Research On Homogeneous Generalized Yield Criterions And Ultimate Bearing Capacity Of Engineering Structurs

Ultimate bearing capacity (UBC) is an important indicator for measuring overall safety of engineering structures, and the numerical solution method for UBC and its application are hot topics. At present, there are mainly three numerical methods for calculating UBC:elasto-plastic incremental analysis (EPIA), mathematics programming method and elastic modulus adjustment procedure (EMAP). The EMAP is a robust method in accuracy and efficiency among them. A new EMAP, called elastic modulus reduction method (EMRM), is proposed recently by our research group. The element bearing ratio (EBR), as an important parameter in the EMRM, is defined based on the generalized yield function. Using the reference EBR and uniformity of EBR, a dynamic criterion to identify the elements with higher EBR is provided. Thus, a self-adaption modulus adjustment strategy is established based on the principle of strain energy conservation, and then the damage and the redistribution of internal force in the process of loading of the engineering structure can be simulated. The EMRM now becomes an important method for ultimate bearing capacity analysis and safety assessment of engineering structures. The further work is conducted in this thesis in view of the problems:the improvement and selection of generalized yield criterions employing partial or all internal forces, the influence regularity of the important parameters on ultimate bearing capacity, application of the EMRM in safety evaluation of gantry of switchyard. The main contents are as follows:(1) A homogeneous method of generalized yield function is presented, and the homogeneous generalized yield functions (HYGF) for rectangular and I-shaped section are established, which can overcome the disadvantages exsiting in combination use of the EMAP and the traditional generalized yield function. The quartic homogeneous polynomial is suggested to be used in the HYGF.(2) The HYGF employing the three internal forces of axial force and two-way bending moment, and the HYGF employing whole internal forces of axial force, bending moment, shear force, torque, buckling torque are compared on the calculation the UBC of lots of frames.The former HYGF is suggested for UBC analysis of the frame structures.(3) The influence regularity of mesh density, convergence tolorence and load incremental steps on the EPIA and EMRM are investigated. The values suggested for these parameters are given.(4) The HYGF-EMRM is introduced into the ultimate bearing capacity analysis of gantry of switchyard, and the corresponding safety assessment method for bearing capacity is proposed. The influence regularity of the lateral support on the structural safety of the structure are given, and the rational practical suggestions for adding lateral support for gantry of switchyard are provided.