Nonlinear Analysis Of Steel-Concrete Composite Ribbed Shell

Steel-concrete composite ribbed shell is described in this paper, which is a new kind of space structure for enclosing large spaces. This kind of shell is made of composite rib and concrete shell: steel rib is formed by three thin steel plates welded in U shape, then concrete is poured to build composite ribs; those composite ribs are used as the formworks to make RC shell, finally the whole composite ribbed shell is completed. During the whole construction process, the founded members are used as the formworks and brackets to the latter. The new structure retains all the benefits of thin concrete shells, while eliminates the need for temporary formwork and minimises the required falsework, declines construction cost, so it is a kind of spatial structural system with good developing prospect.To grasp the structure mechanics and remedy blank of research, the factors to mechanics and bearing capability of single steel rib, composite rib and the whole structure are discussed according to construction order. The main content is described as follows:1. Theory and numerical study on stability and bearing capability of single steel rib, critical bearing capability formula are made.Steel rib arch with U section is presented, the models with and without clapboard are made separately by using APDL language, 30 groups of different sections and more than 180 steel arch examples are researched, the ultimate bearing capability and instable form are investigated, the influence factors including clapboard, different section dimension, half span loading and initial imperfection are discussed in detail, all the above provides abundant information to master the mechanics of steel arch.2. Bearing capability of composite rib members is analyzed considering geometry and material nonlinear, bearing capability formula of composite rib is concluded.Bearing capability analysis methods of composite section are discussed, especially the applied method which is combined by nonlinear finite element method and software analysis, standard concrete compress member, RC beam and steel tube concrete puncheon are validated. The mechanics capability of composite rib section members are simulated by finite element method, which including press, pull and bend. Based on the analysis, the calculation formula of bearing capability is put forward which considering the effects of geometry and material nonlinear and using limit continuum equation. Under different concrete intension, parameter analysis of various section dimension is made, which provides data support for calculation formula of bearing capability.3. Elastic-plastic analysis of composite ribbed shell is made completely, which includes ultimate bearing capability and characteristic of deformation.Based on the virtual work, the composite ribbed shell nonlinear incremental continuum equation is made by using space beam element and layer curved shell element, stiffness matrix is founded considering the eccentricity influence; then internal force distributing, loading transfer fashion and characteristic deformation are researched under the load of deadweight and equal pressure; finally a comparison with RC ribbed shell is made.4. During the stability analysis of composite ribbed shell, stable deformation and post-buckling characteristic are discussed in detail. The conclusions can be resulted in structure design.A new stability analysis method is put forward, which is combined line research and arc-length, and is validated by representative examples; structure stability is judged by tracing the whole process analysis. In order to grasp the bearing capability variation and instable area distribution, a great deal of parameter analysis of influence factors are made, which including rib number, rise to span ratio, section dimension and different loading, all of the conclusions can be consulted to new structure design.The originality of the thesis lies in:1. A new spatial structure named steel-concrete composite ribbed shell is presented, the bearing capability, elastic-plastic mechanics and stability of this structure are studied thoroughly, it has many advantages such as good mechanics of bearing capability and stability, it also can overcomes the trivial objection in RC shell construction.2. From single steel rib stability research, bearing capability formula of single steel rib arch under in plane and out plane buckling are obtained separately, which is valuable to the limit bearing calculation of U section arch; from two different models analysis, it is found that: the bearing capability of steel rib with clapboard is 2 or 3 more than the none one, the appended clapboard can not only avoid concrete sliding along the steel rib axes, but also improve the carrying capability; from influence factor research, the main factor is the steel board thickness, then the section dimension of height and width, the influence of clapboard is the smallest.3. The bearing calculation formula under 3 loading condition are obtained based on the nonlinear finite element research, a comparison between formula calculation and nonlinear finite element are made, the discrepancy of them is only 2%, which is proved that the formula can be used to U section member.4. From the elastic-plastic analysis of composite ribbed shell, it is found that: two composite ribs through structure mid are the main members which transfer loading to other parts, the whole loading path is definitely and smoothly; for the existing of steel ribs, mechanics of the structure is improved in a certain extent, the variety range of axial pressure and moment in composite ribs is adjusted, the internal force distribution goes to uniformity. After local instable area appeared, the bearing capability can be improved yet, the whole structure behaves certain post-buckling strength, and it is distinct to lattice shell structures. So to composite ribbed shell, it is unreasonable to take the first limit point as critical load, post buckling strength should be considered and used.