Effect Of Vertical Component Of Earthquakes On Base-Isolated Building System

Earthquake is one of the most serious natural disasters that human are suffering, and it will bring a huge threat to human life and their properties. Seismic waves include level seismic component and vertical seismic component, for a long time, people hold the opinion that the level seismic component is the main reason of earthquake damage to buildings. But in recent years, according to lots of damage phenomenon and seismic records, it shows that the impact of the building caused by vertical seismic component is obvious in high intensity earthquake zones. A lot of structural damage shows level ring gaps or a fall of the top part of structures, some others show that the upper structure falls perpendicularly after the bottom of structure is destroyed. All these phenomena indicate that vertical seismic component in some certain earthquakes can not be ignored. Isolated structure system, which is different from traditional anti-seismic structure systems, is one of the damping control systems of engineering structures, by setting a kind of isolated device to absorb and deplete the power of seismic energy, reducing the seismic response of structure that beyond the isolation layer. The level stiffness of isolation device is much smaller than that of upper structure, so that the horizontal displacement of structure focuses on the isolation device, the for the upper part of a small earthquake in the structure of the system focused on the substrate isolation devices, the level displacement between layers of upper structure is very small, upper part of the structure just does translational movement integratedly, so the seismic reflect is very small. The importance of vertical earthquake is confirmed, it has to be considered in seismic design of some certain structures. While because of its particularity of isolated structure, the seismic design of isolated structure must take into account the impact of vertical earthquake.The main research work of this paper is that how does vertical seismic component effect isolated structures. This paper sets up a group of base-isolated structure models to do nonlinear time-history analysis, using sap2000 structural analysis software. Two kinds of importing forms of seismic wave are adopted: one is to import level seismic acceleration and vertical seismic acceleration at the same time, the other is to import level seismic acceleration only. By comparing dynamic response of structures in these two cases to study how does vertical seismic component affect isolated structure. In aspects of selecting seismic waves, the paper selects two groups of real seismic records and one artificial seismic wave to do time-history analysis of structure. By analyzing and comparing the displacement and acceleration of isolation layer and roof and some other indicators of structures when consider and don't consider the vertical seismic component to know how much does vertical seismic component effect isolation structures. According to the example in this paper, the conclusions are as follows:(1)The roof displacement of isolated structures is quite small which illustrates that the main displacement generated in the isolation layer. Isolated structure under both horizontal component and vertical component of seismic simultaneously, the horizontal vibration and vertical vibration will be coupling to each other because of structure'geometrically nonlinear, vertical component of seismic will enhance the effect of level ground motion, thereby increasing the level response of structure.(2)Under 7 degrees frequent seismic and 7 degrees rare seismic, vertical seismic component will increase isolated structure'peak and frequency of level acceleration and displacement, due to the difference of peak and frequency between seismic waves, the impacts are different. According to this example, the vertical component seismic will increase structure'level acceleration by 10% -20%, even more. The impact on the roof is greater than that of the isolation layer. The impact caused by vertical component seismic on displacement of structure is very different under different seismic waves. Under the artificial seismic waves, the impact is very small, less than 2%. However, under EL-Centro wave and Taft wave, the increase is up close to 10%.(3)Under 7 degrees frequent seismic and 7 degrees rare seismic, vertical seismic component will increase isolated structure's vertical peak acceleration and frequency, and the impacts vary when chose different seismic waves. But the impact on vertical direction of structure is bigger than that on the level direction of structure.