Shake-Table Collapse Tests of a Reduced-Scale, 4-Story Steel Moment-Resisting Frame

Shake-table tests of a steel moment-resisting frame were conducted to obtain detailed data on the occurrence and propagation of damage leading to the collapse of steel structures. A 2/5-scale, 4-story, 2-bay, planar specimen was subjected to in-plane, unidirectional ground motions. The specimen was intended to sustain very large deformations, or story drift ratio greater than 0.10 rad, and avoid a first-story collapse mechanism. The specimen comprised I-section beams and square-HSS columns. As in typical Japanese construction, the Complete Joint Penetration (CJP) groove welds between the beam flanges and column diaphragm plates were completed with no weld-access-hole. The ground motions included the JMAKobe NS record scaled from 10 to 100% and white noise excitations. The 100%-scale record was repeated four times. Each of the100% motions induced significant yielding of the beams, columns, and some column panels, which resulted in story drift of +0.08 and -0.02 rad, and added a residual story drift of +0.02 rad. Although beam fracture occurred at two locations on the second floor, and the maximum story drift reached +0.15 rad, the specimen did not collapse due to the high strength of the columns. The fundamental period remained constant until beam fracture occurred. Supplementary tests were conducted on beam-column subassemblages constructed from the same materials and fabrication process as the shake-table specimen. The subassemblages exhibited more rapid development of local buckling deformation and associated strength degradation due to axial deformation restraint in the shake-table test beams that was not present in the subassemblage tests.