Cyclic Tests of Steel Frames with Concealed Vertical Slits in Reinforced Concrete Infill Walls

Abstract

Experimental testing revealed that installing concealed vertical slits in reinforced concrete (RC) infill walls enabled the RC infill walls to behave in a more ductile manner (as compared to conventional solid RC walls), leading to better seismic performance for a partially restrained (PR) steel frame with the innovative walls. To better understand the new system behavior, four subassemblages of steel frames with the prescribed concealed vertical slit RC walls were tested at a 1/3 scale under horizontal cyclic loading and are presented in this paper. Three of the steel frames were PR, and one frame was fully restrained. The hysteretic behavior, failure mode, deformability, ductility, stiffness degradation, and energy dissipation capacity of the steel frames with the concealed vertical slit RC infill walls were investigated. The effects of the height-to-width ratio of vertical channels, concrete type of concealed vertical slits, section type of steel columns, and boundary condition of test specimens were examined and compared. All of the test specimens exhibited high lateral strengths, stiffness values, and overstrength capacities without failing in a brittle manner, and a two-stage mechanical characteristic was observed in each specimen. When the test specimens were pushed to a target interstory drift ratio of 0.75%, the concealed vertical slits started to penetrate through the wall thickness. At the interstory drift ratio of approximately 1.00%, the test specimens reached the peak load, which corresponded to the onset of the second-stage mechanism. After the concealed vertical slits crushed, the lateral strength and stiffness decreased gradually. Specimen S-CVSW3, which had steel fibers added inside the RC infill walls, had the best seismic performance of the four specimens. The test specimen with concrete-filled, square tube columns exhibited hysteretic loops that were much more pinched than the other specimens. The concealed vertical slits demonstrated great ability to reduce the degradation of the postpeak strength, achieving the desired ductile failure mode.