Performance and Analysis of a Full Scale Special Concentrically Braced Frame

Abstract

Measuring 6.7 meters wide and 6.66 meters tall, a full scale 2-story special concentrically braced frame (SCBF) was tested in National Center for Research on Earthquake Engineering (NCREE) in Taiwan. This is a cooperative project between researchers from Taiwan and U.S. to investigate the seismic design methods for brace-to-gusset connection details. The objectives of this study are to understand the cyclic behaviors of the SCBF and develop the valid design and analytical procedures. Tests HSS-8t and HSS-2t were conducted using hollow structural section braces by two different brace-to-gusset details. The WF-8t using the wide-flange section braces was conducted to compare the responses with the HSS-8t. The performances of these three tests are presented in this study, focusing on the investigations of the overall structure and local members. For this purpose, in the beginning this study discusses the setup and the key experimental results of the specimen frame, such as the peak inter-story drifts and buckling of braces. And then nonlinear FEM program ABAQUS was used to simulate the responses of the specimen. This study describes the detailed analytical model and the modeling techniques, such as material model, boundary conditions, initial imperfections, load applying techniques. Large out-of-plane displacement and local buckling of braces were observed in these three tests. However, except the fracture of some bolts in the beam-web-to-column connections there were no any facture found on beams and columns of specimen. The cyclic base shear versus the story drift relationships obtained from the test and the FEM analytical results are quite agreeable. The analytical results confirm that the magnitude of the severe out-of-plane buckling of the braces can be accurately simulated. Tests show that the ductile brace fractures occurred when the brace has undergone large out–of-plane deformations and developed localized plastic hinge. This local buckling can be observed in the ABAQUS responses. FEM analyses also illustrate that the brace members take about 90% story shear at low level inter-story drifts under 0.0028 radians, but gradually decrease to 60% story shear when the inter-story drift is greater 0.02 radians. This paper concludes with the procedures for finite element analysis of steel SCBFs.