| A new adding-storey structural system named double-column and vierendeel truss structure is proposed to overcome the shortcomings of ordinary separated masonry-in-frame system, i.e. abrupt change in stiffness and large span at bottom storey. At present, there are no experimental or theoretical data available or any earthquake disasters, as well as no related standards on this structure in design code. In seismic region, because of lacking of reliable design basis, it is necessary to do some profound research on the structural optimization and seismic behavior.On the basis of application of finite element program SAP2000, Response spectrum and static analysis on different double-column and vierendeel truss structures have been done, studying how the type and number of bracing affect lateral rigidiy and how the truss rod arrangement and quantity affect lateral stiffness ,moment, shear, deflection in middle-span etc. the result show that : vierendeel truss and double limb-column with diagonal bracing structure can effectively improve lateral stiffness of bottom floor, vertical lateral rigidity is homogeneous and the peak of moment at different floors reduced apparently, drive to homogeneous as well.On the condition of above analysis, making modal analysis and elastic time-history analysis of frequent earthquake on out-jacket adding-storey structure. The result of model analysis show: as the storey increased, basic period elongate, participation mass coefficient is easy to satisfy code standard, and Tt/T1 ratio enlarged gradually. From the model figure, getting the conclusion that there is a break between the first and second floor, which is must be attention when it is designed. At seven and eight intensity, groupâ… ï½žâ…¢,the time-history analysis indicate: the storey drift and storey drift angle is extraordinary less than the limited values in code for seismic design of buildings. vierendeel truss and double limb-column with diagonal bracing structure have stronger stiffness.Finally, static nolinear analysis on the vierendeel truss and double limb-column with diagonal bracing structure has been done, the result indicate that: the structure will not collapse in eight degree, the hinges subsequence meets the design conception"strong column and weak beam"; at the displacement corresponding to performance point, it will not form mobile structure and double limb-column emerges no hinges, the hinges emerge on the diagonal bracing, which indicate it possess good dissipative ability.The results from above research indicate:the structure is simple in style, reasonable force,significantly improve the"piloti construction"defect of general out-jacket frame, at the same time, it across a larger span and reduced sectional dimension of components, try for construction space, reduce the project cost. This structure can widely popularize in rebuild of existed brick house. The double limb-column have effectively improve the bottom stiffness, perfect the shortcoming in bottom and will not influence on the space , increase hyperstatic frequency.
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