Slip-resistant shear connections with preloaded bolts have traditionally been used in steel structures exposed to cyclic / fatigue loading or in cases when bolt slipping or connection deformations should be restricted. Hence, shear load is transferred through friction surfaces rather than through contact between the bolt surface and the hole. The main influencing parameters determining slip resistance of the connection are the friction between contact surfaces and the bolt preload level. This paper presents an experimental study of preloaded bolted connections under cyclic load, the main objective being to investigate the influence of cyclic load on the losses of preload force in high strength bolts and lock bolts.@en