| Steel frame is the major form widely employed in the high-rise buildings of steel structure. The rigid box-column-and- H-beam joint is the primary way popularly used in steel frame structure. In the traditional column-beam joint, two stiffing plates are set in the box-column, the height of which usually corresponds to two flanges of H-beam. In doing so, the two plates will effectively transfer the force concentrating on the beam end to the box-column and improve the rigidity of the joint and the carrying capacity of the joint region. Chinese Code for Design of Steel Structure (GB50017-2003) regulates that when H-beam is rigidly connected to H-column, the stiffing plates are not necessarily set in the column web if the joint region satisfies certain conditions. However, the code doesn't account for the instance that H-beam is rigidly connected to box-column. The dissertation is to research the strength design condition of the middle joint when two H-beams form a horizontal line and rigidly connect to box-column without stiffing plates under non-aseismatic conditions.However, the relevant research is rare both in our country and in other countries and no systematic analysis method can be followed. The dissertation will integrate and employ internationally-accepted theories such as tensile performance of plates, the yield line form, and take the calculational methods of the plate's carrying capacity. The research will be done in three aspects.â‘ On the basis of FEM model, the author selects each model for FEM analysis. Some hypotheses are made during the model building. For example, the influence of remained stress of weld and initial defects is not considered. The employed materials are perfect elastic-plastic. The character of the butt weld is supposed to be the same as other components. A reasonable model is the key to study factors which influence the performance of a joint. The model will take two methods of choosing section: the width and thickness of column section is changed with beam section fixed; and the width of beam flanges is changed with column section fixed.â‘¡The model will be analyzed in FEM program and the relevant statistics will be studied so that the factors which influence the performance of a joint will be concluded. During the analyzing process, the model will be continuously loaded. First, the axis force will be added to box-column, which is confirmed by proper ratio of axis force to pressure. Second, concentrated node force will be loaded to the free end of beam. Third, the model will do calculation until the program stops. According to the analysis of the collected statistics, P-â–³curve of key node will be drawn and the factors of column width, column board thickness, the ratio of width of column to thickness of column and the ratio of width of column to width of beam flange that influence the performance of a joint will be illustrated.â‘¢On ground of the yield line form, the limited conditions of column flange thickness of mid-joint will be deducted under the strength conditions when the stiffing plates are not used. The calculation adopts equal-strength principle that says the carrying force of the yield line is not less than the force transformed from H-beam. Finally, the analyzed result of FEM model will be contrasted to the result of theoretical formula. According to the contrast, the author suggests that the formula can be simplified and the methods in the dissertation are feasible.This dissertation uses ANSYS program to build and analysize all FEM models. Acoording to analyzing a great deal collected statistics of designed examples, the strength desige condition of the mid-joint will be deducted when H-beams rigidly connect to box-column without stiffing plates.
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