Monitoring Bridge Dynamic Behaviour Using an Instrumented Two Axle Vehicle

Highway structures such as bridges are subject to continuous degradation primarily
due to ageing, loading and environmental factors. A rational transport policy must
monitor and provide adequate maintenance to this infrastructure to guarantee the
required levels of transport service and safety. Increasingly in recent years, bridges are
being instrumented and monitored on an ongoing basis due to the implementation of
Bridge Management Systems. This is very effective and provides a high level of
protection to the public and early warning if the bridge becomes unsafe. However, the
process can be expensive and time consuming, requiring the installation of sensors
and data acquisition electronics on the bridge. This paper investigates the use of an
instrumented 2-axle vehicle fitted with accelerometers to monitor the dynamic
behaviour of a bridge network in a simple and cost-effective manner. A simplified
half car-beam interaction model is used to simulate the passage of a vehicle over a
bridge. This investigation involves the frequency domain analysis of the axle
accelerations as the vehicle crosses the bridge. The spectrum of the acceleration
record contains noise, vehicle, bridge and road frequency components. Therefore, the
bridge dynamic behaviour is monitored in simulations for both smooth and rough road
surfaces. The vehicle mass and axle spacing are varied in simulations along with
bridge structural damping in order to analyse the sensitivity of the vehicle
accelerations to a change in bridge properties. These vehicle accelerations can be
obtained for different periods of time and serve as a useful tool to monitor the
variation of bridge frequency and damping with time.