ABSTRACT

Recent worldwide earthquakes have emphasized the severe damage potential of pulse-like ground motions caused by forward directivity close to a fault rupture. We investigate the effect of such directivity-induced pulse-like ground motions on the fracture fragility and fracture risk of pre-Northridge welded column splices (WCSs) in near-fault regions. To this aim, incremental dynamic analysis (IDA) is employed to explicitly quantify the pulse effects on WCS stress demands. Two case-study nonlinear welded-steel-moment-resisting-frame (WSMRF) models featuring WCSs (i.e., 4 and 20 story) are developed and subjected to (1) a set of pulse-like ground motions with varying pulse periods; and (2) a suite of ordinary (i.e., non-pulse-like) ground motions. Fracture fragility curves for both ordinary and pulse-like records are then derived from the IDA results. These are finally combined with state-of-the-art near-source probabilistic seismic hazard analysis (NS-PSHA) for a case-study scenario rupture and six representative near-fault sites to assess WCS fracture risk. Findings from the study highlight that directivity-induced pulse-like ground motions affect the estimated fracture fragility and potentially increase the fracture risk of pre-Northridge WCSs in near-fault regions. These findings can guide similar performance-based assessment exercises for WSMRFs to inform, for instance, the planning and design of retrofitting strategies for those vulnerable connections in near-fault regions.

摘要

最近世界范围内的地震强调了由断层破裂附近的前向方向性引起的脉冲状地面运动的严重破坏潜力。我们研究了这种方向性引起的脉冲状地震动对近断层区域北岭前焊接柱接头 (WCS) 的断裂脆性和断裂风险的影响。为此，采用增量动态分析 (IDA) 来明确量化脉冲对 WCS 应力需求的影响。开发了两个具有 WCS（即 4 层和 20 层）的非线性焊接钢抗弯框架 (WSMRF) 模型并经受了 (1) 一组具有不同脉冲周期的脉冲状地震动；(2) 一套普通的（即非脉冲的）地面运动。然后从 IDA 结果中导出普通和脉冲样记录的断裂脆性曲线。这些最终与最先进的近源概率地震危险分析 (NS-PSHA) 相结合，用于案例研究场景破裂和六个具有代表性的近断层站点，以评估 WCS 断裂风险。该研究的结果强调，方向性引起的类似脉冲的地面运动会影响估计的裂缝脆弱性，并可能增加北岭前 WCS 在近断层区域的断裂风险。这些发现可以指导 WSMRF 的类似基于性能的评估活动，例如，为近断层区域的脆弱连接的改造策略的规划和设计提供信息。该研究的结果强调，方向性引起的类似脉冲的地面运动会影响估计的裂缝脆弱性，并可能增加北岭前 WCS 在近断层区域的断裂风险。这些发现可以指导 WSMRF 的类似基于性能的评估活动，例如，为近断层区域的脆弱连接的改造策略的规划和设计提供信息。该研究的结果强调，方向性引起的类似脉冲的地面运动会影响估计的裂缝脆弱性，并可能增加北岭前 WCS 在近断层区域的断裂风险。这些发现可以指导 WSMRF 的类似基于性能的评估活动，例如，为近断层区域的脆弱连接的改造策略的规划和设计提供信息。