Study On Seismic Behavior Of Concrete Frame Columns With Large Diameter High-yieldstrength Rebars

In this dissertation, the seismic behaviors of concrete frame columns employing large diameter high-yield-strength longitudinal rebars and high-yield-strength stirrups are analyzed in detail by means of specimen tests, theoretical analyses and numerical models. The main research contents and results are enumerated as follows.(1) 6 concrete columns reinforced with 500 MPa grade 36 mm diameter longitudinal rebars and 500 MPa grade stirrups were tested under the low frequency cyclic loading, another 2 columns with 25 mm diameter longitudinal rebars were tested as control group. The failure phenomena, the hysteretic curves of longitudinal and transverse bars strain and beading capacity have been analyzed. And the investigation focuses on the influence of three factors— volumetric ratio of stirrups, diameter of longitudinal rebar and exist of construction joint— on the seismic behavior of the specimens as well.(2) The test results show that force-displacement hysteretic curves of the specimens are plump, the specimens have good energy dissipation capacity in earthquake. The displacement ductility factors of specimen are from 4 to 5.5, while the displacement factors from 1/20 to 1/30. The seismic performance parameters of columns with large diameter longitudinal rebars are similar to the control group in the mass.(3) ABAQUS software-based non-linear finite element models were established to analyze further performances of columns reinforced with 500 MPa grade large diameter longitudinal rebars and stirrups. The results show that the finite element model has an accurate expression on the seismic performance of the specimens.(4) The comprehensive comparison was made on the requirements for confinement stirrups in potential ductile plastic regions of frame columns specified in the concrete structure standards/codes developed by China, the United States, New Zealand and Europe. Through the calculating examples, the influences of axial compression ratio, strength of stirrup and concrete on the limits of volume-stirrup ratio are analyzed, and some recommendations of modification as to the relevant contents of Chinese code were presented.