Parametric collapse evaluation of steel moment resisting frames with fuse connections

Gilroy, Joseph
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Recent research has investigated a low damage seismic design concept for steel moment resisting frames (MRFs): the moment resisting fuse connection. Fuse connections are moment resisting connections that yield prior to the beam or column they connect. The connection acts as an easily repairable structural fuse of the seismic system instead of the beam, which is the typical fuse in a steel moment resisting frame designed to resist seismic loads, which can be very challenging and costly to repair after an earthquake. In most proposed fuse connections, energy dissipation is achieved by means of connection component yielding or friction slip. In AISC 358-16 (AISC, 2016c), the first prequalified fuse connection was added to the specification: the Simpson Strong-Tie™ Yield-Link® (SST-YL) connection. Although the connection has shown sufficient strength and ductility at large levels of drift to reach prequalified status, there is some concern that steel MRFs with optimized fuse connections will not have the typical overstrength of traditional steel MRFs, which are usually controlled by drift limits rather than strength requirements. This concern raises the question: Are steel moment resisting frames with fuse connections adequately designed to prevent sidesway collapse during earthquakes when using typical seismic performance factors (R = 8, C [subscript d] = 5.5, and Ω₀ = 3.0) for steel special moment resisting frames (SMRFs)? To investigate this concept, four three-bay steel special moment resisting frames with fuse connections were designed using provisions in ASCE7-16 (ASCE, 2017), AISC 341-16 (AISC, 2016a), AISC 360-16 (AISC, 2016b), and AISC 358-16s20 (AISC, 2020) with steel SMRF seismic performance factors. These frames were 2 stories, 4 stories, 6 stories, and 8 stories in height. These four archetypes were also redesigned with modified capacity design requirements more comparable to typical steel MRFs for a total of four design cases. These designs were evaluated using the FEMA P-695 methodology (FEMA, 2009) to determine if they have adequate collapse capacity. Different post-yield behaviors and failure criteria were modeled to determine their effect on system collapse capacity. Nonlinear pushover and response history analyses were done using OpenSEES (McKenna et al., 2010). The results of this investigation support that the seismic performance factors for typical SMRF frames are appropriate for use in SMRFs with fuse connections. However, there are several sources of uncertainty that require further investigation and research to determine to what extent this conclusion is accurate, particularly for new fuse connections that may be proposed. Suggestions for future research into numerical modeling and analysis of SMRFs with fuse connections are presented.