ABSTRACT
Indirect approaches are referred to as those methods in which dynamic properties of bridge structures are inferred from the dynamic response of a passing vehicle. Such an approach is low cost and is aimed at reducing the need for any direct installation of sensing equipment on the bridge itself. The measured vehicle response needs to include relatively high levels of bridge dynamic response arising from vehicle-bridge interaction (VBI). In the case that only bridge frequency is required, the indirect approach has many advantages in comparison with direct methods in terms of equipment needed, specialist personnel on-site, economy, simplicity, efficiency, and mobility.
This paper summarizes these approaches and provides recommendations for future development. It also helps readers in understanding and implementing the available bridge damage identification algorithms and signal processing methods based on the dynamic response of a moving vehicle.
Generally indirect bridge monitoring methods can be divided into two main groups; bridge identification methods and bridge damage detection (Fig. 1). The main purpose of the first group is to identify the bridge modal parameters (natural frequencies, damping ratios and mode shapes). The second group exists of methods to detect bridge damage using the response measured on a passing vehicle. Summary of indirect bridge monitoring methods. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig79_1.tif"/>
Most of the reviewed methods in this paper can be explained based on the main component of the vehicle response. In most of the studies considered, the vehicle speed is assumed to be constant. In practice, it may not be easy to maintain this during the vehicle crossing. This factor becomes more significant when the signals of two axles are subtracted to minimise the influence of road profile. Therefore, speed variation should be investigated in future studies. On the other hand, temperature/environment can have a significant effect on most damage indicators and this influence is difficult to distinguish from real damage. This can be addressed by instrumenting vehicles that travel on the same route frequently as this allows environmental effects to be averaged out (Malekjafarian et al., 2015).
In summary, the main challenges for indirect bridge monitoring methods are:
The road profile.
The limited VBI time.
Environmental effects.
