Fatigue Performance of Base Plate Connections Used in High Mast Lighting Towers

This research study examined the fatigue performance of several base plate connections used in high mast lighting towers. Recent failures of these non-redundant structures have increased the awareness of their fatigue susceptibility and the hazard posed by their potential for collapse. Failures have commonly occurred due to fracture of the pole shaft directly above the base plate connection, which indicates that wind-induced fatigue is the cause. Though design of these structures is governed by the 2001 AASHTO specifications, a recent study has found that these design provisions can be unconservative (Rios, 2007).

Several common high mast base plate connections were compared based on their fatigue performance. These comparisons were supported with the results of both full-scale experimental testing and finite element modeling in Abaqus. Additional untested connection details were investigated in analytical parametric studies.

The experimentally tested details incorporated the use of full penetration welds, external collars, and continuous stool stiffeners. Additionally, specimens from two manufacturers were considered to observe the effect of this variable. The results of the study suggest that fatigue performance can be greatly improved through the use of external collars, especially when combined with full penetration welds. The experimental results also confirmed the importance of unequal leg fillet welds for fatigue-critical details.