The Elastic-Plastic Analysis And The Second-Order Simplified Calculation Of Semi-Rigid Space Steel Frames Using T-stub Connections

In conventional analysis of steel beam-to-column connections, the behavior of beam-to-column joints is treated as either pinned or rigid joints. But in practice engineering, many of connections are semi-rigid joints whose behavior lies between rigid joints and pinned joints. In conventional design of steel frames, elastic analysis is used and effective length factor is introduced to check the stability of individual members. However, there is limitation of such methods. A method analyzing the second-order elastic-plastic performance of semi-rigid space steel frames is built up in this thesis which takes the connective, geometric and material nonlinearity into consideration. Based on it, the analysis of the elastic-plastic large deformation and the ultimate strength is successfully developed.In the analysis of T-stub connections, the formulas calculating its ultimate moment and initial stiffness are firstly researched, and a four-parameter index model is proposed to describe its moment-rotation relation. Then a program named QMURKI which is used to calculate its ultimate moment and initial stiffness by the computer is established. Through the program and the model above the main influencing factors are discussed accordingly.The finite-deformation theory of nonlinear continuous medium mechanics and the internal force yielding surface plastic flow theory are used to deduce the elastic-plastic stiffness matrix of semi-rigid space pole element. On the basis of this matrix, a program is compiled to calculate the second-order elastic-plastic performance of semi-rigid space steel frames. Then through the program and different examples the factors which influence the ultimate strength are enumerated. A example contrasting the load-deformation curve of the rigid and semi-rigid steel frames confirms that it's necessary to consider the effects of semid-rigid while designing semi-rigid steel frames.The simplified second-order elastic design method, which comes from the moment-enlarging theory, is used to calculate the semi-rigid space steel frames, and the results are compared with those of the accruate second-order elastic method.In the examples, the second-order displacements and internal forces of three different frames are contrasted, including 1bay-1story,1bay-2stories and 1bay-3stories frames. The error analysis verifies that the simplified method is reliable and suitable.