Research On The Compressive Behavior Of Rectangular Concrete Columns Reinforced With Bfrp Under The Secondary Load

Because of good ductility,high temperature resistant,corrosion resistant properties and outstanding advantages of cost,basalt fiber reinforced polymer(BFRP)as a new type of composite material has been widely attention in the field of building structure reinforcement.The effect of secondary load is inevitable in the practical reinforcement engineering,namely the original concrete structures have stressed before reinforcement,and it can't be in a state of complete discharge in the process of reinforcement.However the new structures continue to stress after reinforcement,and it makes concrete structures appear level of stress and strain lag phenomenon.There are lots of the research about the application of FRP reinforced concrete columns in order to improve the compressive strength,but most of them are not considered the effect of secondary load,and they are not conform to the actual reinforcement engineering.As the starting point to the engineering practice,this thesis turns to the research of the compressive behavior of the confinement of rectangular concrete columns with BFRP under the secondary load.The paper studies the axial force performance of rectangular concrete columns reinforced with BFRP under the secondary load by axial compression test of three groups of twelve columns,which is covered different reinforcement,different section size and different numbers of BFRP.Test results show that the axial compression ultimate and ductility of rectangular concrete columns reinforced with BFRP under the secondary load are increased significantly,but the extent is lower than what is no initial load.And they have the size effect,namely the increase extent of compressive strength reduces following the increase of the section size,but it increases as the addnumbers of BFRP.The paper compares and analyses some existing stress-strain relationship models of FRP confined concrete columns,and puts forward the compressive strength model and stress-strain relationship model of rectangular concrete columns reinforced with BFRP under the secondary load based on what is under the first load using the method of superposition theorem and substitution of strength,considering cross section shape,strength of concrete,effectiveness of BFRP,numbers of BFRP and corner stress concentration etc.In the last part,the paper deduces the calculation method of axial compression ultimate of rectangular concrete columns reinforced with BFRP under the secondary load,which coincides with the value of the test results,and it can provide some reference for actual reinforcement projects.