Column splice fracture effects on the seismic performance of steel moment frames

Abstract

The influence of welded column splice fracture on the seismic response of steel moment frames is examined. The study is motivated by pre-Northridge moment frames with welded column splices with crack-like flaws that are highly vulnerable to fracture. Costly retrofit strategies to repair these splices are usually intentioned to preclude splice fracture, without an explicit examination of its effects on global response. This study simulates post-fracture response of splices through a new material model, which is informed by fracture-mechanics based estimates of splice strength, and reproduces phenomena such as gapping and re-seating that occurs in the splices after fracture. Nonlinear response history simulations (incorporating this model) are used to examine the response of 4-and 20-story moment frames. The simulations, using 100 ground motions, and reflecting key aspects of nonlinear response are conducted within a Performance Based Earthquake Engineering (PBEE) framework, to examine global and local structural response in a probabilistic sense. The simulations indicate that neither the collapse potential nor building deformations are significantly affected by splice fracture when compared to benchmark simulations without fracture. This is attributed to a combination of phenomena; these include the mobilization of building rocking due to splice fracture, and the tendency of fractures to cascade upwards through individual columns rather than across a story. The results suggest that splice fracture may not necessarily trigger structural collapse, and retrofit strategies that consider global, rather than local response may be more cost effective. Limitations of the study are outlined.

Advancing fracture fragility assessment of pre‐Northridge welded column splices

“…A bilinear kinematic hardening relationship is utilized to model the cyclic response of steel in the fiber sections, with modulus of elasticity E equal to 2.0×10 5 MPa, a hardening slope equal to 5% of the initial elastic modulus, and yield strength y F equals to 380 MPa. These values were calibrated to match an extensive empirical dataset of plastic hinge responses obtained by Lignos et al [43] and are consistent with the previous modellings by Shaw et al [15] , Galasso et al [8] as well as Stillmaker et al [44] .…”

“…Nonetheless, propagation of fracture and its effect on building response is critical for a more holistic development of retrofit strategies. This has been addressed by the authors in Stillmaker et al [44] , which required development of a special material in OpenSees to represent flange fracture.…”

Seismic Design of Bolted Connections in Steel Structures—A Critical Assessment of Practice and Research

“…Fractures due to microstructural issues in steel alloys, welds, and thermally affected zones have been studied by Stillmaker et al with a focus on column splice fracture in seismically loaded MRFs [235] and by Liao et al concerning microstructural modelling of steel alloys' fracture under strong earthquake motions [236].…”

تحلیل عددی ایمنی قاب خمشی فولادی تحت بارهای دینامیکی لرزه‌یی

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