Experiments And Mechanical Behavior Analysis Of Different FRP-Strengthened Reinforced Concrete Columns Under Compression Or Shear Forces

After long-term operation,civil structures such as buildings andbridges may not be able to meet the requirement of existing loads due to fatigue damage,material deterioration or usage changerequirements.Then such structures should be demolished and rebuilt or directly strengthened.As the main load-bearing components of frame and bridge structures,strengthening columns and piers can adopt the methods such as increasing their cross sections,embracing profile steel,planting steel bars and bonding fiber reinforced polymer(FRP).Among these methods FRP strengthening has been widely utilized due to convenient implementation,keeping the original cross sections and weights of components and great increase in load capacities.Therefore,this thesis focuses on the experimental and theoretical studies on different FRP-strengthened reinforced concrete columns under axial compression,eccentric compression and hysteretic shear forces.The main contents include:1)In order to investigate the strengthening effects of different types of FRP cloths on the mechanical properties and failure modes of concrete square columns,1/4 arc was first adopted to replace the traditional second-degree parabolas for distinguishing effective confinement areas from weak areas.Then shape coefficients of five different strength models were improved and unified into one for the purpose of convenient engineering applications.The performance of the five strength models after improvement was evaluated using 138 experimental columns strengthened by different types of FRP cloths.Satisfactory agreements between the improved models and the experiments were found.Lastly,in the interest of extending the application range of the improved models,8 BFRP jacketed concrete columns were further tested,by which means the feasibility of the improved models in predicting the load capacities of such columns was confirmed.2)In the interest of investigating the mechanical and strengthening performance of eccentrically loaded RC columns having different FRP jackets,5 strengthened columns,together with an unstrengthened column,were tested under eccentrically loads.The failure modes,lateral bending deflections and load bearing capacities of these columns having different eccentricities and FRP jackets(AFRP,BFRP,CFRP)were first discussed,which found the fact that all the FRP types contributed to the improvement of load bearing capacities and ductility of the strengthened columns.Then the prices and material properties of different FRPs were taken into account for the purpose of comparing the comprehensive strengthening performance.It was found that BFRP showed satisfactory cost performance and practicality.Subsequently,the key shape coefficient for the strength model of confined concrete was proposed and the equivalent stress distribution of concrete under compression was obtained.Lastly,the ultimate load formula for eccentrically loaded RC columns was newly deduced based on the updated second-order eccentricity calculation method.The reliability of the formula has been validated using 24 experimental columns.3)In order to study the failure modes and energy dissipation performance of BFRP-strengthened short RC columns under low-cyclic cyclic loads,two BFRP-strengthened RC columns,together with an unreinforced column,were tested.Through analyzing the characteristics of load-displacement hysteresis curves,skeleton curves,strength degradation,stiffness degeneration and BFRP strain,it is found that short RC columns having BFRP jackets showed better energy dissipation performance,and the strength degeneration tends to be stable.The ultimate displacement Increased,ductility improved,help to improve the seismic performance of RC short columns.