Indirect Methods for Evaluating the In-Situ Performance of Building Base Isolation

Abstract

Mitigation measures against railway vibration in buildings include elastomeric mounts or springs inserted between building foundations and upper-structures. This paper aims at evaluating on site the field performance of such building base isolation. Two performance indicators are defined and used, both expressed as insertion gain: a Power Flow insertion Gain (PFIG) based on the power transmitted to the building upper-structure, and a Building Insertion Gain Indicator (BIGI) based on the building floor velocities. The paper shows that both indicators can be used to evaluate the field performance of base-isolated buildings: the PFIG can be indirectly obtained from local measurements of the isolator transmissibility and some knowledge of the mobility magnitudes of the building structures in contact and the BIGI indirectly obtained from measurements of the treated building transmissibility (as defined in ISO/TS 14837-31) and some knowledge of the transmissibility of similar but untreated buildings. The methods are successfully validated using a numerical model of a 2D ground-building configuration easy to calculate and assumed realistic enough. The paper ends with a discussion on the practicality of obtaining these performances on- site in real buildings.