Loosening of Bolted Connections under Transverse Loading in Timber Structures

Abstract

Bolted joints are widely used in timber structures, and the loosening of bolt connections will reduce the structural performance. In this paper, a mechanical model of bolt connection for timber structures is established, and the process of bolt loosening under a transverse load is investigated. By using the finite element method to construct an accurate thread model with a helix angle, the thread contact state during the bolt loosening procedure was analyzed in detail, and the factors such as load amplitude, load frequency, load location, and different timber materials on bolt loosening are also studied. In the timber structure, the load amplitude is the main factor affecting the bolt loosening, the decay rate of the preload in the bolted joint is positively correlated with the amplitude of the cyclic transverse load. The frequency of the loading has a smaller effect on the looseness, the preload decreases as the frequency increases. When the load is applied to the smooth rod part of the bolt, the preload force will decrease rapidly, and the distance between the load position and the bolt has no effect on the change in looseness. The decreasing range of the preload is different with different timber material, but the decreasing law is the same. The model can be applied to analyze the loosening rule of bolted connections in timber structures.

Assessment of the Durability of Threaded Joints

“…Plastic failure is unreal in threaded joints; hence, only the progressive shape change condition is analysed in the present work. The shakedown diagram of the threaded joints M52×4 was designed according to dependencies (22) and (24). Figure 13 shows the shakedown diagram built according to [46] (p. 42) and the experimental data according to the established pattern, that is, after about 50 cycles, when the stress is constant in the joints.…”

“…The extension of the root of the radius of the bolt root improved the fatigue limit of the bolt by more than 30% because both the stress amplitude and the mean stress can be reduced. Other articles deal with anti-loosening problems [21][22][23][24][25] or analyze the performance of specific threaded joint fatigue strength [26][27][28][29].…”

Effects of Loaded End Distance and Moisture Content on the Behavior of Bolted Connections in Squared and Round Timber Subjected to Tension Parallel to the Grain

“…For a double shear steel-to-timber connection with a steel plate of any thickness as the central member, the characteristic load-carrying capacity of one fastener for a single shear plane is determined as the minimum value according to Equation (2) for the failure modes shown in Figure 2 (failure mode a represents embedment of the timber, failure mode b represents bending of the fastener and failure mode c is the combination of both mentioned failure modes) or in [27]. The first member in the formula is the load-carrying capacity based on the Johansen yield theory [32] and the second member represents the so-called rope effect [39,40], which in Eurocode 5 has to be limited to 25% of the Johansen part for bolts. If the contribution from the rope effect is unknown, then it is taken as zero.…”

Vision-Based Detection of Bolt Loosening Using YOLOv5

“…The mechanical performance of the bolted connection is related to pretightening torque, thread pair contaction and friction of contact surfaces [ 6 , 7 , 8 ]. In order to explore the mechanism of bolt loosening, Goodier et al [ 9 ] tested the behavior of bolted connections under dynamic load.…”