Theoretical investigation and design recommendations for the initial stiffness of Fe-SMA/steel bolted joints in shear

Abstract

Due to the self-stressing performance and easy-to-install, iron-based shape memory alloy (Fe-SMA) has been successfully applied to the prestressed rehabilitation of deteriorated long-span steel bridges, through bolt anchoring joints. The initial stiffness of Fe-SMA/steel bolted joints affects the transfer and distribution of external load and initial preload, which is significant in investigating the mechanical behavior of Fe-SMA plates for structural reinforcements. However, the current leading design standards for the bolted joints are based on mild steels, whose reliability requires investigation when employing Fe-SMA. For this purpose, the applicability of EN 1993-1-8 in predicting the initial stiffness of Fe-SMA/steel bolted joints is evaluated by experimental and numerical results. A parameter study exploring the influencing parameters of Fe-SMA plate thickness as well as end and edge distances on the initial stiffness of Fe-SMA/steel bolted joints is conducted via the numerical models validated with experimental results. Furthermore, the theoretical formula for predicting the initial stiffness of Fe-SMA/steel bolted joints is proposed. The study indicates that when e/d rises from 1.0 to 4.0, the initial stiffness of single-hole Fe-SMA/steel bolted joints improves by 20% to 35%. The influence of edge distance on the initial stiffness of single-hole Fe-SMA/steel bolted joints is found significant but neglected by EN 1993-1-8. Compared with the recommended formula in EN 1993-1-8, the proposed theoretical formula improves the accuracy by 23% in predicting the initial stiffness of single-hole Fe-SMA/steel bolted joints. The research achievements contribute to the theoretical improvements in the reinforcement design of Fe-SMA in civil engineering.