Tightening and loosening torque of M253M bolts: Experimental and analytical investigation

Abdalla, Khairedin and Kaziolas, Dimitrios and Baniotopoulos, Charalambos (2011) Tightening and loosening torque of M253M bolts: Experimental and analytical investigation. Pollack Periodica, 6 (2). pp. 69-83. ISSN 1788-1994

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Abstract

The present paper deals with the study of the installation behavior of high-strength bolts under friction. For this purpose an experimental program was conducted to evaluate the energy of these bolts that is dissipated due to tightening and loosening. The total number of tested specimens was 100 bolts furnished to the requirements of AASHTO specification M253M. The turn-of-nut tightening method is applied experimentally to evaluate the pretension and the torque for tightening and loosening of bolts. It is mentioned that a number of 56 bolts has 76 mm length while the rest is of 152 mm. The experimental preloading and the lost torque that overcomes friction are compared with the respective analytical values. It is confirmed that the K-nut factor is affected by the type of lubricant and the length of the bolt. Additionally, most of torque is going to overcome friction. The percentage of tightening and loosening torque for both the analytical and the experimental cases is very close.

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