Analysis Of Large-scale Square Concrete Columns Confined By CFRP Under Axial Compression

Existing strength models for square concrete columns confined by FRP(Fiber-Reinforced Polymers)are almost all proposed on the basis of experimental data from relatively small-scale specimens.The possibility of extrapolating those models to predict the compressive strength of real-scale square columns is still uncertain.Especially,the quantitative evaluation on influence of size effect is still a subject requires systematic research.To address such lack of knowledge,this paper analyzed a series of experimental results on 21 large-scale square concrete columns confined by CFRP(Carbon FRP)with different corner radius(300 mm×300 mm×600 mm)under axial compression from research group.The results demonstrate that the CFRP wrapping strain around the perimeter exhibits a certain regularity,even under very high axial stress condition and the rupture strain of CFRP is significantly lower than that from material tests.All of the 191 experimental data of square concrete columns confined by FRP with different size(176 experimental data come from the published literature and 15 experimental data come from research group)are summarized and the efficiency rupture strain factor of FRP at corner is introduced.By comaparing the efficiency rupture strain factor of FRP at corner from large-scale specimens with those of smaller-scale specimens,it is concluded that the efficiency rupture strain factor of FRP at corner from the large-scale specimens is lower than those from smaller-scale specimens and its value shows a declining trend as size of specimen increases and an increasing trend as corner radius ratio of specimen increases.Then,a calculating formula for the efficiency rupture strain factor of FRP at corner of the size and corner radius ratio is proposed in this paper.The size effect is quantified into the calculating formula for confining stress provided by FRP through the efficiency rupture strain factor of FRP at corner and a strength model considering size effect is provided by author.The 191 experimental data is used to assess the ability of the total 14 existing strength models to cope with size effect.The results show that most of the strength models overestimate the compressive strength of specimens significantly and these models are not applicable for predicting the compressive strength of real-scale square columns.The proposed model shows a good correlation with the experimental results.In addition,the axial stress-strain characteristic of the large-scale square concrete columns confined by CFRP and its influence factors were also analyzed on the basis of the experimental results from research group.The confinement effectiveness of FRP wraps shows weak,strong and critical aspects.A calculating called AMCR(Amendatory Modified Confinement Ratio)for distinguishing strong or weak confinement of FRP is presented.All of 8 existing axial stress-strain models are assessed based on the experimental data from research group.The results show that the predictive results got from these models exhibited obvious difference compared with the test results.Through the simplified two-stage curve which included parabola and straight line,the axial stress-strain model of square concrete columns confined by FRP under the weak-confinement condition and strong-confinement condition is proposed respectively.The proposed model has a good correlation with the experimental results from research group.