This study presents a critical assessment of the reliability of current base plate connections in steel special moment resisting frames (SMRFs). Using a probabilistic outlook, this research evaluates the reliability of exposed column base (ECB) connections in SMRFs designed based on the current seismic design provisions; it suggests (and implements) a statistical approach to compute resistance factors for three modes of failure (concrete bearing, base plate yielding at tensile interface, and anchor bolt fracture) of ECB connections to achieve a target reliability index, β, of 4.5. Since ECB connections are limited to short buildings, therefore, this study is conducted on two-story and four-story SMRFs which are analyzed using a suite of 120 ground motions originating from strike-slip and reverse faults. ECB connections for the two-story building are designed to simulate pinned connection, while the bases of the four-story building represent moment connections. Detailed methodology for calculating the β of ECB connections is presented considering the three limit states in a moment–axial load interaction curve. Results indicate that the implementation of current seismic provisions results in β ~ 3.3 for non-moment resisting ECB connections for all tried combinations of resistance factors. For moment resisting ECB connections, however, only the designs based on a resistance factor for concrete bearing failure mode less than the current 0.65 result in an acceptable reliability factor of β > 4.5.

中文翻译：

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特种钢抗弯框架外露式基板连接抗震设计的强度抗力系数

本研究对钢制特殊抗弯框架 (SMRF) 中当前底板连接的可靠性进行了重要评估。本研究使用概率观点，评估了基于当前抗震设计规定设计的 SMRF 中外露柱基 (ECB) 连接的可靠性；它建议（并实施）一种统计方法来计算 ECB 连接的三种失效模式（混凝土轴承、底板在拉伸界面屈服和锚栓断裂）的阻力系数，以实现目标可靠性指数 β 为 4.5。由于 ECB 连接仅限于短建筑物，因此，本研究是在两层和四层 SMRF 上进行的，这些 SMRF 使用一套源自走滑和反向断层的 120 个地面运动进行分析。两层建筑的 ECB 连接旨在模拟固定连接，而四层建筑的底座代表弯矩连接。考虑到力矩-轴向载荷相互作用曲线中的三个极限状态，提出了计算 ECB 连接 β 的详细方法。结果表明，对于所有尝试的阻力因素组合，当前抗震规定的实施导致非抗弯 ECB 连接的 β ~ 3.3。然而，对于抗弯 ECB 连接，只有基于混凝土轴承失效模式的抗力系数小于当前 0.65 的设计才会导致可接受的可靠性系数 β > 4.5。考虑到力矩-轴向载荷相互作用曲线中的三个极限状态，提出了计算 ECB 连接 β 的详细方法。结果表明，对于所有尝试的阻力因素组合，当前抗震规定的实施导致非抗弯 ECB 连接的 β ~ 3.3。然而，对于抗弯 ECB 连接，只有基于混凝土轴承失效模式的抗力系数小于当前 0.65 的设计才会导致可接受的可靠性系数 β > 4.5。考虑到力矩-轴向载荷相互作用曲线中的三个极限状态，提出了计算 ECB 连接 β 的详细方法。结果表明，对于所有尝试的阻力因素组合，当前抗震规定的实施导致非抗弯 ECB 连接的 β ~ 3.3。然而，对于抗弯 ECB 连接，只有基于混凝土轴承失效模式的抗力系数小于当前 0.65 的设计才会导致可接受的可靠性系数 β > 4.5。