The Nonlinear FEA Program Of R/C Frame Structures

The idea of performance-based seismic design(PBSD) is accepted by more andmore people. The premise of the idea is that the simulation by FEA can provideaccurate result with quantities of the seismic performance level. So the challenges are:on one side, the numeric model should be proper to the structural style and shoulddescribe the local micro force mechanic and trace the development and evolution ofweak location; on the other hand, advanced algorithms should be provided proper tothe model characteristics, and all the nonlinear developments of the elements on thewhole structure level can be take in, which gives the effective result within acceptabletime. Different to the shaking table test and dynamic time history analysis, thenonlinear static analysis is faster and more flexible and it can be used repeatedly,which is adequate to the design of general structures (excluded from the large-scaleand complex structures). So this paper takes the research for the RC frame structuresas the follows:Firstly, the calculation flow is improved for force based beam-column elementand flexibility based method. As the force based beam-column element can describethe relationship of inner force in the structural entities, it has obvious advantage inaccuracy than traditional displacement based element. But its shortcoming exists inthe complex calculation process in every load step and the displacement should beadjusted step-by-step for convergence. So the theory of force based element anddisplacement based element are generalized in this paper. And program flow controland iterative methods in every entity from structure and element and section tomaterial is researched in this paper, in which the program flow for flexibility basedelement is improved.Secondly, a new virtual element method is provided to resolve the negativestiffness problem in the full-range nonlinear analysis. The pushover analysis canapproximately simulate the whole process of the damage process under intenseearthquake motion. But for concrete structures it is difficult to break through the limit load to get the descending stage of the load-displacement curve. So a new methodnamed virtual element is developed which can keep the multiple-point style. Theprinciple and operation steps of virtual element method are described. The theory isverified by the example.Thirdly, the sensitivity analysis for the force based element is analyzed. Theresearcher and designer can find the key control parameter from the sensitivityanalysis, and recognize the chief and minor parameters. So the sensitivity analysis forthe structural response is an essential means to optimization and/or reliability and/oridentification for the structures. Some scholars have presented the theory for forcebased element in the sensitivity analysis, but the calculation flow uses the implicitexpression for calculations. So in this paper the general and explicit formulations arepresented and comparisons with the current algorithm are given which verified by theexamples of a cantilever steel beam and a five-story steel frame structure.Lastly, the nonlinear FEA program is compiles using the above theory. Someexamples are provided and the effectiveness of the program is verified by the resultsof the tests or that calculated by the merchant software SAP2000.