Earthquake-Resisting Properties of Confined High-Strength Concrete Frames

Abstract eng:
Objective of this paper is to present experimental information about the seismic properties of confined HSC moment-resisting frames with emphasis placed on effect of the steel strength on the overall performance in term of capacity curve, the damage degree, and the residual deformation of frames.. Eight test frames of about 1/3 scale were fabricated and tested under reversed cyclical lateral force while subjected to constant axial compression. All of the specimens were made of ultra HSC having compressive strength of 90MPa, and the columns of each frame were confined by square steel tubes while the beam was confined by high-strength hoops. Square steel tube was used to confine HSC columns in lieu of common hoops because of its following advantages: 1) to provide strong confinement to HSC easily, 2) to confine the whole column section so that one can expect enhancement not only of ductility but also of ultimate load-carrying capacity. Longitudinal reinforcement in the columns of each specimen comprised of twelve D10 deformed bars distributed uniformly along the perimeter of concrete section to give a steel ratio of 2.14%. Variables among the test are: 1) wall thickness of steel tube, 2) axial load level, and 3) yield strength of longitudinal steels. From the experimental work described in this paper, the following conclusions can be drawn: 1) When columns were confined by square steel tubes having B/t=64 and B/t=112, HSC frames with fc =90 MPa exhibited very ductile seismic response under axial load with axial load ratio of 0.5 and 0.3, respectively. 2) Use of high-strength steel (HSS) with yield strength of 900MPa can not only increase the ultimate load-carrying capacity, but also enhance the deformation capacity of HSC frames. In addition to the enhancement effect in strength and ductility, the high-strength steel can greatly mitigate the damage of frames that usually become serious as the ductility becomes large. 3) As compared with HSC frame with normal-strength longitudinal rebars, the HSC frames with HSS exhibit much less residual deformation, implying that the frames with HSS can be easily and economically repaired after hit by serious earthquake.

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