Research On The Transvers Normal Stress And Total Stability Of Steel Concrete Composite Beams

Steel-concrete composite beam is a new kind of structure,which combines steel and concrete to an integrity by the shearing connecting pieces and make them work together . Because steel is proper to resist tension and concrete is good to resist compression ,the composite beams have the virtues of both steel and concrete. This structure has remarkable benefits of technology and economy,and a lot of research have been done on it and it has some applications in civil engineering.Under the vertical loads lateral stress sometimes can appear in the composed coupling beams.But because of ignoring the influnce of transversal normal stress now , the resistance to overturning of the composed coupling beams precedes the pure steel.but it's possible that the whole destablization will happen before the strength.Although the problem has existed, so far there are no special research on of the resistance to overturning of the composed coupling beams in the step of using.In the actual design code,there are no calculating methods of the resistance to overturning of the composite beams.In this paper the analysis and research are carried out with these problems above.In the course of the analysis of transversal normal stress.owing to the principle whicn is that the sum of bending resistance capacity of the concrete plate and the top flange of I steel beams is invariabile,the section of composite beams is put into pure steel section equivalently.There are four load cases in the analysis:(1)uniformly distributed load on the top flange;(2) uniformly distributed load on the lower flange;(3)concentrated load on the top flange;(4) concentrated load on the lower flange.By the analysis the calculating foemulation of the maximal transversal normal stress in the composite beam.For the correction of the academic analysis transversal normal stress in the composite beam has been get by the finite software ANSYS.in which the result is suit to the result of the calculation with the methods produced in this paper. When considering the influnce of transversal normal stress the beam element is in the condition of multiracial stress,based on the reactions of the multiracial stress strenghth calculation is put forword with Mises buckling criterion,and calculation formulation for design is produced.The reinforcing bars of the concrete flange plates in the composite beams take transversal normal stress into considence,which is produced in this paper.Analysis on the elastic stability of the composite beams. With the resort on finite element we have performed the eigenvalue buckling analysis on the composite beams,and get the most elastic stability capacity .We put the concrete flange plate of the composite beam into the steel ones according to the elastic modulus ratio and keep the width of section unchanged,as a result,get a equivalent section.Modify the stability capacity of the equivalent section as the pure steel beam then get the calculating formulation of stability capacity of the whole composite beam.Analysis on the -plastic stability of the composite beam.Considering the lateral bending as the initiall flaw,perform the analysis on the composite beam in the way of finite element ,then get the top of load-diaplacement curve which has been obtained from the finite element calculation,then we can see the top moment as the stability capacity of the whole beam.According to what we have obtained above we can modify the capacity of the equivalent section as a pure steel one ,and produce the calculating formulation of the elastic-plastic stability capacity of the whole composite beam.