| In recent years, researches of staggered floor frame structure have been paid close attention by academic and engineering circles with the growing application of the structure itself in the civil industry. In the global analysis of the structure, the key problem focuses on the analysis on the loading state of staggered point in earthquake. In this paper as it is, through finite element, analyzing the response of two different structure forms, regular staggered floor structure and Dimension-changeable staggered floor structure under different mass distribution. Based on the result, the paper studies the law of staggered point's shear force and shear force ratio ? in the two structure styles with uniform mass distribution and deduces a simplified formula in theory. Further more, paper studies the law of staggered floor structure in the action of strong earthquake through nonlinear finite element analysis. Finally, paper studies how to improve the loading capability of staggered joint in the situation of uneven mass distribution and the simplified calculation in horizontal earthquake. From finite element analysis , the following conclusions are educed. 1.Mass distribution has a visible effect to staggered part in staggered floor frame structure in earthquake. When the partial quality of the frame is concentrated on the beam-column joint on the side of higher beam of the staggered beams of the frame, it can be concluded that shear force of joint is bigger than the one got when distribution load is considered, the shear force ratio ? is bigger too and the results calculated by the dynamic response under earthquake load are a bit unfavorable. When the partial quality of the frame is concentrated on the side of lower beam of the staggered beams, it can be concluded that shear force of joint is smaller than the one got when distribution load is considered, the shear force ratio ? is smaller too and the results calculated by the dynamic response under earthquake load are a bit favorable. 2.In the regular staggered floor frame structure(staggered height ≤900mm) with uniform mass distribution, the shear force ratio ? of the staggered joints, except ground floor, is smaller than 1.But in dimension-changeable staggered floor structure, the law of shear force of staggered joint is more complex because its column's counting length is different. Only if the staggered height is less than 300mm, the shear force ratio ? of the staggered joints, except ground floor too, approaches to 1. 3.Based on the formula put forward by paper, we can calculate the shear force and shear force ratio ? of all staggered joint. Because of its nonlinear character,we should consider a shear force amplification factor γ' = 1.20 to staggered joint in Dimension-changeable staggered floor structure and ground floor of regular staggered floor structure. 4.Nonlinear finite element analysis states that the law of staggered joint in the action of strong earthquake is similar to the law in minor earthquake when the structure is designed by "strong column-weak beam" rule of Chinese building code. 5.In the design of staggered floor frame structure, if mass distribution is not in average and unfavorable for the loading of staggered points, the difference between the shearing force of staggered points and shearing force of corresponding columns can be reduced by minishing the rigidity of the frame column with a smaller quantity. 6.When the staggered height is small (500mm), under the premise of adding some details of seismic design in the joint zone, symmetrical staggered frame can be predigested, analyzing and calculating the internal force by beam model without considering the regular frame of staggered floor; but when the staggered height is big (>500mm), it can't be predigested in the above way.
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