F10T 高力ボルト単純引張り時の荷重・変形性状

Abstract

Bolts in tension are common in tension type connections and in beam-to-column connections. Some of them may also subject the bolts to combined tension and shear. It is apparent that before not only a connection can be analyzed but to determine the manner of turn of nut method, the behavior of a bolt itself must be known. Therefore, the behavior of a single bolt subjected to the typical loading conditions of tension is discussed in this paper, further in conclusion I proposed some approximate equations to predict the load-elongation relationships for most popular high strength bolts which have different grip conditions. The behavior of a bolt subjected to an monotonic axial load seems to be governed by mostly its threaded part under and included in nut as well as its body part. To determine the actual mechanical properties of a bolt, I examined direct tension test using 420 specimens putting a stress on amount of thread under nut. These specimens are F10T high strength bolts specified in 1979 JIS B 1186 (Specification for high strength bolts in japanese industrial standard). The tested nominal bolt diameters are 4 kinds of M16 through M24, also the bolt length for every size are 6 kinds which varied from approximately 3 to 10 times of diameter. The amount of thread under nut varied from 0 to 8 threads for every bolt length. In practice, the bolt preload force is usually introduced by tightening the nut applying torque to nut. This tigetening procedure results in different stress conditions in bolt. Therefore, the behavior observed in a torqued tension test may differs from the results obtained from a direct tension test. Thus, the behaviors in torqing a bolt until failure will be discussed in my further paper.