Performance Validation Testing of a Full-Scale Composite Buckling Restrained Braced Frame

In the spirit of international collaboration, researchers from Taiwan National Center for Research on Earthquake Engineering (NCREE) in Taipei and United States have been busy preparing to test a full-scale composite braced frame. The test specimen is a three-story, three-bay "CFT/BRB" frame, consisting of concrete filled steel tube (CFT) columns, composite steel (S) beams and buckling restrained braces (BRBs). Measuring 12 meters tall and 21 meters long, this CFT/BRB frame is among the largest frames of its type ever tested.

The three-story prototype structure is designed for high seismic location either in Taiwan or California, following provisions of the International Building Code 2000 for composite structures and AISC/SEAOC 2002 Draft Provisions for BRBs. Displacement-based design procedures have also been applied to proportion the buckling restrained braces. The frame will be loaded pseudo-dynamically using 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. Following the pseudo-dynamic tests, quasi-static cyclic increasing loads will be applied to push the frame to interstory drifts up to 4 percent, which will provide valuable data to evaluate system performance and validate simulation models for large deformation response.

The test has three primary objectives. First, it will provide data to evaluate and validate design provisions for composite CFT/BRB frames. Particular topics of investigation include: the displacement-based design procedure, strong column criterion, composite action of concrete slab and steel beams, integrity of the CFT columns, CFT column-to-foundation connections, BRB-to-gusset plate and composite beam-to-column connections, and overall system response. Second, the test will provide valuable information to validate the analytical models and computer programs for nonlinear simulation and performance assessment. Finally, the full-scale test will provide validation to support the use of innovative composite braced frames as alternatives to conventional steel and concrete frame systems for high seismic regions. Besides these direct benefits, this large scale frame test and study will provide the impetus to accelerate international collaboration and data sharing/archiving envisioned for the NEES research initiative in the US.

Researchers at NCREE are using the PISA3D computer program to perform displacement-based frame design and estimate the nonlinear frame responses in order to properly set up the hydraulic actuators and response measurement instrumentation. Two-surface plastic material property in the PISA3D Program is used for the BRB model. NCREE researchers are also making use of PEERC's OpenSees platform to predict the nonlinear frame response to input ground motions.

This project is a collaborative effort between Professors Cheng-Chih Chen, Chin-Tung Cheng, Lap-Loi Chung, Shea-Lung Hsu, Keh-Chyuan Tsai and research assistants Chui-Hsin Chen, Bo-Chien Hsiao, Min-Lang Lin, Yuan-Tao Weng and Juin-Wei Lai from NCREE, and Professor Subhash Goel and PhD candidate Prabuddha Dasgupta from The University of Michigan at Ann Arbor. These researchers, along with others from the US, Japan and Canada, will visit NCREE to witness the tests to be performed in early October2003 and to participate in a workshop (IWSCCC-2003) to discuss the research findings and other related topics.

Financial support for the frame test has been primarily provided by Taiwan National Science Council (NSC92A06000000-19). On the US side, partial financial support for this program has been provided by National Science Foundation Grant Nos., CMS-9905804 and CMS-0336339. Further up-to-date information about this program is available at http://cft-brbf.ncree.gov.tw.