Keywords: seismic isolation, monuments, friction pendulum system.

The design of base isolation systems that carry relatively small loads, as for example the case of the isolation of a statue, present some difficulties that are related to the particular isolation system. At target displacements Lead Rubber Bearings (LRBs) are susceptible to buckling for relatively small vertical loads and therefore, their use is limited. Friction bearings are more suitable for light loads as friction forces are analogous to the applied load and the fundamental period of the isolation system is independent of the mass of the system.

The main problem for the design of friction pendulum systems is the lack of experimental data for a wide range of pressure values that determine the variation of the coefficient of friction with respect to velocity. The applied pressure corresponds to values that refer mainly to buildings or bridges and usually varies between 16 to 30 MPa [1]. Light loads usually correspond to smaller pressures that result into a relatively jagged behaviour as compared to the high pressure cases.

In this work two alternative configurations are investigated that increase the contact pressure by machining the central part and establishing the contact at the annular surface, or vice-versa by establishing contact at a central part of equal area and appropriate manufacturing of the annulus part. The contact problem is implemented using the FEM method. Numerical results are presented and a number of conclusions are deduced from the comparative study.

From the analysis presented it becomes evident that the selection of either the annular or the central model is of a trade off type. In terms of the durability of the PTFE material the central model is beneficial as compared to the annular, whereas in terms of stability in light loads the annular model is better. Therefore, the decision is based on the assigned weighting factors on these criteria. To our judgement the durability of the PTFE is of primary importance.

1

Constantinou M.C., Mokha A., Reinhorn A., "Teflon bearings in base isolation, Part II: Modeling". Journal of Structural Engineering (ASCE) 1990; 116: 455-474 doi:10.1061/(ASCE)0733-9445(1990)116:2(455)

2

Almazan L., De la Llera J.C. "Physical model for dynamic analysis of structures with FPS isolator", Earthquake Engineering and Structural Dynamics 2003; 32:1157-1184. doi:10.1002/eqe.266

3

Tsopelas P.C., Constantinou M.C., Reinhorn A.M., 3D-BASIS-ME: Computer analysis of seismically program for nonlinear dynamic analysis of seismically isolated single and multiple structures and liquid storage tanks, Report NCEER-94-0010, National Center for Earthquake Engineering Research, State University of New York, Buffalo,1994.

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