Mechanical Behaviors Study Of Prestressed Steel-Concrete-Steel Sandwich Elements

With the further development of urbanization and traffic, many requirements to steel and concrete structure were put forward, such as higher bearing capacity, higher rigidity, smaller section size, easy construction and cost-effective way. Therefore, a new kind of structure, the steel-concrete composite structure has arisen. The outstanding compressive property of concrete and superior tensile property of steel can be fully used in this kind of structure, which has been used in many high-rise building and large-span bridge.Steel-concrete-steel sandwich composite structure is a new kind of steel and concrete composite structure, in which the shear connectors are welded to the upper and lower steel plates. By pouring concrete between steel plates, this shear connector can increase the interaction between the steel plates and the core concrete. The advantages of steel-concrete-steel sandwich composite elements are high bearing capacity, great rigidity, and the upper and lower steel plates can serve not only as load-carrying steels, but also as permanent formwork. In addition, the composite elements have many advantages, such as high bearing capacity, large rigidity, good impervious performance, high shock resistance and anti-explosion load capacity. Currently, the study on steel-concrete-steel sandwich composite elements is still at a preliminary stage at home and abroad, so it is short of systemic and complete experiment study and calculation theory. Thus, the study on work performance of steel-concrete-steel sandwich composite elements has the vital significance. In this thesis, based on the structure mechanical characteristics of the steel-concrete-steel sandwich composite elements, and by experimental research, theoretical analysis and computer simulation methods, the mechanical properties of the steel-concrete-steel sandwich composite elements were studied.Based on the experiment of steel-concrete-steel sandwich composite elements, this paper studied the working mechanism and failure mode of this kind of composite elements, and the strain variation of steel and concrete and the load-deformation relationship, and also discussed the effects of steel plate thickness and concrete thickness on the bearing capacity of steel-concrete-steel sandwich composite elements. The experimental results showed that the steel-concrete-steel sandwich composite elements had large rigidity, its failure mode belonged to plastic collapse, and the bearing capacity of composite elements increased with the increments of steel ratio and concrete thickness.Based on the experiment of prestressed steel-concrete-steel sandwich composite elements, this paper studied the working mechanism and failure mode of composite panels, and the strain variation of steel and concrete and the load-deformation relationship, and also discussed the effects of steel ratio and concrete thickness on the bearing capacity of prestressed steel-concrete-steel sandwich composite elements. The experimental results showed that its failure mode belonged to plastic collapse, the bearing capacity of composite elements increased with the increments of steel ratio and concrete thickness, and the prestressed reinforcement was not yield at the limit state.By energy variational principle, the calculating formulae of the composite section pressure, the interface shear force of steel and concrete, and the deformation of composite element under the influence of interface slip and prestressed action were established. The influences of the rigidity of the connectors, the load, the strength classes of concrete and the steel ratio on the composite elements were analyzed. The calculating results showed that the composite section pressure increased with the increasing of connector shear rigidity and the load, the composite section pressure decreased with the increasing of concrete strength and the ratio reinforcement, and the deformation of composite elements reduced with the increasing of connector shear rigidity, the concrete strength and the ratio reinforcement.The nonlinear analysis program of prestressed steel-concrete-steel sandwich composite elements was developed. The curve of the bending moment-curvature and load-deformation were received. The results of calculation showed that the capacity and the rigidity of composite elements increased with the increasing of concrete strength, the ratio reinforcement, the thickness and width of composite element. The concrete strength and the ratio reinforcement were subordinate factors and the thickness and width of composite elements were main influence factors.Based on the using of age-adjusted-effective-modulus method and time-dependent creep superposition method, the creep effects analysis models of composite elements were established, the computer program of the steel-concrete-steel sandwich composite elements was created. The calculation results showed that the stress of composite section, the deformation of composite element, interface slip between steel and concrete, and other basic variables of composite elements increased with time, which tends to be steady after the rapid change about3months. The bigger the width of composite elements and the thickness of steel plates, the smaller the increments of mid-span deformation with time. The bigger the stiffness of connections, the smaller the increments of end-span interface slip with time.