Application of Steel Frame Bracing System with Indirect Connection on Seismic Retrofit of RC Frame
Date Issued
2014
Date
2014
Author(s)
Yang, Chi-Hsuan
Abstract
It is very important to retrofit exsiting RC buildings in Taiwan. This study used steel frame bracing system with indirect connection to enhance the vertical bearing capacity and lateral strength of RC frames. It is expected that the retrofitted frame can possess strength between brick walls and shear walls and have adequate deformation capacity as well. This study tested six full-scale retrofitted specimens which were design according to Japan Standard and Guildelines for Seismic Evaluation of Existing Reinforced Concrete Buildings.
According to the test results, the corner joints of the mortar connection played an important role for transferring force and maintaining strength. The lateral strength of phase-I specimens can be improved significantly by closely spaced spiral reinforcement and high strength non-shrinkage mortar. However, the morter cracked and strength decreased quickly due to the stress concentration at the corner joints. Although the phase-I specimens exhibited higher strength, however deformation capacity is rather poor. Moreover, the material strength of steel brace and RC frame was not effectively developed. The phase-II specimens employed gusset plate to distribute the brace forces and to avoid stress concentrate at corner. The corner joints of the mortar connection were preserved before peak load. Thus, the retrofitted frame had adequate lateral strength, deformation capacity and ductility. In addition, the use of smaller steel brace can increase the deformation capacity of specimens. The retrofitting ratio is defined as the ratio of retrofitted strength relative to original strength. In this study, deformation capacity is only 1% with the retrofitting ratio of 7, 2% with the retrofitting ratio of 5.5, and 3% with that of 4. As an indicator for school buildings using this retrofitting method, the retrofitting ratio of 4 seems to be an adequate choice. Because the maximum strength of typical columns of school buildings were achieved at lateral drift of 2 to 3%, a deformation capacity of 3% for retrofitted frame is appealing.
The design procedure of this retrofitting scheme is suggested as follow. First step is to select the anchors base on the limitations of existing frame. According to the capacity of anchors, the size of braces can be determined. The gusset plate is then designed accordingly. Finally, the column shear capacity of the existing RC frame is checked for safety.
Subjects
耐震補強
鋼筋混凝土構架
鋼框架斜撐
隅板
補強接合部
變形能力
Type
thesis
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