Effects of the long-term behaviour of isolation devices on the seismic response of base-isolated buildings

Abstract

Summary Seismic isolation is widely used around the world for the protection of buildings, but its long‐term behaviour was not considered in detail in past seismic design of isolated structures. Nevertheless, the American seismic code has recently introduced an explicit procedure aimed at evaluating upper‐bound and lower‐bound values of isolation system properties. Yet there are few studies on the evolution and extent of the deterioration of elastomeric (e.g., high‐damping rubber bearings) and sliding (e.g., flat sliding bearings) isolators during their lifetime and on their impact on the seismic behaviour of the superstructure. To investigate this problem, six‐storey–reinforced concrete buildings, base isolated with high‐damping rubber bearings acting alone or in combination with flat sliding bearings, are designed without considering the variability of mechanical properties of the isolation system due to ageing and air temperature. Then, based on experimental results from accelerated ageing tests at high temperature, mathematical models are implemented to account for oxidation of elastomers and friction changes. The variability of mechanical properties at different mean temperatures, due to seasonal thermal variations, is also considered. Finally, fragility curves are developed for the base‐isolation system and superstructure on the basis of nonlinear dynamic analysis of the degraded test structures.

Long-Term Seismic Response of Buildings With Isolation Devices Affected by Deterioration Effects

“…end sections). With a view to studying the effects of advanced nonlinear modelling of the EBI and ESBI isolation systems, the formulations of the HDRBs and FSBs described in a previous paper [22] are implemented through a computer code already proposed [23]. In the Rayleigh hypothesis, the damping matrix of the superstructure is assumed as a linear combination of the mass and stiffness matrices, assuming horizontal and vertical viscous damping ratios (i.e.…”

“…Finally, Table 5 summarises the geometrical properties for HDRBs of the ESBI systems with reference to low-and medium-type friction of the FSBs. Further details about the design of the test structures can be found in a previous work by the author [22]. Table 5: Geometrical properties of the HDRBs for the hybrid isolation systems (units in cm).…”

Comparing Rubber Bearings and Eradi-Quake System for Seismic Isolation of Bridges

“…Therefore, it can be concluded that strict quality management on the commercial seismic isolators should be implemented. During the lifetime of the isolators, ageing and air temperature are important factors that affect the degradation of the rubber and friction coefficient of the sliding surface, respectively [ 23 ]. Therefore, further research will be conducted with considerations of durability.…”

Observed Seismic Behavior of a HDRB and SD Isolation System under Far Fault Earthquakes

“…The isolation devices were modelled by means of elastic link elements, assigning a linear behavior. The effects of aging were accounted for increasing the shear modulus of the rubber by 15% (G 1a = 1.15 × G 1 = 0.46 N/mm 2 ) [31,32]. Actually, about 12 years have passed from the construction of the building to the seismic events.…”