Bewes, Oliver Guy
The calculation of noise from railway bridges and viaducts
University of Southampton, Insitute of Sound and Vibration Research,
Pandrol Rail Fastenings Limited are a designer and manufacturer of railway rail-fastening
systems. As an organisation they have the capability to reduce the noise impact of bridges
using resilient track components. They also have a commercial interest in providing such
technology. Knowledge of the processes behind bridge noise is important to Pandrol in two
ways; to aid the engineers within the organisation in the design of fastening systems and to
demonstrate a state-of-the-art understanding of the problem of railway bridge noise to
customers, as this will aid in the sale of Pandrol products.
The fitting of new rail components to an existing track form, or failure to meet noise
regulations with a new track form, can be costly. It is important to be able to predict
accurately the effectiveness of noise reduction techniques. Currently, Pandrol’s knowledge
of the problem consists almost entirely of experience gained and data gathered while
working on existing bridge projects.
To expand their knowledge base, Pandrol perform noise and vibration measurements on
railway bridges and viaducts and then use the measured data to predict the performance of
their systems on other bridges. This completely empirical approach to predicting bridge
noise is both costly and situation specific results cannot be provided before the installation
of the fastening system.
Another approach to predicting bridge noise is through the application of analytical
models. Limited analytical modelling in the context of bridge noise is currently conducted
within the organisation. For these reasons, Pandrol are sponsoring research into bridge
noise in the form of this EngD project.
Here an existing rapid calculation approach is identified that relies less on the exact
geometry of the bridge and more on its general characteristics. In this approach an
analytical model of the track is coupled to a statistical energy analysis (SEA) model of the
bridge. This approach forms a suitable basis from which to develop a better model here by
concentrating on its weaknesses.
A mid-frequency calculation for the power input to the bridge via a resilient track system
has been developed by modelling the track-bridge system as two finite Timoshenko beams
continuously connected by a resilient layer. This has resulted in a power input calculation
which includes the important effects of coupling between the rail and bridge and the
resonance effects of the finite length of a bridge.
In addition, a detailed study of the frequency characteristics of deep I-section beams has
been performed using Finite Element, Boundary Element and Dynamic stiffness models. It
is shown that, at high frequencies, the behaviour of the beam is characterised by in-plane
motion of the beam web and bending motion in the flange. This knowledge has resulted in
an improved calculation for the mobility of a bridge at high frequencies.
The above improvements are included in an improved model for use by Pandrol in their
general activities. Data from real bridges is compared to predictions from the improved
model in order to validate different aspects of the model. The model is then used to study
the effect on noise of varying many bridge design parameters. It is shown that the
parameter that has most influence on the noise performance of a bridge is the dynamic
stiffness of the resilient rail fastening system. Additionally it is demonstrated that for a
given bridge and noise receiver location, an optimum fastener stiffness exists where the
noise radiated by the bridge and track is at a minimum.
||University of Southampton
||17 Apr 2009
||18 Apr 2017 21:46
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