Evaluation of the In-Situ Performance of Base Isolated Buildings

Mitigation measures against railway vibration in buildings can include elastomeric mounts or springs inserted between building foundation and building upper structure. The method for predicting the performance is usually simplistic and based on the dynamic transmissibility of a single degree of freedom mass-spring oscillator on a rigid base. One method is to express the isolation performance as an insertion gain based on the building floor velocities. It is named the Building Insertion Gain Indicator (BIGI). Another method, called the Power Flow Insertion Gain (PFIG), has also been proposed in [1]. Then, the isolator performance is expressed as the difference of injected power to the building upper structure. In practice, both indicators need two identical buildings (with and without isolator) to be obtained automatically. A method to indirectly obtain the PFIG, using only an isolated building, has been developed and numerically validated for a 2D case in [2, 4]. It is based on the isolator transmissibility (ratio of velocities on both sides of the isolator) that is corrected with foundation and upper structure mobilities. In this paper, the theory is extended to a construction near railway tracks after being validated through comparisons between experiments and simulations. In this case, the isolator transmissibility and foundation mobility are measured. As the upper-structure mobility cannot be measured, it is obtained with a 2.5D simulation. Finally, it is compared to the other methods of evaluating isolator performance.