Loading Histories for Cyclic Tests in Support of Collapse Assessment of Steel Columns
During the last decade, a number of hysteretic models have been developed to simulate complex deteriorating mechanisms observed in steel components such that earthquake-induced collapse risk can be reliably assessed. Such models are typically calibrated with experimental data on components subjected to symmetric cyclic loading histories. Based on shake table collapse tests as well as collapse simulation studies, the latter loading history does not necessary reflect the actual hysteretic behavior of steel component prior to structural collapse. This paper presents loading histories that can be directly employed for experimental testing of steel columns in order to examine their behavior prior to structural collapse. Such loading histories reflect the ratcheting behavior that a member experiences as part of a building prior to structural collapse. The loading histories can be utilized to investigate the hysteretic behavior of interior steel columns within a steel moment-resisting frame (MRF) in which the applied axial load remains more or less constant during the loading history. The same loading histories can be used in cases that the axial load applied to a column varies due to dynamic overturning effects. Finally, the proposed loading histories can be employed for both unidirectional and bidirectional column testing. The proposed loading histories are utilized to characterize experimentally the hysteretic behavior of steel columns near collapse. It is shown that routinely used symmetric cyclic loading protocols provide insufficient information for modeling the steel column deterioration in flexural strength and stiffness.