Study On The Bending Performance Of A New Hollow Double-tube Composite Beam

With the continuous renewal and development of the construction industry,the building structure has higher and higher requirements for light weight and high reinforcement.As a new type of composite material,FRP has its unique advantages such as light weight,excellent tensile properties and strong corrosion resistance.Therefore,the new FRP-concrete-steel tube composite structure has received extensive attention.This paper mainly researches a new double-tube composite beam.The double-tube composite beam has lower self-weight than the ordinary concrete beam,and the outer wrapped FRP pipe can prevent the internal metal pipe from being corroded and has high ductility and stiffness.Since the internal concrete is mainly responsible for the pressure,in order to realize the waste recycling,the innovative green concrete such as recycled aggregate concrete and sea sand seawater concrete is used as the filler.In order to further realize the lightweight structure,ultra-lightweight concrete is used as the filler.The basic mechanical properties of the new double-tube composite beam are studied separately.The specific research contents are as follows:(1)The basic mechanical properties of CFRP-ultra-lightweight concrete-steel composite beams were studied: the influence of different internal pipe eccentricities on the bearing capacity of composite beams was analyzed.When the eccentricity was increased by 15% and 30%,the maximum bearing capacity of composite beams was Increased by 10.9% and 23.04% respectively;but after the eccentricity is increased by more than 15%,the effect of improving the ductility begins to decrease;when the internal metal pipe uses a circular section,the maximum bearing capacity will increase by 10.03%,and the ductility will also increase;When the inner tube is made of square stainless steel tube,the maximum bearing capacity is increased by 10.5%,but the ductility of the beam compared with the square steel tube is much lower.When the inner tube is made of square aluminum tube,the maximum bearing capacity will decrease,but the ductility is still higher than that of ordinary concrete beam.(2)The basic mechanical properties of CFRP-green concrete-steel tubular composite beams were studied: increasing the eccentricity of internal metal pipes would increase the maximum bearing capacity of composite beams,and the ductility would increase with the increase of eccentricity,but the effect of ductility would not be obvious after the eccentricity increased by more than 15%.The circular section of the inner tube can improve the bearing capacity and ductility.When the stainless steel tube is used as the inner tube,the ductility and stiffness of the composite beam will decrease rapidly.When aluminum tubes are used,the maximum bearing capacity of the composite beam is reduced,but the ductility is still good.(3)The changes of bearing capacity,stiffness and ductility of double-tube composite beams filled with different concretes are compared and analyzed: when the internal pipes are the same,the bearing is mainly determined by the strength of concrete.The greater the concrete strength,the higher the maximum bearing capacity of the composite beams;The initial stiffness of the composite beam filled with recycled concrete is the largest,and the ductility of the composite beam is determined by the joint strength of the inner pipe and the concrete.