Mechanical Analysis Of Unbonded Prestressed Steel-Concrete Composite Girders With Cold Formed Steel U Section

Steel-concrete composite structure is a new structure based on the steel structure and the concrete structure. It combines the merits of the steel structure and the concrete structure, and has significant technical and economic benefits and social benefit. But the composite structure still has some disadvantages including big deformation, the concrete flange in the negative bending moment area of the continuous girder being subjected to tension and so on. It is not ideal in applications, which limits the further spread and application in some degree. Prestressed steel-concrete composite structure overcomes these defects, possess the mechanical behavior of both the steel-concrete composite structure and the prestressed concrete structure, and broaden the application field of the steel-concrete composite structure.The prestressed steel-concrete composite girders with cold formed steel U section is formed by the U steel girder cold formed from one thin-walled steel plate, and connected with the concrete slab through shear connectors, and prestressed reinforcements arranged in the U steel girder or in the concrete slab, concrete poured in the U steel girder or in the concrete slab. In recent years, many experts and scholars have worked on the mechanical analysis of prestressed composite girders, but there are few studies on this type of composite girders.In this thesis, mechanical properties of the unbonded prestressed steel-concrete composite girders with cold formed steel U section are theoretically analyzed. For the simply supported unbonded prestressed composite beams, the equivalent cross-section method is adapted to analysis the section, and the elasticity analysis method is used to analysis the stress. The calculation formula of elastic flexural bearing capacity and ultimate flexural bearing capacity is given; for the continuous unbonded prestressed composite beams, the equivalent cross-section method is adopted to analysis the section, and equivalent load method is used to analysis the stress. The calculation formula of anti-crack capacity, elastic flexural bearing capacity and ultimate flexural bearing capacity of the prestressed composite girders is given. The slip theoretical calculation formula of the restressed composite girders is established, and also the deformation theoretical calculation formula and the axial pressure theoretical calculation formula considering the influence of the slip. At last, the complete process of nonlinear analysis of the prestressed composite beams is numerically analyzed by the nonlinear analysis program. The curves of the bending moment-curvature and load-deformation are received, and the influencing factors are discussed in the thesis.