Static And Stability Analysis For Boiler Steel Structure Of Power Plant

The finite element method and commercial software ANSYS are used to analyze the spatial static peculiarity of boiler steel structure,main girder, connection of main girder with column and the overall stability in this paper.In structural static analysis, the three-dimensional model is established according to the actual instance and members dimension. The mechanical behavior of the structure is analyzed considering the dead loads, live loads, wind loads etc. and their combination, and the recommend-reference is provided for the actual design.Main girder is the main bearing member of boiler steel structure, which bears all of the vertical loads of boiler. In static analysis, contact element and target element are selected to simulate the contact between main girder and arc-shaped support, and spring element is used to simulate the sliding stiffness of column. The static performance of main girder and mechanical behavior of connection between main girder and column are analyzed by adopting state-nonlinear method. The support of girder is always in the shape of arc, and we used to adopt the boundary condition of simple (totally pin-jointed) support or sliding support in analysis. But the two types of boundary conditions are not appropriate, the first one cause big stress centralization, and the second one cause big deflection. Comparison is made between the method used in this paper and the former two cases, it is concluded that the contact analysis is more reliable.For the overall stability of boiler steel structure, there is not sufficiently effective design and analysis method yet. When the frame is designed, the whole stability is not calculated, while being replaced by the stability of poles. To ensure the security and economy condition, the global stability must be calculated accurately, so the P-△and P-δeffect should be considered, in the other word, the nonlinear effect must be considered. In this paper, the large deformation and the matrix of geometric rigidity is calculated to analyze the global stability of the boiler structure accurately by two types of buckling methods in ANSYS. By the two buckle analyses of ANSYS, the nonlinear load-displacement relationship curve is simulated and the structure buckling load is calculated. The two methods are as follows.①Linear stability analysis: This method is based on two kinds of models, one is unbraced frame and the other is strong braced frame. Use ANSYS to calculate the first four buckling modes and eigenvalues, and the buckling mode of unbraced frame is sliding instability ,but the mode of the other is non-sliding instability.②Non-linear stability analysis: The geometric and double nonlinear iterative calculation is carried out on the base of initial disfigurement of first buckling mode and sliding deformation under wind load. From the above analysis, the Load-Displacement curve and the buckling load can be obtained. The comparison of different buckling loads shows the effect of initial disfigurement on the mechanical behavior of the whole structure.Through the analysis above, the basic introduction of braced frame is presented, and the analysis of global stability of boiler steel structure under different initial disfigurement is carried out. Besides the first buckling disfigurement, the sliding disfigurement under imaginary horizontal load and wind load are also used in this paper, hope to provided a number of recommend-reference for the actual design.