Study On The Performance Of A New CFRP-ultra-lightweight Concrete-steel Pipe Composite Column

With the development of science and technology,high-rise buildings and long span structures have become the development tendency,which put forward higher requirements for lightening design and high performance structure.More and more studies have been concentrated on a new type of FRP-concrete-steel-double skin tubular column due to its light weight,high stiffness and good seismic performance.The Ultra-Lightweight Concrete is a new material which has a lighter deadweight compare with regular concrete,it can meet the requirements of structural and wastes recycling.In order to create a lighter structure,this paper proposed to replace the ordinary concrete in the double skin tubular column with ultra-lightweight concrete and to create a new type of FRP-concrete-steel pipe-double skin composite component with high strength and high ductility.By developing Ultra-lightweight Concrete and analyzing the mechanical properties of the concrete confined by FRP,to have a further research on the mechanical properties of this new double-pipe composite member,the studies conducted during the research are as follows:(1)The development of Ultra-lightweight Concrete.Taking the compressive strength,density and workability as the assessment basis,we screened from the cenospheres and fibers,developed a kind of lightweight concrete with high strength and low density.We found the influence laws on the ULCC strength are affected by the cenospheres binder ratio,the water binder ratio and the curing environment,with the decreases of the two ratios and the increase of the temperature,the strength of concrete gets higher.Through continuous optimization,we final got the optimum proportion.(2)Experimental studies on the FRP constrained ultra-lightweight concrete are conducted,by analyzing the influences on the strength and ultimate strain exerted of the constrained concrete by the thickness of FRP layer and ultra lightweight concrete strength,we found that the concrete strength increases up to 62%-158% and the strain increases up to 70%-760% under the constraint of FRP.The thicker of FRP,the more strength and strain rise;the lower the concrete original strength is,the more obvious increases.Compared the experimental results with the predictions made by the established FRP constrained stress-strain constitutive model;we found that they are closely fit.(3)Studies the mechanical systematically of the new FRP-ULCC-double skin columns,by analyzing the influences on the mechanical properties of the composite members brought by hollow section ratio,FRP layer and diameter thickness ratio of steel tube,the influences of hollow ratio and diameter thickness ratio on ultimate bearing capacity are negligible;with the increase of hollow ratio,the ultimate strain of concrete increases while the diameter thickness ratio shows no obvious effect.Based on the FRP constrained stress-strain constitutive model established above,we established a mechanical property analytical model for the double pipe composite columns and the prediction accuracy is very high.