HIGH-STRENGTH FRICTION GRIP BOLTS - OPTIMAL PARAMETERS FOR THE COMBINED METHOD OF TIGHTENING

The economic need to realize high preloads in slip resistant connectio ns has promoted the tightening of fasteners above the yield stress. Th e tensile and torsional stresses at this tightening level and the even tual consecutive deteriorations of the screws and the nuts are more or less unknown.An experimental research program undertaken in Belgium h as given more precise information on the behaviour of the fasteners du ring tightening until the ultimate state (maximal preload) as well ind ications of how to improve this behaviour by using nuts of a higher ha rdness and better lubricants. The tests have shown that when tightenin g with the combined method, as specified in Eurocode 3, and when using higher grade nuts and better lubricants, no excessive deformations oc cur.