High Strength Bolted Galvanized Joints

Tests on steel plates without overt stress concentrations show that hot dip galvanizing reduces the fatigue strength by only about 4% in zero to tension cycles. Galvanizing, in the presence of a notch, reduces fatigue strengths by up to 28% at some stress levels in zero to tension cycles. An analysis of the results indicates that this reduction is due to the loss of ductility of the galvanized steel plate as compared to the as-rolled (black) plate. Initial coefficients of friction for galvanized plates in these tests (0.12) were about one half of the value for plates with mill scale (0.21). In tests on high strength bolted joints, under reversed loading, galvanized joints locked up after a few cycles of load, and cyclic slip ceased. Because of this action and the fact that fatigue failures of the connections occurred in front of the net section, the fatigue strength of galvanized friction type connections was comparable to that of identical black connections in zero to tension and one half compression to tension cycles.