failure at the sleeve connection and to mitigate the problem, a study of 10 sample failure cases and a series of finite-element analyses were performed. The finite-element analyses showed that the actual load-transfer mechanism in the sleeve connection was not very consistent with that assumed in design. In addition, very high-stress concentration caused the weld-toe crack to propagate into the pipe section. The common practice of strengthening the connection by welded gusset plates did not alleviate the problem. A frequency analysis indicated that the second-mode resonance because of wind-induced vortex shedding may cause a large number of damage cycles. Two alternative connection details were proposed to mitigate weld cracking.