The Research On Mechanical Behavior Of Steel Frames With Semi-rigid Connections

With the development of national economics and some favorable policies to develop steel structures in my country, more and more high-floor steel structures are built, and framework system of steel structure is very universal in high-floor buildings. Beam-to-column connections are so important parts in steel frames that how to choose joints is also pivotal when joints are designed in high-floor steel structures. And it's performance affect directly frame ultimate load-carrying capacity, the strength and the rigid as well as the stability of structure and so on. In the traditional design and analysis on steel frames, the behavior of beam-to-column connections is assumed as either pinned or rigid joints entirely. Although these idealized assumptions simplify the analysis and design of steel frame consumedly, they could induce unreasonable results in many cases and they also could not reflect the actual work conditions of the structure, and the errors of the results are big because the joints in practice engineering are semi-rigid. In order to forecast actual load-carrying performance of steel frame reasonably and more accurately, it should take account of the effect of semi-rigid connections in the analysis and design of steel frame. In this paper, it focuses on simulation on top and seat angle with double web angles semi-rigid connection and extended-end-plate connection. The research on steel frames with semi-rigid connections take the structure as a whole considering semi-rigid of joints, material nonlinear and second-order effect and so on, not divide it into many parts and study one by one. So it can reflect actual work capability of steel frame system exactly. When it deduces the beam-column element stiffness matrix before appearing plastic hinge considering the effect of plastic, it simulate the development of plastic by two zero-length spring on the two ends of the element, and one end of the spring is connecting with the section of the element, another with node. A finite element program is designed to analyze the semi-rigid steel frame by the VC++ computer language. Based the practical situation of the program, the modified Newton–Raphson method is introduced to solve the nonlinear finite element equation set. The numerical examples show that this method and VC++ computer language are accurate method and efficient. In this paper, some conclusions in construction as follow have been drawn: the effect of semi-rigid connection on internal force and deformation of the frame could not be neglected. The reasonable M-θrelationship of the connection should be considered in the design of actual engineering. On the condition that the dimension of the section is controlled by end-moment, semi-rigid connections not only can save material on the node, but also make the dimension of the beam's section lessen, then reduce the quantity of the steel. The design method which allows some sections to be part-plastic can improve load-carrying more greatly than elastic design method does. In the code for design of steel structures (GB50017-2003),the hypothesis that the horizontal force formula Hni has nothing with the types of frame (pinned,semi-rigid or rigid joints) can not reflect the influence of the second-order effect accurately, so it should be modified. Finally, some prospects have given about the research of semi-rigid connection steel frame. In conclusion, the research on mechanical proprieties of steel frames with semi-rigid connections is of great significance in both theory and practice.