SHAKE TABLE TESTS OF A FULL-SCALE THREE-STORY STEEL BRBF WITH SLIDING SLABS IN CHIHSHANG EARTHQUAKE

The moderately built-up box column cannot be used in the Buckling Restrained Braced Frame (BRBF) in a high seismic area based on AISC 341 (2022). This study is an international collaboration work between NCREE, NTU, UCSD, UTA and NCKU. The objectives were to: (1) assess the seismic behavior of steel built-up box columns that satisfy only the moderately ductile member requirement (i.e., width-thickness ratio) in AISC 341 (2022), (2) evaluate the dynamic response of all-steel sandwich buckling restrained braces (SBRBs) in multiple tests, and (3) examine the effect of a sliding slab on the frame response. To achieve this, a full-scale three-story steel dual frame, composed of a Special Moment Frame and a BRBF in 9 m high and 7 m wide, was designed and tested using a shake table at the NCREE Tainan laboratory. The shake table test was conducted in two phases. In phase 1, the slab was allowed to slide with respect to the steel frame, activating the energy dissipation of low-capacity SBRBs connected between the slab and beam. In phase 2, the slab was rigidly connected to the frame with high-stiffness structural members. Seven tests were conducted in phase 1, and ten tests were conducted in phase 2, all using the 2022 near-fault Chihshang earthquake in Taitung, Taiwan (EYUL station record) with increasing amplitudes. The specimen was tested three times beyond the Maximum Considered Earthquake (MCE) level (=0.44 g), reaching a maximum peak ground acceleration of 1.05 g. The test results showed that the maximum interstory drift angle was 0.045 rad during the last test, and all moderately ductile box columns did not show buckling and strength degradation. Although the moderately ductile box column is not allowed in the BRBF in AISC 341-22, it did perform satisfactorily in all shake table tests. The first-story SBRB reached a maximum axial strain of 2.6%, showing stable hysteretic response in 17 seismic tests. SBRBs were then removed from the frame specimen and statically tested to reproduce the dynamic test response and possible failure modes in a post-earthquake evaluation. The sliding slab system was effective in reducing the floor acceleration up to 25% compared to a rigid slab system. The maximum table base shear was about 3.2 times the design shear force in phase 2 test. The test data indicated that the AISC 341-22 is too stringent on the compactness requirement of steel highly ductile built-up box columns in high seismic areas.