A Reliability Study of Joints with Bolts Designed with Threads Excluded but Installed with Threads Not Excluded

Abstract

This paper presents a reliability and probability study focusing on connections using relatively short bolts that in a companion paper have been shown to have the potential to have been designed with threads excluded from the shear plane and then subsequently installed with the threads not excluded from the shear plane. After an introduction outlining the background of the shear strength and associated design of joints in various editions of the AISC Specification, the paper presents a structural reliability analysis as well as a probability study using Monte Carlo simulations, and then finally a discussion of additional considerations and mitigating factors associated with this potential problem. Calculated reliability coefficients and probabilities of failure are tabulated for joints using two diameter groups of 120-ksi bolts (from ? in. to 1 in. and from 1? in. to 1¼ in.) and for joints using 150-ksi bolts. The paper provides an evaluation of the reliability of joints with bolts that have been designed with the threads excluded from the shear plane but installed with the threads not excluded from the shear plane. Although it is recommended that future designs involving short bolts be based on the assumption that the threads are not excluded from the shear plane, this study provides a measure of the reliability of structures that have already been constructed with bolts designed assuming that the threads were excluded but installed with the threads not excluded. The results show that the reliability of joints in this class is dependent on the grade and size of the bolts used, on the length of the joint, and on which edition of the AISC Specification was used for design. It was found that some joints in this class still meet the AISC target reliability for connections, and that many joints meet the AISC target reliability for members.