Author(s): Moschen Lukas, Fink Josef, Suppin Patrick, Achs Günther, Weiß Bernhard
In urban areas infrastructure systems such as rail tracks represent probably the most important backbone in terms of transportation requirements of a society. Nowadays, vehicles of e.g. commuter trains are tuned to meet comfort criteria for the passenger. In dense populated areas it is very likely that residents and facilities are close to rail tracks. Hence, there is the need to evaluate (i) vibration criteria and (ii) noise limits to assure that human beings are not disturbed and/or to satisfy the serviceability of sensitive equipment in facilities. Codes and guidelines provide the engineer with a relative simple framework to evaluate comfort criteria. However, for assessment of sound radiation of railway bridges simplified procedures often yield unreasonable predictions, and subsequently leading to questionable proposals for acoustic upgrading. To understand this, consider a train running over a bridge. It is very common in acoustic engineering to represent sound radiation of a bridge by an equivalent line source. Therefore, the sound level obtained from an ordinary straight track (i.e. not on a bridge) serves as a reference measurement, which will be amplified to represent the equivalent line source of the bridge. This methodology may be reasonable to estimate sound levels in the far field. Acoustic upgrading of the bridge, however, requires careful examination of the source of sound radiation. Hence, it is reasonable to separate between (i) primary sound radiation associated with the vehicle, and (ii) secondary sound emission due to vibration of sensitive members of the load bearing bridge. Focus in this paper is on the latter, more precisely on a novel methodology to estimate the probabilistic distribution of structure borne sound of railway bridges. Consequently, the engineer is in the position to consider dynamic properties of the bridge to estimate structure borne noise, and required acoustic upgrade strategies more reliable.
Name: Dr Lukas Moschen