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

A method for calculating plastic clamp force from tightening torque was presented by considering a bi-linear model obtained from experimental tightening torque-clamp force relationships. The practical applicability of the calculation method was verified by tightening tests of Cryptomeria japonica bolted joints using metal washers of various sizes. Results were as follows : It was found that a ratio of side length (diameter) to thickness of metal washers ranging from 7.8 to 16.0 did not affect the torque coefficient. In addition, the ratio of maximum plastic torque coefficient to maximum elastic torque coefficient, gamma(max) and the ratio of minimum plastic torque coefficient to minimum elastic torque coefficient, gamma(max), which are elements of the calculation method, tended to increase depending on embedment into timber of metal washers in side-length (diameter) to thickness ratios of 10.0 (washer size : 32 x t 3.2 mm), 10.9 (washer size : 35 x t 3.2 mm) and 7.8 (washer size : 35 x t 4.5 mm). Furthermore, calculated tightening torque values were verified by tightening tests using a digital torque wrench. As a result, plastic clamp force values obtained by experiment agreed with calculated values ranging from minimum clamp force F-min to maximum clamp force F-max. However, the method of reducing variation in gamma(max) and y(min) remained to be investigated.