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 4and a 20story 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.

中文翻译：

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推进预北岭焊接柱接头断裂脆性评估

提出了对焊接钢抗弯框架 (WSMRF) 中焊接柱接头 (WCS) 连接的抗震要求和断裂能力的精确概率评估。地震需求评估是通过基于云的非线性时程分析 (NLTHA) 对两个案例研究结构（即 4 层和 20 层 WSMRF）进行的。NLTHA 的结果通过概率地震需求分析框架进行评估，以推导出 WCS 连接的断裂脆性。为此，该研究调查了 (1) 根据全局（即最大层间漂移比）和局部（即 WCS 法兰中的峰值拉应力）调节概率地震需求模型的最佳地面运动强度措施WSMRF的工程需求参数；(2) 地震动垂直分量对 WCS 连接纵向翼缘应力及其产生的断裂脆性的影响；(3) WCS 容量不确定性对这些连接的断裂脆性估计的影响。对于后一种情况，作者提出的基于有限元断裂力学的先进方法用于捕获影响断裂能力的偶然和认知不确定性。重点是北岭前 WCS 连接具有部分接头穿透和脆性材料，使它们极易受到地震断裂的影响。对案例研究结构的断裂易损性结果进行了比较和讨论，强调了所考虑问题对易损性估计的重要性，特别是在高层结构的情况下。研究结果有助于阐明地震需求和容量不确定性对 WCS 连接断裂脆性评估的影响。这些发现可以指导 WSMRF 的类似基于性能的评估练习，例如，为这些脆弱连接的改造策略的规划和设计提供信息。