Experimental Study On Axial Compression Performance Of Damaged Square Concrete-filled Steel Tube Columns Strengthened By CFRP

Square concrete-filled steel tube(SCFST)is widely used in recent years due to its advantages such as simple joint structure and convenient construction.During the service period,SCFST columns may be damaged to a certain extent due to accidental effects such as overload,environmental degradation,fire and earthquake,or other situation.The existing experimental research show that some SCFST columns still remain considerable residual bearing capacity after being damaged.If reasonable measures can be taken to strengthen SCFST columns with minor damage,It is expected to further extend the service life of SCFST column.Therefore,finding a simple and effective method for SCFST column strengthening has important engineering application significance.In recent years,circularizing a square section columns and then wrapping with fiber reinforced polymer(FRP)as a feasible strengthening method has been widely concerned by scholars at home and abroad.At present,the relevant research on CFRPconfined square section columns is mainly focused on non-damaged columns,while the research on CFRP hardening of SCFST columns under stress damage is still very limited.This paper intends to take the damage grade,strengthening method(square/section circularized)and the number of CFRP layers as the main test parameters to conduct experimental research on the axial compression bearing performance of damaged SCFST short columns strengthened by CFRP.The combination formula of bearing capacity calculation is established to provide certain reference for further application of damaged SCFST columns strengthened by CFRP.This paper mainly completed the following work:(1)Complete the production of 40 specimens of SCFST columns,and obtain 5specimens with different damage grades through the pre-damage test.Based on the axial compression loading tests of SCFST columns with different strengthening methods,the effects of damage grade,strengthening method and the number of CFRP layers on the axial compressive properties of SCFST columns were studied.The test results show that the bearing capacity of SCFST columns strengthened by CFRP is increased by 77.2% to 177.1% compared with that of SCFST columns strengthened by CFRP directly.The section roundness treatment effectively improves the constraint capacity of CFRP,and thus improves the reinforcement effect.(2)The failure modes of damaged SCFST columns with section circularized strengthened by CFRP are similar to reinforced concrete columns strengthened by CFRP,the load-strain curve exhibit evident two-segment bilinear shape.(3)Based on the Han Linhai model and the Du model,considering the adverse effects of damage,a strength model of damaged SCFST strengthened by CFRP is established,and the calculated values are in good agreement with the experimental values.(4)Based on the unified theory of strength,the Han Linhai model and the Lam and Teng model,the strength model of damaged SCFST with section circularized strengthened by CFRP is established,and the experimental values are in good agreement with the calculated values.