Marshall Day Acoustics was commissioned to evaluate the vibration impact of an over rail development at the western end of the Southern Cross Station in Melbourne. The proposed development consisted of two schemes; one high rise and one low rise that were each constructed on a deck supported by pairs of Y shaped columns along the centreline of the suburban and freight rail line platforms below.

As the main transport hub for Melbourne, the Southern Cross Station is the focal point for all suburban rail, country rail and freight transport activity, and there are many hundreds of train movements per day, which have the potential to cause excessive vibration and structure-borne noise.

Most information on the attenuation of rail vibration into structures is based on conventional crash wall designs. 664 Collins Street, the proposed design was unique for which no technical data was available. As a result, Marshall Day Acoustics was commissioned to undertake a finite element (FEM study) to determine the amount of vibration transmitted from the rail into the deck above.

For this project, a conventional crash wall, for which site attenuation data is available, was modelled. This enabled a comparison to be drawn between the two finite element models of the crash wall and the proposed structure for 664 Collins Street. In addition, given the element data available for crash walls the appropriate scaling between the two finite element models were used to determine the vibration attenuation between the ground and the deck, approximately 16m above ground level.

Following the modelling of the deck support structure, a model was also prepared of the low rise scheme which consisted of three car parking levels and eight office levels. The Collins Street Concourse deck extends almost an entire city block. As a result, the proposed development is substantial, and given the importance of the potential clients for this site, concerns with regard to train vibration and structure-borne noise were a major issue.

Marshall Day Acoustics was able to demonstrate, that structure-borne noise and vibration could be controlled. Whilst vibration on the deck level was perceptible with higher than permissible levels of structure-borne noise, the three levels of car parking provided sufficient attenuation to reduce the vibration and structure-borne noise.

A subsequent survey on the constructed deck enabled a comparison to be made between the Marshall Day Acoustics' predicted vibration levels and the actual measured levels. Overall a net comparison between the two sets of vibration data showed good agreement in the overall vibration levels and structure borne noise levels within the occupied levels of the 664 Collins Street building. This exercise demonstrated Marshall Day Acoustics' ability in rail vibration assessment, finite element and structure borne noise prediction to the satisfaction of potential prestigious clients occupying this major development site.