The Study On Mechanical Behavior Of Negative Moment Area Of Steel-concrete Composite Beam With Additional Longitudinal Reinforcement

In recent years, concrete-filled square steel tubular column and steel-concretecomposite beam are widely used in structural engineering. In addition to thecommonly used beam-column joints recommended in the correlative codes andspecifications, the form of concrete filled steel tubular (CFST) joints is varied inpractical construction. In mid-rise and high-rise buildings, in the meantime, the typesof Beam-column connection receive more and more attention from domestic andforeign researchers due to the special structure of concrete filled square steel tubes. Inthe present much experimental study and theoretical analysis about the concrete-filledsteel square tubular column and beam joint have been conducted, rich experimentaldata has been accumulated and the mechanical properties of this type of connectionhave a more fully understanding. However, existing studies are mostly limited to themechanical performance of various forms of connection, some insufficiencies are inexistence about the influence of the joint structure form on the mechanical behavior.According to above present situation, combining with the practice of anengineering this paper studies the influence of different types of additionallongitudinal reinforcement in the concrete flange plate on the load capacity, stiffnessdegradation, stress distribution and concrete cracking in the steel and concretecomposite beam hogging moment area.Based on the purpose of the research, two groups of real scale specimens aremade according to the engineering practice of beam-column joints and the influenceof the different types of additional longitudinal reinforcement in the concrete flangeplate on the mechanical behavior of beam-column joints; secondly, finite elementanalysis model has been established and theoretical calculations and experimentalresults are analyzed; Finally, the influence of the different types of additionallongitudinal on the mechanical behavior of beam-column joints are discussed byadjusting the detail structure parameters.Taking account of all the connecting joints of the concrete-filled square steel tubular column and steel-concrete composite beam,this paper proposes a new type ofjoint in which the additional longitudinal reinforcement in the concrete flange plate isconnected with the concrete-filled square steel tubular column by sleeve. the study ofthe influence of this kind of joint on the mechanical performance of steel and concretecomposite beams has not been conducted in our country, so a certain degree ofinnovation exist. Comparing with those joints with no additional longitudinalreinforcement，studies have shown that the additional longitudinal reinforcement inthe concrete flange plate can improve the flexural resistance capacity and increase thedeformation capacity of the composite beam hogging moment area, and no significantstress concentration occurred in the steel beam, elastic and plastic neutral axis are inthe vicinity of the flange, which reduces the weld damage of the top flange and theconcrete-filled square steel tubular column to some extend. The composite beamfailed in compressive yield of the steel beam bottom flange and the fissure that cannot meet the ultimate limit states in the flange plate. In addition, Concrete slab wastensioned in the negative moment area, the bond-slip phenomenon of the top flange,studs and steel bars existed, and complex situation need to be researched deeply.The study of influence of different types of additional longitudinal reinforcementin the concrete flange plate contributes to the research of composite frame and canguide the design of composite components and joints in practice, which has somepractical significances.