Simplified Analysis Of Semi-Rigid Steel Frames Under Vertical Loading

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 page, two practical methods suitable for design of semi-rigid steel frames under vertical loads are introduced.In this page we adopt the linear spring to simulate semi-rigid connections, analyse the internal force of non-sway semi-rigid steel frames by introducing correctional rotational stiffness,transmitting coefficient and fixed end moment to traditional moment distribution method and layered method.This method not only could be used to estimate the section size,but also proofread the results by computer. The proposed method may supply references for the engineers.A new moment distribution method is given in this paper by replacing with the new unbalance moment and corrected by the same method as mentioned above. ANSYS is employed to validate the feasibility of correctional moment distribution method and layered method.Comparisons the internal force between the rigid steel frames and the semi-rigid steel frames,we could conclude as follows that the flexibility of the con- ections affects the behavior of the steel frame obviously. It can decrease the negative end moment of beams and the end moment of columns and increase the positive moment at the mid-span of beams. It can also decrease the axial force in beams and the share force within the columm end in the singly span frame.In the double span frame the change laws that share force and axial force of beams and columns are complicated.In the different conditions of initial rotational stiffness we research the law that the internal force change with the initial rotational stiffness.It can be concluded that the changed curves are linear and similar,when the initial rotational stiffness is bigger than a value ,the changed curves run to results of rigid connections and when the initial rotational stiffness is smaller than a value, the changed curves run to results of simple connections.The relation between the internal force coefficient and connective stiffness coefficient of beam is studied and also the factors that affect the relation. The formulas of moment coefficient and connective stiffness coefficient single with the single span–layer frame under vertical loads are presented.