Fatigue Testing of Galvanized and Ungalvanized Socket Connections

SUMMARY

The fatigue tests on specimens from fabricator 1 showed how workmanship greatly influences the fatigue strength of socket connections and may govern over any effect galvanizing may have. The tests revealed that the poor performing welds had equal legs with undercuts, while the better performing welds had unequal legs and evidence of peening. This may speak to larger issues of quality control or the need for industry specifications for fatigue control in sensitive structures.

The test data from fabricator 2 show a pronounced difference in fatigue strength between galvanized and ungalvanized specimens, with galvanizing producing about a one category fatigue life reduction. However, current AASHTO specifications do not recognize the increase in fatigue life of ungalvanized specimens, and most of the fatigue data used to create the specifications were based on galvanized specimens.

Both sets of fatigue test data showed the galvanized specimens had a resistance much less than Category E'; however, the new AASHTO Standard Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals, 6th edition, still predicts the tested geometries have Category E' resistance.⁽¹¹⁾ There still appears to be a disparity in the new specifications, either in the determination of allowable stress range or in the workmanship standards to which these structures are fabricated.

A plastic cracked section analysis can accurately assess the remaining moment capacity of poles with cracks. To implement this analysis, one should also demonstrate confidence in the fracture toughness of the plate material. This project did not evaluate the fracture toughness, but except for one of the specimens, the fracture toughness was certainly high enough to sustain 12-inch-long cracks at temperatures to -30 °F.