Impedance model for estimating train-induced building vibrations

Abstract

In recent years, the exploitation of over-track construction in populated Chinese cities has resulted in buildings being subjected to potentially disturbing vibrations from rail lines in metro depots. Building owners and engineers are concerned about occupants’ complaints related to structure-borne noise and vibration related to human comfort. Similar concerns exist for laboratory buildings and manufacturing plants that use vibration-sensitive equipment.In Chinese metro depots, the subway trains usually run on the bottom floor of the metro depot and the vibrational energy they generate transmits through the primary building support structures, including columns and load-bearing walls, to the upper floors of the over-track buildings. In order to predict train-induced vibration levels in over-track buildings, a new impedance model is presented. The model accounts for the propagation of axial and bending waves through the columns and load-bearing walls from the foundation into the upper floors. The primary mode of transmission is through higher impedance axial waves across impedance discontinuities at the floors; while the transmission due to bending waves is attenuated more rapidly by the floors. The input for axial wave transmission is the measured vertical vibration levels at the base of the column at the foundation. The contributions from multiple columns/walls into a given floor have been found experimentally to be statistically independent so that the total response of a floor is obtained from a simple energy summation of contributions from all columns/walls where the inputs to each may vary depending, in part, on their distance from the train track.Measured train-induced vibrations at the foundation level and on upper floors in 14-story and 25-story buildings in Shenzhen metro depot were used to validate model predictions of vibration levels at upper floors relative to the foundation vibration. The support structures for both buildings include both columns and load bearing walls where the transmission involves both in-plane shear and dilatation at various angles within the wall though a conclusion from this study is that axial propagation in the vertical direction dominates. The impedance model predictions are in good agreement with the measured floor vibration levels.