| Steel-concrete composite beams are widely applied in engineering owing to its good socio-economic effects and full usage of two materials.However,due to the shrinkage and creep of concrete,the stresses in the structural sections are redistributed as time goes on.For statically indeterminate structures,the internal forces of the structures will also be redistributed,which results in large additional deformation.In this paper,the theoretical analysis method was used to analyze and study the working performance of steel-concrete composite continuous beam structure under long-term load.The main research contents and results are as follows:1.On the basis of conversion section method,the influence of shrinkage and creep of concrete on the long-term performance of composite beams was analyzed using the age-adjusted effective modulus method,and the long-term change formula of support reaction force and the calculation method of cracking range were derived.The author then analyzed the development law of the cracking range of the concrete in the negative bending zone and the inner support reaction force,the deflection change of the composite beam considering cracking and not considering cracking were compared and analyzed.The results shows that crack should be considered while calculating the deflection of steel concrete beams,otherwise,the calculated deflection is underestimated.2.The previous experimental results of cantilever structures beams were used to verify the reliability of the numerical method.The calculated results are in good agreement with the experimental results.The author analyzed long term performance of composite beams under the influence of creep or shrinkage,it was found that the effect of shrinkage on the composite beam is significant to the creep effect.For the cantilever beam,the shrinkage effect decreases the deflection and the creep increases the deflection of the beam.For the mid-span deflection of continuous beam,both shrinkage and creep increases the structure deflection.3.The theory of slip effect analysis of composite beams was studied and applied.The short-term differential equations and long-term incremental differential equations of two-span steel-concrete composite beams were solved by programming.The short-term analysis focused on the effect of connection on the section force,deflection and slippage between the concrete and steel;the long-term analysis focused on how the creep and shrinkage affect the slippage,deflection and section force.The analysis shows that the short-term deflection of the structure decreases with the increase of the connection strength,as slip weaken the effect of shrinkage,the long-term deflection of composite beams decreases with the decrease of connection strength.In general,the bending moment of the cross-section taken by the concrete plate decreases with time,on the contrary,the bending moment taken by the steel girder increases with time,so that the deflection of the structure continues to increase.4.The effects of environmental humidity,loading age,stiffness ratio of concrete to steel girder,connection strength and load level on the long-term performance of the composite girder were studied by a large number of numerical calculations with different parameters,including the crack range,reaction force and deflection of the structure.The study shows that the increase of environmental humidity and concrete age can effectively delay the cracking time and reduce the cracking range,thereby reducing the long-term structural deflection;the long-term deflection increases slower if the connection strength is smaller as the slip weaken the shrinkage effect. |
