Advancing fracture fragility assessment of pre‐Northridge welded column splices

Abstract

A refined probabilistic assessment of seismic demands and fracture capacity of Welded Column Splice (WCS) connections in welded steel moment resisting frames (WSMRFs) is presented. Seismic demand assessment is performed through cloudbased nonlinear time history analysis (NLTHA) for two case-study structures, i.e. a 4-and a 20-story WSMRFs. Results from NLTHA are assessed through a probabilistic seismic demand analysis framework to derive fracture fragility of WCS connections. To this aim, the study investigates (1) optimal ground-motion intensity measures for conditioning probabilistic seismic demand models in terms of global (i.e., maximum inter-story drift ratio) and local (i.e., peak tensile stress in the flange of WCSs) engineering demand parameters of WSMRFs; (2) the effect of ground-motion vertical components on the longitudinal flange stress of WCS connections and their resulting fracture fragility; and (3) the effect of WCS capacity uncertainties on the fracture fragility estimates of those connections. For the latter case, an advanced Finite Element Fracture Mechanics-based approach proposed by the authors is employed to capture aleatory and epistemic uncertainties affecting fracture capacities. The focus is on pre-Northridge WCS connections featuring partial joint penetration and brittle materials, making them highly vulnerable to seismic fracture. Fracture fragility results for the case-study structures are compared and discussed, highlighting the importance of the considered issues on fragility estimates, particularly in the case of high-rise structures. Findings from the study contribute shedding some light on the influence of seismic demand and capacity uncertainties on the assessment of fracture fragility of WCS connections. These findings can guide similar performancebased assessment exercises for WSMRFs to inform, for instance, the planning and design of retrofitting strategies for those vulnerable connections.

Probabilistic seismic performance assessment of steel moment‐resisting frames considering exposed column‐base plate connections with ductile anchor rods

“…Secondly, this study utilized a state‐of‐practice IM (i.e., S a ( T 1 ) of the code‐based fundamental period) to handily interpret results in accordance with design codes. It is important to recognize that the code‐based fundamental period is typically lower than the computer‐based period for the considered SMRFs, 16 and S a ( T 1 ) itself may not be an efficient IM for the probabilistic seismic demand analysis 72 . The adoption of code‐based S a ( T 1 ) in this study may slightly affect the accuracy of the seismic performance assessment.…”

“…It is important to recognize that the code-based fundamental period is typically lower than the computer-based period for the considered SMRFs, 16 and S a (T 1 ) itself may not be an efficient IM for the probabilistic seismic demand analysis. 72 The adoption of code-based S a (T 1 ) in this study may slightly affect the accuracy of the seismic performance assessment. Thirdly, bias in the simulation and NLTHAs cannot be discounted.…”

Influence of the design objectives on the seismic performance of steel moment resisting frames retrofitted with buckling restrained braces

“…46 These ground motion records are selected by using the BSE-2E spectrum as a reference, considering a period range from 0.2T 1-min to 1.5T 1-max (i.e., from 0.1 to 2.82 s for case study structure A). This period range is based on the ranges often considered in literature (e.g., 47,48), which are used to consider the contribution of higher modes and the possible elongation of the fundamental period. The selected ground motions for case study structure A are characterised by magnitudes from M w = 5.2 to 7.36, and correspond to far-field records with a mean significant duration (D 5-95% ) of 18.59 s, and a mean rupture distance (R rup ) of 29.79 km.…”

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