Research On Seismic Performance Of Concrete Columns Reinforced With HTRB600 High-strength Bars

Currently,a few domestic researches have been conducted on concrete structure reinforced with HTRB630 high-strength bars.14(including comparative samples)concrete columns reinforced with high-strength bars have been designed and low-cyclic loading experiments have been performed to evaluate changes on seismic performance of the samples whose longitudinal and transverse steel was replaced with HTRB630 high-strength bars according to strength and volume principles.A finite element model considering the effects of bond-slip and shear deformation has also been established in the basis of OpenSees.Compared with hysteretic curve measured,the accuracy of the model has been testified.Based on damage index measured,the accuracy of 6 modified Park-Ang models on evaluating the damage of concrete columns reinforced with high-strength bars is compared.Parameter fitting and model modification have been conducted on models lacking accuracy.Major content and conclusion are as follows:1)11(including comparative samples)concrete columns reinforced with high-strength bars and 3 high-strength concrete columns confined with high-strength stirrup are designed and tested.All samples show the characteristic of flexural failure and hysteretic curve appears to be bow-shaped,which means HTRB630 high-strength bars are compatible with concrete and columns with HTRB630 bars are of good ductility and dissipation capacity.2)Comparison has been made on seismic performance in terms of backbone curve,bearing capacity,ductility of displacement,dissipation capacity and degradation of strength(stiffness).Major conclusion is:(1)seismic performance of columns with high-strength longitudinal bars is similar to that of common bars;(2)replacing stirrup with high-strength bars according to strength principle improves seismic performance only if the confinement level remains adequate;(3)replacing stirrup with high-strength bars according to volume principle is prone to obtaining better seismic performance;(4)the drawback of brittleness of high-strength concrete can be overcome by applying confinement stirrup densely and the seismic performance can be improved by replacing stirrup with high-strength bars according to strength principle.3)In the basis of OpenSees platform and fiber model,a rotation spring element and a shear spring element are added to finite element model to take consideration of bond-slip and shear effect.The accuracy of this OpenSees model has been proved by making comparison between simulated hysteretic curve and that measured through experiments.4)Damage index of the samples has been calculated using 6 typical modified Park-Ang model(Kunnath model,Chai model,Kumar model,Fujianping model,Wongdongsheng model and Fugo model).Great otherness has been found by comparing calculated damage index with index evaluated through experiment observation.A parameter fitting has been carried out on the 4 inaccurate models according to the experiment data before failure.Fitting results show that modified Fujianping model,modified Wangdongsheng model and modified Fuguo model can be used to evaluate the damage of columns reinforced with high-strength bars.