Mechanical Performance Of Steel-Concrete Composite Beams Strengthened With Prestressing CFRP Sheets

Fiber Reinforced Polymer (FRP) has many advantages, such as high load-carrying capacity, quality light, high bearing fatigue and bearing corrosion etc. The superior physical and mechanical properties of FRP make them excellent candidates for repair and retrofit of concrete structure. Research results show that the load-carrying capacity of steel structure beam and concrete beam have not been enhanced before steel bar yield in concrete or the steel yielding using FRP sheets strengthening, and the best action is that steel bar yield in concrete or the steel yielding. Applying prestressing FRP sheets to steel and concrete beam can enlarge elastic range of materials, increase bearing capacity and fatigue resistance, decrease deformation, and reduce engineering cost. Now, the research report has not appears to the steel and concrete composite beam using prestressing Carbon Fiber Reinforced Polymer (CFRP) sheet strengthening yet, theory analysis and numerical simulation are combined in this paper to study the mechanical behaviors of the steel-concrete composite beams strengthened with prestressing CFRP Sheets. The main contents are:The calculation formulas of interfacial shear stress are therefore derived on the basis of the theory of elasticity and mechanical characteristic of strengthening steel box-concrete composite girders with prestressing CFRP sheets. The stress status of each elastic stage of prestressing CFRP sheet composite beams are analyzed, and then the calculation formulas of elastic bending strength and ultimate bending strength are established.According to the structure and bearing characteristics, the interface slip differential equations considering the effect of internal force increment were established based on elasticity theory, and the interface slip calculation formulas were presented. The deformation differential equations that considering the effect of interface slip and internal force increment of CFRP sheets were established based on elasticity theory, and the deformation calculation formulas were presented. Shear force differential equations considering the effect of interface slip and internal force increment of prestressing cable were established based on elasticity theory, and shear force calculation formulas were presented. The effect of connecting rigidity ,the loading ,and the internal force increment of prestressing cable are analysed to the interface slip ,deformation and shear force of composite girders.The creep effects analysis models of the steel-concrete composite beams with prestressing CFRP sheets are established by use of age-adjusted-effective-modulus method and time-dependent creep superposition method. Furthermore, the calculation procedures considering creep effects are developed; the section internal force, deformation and interface slip of composite beams considering creep effects are studied, and the effects of main parameters to them are discussed too.Nonlinear full-range analytic programs of the steel-concrete composite beams with prestressing CFRP sheet are developed by use of ribbon method, the effects of main parameters to moment-curvature relationship curves are discussed, The effect of concrete strength, steel percentage, and the prestressing force are analyzed to the moment-curvature of load-deformation of composite girders.The whole load-bearing process of the steel-concrete composite beams with prestressing CFRP sheets is simulated by use of ANSYS procedure. The stress and strain distribution of concrete and steel are analyzed after applying prestressing force, steel yield and ultimate status, the development rules of deformation and the interface slip of composite beams are analyzed too.