Behavior of Noncompacted High Strength Bolted Joints

摘要

This investigation into the behavior of non-compacted high strength bolted joints included a total of 18 static and 54 fatigue tests of joints of varying geometry and degree of non-compaction. All tests were continued until failure of the joint; all joints were of a butt type utilizing double lap plates and 3/4 inch A325 high strength bolts. Non-compaction ranged from the fully compacted state up to 1/8 inch difference in thickness of connected plates. Non-compaction was observed to significantly reduce the load level at which joints slip into bearing. Ultimate static loads were not affected by non-compaction, however. Under repeated loads the joints tended to slip into bearing even though nominally designed as friction connections. Fatigue failures were observed to occur though the minimum net section, usually, though not always, in the lap plates. Fatigue life was often lower than expected, based upon AASHTO Category B criteria, if one assumed the joint would behave as a friction connection. When the actual behavior of the joint was taken into account, and stress level computations based on net rather than gross sections, the AASHTO criteria did not seem unreasonable. Based upon net sections, stresses in many of the joints approached and even exceeded yield, thus explaining the observed low fatigue lives. The greatest reduction in slip load was in the shorter non-compacted joints; those with two or three bolts/row only. It is recommended that non-compaction be accounted for in these types of joints if it is necessary to maintain a friction-type connection. Non-compaction would not seem to be significant for bearing type connections.