Effect Of Joint Stiffness On The Portal Frame Stability

Portal frame is the most common used light weight steel system for single story industry factories and civilian buildings. When design portal frame structures, the beam-column connections are usually considered as full-rigid. In fact, lots of researches carried out by domestic and overseas academicians showed that most of the commonly used portal frames are semi-rigid. Thus, the frame stability capacity could be over estimated. Compared to the currently design codes used in Europe and American, Chinese code is weak at calculating the bolt end-plate beam-column connections and semi-rigid frames. Researches on the semi-rigid portal frame stability capacity are conducted.Research works on the end-plate connections and design specification are reviewed., The semi-rigid connection characteristics and the semi-rigid connection simulation methods are summarized.The high-strength bolts end-plate connections were analyzed with 3D finite element model. Joint stiffness and capacity characteristics were got for further study. The joint stiffness values calculated with the finite element method and calculated using the Eurocode 3 are compared, they were nearly the same.The stiffness of semi-rigid beam-column connections are simulated with rotational spring. The frame stability capacity formula were derived. The results from these formula can meet the results from the traditional theory when the connection stiffness reaches infinity or equals to zero.Influence of the beam-column connection stiffness on the frame stability capacity when beam-column linear stiffness ratio changes is analyzed. The effect of beam-column joints stiffness on frame stability is more significant if the beam-column linear stiffness ratio is higher. Special attention should be paid to the beam-column joint stiffness when the beam-column linear stiffness ratio is relatively high.Based on the national standard, the column length factor was modified considering the joint relativistic stiffness. The frame stability capacity can be predicted more accurately with the formulas proposed.According to the research work issued in this thesis, the frame stability capacity can be affected by beam-column stiffness significantly. The stability capacity of portal frames may be over estimated if designing with the fully-rigid joint assumption. Design suggestions were put forward.