APPLICABILITY OF TURN-OF-NUT BOLTING METHOD FOR FRICTION TYPE CONNECTION BY F10T HIGH STRENGTH BOLT

Abstract

 This study investigates the applicability of turn-of-nut method by F10T high strength bolt (Tensile strength is 1000MPa). Conventionally, turn-of-nut method is allowed only for F8T of lower yielding stress. In addition, torshear type high strength bolt such as S10T also can be found in many constructed works. Though S10T shows good workability, it requires finishing of tip of bolt and daily check of axial force by sampling. Turn-of-nut method of F10T can enhance the efficiency of the bolting process. In this study, at first, snug tight test was carried out by professional fastening workers. The result of axial forces of the bolts varied in a wide range, and the average axial force was almost equivalent with 150 Nm that is specified in railway design code. The appropriate turn-of-nut angle was investigated by the experiment, changing the length and diameter of bolt with the steel plates coated by inorganic zinc silicate primer. The result showed that the bolts get in the yielding area more than 90 degrees. Based on the optimum nut angle from the experiments, relaxation and slip tests were carried out. The one month relaxation test showed that the decrease of axial force of the bolts was ranged within 10%. The slip coefficients by the tests satisfied 0.45 that is specified in Japanese Road Association bridge design code.