WEIGH - IN – MOTION: RECENT DEVELOPEMENTS IN EUROPE
ICWIM`s Committee
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Pan-European and national projects are reported plus
developments in sensor technologies and system design. Recent
developments in multiple-sensor WIM systems are given particular
attention. The coming of prototype fully-automatic overload systems is
discussed and the technologies and legal framework necessary for their
success. The commercialization of Bridge WIM in Europe since the ICWIM3
is considered and the continued development of this technology towards
almost maintenance-free systems. WIM applications are also discussed
including pavement and bridge design and assessment. (B. Jacob, E.J.
O’Brien)
THE USE OF FUNCTIONAL NETWORKS TO OPTIMISE THE ACCURACY OF MULTIPLE –
SENSOR WEIGH-IN-MOTION SYSTEMS
The accuracy of multiple-sensor weigh-in-motion systems
is severely limited by the magnitude of noise and vehicle dynamics.
Neural networks have been recently tested for removing noise and
identifying patterns of spatial repeatability. However, this technique
might require an impractical number of statically weighed trucks for
calibration/training. This paper proposes the use of functional networks
as an alternative to neural networks. Unlike neural networks, which are
"black boxes", functional networks arise directly from the equations
governing the weigh-in-motion problem. The functional network equations
are taken from given families of functions. The function parameters are
calculated during the learning process and adjustment of scalar
"weights" is not necessary. Vehicle simulations are used to show the
potential of this approach. (A. González, E.J. O’Brien)
BRIDGE WIM BY REACTION FORCE
METHOD
When a truck runs over the bridge, sharp edges occur in
the reaction force response wave. The amount of the edges corresponds
linearly to independent axle loads. Instrumentation is carried out at
both sides of a bridge. Velocity of trucks can be estimated through
comparison with edge patterns in the two reaction forces. Simple
supported steel plate girder bridges with no skew angle are suitable for
this method. Strain gauges are attached on end vertical stiffeners just
above bridge supports. This paper describes the methods principle, its
accuracy, and results of the 168 hours` truck load monitoring. (T. Ojio,
K. Yamada)
SLOVENIAN EXPERIENCE OF USING WIM DATA FOR ROAD PLANNING AND MAINTENANCE
A demonstration of
graphical and numerical data gathering
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Over the last three (3) years a network of 30 WIM sites
has been established in Slovenia to cover all major routes of the main
state road network with portable bridge WIM system. Results of
measurements revealed that everywhere the real traffic loading was
higher than if calculated according to the Technical specifications for
traffic loading. Furthermore, overloading turned to be a serious problem
and thus WIM system were used also to select locations and periods for
static weighing control with police. Consequently, a high-speed WIM
enforcement procedure is being discussed. A study based on measured WIM
data showed that when applying appropriate tolerances of WIM system the
sum of overloading fines could exceed 300 million Euros per year which
is approximately 30 times more than it is collected at present from
static weight controls. Unfortunately, the present legislature in
Slovenia does not allow yet using weigh-in-motion data for direct
enforcement of the overloaded vehicles. (R. Brozovič, A. Žnidarič, V.
Vodopivec)
NOTHING-ON-THE-ROAD AXLE DETECTION WITH THRESHOLD ANALYSIS
As any other weigh-in-motion system,
the bridge WIM requires information about axle spacing to successfully
calculate the axle loads. On some bridges this axle spacing information
can be obtained from the strain signals measured at specific locations
under the bridge rather than from the conventional axle detectors. After
the first successful attempts of a Free-of.-Axle Detector bridge WIM
system at the end of last century, further developments is needed before
such procedure, also known as NOR (Nothing-On-the-Road), could have been
used for real long-term measurements. The paper describes the method
which first cross-correlates the measured strain signals from two
different longitudinal positions to obtain accurate estimate of its
velocity. Then they are processed and optimized to define the exact
number and spacing of the axles. Efficiency of this robust method is
illustrated with results from a short span slab bridge and a longer
beam-deck bridge. Successful implementation of the new improved
algorithm resulted in almost 50% of all WIM installations in Slovenia
(around 20 bridges every year) being of the NOR type. (A. Žnidarič, I.
Lavrič, J. Kalin)
