PSEUDO DYNAMIC TESTS OF A FULL-SCALE CFT/BRB COMPOSITE
DISPLACEMENT BASED SEISMIC DESIGN AND RESPONSE EVALUATIONS
K.C. TSAI , Yuan-Tao WENG , Min-Lang LIN , Chui-Hsin CHEN, Juin-Wei LAI and Po-Chien HSIAO
At the time of this writing, a full scale 3-story 3-bay concrete filled steel tube (CFT) composite braced frame has been constructed in NCREE with buckling restrained braces (BRBs) and scheduled to be tested in October 2003. The full scale CFT/BRB frame test is part of an international collaboration among researchers in Taiwan, United States and Japan. Measuring 12 meters tall and 21 meters long, the frame is among the largest frame tests of its type ever conducted. The frame is to be tested using the pseudo-dynamic test procedures applying input ground motions from the 1999 Chi-Chi and 1989 Loma Prieta earthquakes, scaled to represent 50%, 10%, and 2% in 50 years seismic hazard levels. This paper describes the displacement-based seismic design procedures adopted in the design of the structural members. A target story drift limit of 0.025 radian for the 2% in 50 years hazard level governs the design strength of the frame. Nonlinear analyses illustrate that the response of individual BRB member can be satisfactorily simulated by using truss elements implemented in two different general purpose nonlinear response analysis programs. Nonlinear dynamic analyses suggest that the peak story drift is likely to reach 0.025 radian after applying the 2/50 design earthquake on the frame specimen. Analytical results also suggest that the arrangement of 4, 3 and 3 actuators, each having 980 kN force capacity, might be necessary for the 1st, 2nd and 3rd floor, respectively. The BRBs at the upper two floors are more vulnerable than those in the first floor. The failure of moment connections is not likely to occur after applying four earthquake load effects. CFT columns hinging at the base is expected, but columns should not fail as the rotational demand is moderate.
Keywords: concrete filled tube, buckling restrained brace, pseudo-dynamic tests, displacement based seismic design, nonlinear analysis
paper in PDF format