Tightening Torque Calculation Method for Plastic Clamp Force of Bolted Timber Joints

Elastic interaction in multiple bolted timber joints

“…Washer embedment stiffness greatly depends on the side length ratio of the washer (washer's side length to thickness) [27,28]. The side length ratios of the washers used in these experiments were 7.8 (35 mm/4.5 mm ≈ 7.8) and for such side length ratios, it is considered that there is almost no bending deformation of the washers due to bolt tightening [11,27,28]. It is also assumed that the washer became embedded into the wood side while maintaining an almost rectangular shape (a state in which the washer can be regarded as a rigid body).…”

“…Note that this bolt was subjected to the tightening experiment after calibrating the axial force with a universal testing machine. The initial axial force of the bolt was set to 2 kN, which is estimated to be within the elastic range [11], and tightened with a torque wrench. Once the axial force reached 2 kN, tightening was stopped and, after waiting for 1 min, the next bolt was tightened.…”

“…However, to implement these joining methods in actual buildings, it is important to maintain the axial force for a long period of time, and, in addition, axial force management during construction is also an important issue. Thus far, the authors have revealed, with regard to axial force management, that the so-called torque method, which manages wood joints using a single bolt or a single lag screw with a tool, such as a torque wrench, can be applied and that axial force generated while tightening a lag screw is lower than the pull-out strength of the lag screw, owing to the effects of friction at the threaded part [10][11][12][13][14]. However, for joint types formed with multiple bolts, such as the wood friction connectors proposed by the authors, sequential tightening of each bolt affects deformation around each of the other bolts.…”

The load factor in bolted timber joints under external tensile loads

“…The authors have long been interested in developing load-bearing walls, which leverage the friction created when wooden members are fastened together (or to steel plate) with bolts or lag screws. Our team has already reported on the structural performance of these joints [9][10][11], how to control the initial tightening force [12][13][14][15], and their long-term stress relaxation behavior [16][17][18]. In the last case, we have shown that these joints can withstand relatively high stress when the initial tightening force exceeds the compressive yield point of the wood, even when exposed to repeated wetdry cycles [18]; and that they can withstand at least 70% of any vertical compressive stress applied to the wood, even in a high-temperature, constant-humidity environment [17].…”

Effects of tightening speed on torque coefficient in lag screw timber joints with steel side plates

“…Tightening generates a clamp force, which in turn generates a frictional resistance force between two timber members, or between one and a steel plate [5]. Our later research investigated how to apply torque control methods to control this clamp force, a serious issue that must be addressed to control the expression of this frictional resistance force [6,7]. One of the resulting challenges we faced in developing our high damping shear wall was how to determine the effects of lag screw tightening speed on the joint's torque coefficient.…”