Numerical Study of Stiffened Socket Connections for Highway Signs, Traffic Signals, and Luminaire Structures

Sparse fatigue test data was available for gusset stiffener details on through plate socket connections when the AASHTO 2001 specification for signal, sign, and luminaire structures was developed. An effort was carried out to investigate the effect of base plate thickness on various sizes and geometries of gusset stiffener details for through plate socket connections, based on previous research study results at Valmont, the University of Minnesota, and the University of Texas at Austin. Fatigue test results revealed an improved fatigue resistance for socket connections compared to stiffened details. Parametric studies using the finite-element method revealed behavior that tends to contradict current AASHTO specifications. Local stresses were nearly constant after the stiffener reached a $102\mathrm{mm}$ $\left(4\mathrm{in.}\right)$ vertical length. Further, local stresses appear highest for short stiffeners that are currently recognized as Category C details. The study also demonstrated that fatigue investigations and experiments are essential to validate current fatigue categories for such structures.