Study On Advanced Analysis Method Of Space Steel Frames

Traditional analysis and design methods have many limitations. With the development of computer technology and theories of structural analysis and design, the advanced analysis and design method must be an important trend in future analysis and design practices. A three-dimensional beam element, which based on stability functions of beam-column theory and refined plastic hinge model, has been developed. Nonlinear effects, such as geometic nonlinearity, material nonlinearity, shear deformation, effect of curvature shortening, residual stress and connection flexibility, can be considered in element formulation.Element routines are developed using the redevelopment technique of commercial finite element ANSYS software, and run on the platform of ANSYS software. Element can be used for static or dynamic advanced analysis of three-dimensional steel structures. The followings are the mian contents in detail. The slope-deflection equations including shear effect are derived and used to compute element internal forces, in which the element P ?δeffect can be accurately captured by the stability functions. Methods to consider the effect of curvature shortening (bowing effect) are discussed. Results of analysis examples show that the bowing effect can be taken into account effectively by an approximate non-iterative method. Using virtual displacement principle and stability interpolation functions, stiffness equation of a three-dimensional thin-walled beam element is derived. Influences of different types of element stiffness matrixes on the accuracy of element are observed. It is found that the form and accuracy of the geometric stiffness matrix used in a nonlinear analysis almost have no effect on the accuracy of the final solution when the same expressions are used to calculate the internal forces. The element transformation matrix is updated either by joint orientation matrix or by element rigid body rotation, and difference between two methods is analysed. It is found that the results of two methods are close in static analysis, whereas in dynamic analysis the former has better robustness and convergence than the latter.In elastic analysis, algorithm for internal forces calculation based on the total equilibrium condition is better than that based on the incremental equilibrium condition. As far as geometric nonlinear analysis is concerned, the performance of proposed beam element is better than that of BEAM4 element, and is comparable to, to some extent even better than, that of BEAM189 element in ANSYS program.Material nonlinearity is modeled using refined plastic hinge approach. Inelastic strength limit state of planar and space steel frames can be captured by proposed element. The analytical results of proposed element are compared fairly well with those of plastic zone based beam element BEAM189. In structural inelastic analysis, only one or two proposed elements for each member loaded by nodal loads or by distributed loads, respectively, in contrast to three to five BEAM189 elements for each member, are needed to achieve acceptable accuracy. The proposed beam element has excellent efficiency since it does not do any numerical integration operation. A lot of computing time can therefore be saved in the analysis of large-scale structures by using proposed element, as compared to using numerically integrated element.Modified beam element method is used to account for the effect of connection flexibility on the structural behavior. The analytical results of proposed element are compared reasonably well with the test results. Effect of connection flexibility can also be taken into account in analysis by connection element, such as COMBIN39 element in ANSYS program. The analytical results by use of COMBIN39 and BEAM189 elements are very close to those by proposed element. Using proposed element is quite convenient, because the same structural model as the rigid frame can be used. However, using COMBIN39 element is more complicated since the creation of structural model and the determination of real constants are troublesome, and the number of nodes and elements in finite element model is large.Routines of the refined plastic hinge based beam element are written in FORTRAN language using User Programmable Features (UPFs) of ANSYS program. Customized ANSYS program has been obtained after these routines are compiled and linked into ANSYS program. The user beam element can be easily activated in customized ANSYS program and then can be used for static or dynamic analysis of planar and space steel structures. The user beam element can be used with standard elements in ANSYS program, therefore, the advantages of ANSYS program, such as the abundant elements, the powerful solution tools and the convenient pre- and post-processor can be readily and well used in the structural analysis.Elastic and plastic comparison analyses between two types of elements, namely the refined plastic hinge based beam element and the numerically integrated beam element, are performed for rigid and semi-rigid steel frames under earthquake excitations. High accuracy results can be obtained using proposed beam element in the time-history analysis for rigid and semi-rigid structures where spread-of-plasticity is not significant or where redundancy is high, such as for braced frames. However, numerically integrated elements should be employed in the time-history analysis to obtain accurate results for structures where spread-of-plasticity is significant and abrupt reduction in lateral stiffness of some story may be induced.In comparison with rigid frames, semi-rigid frames may have lesser total base shear response under earthquake excitations. As the stiffness of connection decreases, the maximum total base shear resulting from the same earthquake excitation decreases. However, the maximum lateral drifts and the maximum inter-story drifts of the semi-rigid frames do not always increase with the decreasing of connection stiffness.