Civil Engineering Reference
In-Depth Information
Chapter 10
Using an Instrumented Tractor-Trailer to Detect Damage in Bridges
Eugene J. OBrien and Jennifer Keenahan
Abstract
This paper investigates an alternative to Structural Health Monitoring (SHM) which involves no sensors on the
bridge itself. It uses a vehicle fitted with accelerometers on its axles as a method of monitoring the dynamic behavior of the
bridge, which in turn gives an indication of the bridge's structural condition. The concept, known as 'drive by' bridge
inspection, may be of particular value after an extreme event, such as an earthquake or a flood, where a rapid indication of
bridge condition is needed. In the paper, a two dimensional numerical model is described of a 3-axle truck towing a half-car
trailer. The vehicle-bridge dynamic interaction is modeled to test the effectiveness of the approach in identifying the
structural damping of the bridge. The damping of the bridge is used here as an indicator of damage. The accelerations in the
two axles of the trailer are subtracted to remove the effect of the road profile. Results indicate that the algorithm works well
and is not sensitive to transverse position of the vehicle on the bridge.
Keywords
Bridge monitoring • Bridges • Damage detection models
10.1
Introduction
The task of detecting damage in bridges traditionally consists of visual inspections. These however are labor intensive and
are often an unreliable way of determining the true condition. Recently there has been a move towards sensor based analysis
of bridge condition. Existing monitoring techniques involve the direct instrumentation of the structure - commonly referred
to as Structural Health Monitoring (SHM) [
1
-
3
]. More recently, a small number of authors have shifted to the instrumenta-
tion of a vehicle, rather than the bridge, which can be less expensive and less time-consuming. This approach is referred to as
'drive-by' bridge inspection [
4
]. The feasibility of detecting frequencies from the dynamic response of an instrumented
vehicle passing over a bridge has been verified theoretically by Yang et al. [
5
], in field trials [
6
,
7
] and in laboratory
investigations [
4
,
8
-
10
]. As an alternative to detecting changes in frequency, Yabe and Miyamoto [
10
] use the mean
displacement of the rear axle of a city bus passing over a bridge a large number of times as a damage indicator. Kim et al.
[
12
] construct scaled Vehicle Bridge Interaction (VBI) laboratory experiments and consider the use of autoregressive
coefficients as a damage indicator. The analysis of damping has been considered to a lesser extent [
13
]. However, recent
evidence suggests that damping is quite sensitive to damage in structural elements and in some cases, more sensitive than
other indicators [
14
,
15
].
This paper describes a novel approach that uses a truck-trailer vehicle system, fitted with accelerometers on the trailer
axles, to detect changes in the damping of a bridge which would indicate deterioration of the bridge's condition. The concept
is that the relatively heavy truck dynamically excites the bridge while sensors in the trailer are used to monitor the resulting
vibrations. For numerical simulations, a VBI model is created in Matlab. The trailer axles are assigned identical properties -
as can easily be the case with a simple trailer. The axle accelerations from the front and rear axles of the trailer are
subtracted
from one another. Each trailer axle is excited by the same road profile and by an element of bridge vibration at a different
