Seismic Performance of Reinforced Concrete Building Retrofitted by Multi-story Steel Braced Frame Subjected to Tri-lateral Earthquake Excitations

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Two principal subjects mentioned below were studied for good estimation of earthquake resistant performance in a reinforced concrete (R/C) building retrofitted by a multi-story steel braced frame subjected to tri-lateral earthquake excitations. This study focuses on the column tension failure due to bending moment in a R/C sub-assemblage with a multi-story steel braced frame.Subject A; to investigate seismic behavior of a retrofitted R/C building subjected to in-plane shear, out-plane bending moment and column axial load, and Subject B; to observe and grasp kinematic behavior of a R/C pilotis-column under a shear wall when a steel-braced frame is installed adjacently to the pilotis-column for preventing the column from collapse due to severe axial compression.Following studies were carried out to resolve these subjects; tri-lateral static loading test using a plane R/C frame and a three-dimensional R/C building with a pilotis-column which were retrofitted by a multi-story steel braced … More frame, tri-lateral static loading analysis using a 3-D R/C building with a pilotis-column retrofitted by a multi-story steel braced frame and nonlinear three-dimensional finite element analysis of a plane R/C frame retrofitted by a multi-story steel braced frame under out-plane bending moment. Concluding remarks taken by these studies are as follows.(1) Lateral resistance of a retrofitted R/C frame subjected to bi-directional horizontal loading was by approximately 10 percent smaller than that without out-plane loading. This was caused by premature compression failure of concrete at the bottom of R/C edge columns subjected to bi-axial bending moments.(2) When lateral resistance reached the peak, concrete failed in compression at the bottom of not only one R/C edge column retrofitted by a steel-braced frame, which is identical to a pilotis-column, but also another edge column which suffers additional compression due to force transfer derived from restraining effect of a transverse shear wall in the second story on the R/C sub-assemblage with a steel-braced frame. Steel vertical chords in a steel-braced frame contributed to prevent two R/C edge columns from axial collapse due to resisting compression force instead of concrete.(3) In the design for seismic rehabilitation to a R/C building, note that concrete may fail in compression at the bottom of a R/C edge column as well as the pilotis-column retrofitted by a multi-story steel-braced frame which is designed to form column tensile yielding at the base of a I-shaped section consisting of two R/C edge columns at both ends and a steel-braced frame at the middle portion. Less