Secondary Development Of Advanced Analysis Of The Steel Framework Based On OpenSees

The traditional design method of steel structure contains two stages: so-called two stages methods. The first stage: Linear elastic analysis is used to determine the internal design forces of each member of a structure. The second stage: the strength of every member of a structure is determined through an inelastic analysis and compared against the design forces with the aid of interaction equations. The traditional design method has large limitations, ignoring the verification of compatibility between the isolated member and the member as part of the whole structure, whereas the advanced analysis method which eliminates the aforementioned disadvantages of traditional design approach is actually a kind of second-order elastoplastic analysis. This method is here to use any method of analysis that can sufficiently capture limit state strength and stability of a structure and its members so that separate member strength checks are not necessary. So the advanced analysis method can reflect the actual force state of a structure under diffident loads more actually. The advanced analysis method of truss and steel frame structure applying in OpenSees was comprehensive studied. The main research works and results are as follows.(1) Based on the theory of increment of UL and using the virtual displacement principle, the stiff matrix of space truss considering geometric nonlinear is deduced and the high order nonlinear truss element is developed in the general finite element program OpenSees. Through the validation of several numerical examples, the nonlinear element developed can achieve high efficiency and accuracy when the nonlinear analysis of truss structures is performed.(2) To better consider the post-buckling behavior of truss structures under cyclic load or earthquake load, elastic post-buckling(EPB) and inelastic post-buckling(IEPB)constitutive model of space truss are developed in OpenSees platform. The constitutive model contains the influences of buckling、inelastic post-buckling、unloading and reloading. Several numerical examples illustrate that it tend to overestimate the ultimate capacity of a structure not considering the impact of post-buckling of the material, and that the constitutive model developed in OpenSees has high accuracy and can better consider the post-buckling behavior of truss structures.(3) Based on the beam-column theory, a geometric nonlinear beam-column element which contains the influence of shear deformation is developed in OpenSees. The geometric nonlinear beam-column class is based on the element class in OpenSees. The contrast analysis are performed through several numerical examples with the element and the nonlinear beam-column based on flexibility and the results illustrate that the element in this article has higher efficiency and accuracy.(4) Based on the beam-column theory and the geometric nonlinear beam-column element, the influences of material nonlinearities、residual stress、stiffness degradation are considered. The refined plastic hinge beam-column element which can consider the effects of geometric and material nonlinearities is developed in OpenSees. The results of several numerical examples illustrate that an element per member can achieve high accuracy in structural analysis.