Study On Analysis Method Of Nonlinear Seismic Response Of Steel Mega-Frame Structures

Steel mega-frame structures are large-scale structure, which has hugelateral resistance stiffness and overall performance. In recent decades, it hasbeen broadly used because of its flexible layout, less material consuming, fullytaking advantage of material strength and well seismic behavior. Under the rareseismic load, some elements tend to yield, so the nonlinear analysis of structuremust be conducted. The composition of the mega beams and mega columns inthe steel mega-frame structure are complex. The proper nonlinear analyticalmodels of elements and nonlinear analytical methods of structure have not beensolved. In this paper, theprecise and practical methods of the nonlinear analysisof the steel mega-frame structures and their applications are studied, whichprovide effective tools for seismic response analysis, seismic performanceresearch and seismic design of this kind of structures. The main work includes:The current 3-D nonlinear analytical methods of steel mega-framestructures and their vantage and disadvantage have been systematically reviewedand summarized, which lay the foundation for the research work in this paper.A 4-node reduced integration shell element, which has high accuracy andcomputation efficiency, is adopted to discrete the mega elements and establishthe analytical model. The nonlinear seismic response analysis method of steelmega-framestructures based on 3-D shell element model is given, and the FEMsoftware MSC.Marc is used to achieve the method. The parallel computationtechnique is explored to reduce the computing time. The method can be used asa precise analytical method for the mechanical behavior analysis of the elementsand nodes or the nonlinear analysis of small-scale structures. The method wasused to study the bracing types of the mega columns. Selecting bracing barswith various length to slenderness ratios, comparing the stiffness, ductility andenergy absorption ability of the mega columns with three common bracing types,the suggest of bracing type choice is given.Combining Timoshenko beam theory and fiber model, the element stiffnessmatrix can be derived based on stiffness method. And the fiber model whichconsiders shear yielding and flexural yielding separately is established. Theinfluence of element stiffness from shear deformation is achieved. The stiffnessmatrix of Timshenko beam-fiber model can be implanted into softwareMSC.Marc by the second development interface. Thus the nonlinear seismicresponse analysis method of steel mega-frame structures based on Timoshenkobeam-fiber model can be realized. Using V. Mises yielding conditions, plasticity-related V. Mises flow lawsand Zeigler incremental strengthening laws, the material elastic-plastic matrixwhich can consider one principle stress, two shear stresses and torsional stresseshas been derived. On the basis, the finite segment element plastic zone stiffnessmatrix was built based on Timoshenko beam theory. This stiffness matrix can beimplanted into software MSC.Marc by the second development interface. Thusthe nonlinear seismic response analysis method of steel mega-frame structuresbased on the finite segment element plastic zone can be realized.The three methods given by this paper is used to analyze the nonlinearresponse of deep beams and short beams. Though comparing computationaccuracy and efficiency, the method based on Timshenko beam-fiber model isregarded as a practical method of nonlinear seismic response analysis method ofsteel mega-frame structures. And the method was used in nonlinear seismicresponse analysis of an actual mega-frame structure to illustrate the applicabilityof the method.