Experimental Study On The Mechanical Properties Of Column With Hybrid Reinforcement Of FRP Bars And Steel Bars

The performance degradation of concrete structure induced by reinforcement corrosion will affect its safety,applicability,economy and other requirements during the life cycle of structure.Fiber Reinforced Polymer(FRP)can be applied to concrete components as a potential reinforcing steel substitute owing to its good corrosion resistance and high tensile strength.However,the single application of FRP bars to the structure will cause brittle failure of the structure due to the generally small elastic modulus of FRP bars and the characteristics of tensile stress-strain approximate linear elasticity.Therefore,scholars from various countries are committed to replacing FRP bars with steel bars partly in concrete structures and exploring for their feasibility of being mixed with ordinary reinforcement.With the support of the National Natural Science Foundation“Research on Design and Performance of Concrete Components Mixed by FRP Bars and Ordinary Bars Based on Durability(51578267)”,In view of the corrosion of steel bars,FRP bars and steel bars are reasonably applied to concrete columns from the perspective of improving the durability of components.Without affecting(or even improving)the bearing capacity of concrete columns,the aim is to make the best of both performances.The main works of the thesis are as follows:1.Experimental research and comparative analysis of compression performance of FRP bars.The compressive properties of FRP bars with different diameters(BFRP,CFRP and GFRP bars)were tested by standard method,sleeve method and concrete wrapped FRP bar method.The effects of different length-diameter ratios on the compressive strength of FRP bars were analyzed and different test methods were compared.The test results show that the measured compressive strength of FRP bars is much lower than the tensile strength.The compressive strength of BFRP,CFRP bars and GFRP bars with a diameter of 12 mm are only 10%,22% and 54%.The compressive stress-strain curve of FRP bars is similar to the tensile stress-strain curve,showing a linear relationship.With the increase of the length-to-diameter ratio,the compressive capacity of the three FRP bars showed a downward trend.The method of directly testing the compressive strength of the FRP bar in China's specifications is conservative and setting the sleeve can increase the end constraint and the test result is closer to the actual value.2.Experimental study on the bond performance between FRP bars and concrete and its degradation analysis under aggressive environment.The bond performance test between different types of FRP bars(BFRP,CFRP and GFRP bars)and concrete were carried out,the test results showed that FRP bars and concrete have better bond properties.The bond strength between CFRP bars and concrete is highest,while the bond strength between BFRP,GFRP bars and concrete are relatively close.In order to consider the influence of external environment on bond strength between FRP bars and concrete,the immersion test of pull-out components with FRP bars and concrete under alkali and salt environment was carried out.The degradation of the bond strength between FRP bars and concrete under alkali and salt environments were compared.The surface deterioration of FRP bars after erosion was analyzed.Based on Fib Bulletin 40,the long-term bond strength retention between FRP bars and concrete was predicted.3.Experimental research and theoretical analysis on the mechanical performance of columns with hybrid reinfircement of FRP bars and steel bars.Considering the influence of parameters such as the reinforcement ratio and the types of FRP bars(BFRP,CFRP and GFRP bars)on the bearing capacity of the components,a total of 10 doublelayer reinforced concrete columns were designed.The eccentric compression test was used to compare the difference in load-bearing capacity between concrete columns with ordinary steel bars,FRP reinforced concrete columns and concrete columns with FRP bars and ordinary steel bars.The test results show that the mixed reinforcement of FRP bars and ordinary steel bars can effectively increase the ultimate bearing capacity of the columns and the bearing capacity value can be increased by 15.2% to 35.8% compared with columns with ordinary steel bars.Increasing the reinforcement ratio can effectively improve ultimate bearing capacity and reduce lateral deformation of components.For these three types of columns,FRP reinforced concrete components have the smallest cracking load,minimum bearing capacity and maximum lateral deformation.Its lateral deformation is 4-7 times of reinforced concrete columns.The theoretical calculation method of the bearing capacity of the concrete columns mixed by FRP bars and ordinary steel bars is established.The comparison error between the calculation results and the test values is within 7%.This method has high accuracy and provides a reference for engineering design.