high strength friction grip bolted joints - effects after one year of weathering under load

the first year of a five year study of the behaviour of high strength friction grip bolted joints under the combined action of continuous loading and weathering is reported. the plies of specimen joints were given various surface treatments and were weathered before assembly. some joints were tested for slip factor and the results compared with those of tests on joints having unweathered plies. similar joints are now weathering under continuous loading, and slip is being monitored. the slip factors of unprotected joints, particularly those made from weathering steel, were increased by pre-assembly weathering, but were reduced for joints having corrosion resistant treatments. slip has occurred in most of the loaded joints and the largest movements have taken place in the joints having corrosion resistance treatments containing zinc. it is concluded that, when some corrosion resistant treatments are used on the interfaces of high strength friction grip bolted joints, the efficiency of the joint is impaired if the surfaces weather before assembly. it is recommended that, when these treatments are used, the interfaces should be protected to prevent weathering in the time between preparation of the surfaces and assembly of the joint.(a)