GROUNDBORNE NOISE AND VIBRATIONS IN A BUILDING DUE TO MASS RAPID TRANSIT TRAIN PASSBYS

Abstract

A finite element model has been developed to predict levels of groundborne noise and vibration in the podium black of the Chartered Bank Building caused by transit train passbys in underlying subways. The model provides an analytically-consistent account of the complex subway-soil-building interaction problem, unlike the case of current highly-approximate empirical models. Furthermore, the train loading spectral input to the model has been computed via a mathematical procedure to simulate actual loading more closely than these empirical models which adopt measured vibration response envelopes on relatively few existing transit systems as input. Groundborne vibration and noise levels in the podium from two alternative track systems, namely direct fixation and floating slab tracks, have been determined. Groundborne vibration levels for direct fixation tracks have been found to fall well within limiting vibration criteria for office use. However, sound levels on the podium could be intrusive. On the other hand, floating slab tracks produce sound levels well below limiting noise criteria for offices, but when the resonant frequency of the floating slab approaches that of certain spans of the open banking floor, vibration levels may possibly exceed limiting vibration criteria. When train speeds are reduced, train loading spectrum from either track systems and corresponding groundborne vibration are reduced for all frequency components. Increased damping ratio of elastomer pads supporting the floating slab, on the other hand, only reduces the train loading spectrum and corresponding groundborne vibration for frequencies around the resonance frequency of the floating slab system. The effects of these parameters on sound levels generated have also been examined.