Development of a loading protocol for long links in eccentrically braced frames

Abstract

Loading protocols are generally used for qualification testing of structural members. In eccentrically braced frames (EBFs), the connections of short links attached to columns are evaluated based on the loading protocol given in the AISC Seismic Provisions for Structural Steel Buildings (AISC 341–16). Behavior of many short links without column attachments was also investigated by making use of this loading protocol. The AISC341 loading protocol is suitable for only short links and does not take into account the one-sided nature of link rotation angle (LRA) demands due to mean effects. Long link behavior differs from short link behavior in a sense that long links are subjected to strength and stiffness degradation due to local buckling effects. A nonsymmetrical loading protocol for long links was developed as a part of this study. Twenty-four long link EBF archetypes with variable floor plans, bay widths, number of stories and link length to bay width (e/L) ratios were designed according to the US standards. The responses of EBFs under maximum considered earthquake (MCE) and collapse level earthquake (CLE) were obtained by making use of numerical analysis employing degrading link models. The link rotation angle time histories were reduced and converted into a series of cycles and the peaks of the LRA response were identified by using the rainflow counting algorithm. The nonsymmetrical loading protocol was represented as a function of maximum rotation range, which depends on the seismic hazard and e/L ratio.