EARTHQUAKE RESISTANT PERFORMANCEOF REINFORCED CONCRETE FRAMESTRENGTHENED BY MULTI-STORY STEEL BRACE

摘要

Earthquake resistant performance in plane R/C frames strengthened by multi-story steel brace wasinvestigated through the tests under cyclic load reversals focusing on the base uplift rotation of thebrace and the entire flexural failure at the bottom of the brace caused by tensile yielding of alllongitudinal bars in a R/C edge column beside the brace. Two plane frame specimens with two-storyand three-bay were tested placing multi-story steel brace at central bay. Lateral resistance dominated bybase uplift rotation of a multi-story brace decreased gradually after flexural yielding at the end ofboundary beams and the bottom of first story bare columns. Lateral strength in the test agreed wellwith that computed by taking account of restraining effect of both boundary and foundation beams onuplift rotation. For another specimen failing in entire flexure at the bottom of the brace, controlled bytensile yielding of all longitudinal bars in a R/C edge column beside a brace, lateral resistancediminished abruptly by concrete crushing and fracture of column longitudinal bars at the bottom ofboth edge columns. Ultimate limit deformations in specimens were underestimated by the computationconsidering deformation ability of neighboring beams and isolated multi-story steel brace. The amountof energy dissipation for entire flexural failure at the bottom of a brace was by 50 percent greater thanthat for base rotation failure. Earthquake resistant performance of strengthened R/C frames which sufferthe entire flexural failure at the bottom of a multi-story steel brace is superior to that in the failure dueto the brace uplift rotation within the range of the drift angle of 2 %.