Bridge Weigh-in-Motion

Bridge weigh-in-motion (B-WIM) is the process by which axle and gross vehicle weights of trucks travelling at highway speeds can be determined from instrumented bridges. B-WIM systems involve attaching strain transducers to the soffit of a bridge and placing sensors for detecting axles in order to provide information on vehicle velocity, axle spacings and position of each vehicle. This is done either with axle detectors on the road surface axle detectors or by placing additional strain transducers under the bridge. This is called Nothing-On-the-Road (NOR) or Free-of-Axle Detector (FAD) B-WIM system.

As the measurements are performed through the period in which the whole vehicle is passing over the structure, the system is less influenced by dynamic effects. Bridge WIM systems also provide information about impact factor, lateral distribution factor and strain records which are used for further bridge analysis.

In Europe, extensive research was under way in the late 1990's as a part of the WAVE project. Work on the further development of B-WIM was focussing primarily on increased accuracy for typical bridges, extension of B-WIM to various types of bridges, on dynamic analysis of typical bridges and on calibration procedures.

Today Bridge WIM is due to its unique features regaining popularity and is a well established WIM technology that is used in many European countries, in India and in Canada. Their main advantages are:

full portability: all equipment can be detached from one site and be in a few hours installed on another site,
high accuracy of results: long weighing platform (entire length of the bridge) proves beneficial in dealing with dynamic vehicle loading,
swift installation an maintenance: no need for stopping the traffic and no direct contact with pavement,
price efficiency.

BRIDGE WIM and BRIDGE APPLICATIONS OF WIM - what is the difference?

This is a question that B-WIM people are asked a lot.

Bridge WIM is the process described above where an existing bridge is used as a WIM system. The resulting data can be used for any WIM application such as pre-selection of overweight trucks for static weighing, pavement design/assessment or bridge design/assessment.

In bridge applications of WIM, the WIM data can be collected using any WIM technology such as bending plate or strip sensors or bridge WIM. The resulting traffic data is being used for the assessment of loading on bridges. Nevertheless, if B-WIM system is installed on the bridge, which is assessed, it can provide additional usefull information about the behaviour of the structure (influence lines, Dynamic Amplification Factor, distribution of loads, strain records etc.).

Last updated on 17^th of July, 2006, by A.Znidaric