Theoretical And Numerical Analysis Of FRP Strengthened Concrete Column Under Preload

Fiber reinforced polymer（FRP）composites have been widely used in civil engineering for structural strengthening due to its high strength-to-weight ratio,excellent corrosion resistance,fatigue resistance and ease of construction.For circular concrete columns,the confining pressure provided by the FRP jackets distributes uniformly around the circumference under axial load,and it is relatively simple to conduct the mechanical analysis.Therefore,many researches have been carried out to investigate the axial compressive performance of FRP confined cylinders.However,in practice,the cross-section of most concrete columns are square or rectangular for ease of construction.In addition,because of the design needs,construction errors and accidental factors,such as earthquake,wind load and so on,concrete columns may carry the axial load and bending moment simultaneously.Consequently,the influence of the above-mentioned two factors on the mechanical performance of FRP strengthened concrete columns have been extensively conducted in the last decade.Nevertheless,it is noteworthy that as a result of the service loads,the wet layup process of FRP reinforcement is carried out under the condition of preload,and this phenomenon has been ignored in the majority of researches.Therefore,it is of great significance to study the behavior of FRP strengthened concrete columns under preload.The specific content of this paper is listed as follows:（1）The mechanism of the influence of preload on the FRP confined concrete was investigated,and a comprehensive database of FRP confined concrete columns under preload with different cross-section shapes,strengthening forms and preloading levels was established.Based on the database,the existing theories of FRP confined concrete with preload effect were analyzed and compared.The influence of preloading level on the mechanical behavior of FRP confined concrete was determined,leading to a new stress-strain model of FRP confined concrete.Based on the new model,a method was proposed to predict the bearing capacity of eccentrically loaded RC columns wrapped with FRP jackets under different preloading levels,and the comparisons between the experimental observations and theoretical calculations revealed that better performance can be achieved by the proposed model.（2）According to the finite element method of FRP confined concrete,a new virtual stressstrain rule was obtained by analysis and fitting with taking the influence of preload into consideration,which can accurately depict the hardening/softening behavior of FRP confined concrete.Combined with other plastic parameters developed in literature,a new finite element model for FRP confined concrete with preload was established in the present study,and the existing test results were used to validate the accuracy of the proposed model.The development of stress of FRP and concrete was then simulated by the FE method to explore the influence of preload on the whole loading process of FRP strengthened concrete column,which can better explain the exact interaction between FRP and concrete under preload.Moreover,the parametric analysis was carried out to determine the influence of concrete strength,FRP confining stiffness and preloading level on the mechanical properties of FRP confined concrete.（3）Based on the proposed FE method,more extensive parametric analysis was conducted to verify the accuracy of the above-mentioned predicted model of ultimate stress and strain for FRP confined concrete with preload based on experimental data.According to the FE simulation data,the lateral strain-axial strain relationship considering the preload effect was developed through regression analysis to predict the dilation behavior of FRP confined concrete with preload effect.