Study On The Sliding Displacement Of Sliding Isolation Structure

Base isolation is an effective way to protect structures from damage in severe earthquake. It can ensure the safety of people's lives and properties. Sliding isolation is one form of base isolation. It has the characteristics of simple technique, excellent isolation effect, bearing capacity keeping the same after slide and lower investment, etc. Sliding displacement is a key factor in sliding bearing design. Therefore every factor influencing the sliding displacement is investigated on the basis of summarizing the study results on sliding isolation over the past 20 years. The contents studied in this paper are as follows: The constitution of the sliding isolation system is studied, including the sliding device, recentering device, the characteristics of frictional material-Teflon, the constitution measure of isolation structure. The model of frictional forces is summarized. The analysis method of nonlinear dynamical equation of sliding isolation structure is studied. The criteria of how to choose the time step and convergence is confirmed. The responses of sliding isolation structure are studied by varying different earthquake intensity and coefficient of friction under single-component earthquake excitation. The responses include the maximum acceleration on the top of structure, maximum shearing forces at the bottom of structure, sliding displacement produced in the isolation layer, remnant displacement and ratio of isolation. The proper coefficient of friction is given by comparing the sliding displacement and ratio of isolation. It is also studied to the influence on sliding displacement of different period of superstructure, site and stiffness of restoring spring. The result shows that the sliding isolation structure applies in the short period, big stiffness multi-storey structure and does not apply in the site â…£. The proper stiffness of restoring spring is given. The responses of sliding displacement and acceleration of superstructure under bidirectional harmonic excitation are studied by varying the frequency ratio of excitation, amplitude ratio of excitation, the period of superstructure and coefficient of friction, considering and ignoring the interaction of frictional forces. They are also studied under bidirectional earthquake excitation. The results show that the sliding displacement is significantly influenced by the interaction of frictional forces, but the acceleration of superstructure is not. So to get the response of sliding isolation structure, we can not only get the maximum value of two directions respectively. To get the exact result, the interaction of frictional forces must be considered. Eccentricity may exist in the structure for the reason of itself. The sliding displacement of structure with eccentricity in single direction is studied under the single direction and bidirectional harmonic and earthquake excitation. The sliding displacement is calculated in different ratio of eccentricity. The sliding displacement in the symmetric structure is compared with that in the eccentric structure under different excitation angles. Numerical results show that the period of superstructure increases with the ratio of eccentricity increasing. But the sliding displacement produced in the sliding support does not increase with the eccentricity. It is required to keep stable for sliding isolation structure under wind load. Several methods are applied to study the wind resisting stability of sliding structure in different coefficient of friction and reference wind pressure: (1) Equivalent static method considering the 1st mode; (2) Wave superposition method is applied to simulate approximate turbulent wind with given function of power spectrum density. The wind is applied on the structure and the time domain dynamic analysis is used; (3) Probability method is applied to calculate the turbulent wind pressure according to the function of power spectrum density; (4) The following aspects are computed for the sliding structure: wind resisting reliability under maximum wind pressure, disabled probability of structure under single strong wind, wind resisting reliability in design reference period; (5) Upset resisting is checked. It is observed that the wind loads obtained by the time domain analysis and the probability method are similar, both greater than the wind load obtained by the equivalent static method. According to the numerical results obtained by the wind resisting reliability, the coefficient of friction applied to the area of different wind pressure is given. Finally, the work in this paper is summarized and some conclusions about the study are drawn, besides, the further research problems are indicated.