The valuable data
delivered by bridge WIM
must be used. A recent
development is a highly accurate
data-grabbing system with up
to 3,000 Hz sampling rate
permanently on 10 channels.
Environmental conditions
such as temperature, humidity
and pollution can severely affect
structures and must be
monitored. For example,
bridges are highly affected
by temperature changes,
a phenomena which affects the
traffic loading stresses on the
structure. Bridge surveys should
also measure deterioration, such
as the breaking of bridge tendons
or reduction of reinforcement
caused by corrosion.
Deformation of the bridge
is clearly a critical factor, and
recently, PSP has developed
its own sensor to measure
curvature to an accuracy within
the milli-radians range. The
advantage is its temperature
independence and low noise
making it suitable for longterm
observations.
The BWIM system is designed
to capture data autonomously
with almost no maintenance.
This demands hardware and
sensors that consume minimal
power, and have an embedded
connection to a WAN. The
Technology Profile |
Abridge’s lifetime depends
Traffic Technology International July/August 2019
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070
on the nature and
frequency of the vehicles
that cross it. If you have accurate
information about a bridge’s
traffic, then you can predict its
maintenance requirements with
greater certainty.
BWIM (bridge-weigh-inmotion)
can improve these
predictions. It uses the bridge
as a weigh-platform and the
parameters of heavy vehicles
are measured to obtain data
that can help to predict the
remaining lifetime of the bridge,
and therefore inform
maintenance decisions.
PSP manufactures several
dynamic measuring systems,
including the BWIM system.
BWIM typically captures data at
1kHz. As the bridge is monitored
continuously, the BWIM builds
up a detailed history of traffic
moving over, and the loading
on, the bridge.
What should be monitored?
In order to model the bridge, we
need to account for the bridge’s
current physical condition, its
environment, loading and
deformation caused by traffic.
Before beginning bridge
analyses it is necessary to have
knowledge of the structure.
Structural health monitoring
(SHM) helps to give a complete
picture and can highlight the
effects of traffic on a bridge.
Once the survey has been
completed, the weight sensors
and measurement plan that are
optimal for the bridge must be
chosen. The mathematical
framework for this selection is
given by Bayes’ theorem. This
helps to ensure the accuracy of
the sensors is appropriate for
the task in hand.
In order to be able to observe
minimal changes in resistance,
very sensitive sensors and
appropriate hardware behind it
| Need to know design must also minimize the
Features of PSP’s
(Petschacher
Software und
Projektentwicklung)
iBWIM system include:
> Assessment of bridge
structures
> Pre-selection of vehicles
planning to travel over
bridge structures
> Providing reports on
structural statuses
amount of data transfer and
optimize the data protocol.
Measuring traffic
Once BWIM sensors are
installed under a bridge they
can measure data like the speed,
axle load and weight of each
vehicle that passes over the
bridge. The BWIM system can
then deliver a report on these
factors, as well as assessing
overall traffic flow. Heavy goods
vehicles can be classified into 67
classes from six groups.
The information acquired
about traffic flow across the
bridge can be used to develop
a load model of the bridge. This,
in turn, can be used to predict
the remaining lifetime of the
bridge and suggest appropriate
maintenance actions. Up to four
influence lines for four traffic
categories, for bridge lengths from
10-50m, can be calculated. The
road surface of the bridge is not
Above: The iBWIM system can
help to increase a bridge’s
lifespan by monitoring its
structural state
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