Study On Rotation Angles At Seismic Performance Points For Reinforced Concrete Columns

Reinforced concrete (RC) column is one type of important vertical components forthe building structure. Though there are some research achievements on the seismicbehavior of RC columns which have the stirrup characteristic value in the plastic hingezone meeting with the minimum requirement specified by “Code for seismic design ofbuildings” GB50011-2010, there is a limited study on its rotation at performance pointstill now. As a result the damage extent of the RC columns after earthquakes is not ableto be assessed by quantity. In this dissertation, by quasi-static test and numericalanalysis, the seismic behavior and the elastic-plastic displacement rotation at theperformance points of the RC column which have the stirrup characteristic value in theplastic hinge zone meeting with the minimum requirement specified by Chinese codeare studied. The purposes of this study are to provide a scientific basis for assessing theseismic damage extent of RC columns by quantity, for assessing the seismicperformance levels and seismic performance objectives of the RC frame structure. Themain works and outcomes are as follows:(1) Quasi-static tests on nine specimens were conducted to study and to reveal theseismic behavior of different seismic grade RC columns, including failure mode,load-carrying capacity, deformation capacity, energy dissipation capacity and secantstiffness, as well as the influence of the lateral loading cycle number on the seismicbehavior of RC columns. The test results indicated that the lateral force-displacementhysteretic loops were plump and the RC column specimens had excellent seismicbehavior.(2) Based on the reasonable concrete material constitutive model and steel materialconstitutive model, using the fiber model-based OpesnSEES program,force-displacement (F-Δ) hysteretic loops of9RC column specimens subjected to aconstant axial compressive load and cyclic lateral forces were obtained. According tothe F-Δ hysteretic loops, the moment-rotation (M-θ) hysteretic loops and the rotation atcharacteristic points of the M-θ skeleton curve of the RC column specimens weredetermined, and the determined plastic rotations had good agreement with the testvalues. The reliability of the numerical simulation of program OpenSEES on RC column M-θ hysteretic loops is confirmed.(3) A four-linear moment-rotation skeleton curve of the RC column is proposed.Using OpenSEES, M-θ hysteretic loops of22RC columns subjected to a constant axialcompressive load and cyclic lateral forces were obtained. The stirrup characteristicvalue of the calculated RC columns meets the minimum requirement for seismicgradeⅠ, Ⅱ and Ⅲ (Ⅳ) respectivelyspecified by the Chinese code. According to thecalculated M-θ skeleton curves, the rotation at the characteristic points of the four-linearmoment-rotation skeleton curve and at performance points of RC columns weredetermined, and the determined rotations of the RC column specimens had goodagreement with the test values. The relationship among the damage extent of the RCcolumn after earthquakes and its characteristic points and performance points isproposed. It provides a base for assessing the damage extent of RC columns by quantity(4) Adopting program MSC.Marc2007, using the fiber model-based programTHUFIBER for member structures developed by Tsinghua University, the elastic or theelastic-plastic time history analysis of a six-storey RC frame structure with7degreeseismic precautionary intensity and0.15g design basic acceleration of ground motionunder frequently earthquake, precautionary earthquake, abnormal earthquake andextreme abnormal earthquake were performed. Three earthquake records were selectedas the ground motion input. According to the time history analysis results and theproposed four-linear moment-rotation skeleton curve (M-θ) of RC column, the damageextent of the first story RC columns and the second story RC columns of the framestructure was assessed by quantity; furthermore the seismic performance levels and theseismic performance objectives of the RC frame structure were assessed.