Analysis Of Earthquake-resistance Of Integral Structure After Adding Steel Structures On Top Of Concrete Frame

In recent years, the city building cost is becoming more and more nervous due to the rapid development of the city industrialization and commercialization. Many original buildings need the further extension of utilization area in order to satisfy the new demand. In this case, adding stories on the original building becomes a good method to enlarge the area and adding steel stories is the popular form in reinforcing and rebuilding the buildings at the present time. As most of the original buildings are bricking-up structure or the reinforced concrete frame structure, the combined structures belong to the hybrid construction. This hybrid construction is composed by two kinds of materials with different damping ratio, so it is non-classically damping structural system.For adding storey structures, you should not only to calculate the adding storey part, but also to make the global analysis of the structure. After adding stories, the dynamic properties of the overall structure vary from the original structure. Our country, which is a country with frequent earthquakes, the seismic performance research of adding storey structures can't be neglected particularly.In this paper, the structure of two-storey steel frames adding on the top of original concrete frame is selected in the direct elastic dynamic time-history analysis which the non-classically damping is considered by software NDAS2D. On base of the analysis, the seismic performance influences to the integral frame are compared by changing the damping ratio and stiffness. The results indicate that there is a rather large whiplash effect on the steel frame on top of concrete frame. The whiplash effect is caused by the sudden decrease of the stiffness and damping, we can, t calculate the displacement and internal force of the structure exactly if we neglect of either of the reasons, and it will bring incipient fault to the design. So in the structure design, we should not only consider the influence of the stiffness but consider the influence of the damping. The results also indicate that if the reduced damping method which has not considered the sudden decrease of damping ratio of the steel frame is used to design, it will bring unsafe results. Compare the results of internal force and displacement which are calculated by the non-classically modal superposition method with the results are calculated by the direct integration method and you will see that the non-classically modal superposition method can raise the efficiency. At last, some suggestions about the structure design are put forward.