Date of Award
Doctor of Philosophy
Civil, Construction, and Environmental Engineering
J. Jay Shen
Special concentrically braced frames (SCBFs) have become more popular as lateral load resisting systems after disappointing performance of special moment resisting frames (SMRFs) in the 1994 Northridge earthquake. SCBFs dissipate earthquake energy through buckling of compressive braces and yielding of tensile braces. V-type, inverted V-type, and two-story X-bracing are three major categories of SCBF bracing configurations. According to the current design approach implemented in AISC 341-10, beams and columns in SCBFs shall be designed based on the capacity of the braces to keep the beams and columns in the elastic region. However, a limited number of studies have shown that braced-intersected girders in two-story X-braced frames do not always remain elastic during an earthquake, violating current design code assumptions. Inelastic behavior in girders is due to the unsymmetrical cyclic behavior of the braces that creates a considerable unbalanced force. In an attempt to achieve symmetrical behavior, buckling-restrained braces (BRBs) superior to conventional braces in terms of ductility and cyclic behavior have been developed, but the majority of the developed BRBs are relatively complex and costly, resulting in hesitancy in the engineering community to accept them as a proper substitute for conventional braces. The present study is intended to investigate whether SCBFs designed based on current design codes meet the current design codes requirements. A newly developed buckling-controlled brace (BCB) is also introduced and the effect of such braces on the seismic demand of SCBFs is studied. For this purpose, three SCBFs with different beam sizes and bracing configurations were designed in accordance with current design codes and a group of earthquake ground motions was applied to them to investigate their seismic responses. Conventional braces of these frames were also replaced with BCBs to evaluate the influence of the new developed braces on the seismic response of the SCBFs. The results point out that girders and columns in TSXBFs yield under earthquake ground motions, while they are designed for the capacity of the braces and are expected to remain elastic. In addition, SCBF seismic demand is substantially reduced by replacing the conventional braces with BCBs, so it seems that BCBs would be a suitable substitute for conventional braces.
Momenzadeh, Seyedbabak, "Seismic design study of concentrically braced frames with and without buckling-controlled braces" (2017). Graduate Theses and Dissertations. 15579.