Seismic Design and Response Analysis of RC Frames with Buckling Restrained Braces
Date Issued
2015
Date
2015
Author(s)
Huang, Jie-Lun
Abstract
The buckling-restrained brace (BRB) has been evolved into a cost-effective energy dissipation member for seismic resistant steel buildings. A BRB can develop full yield strength under both tension and compression through its restraining member by preventing its steel core from undergoing flexural buckling failure. In recent years, many studies and tests have proved BRBs can improve stiffness, strength, ductility and energy dissipation mechanism for structures. BRBs have been widely applied in steel structures in the past decades. However, researches on applying BRBs to new reinforced concrete frames (RCFs) are somewhat limited. This study consists of two parts. In order to study the performance of RC frame with BRBs (BRB-RCF) under earthquakes, in the first part, an analytical model is constructed using PISA3D for predicting the responses of a two-story BRB-RCF tested at NCREE. The full-scale two-story BRB-RCF has been tested using four hybrid tests and cyclic loading test. Details of the specimen design and test results can be found in Mr. Hsun-Horng Yang’s thesis. Ground motions adopted in the tests are selected by using the prediction model analyses and 60 ground motion records. After the tests, the prediction model is calibrated into a simulation model based on the experimental results. Very satisfactory agreements with the test results can be achieved from the simulation model analyses. In order to further study the seismic performance of low-rise BRB-RCFs, this study uses six-story building design examples, one BRB-RCF and one RC moment resisting frame (MRF). The six-story BRB-RCF and MRF analytical models are constructed using PISA3D and the proposed modeling methods. For the purpose of saving analysis time while achieving accuracy, a simplified model is proposed for the 6-story BRB-RCF response history analyses. The analytical results show that the ratios of maximum total BRB shear and BRB-RCF shear in transverse direction are about 35% (50/50 hazard level earthquake), 40% (10/50 hazard level earthquake) and 40% (2/50 hazard level earthquake). These are larger than those computed for longitudinal direction with 24% (50/50 hazard level earthquake), 26% (10/50 hazard level earthquake) and 28% (2/50 hazard level earthquake). The maximum story drift in the BRB-RCF and MRF under the 2/50 hazard level earthquake are 1.5% and 1.8%, respectively. In order to improve the BRB efficiency in the BRB-RCF, this study propose to configure the RC BRBFs as primary lateral force resisting systems, and treat the remaining RC beam and column members as a gravity system. This scheme can significantly reduce the sizes of a number of RC beams and columns and improve the efficiency of BRBs. This study uses the PISA3D to construct the two-dimensional analytical model of one half of the building structure in transverse direction and perform nonlinear dynamic analysis. Analysis results confirm that the RC-BRBF scheme enables the total BRB shear ratio of the RC-BRBF to increase to 75%, while the story drift responses are similar to the aforementioned BRB-RCF system. This series of experimental and analytical researches has confirmed the effectiveness of the design, fabrication and modeling methodologies for the proposed BRB-RCF. Tests have confirmed that the use of the proposed steel embedment as the interface for the BRB and RC members can be successfully implemented into real RC frames. Analytical results of the 6-story RC-BRBF and BRB-RCF show that a large shear demand exists in the in D-region of the lower floor beams. These beams must be designed wider than those in the upper floor beams. In addition, the BRBs in the proposed RC-BRBF or BRB-RCF are arranged in a zigzag configuration. This should reduce the axial force demand on beams. This paper discusses the axial force demands computed from the response history analyses. Implementing the BRBs into low-rise RC building can somewhat reduce the responses of the structures. However, due the significant stiffness of RC members, the sizes and their effectiveness of the BRBs in reducing the seismic drift response of RC buildings is limited.
Subjects
reinforced concrete frame
buckling restrained brace
hybrid test
nonlinear response history analysis
simplified model
two-dimensional analysis
Type
thesis
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