Research Of Performance And Design Method Of Reinforced Concrete Stub Column Based On ICCP-SS

Reinforced concrete(RC)stub columns are commonly featured in the construction industry,used in structures such as buildings and bridges.In coastal areas,bridge piers are subjected to serious corrosion damage,which may result in safety issues and huge economic lossed.Currently,one of the most widely used retrofitting methods is the application of fiber reinforced polymer(FRP)sheets.This strengthening method can effectively improve the column capacities.However,as time goes by,the corrosion of re-bars will continue,leading to less force resistance.Impressed current cathodic protection(ICCP)is a well known,efficient method to prevent further corrosion of the re-bars.Therefore,this study uses both ICCP and structural strengthening(SS)technique to strengthen corroded RC columns.This research has the following objectives:1.In the ICCP-SS technique,the impressed current will prevent the corrosion of the steel re-bars in the column.2.In the ICCP-SS technique,the current density and protection time of the ICCP will have different effects on the protection effect of the re-bars and anodic surface.3.The experimental results show that ICCP-SS technique is effective for the reinforcement of columns and prevent further corrosion of the steel re-bars.4.Whether the existing code can predict the bearing capacity of confined reinforced concrete columns is suitable for reinforced concrete stub columns strengthened by ICCP-SS dual repair technique.In order to achieve the above research objectives,this thesis has completed a series of work including:1)Pre-test preparation.The parameters of this experiment include the initial corrosion of the specimen,the anode current density,and the duration of the cathodic protection.A 3%NaCl solution was added to the concrete sample during casting in order to simulate sea-sand concrete,meanwhile a control group without NaCl solution was set up.The reinforced stub columns were subjected to accelerated corrosion procedure through a wet-dry cycle.The first series of experiments consisted of 10 columns subjected to 100 days of dry and wet cycle.The anode current density was 26 mA/m~2 and 80 mA/m~2,and the applied cathodic protection time was 3 months.The second series of experiments consisted of 9 columns subjected to 100 days of dry and wet cycle.The anode current density was 20 mA/m~2 and 60 mA/m~2,and the applied cathodic protection time was 6 months.The results showed that the ICCP in the ICCP-SS system prevent further corrosion of the steel bars.2)Loading of test samples and analysis of experimental results.Firstly,the experiments on the material properties were carried out,including the concrete compression test,the steel bar tensile test,the bending and compression resistance test of the cement paste,the tensile test of the carbon fiber mesh and the C-FRCM composite plate.Secondly,the axial compression test of the specimen was carried out with a loading speed of 0.3 mm/min.Finally,the steel bars were removed from the specimens for rust removal and weighing.The following experimental results were discussed and analyzed:failure mode of the specimens,analysis of bearing capacity,concrete strain analysis,effective tensile strain of C-FRCM,and the weight loss of the steel bars.The experimental results showed that:1.the failure mode of the column using ICCP-SS technique is that the carbon fiber mesh is broken in the direction of the column's circumferential direction;2.the reinforced sea-sand concrete column has a lower bearing capacity than ordinary concrete due to the corrosion of steel bars;3.carbon fiber mesh reinforcement can improve the compressive bearing capacity and ductility of the reinforced concrete column;4.the ICCP technique prevent the corrosion of the steel bar;5.compared with ICCP technique or SS alone the columns that have been repaired by ICCP-SS have significantly improved the bearing capacity of stub columns;6.In view of short-term and longer-term performance,ICCP-SS repair technique using C-FRCM as anode and reinforcement material applied to concrete stub columns can play a better protection and basically meet the requirements of engineering restoration.3)Comparison of the repairing method using ICCP-SS technique with the existing codes.Firstly,the predicted bearing capacity was the calculated using formula provided by Chinese Code(GB 50367.2013),American Code(ACI440.2R.08,ACI549.4R.2013),European Code(fib),and Canadian Code(ISIS)or the reinforced concrete columns reinforced with CFRP,and then compared to the values obtained from the axial compression test of the specimens.The comparative analysis showed that the predicted values of the bearing capacity obtained by existing codes are conservative.In order to better predict the bearing capacity of the column reinforced by ICCP-SS technique,the thesis proposes a new design method of bearing capacity suitable for repairing stub columns,and establishes a theoretical basis for future engineering applications.