An Experimental Appraisal of the Load-Deformation Properties of A325 High-Strength Bolts

Abstract

Abstract Current specifications and testing procedures of high-strength bolts are based on the results of early research performed in the late 1950s and the early 1960s using the testing technology available at that time. Within the past few decades, the development of new, advanced testing equipment and computerized data acquisition systems has brought about significantly improved capabilities for materials testing. In light of these advancements, conducting a new set of bolt tests was considered essential in appraising the load deformation properties of high-strength bolts using the new testing technology. In this study, samples of randomly obtained A325 high-strength bolts were tested in accordance with the ASTM standard test methods, utilizing a servo controlled universal testing machine and a computerized data acquisition system. This equipment differs from that used in the early research in the accuracy of the data collected and the existence of many available options for specimen loading. The new testing technology provides an easy determination of the yield point, the proof load, and ductility of the bolts. The study aimed at experimentally determining the load-deformation properties of high-strength bolts and comparing them with those generated by early research. The proof load, the yield strength, and the teasile strength obtained were much higher than the specified ASTM and AISC values. Additional studies were pursued to gain an improved understanding of the behavior of the bolts as affected by the exposed thread length in the grip. The tested bolts showed higher strength and lower ductility as the number of the thread exposed in the grip length decreased.