Suitability of Seismic Isolation for Buildings Founded on Soft Soil. Case Study of a RC Building in Shanghai

Abstract

Base (seismic) isolation is a promising technology for seismic protection of buildings and other constructions. Nowadays, it is accepted that such a technique is efficient and reliable; however, it has two major limitations: soft foundation soil, and tall buildings. The first issue restrains the seismic isolation spreading, given that soft soil is frequent in densely populated areas, and usually such a soil type concentrates the highest seismicity levels. This paper aims to contribute to demonstrating that base isolation, if properly implemented, can be suitable for soft soil. A representative case study is analyzed: a 6-story reinforced concrete (RC) building with base isolation that has recently been built in Shanghai. Since the building is founded on soft soil, concern regarding base isolation suitability arose; even the Chinese design code does not recommend this solution for soft soil. To clarify this issue, non-linear time-history analyses are carried out for a number of natural and artificial seismic inputs that represent the site seismicity; the superstructure behavior is linear, while nonlinearities are concentrated in the isolation layer. The adequacy of base isolation is assessed in the superstructure (in terms of reduction of interstory drift, absolute acceleration and shear force) and in the isolation layer (in terms of axial force, torsion angle and shear strain). The relevance of soil–structure interaction is discussed. The behavior when the mechanical parameters of the isolation units have experienced important changes is also analyzed. The major conclusion is that base isolation of ordinary mid-height RC buildings founded on soft soil can perform satisfactorily in medium seismicity regions.

Application of Mode-Adaptive Bidirectional Pushover Analysis to an Irregular Reinforced Concrete Building Retrofitted via Base Isolation

“…It should be mentioned that the foundation compliance and kinematic soil-structure interaction were not considered for the simplicity of the analysis. Almansa et al [60] investigated the performance of a rubber-isolated six-story RC building in soft soil. They concluded that the soil-structure interaction effect is rather negligible in the case of isolated buildings.…”

Two-Stage Optimal Design Method for Asymmetric Base-Isolated Structures Subject to Pulse-Type Earthquakes

“…The growing popularity of the seismic isolation technology is primarily attributed to its ability to isolate the majority of the energy from earthquakes by extending buildings' natural period [1][2][3]. However, recent research suggests that the efficacy of isolators diminishes under long-period pulse-type earthquakes [4][5][6][7].…”

Investigation on the Seismic Performance of RC Frame Buildings with Rubber Isolation Bearing Installed in Staircases

“…By comparison with the conventional seismic design approach, which is based on an increased strengthening of the structures, the seismic isolation concept is aimed at a significant reduction in dynamic response induced by the earthquake. To date, extensive isolation devices, including rubber bearings (RB), lead plug rubber bearings (LRB), frictional-sliding bearings, and roller bearings, have been developed [19][20][21][22][23]. Though those isolation bearings have been applied to the area of base isolation, the application of the seismic isolation devices into the staircases is still rare.…”