Experimental Research On Compression-Bending-Shear Mechanical Properties Of Square-CFRP-Concrete-Filled Steel Tubes

The emergence and development of concrete has experienced more than 200 years.Many scholars have studied the performance of concrete for many years,and have achieved a lot of research results.At present,concrete-filled steel tube(CFST)as a new type of structure appears in front of the public.Because of its high bearing capacity and excellent economy,it is more suitable for the requirements of safety,applicability and durability in structural engineering,it is widely used in bridge structure,industrial workshop,military building,super high-rise building and other structures with higher requirements on materials.With the rapid development of concrete-filled steel tube(CFST),scholars have put forward the ideas of GFST and CFST.Carbon fiber(CFRP)has excellent properties such as light weight,high strength and good durability.CFRP is wrapped in the outer wall of the steel pipe to form the concrete inside the CFRP steel pipe.At present,it is common to study the axial compression performance,shear performance and fire resistance of CFRP CFST.However,in engineering practice,the mechanical properties of cfrp-cfst under compression,bending and shear have not been seen.Therefore,in this paper,the static and hysteretic tests of 18 CFRP concrete filled steel tube specimens were carried out by self-designed experimental loading device.In the static test,the experimental phenomena,the characteristics of shear displacement curve and shear stress shear strain curve and the cooperation between steel pipe and CFRP are analyzed.In the hysteretic test,the experimental phenomena are analyzed according to the experimental data,and the V-Δ curve,skeleton curve strength degradation,stiffness degradation and energy dissipation effect curve are made.On the basis of the test,the expression of compression bending shear bearing capacity of CFRP CFST is fitted.The experimental results show that:in the static test,the number of carbon fiber layers has no more than 10%increase in the ultimate bearing capacity of the specimen;almost no influence on the stiffness and index curve shape of the specimen;under the same environment,the greater the axial compression ratio,the longer the elastic stage of the specimen,the greater the ultimate load,and the first to reach the ultimate bearing capacity;the increase of shear span ratio can greatly improve the maximum bearing capacity of the specimen in the elastic stage.At the same time,in the experimental process and curve data analysis,carbon fiber and concrete-filled steel tube are under common stress and deformation,showing excellent synergistic effect.In the hysteretic compression bending shear test,CFRP concrete filled steel tube shows good against seismic performance.The change of axial compression ratio has almost no effect on the stiffness in the early stage of the test.After the end of the elastic stage,the greater the axial compression ratio is,the smaller the stiffness degradation is;the increase of axial compression ratio can reduce the stiffness degradation after Δ/Δy;the larger the shear span ratio,the smaller the ultimate bearing capacity of the specimen,the greater the ductility,the greater the stiffness degradation;the number of carbon fiber layers has little effect on the energy absorption of the specimen.This paper provides the experimental basis for the follow-up study on the mechanical properties of CFRP steel tube under complex stress conditions,and also lays a foundation for the wider application of CFRP steel tube concrete in production practice.