# Comparative Accuracy Analysis of Truck Weight Measurement Techniques
## 2 Material and Methods
### B-WIM Instrumentation  
The B-WIM measurement technique relies on using the space under a bridge to install measuring devices to not interfere with the flow of traffic measurements. It requires the installation of necessary instruments. The bridge's selection was based on its proximity to the Cleburne truck weigh station and a WIM station. The bridge located at kilometer 327.242 of interstate highway I-20 in Cleburne County, Alabama, was selected. The exact location of the bridge is 33\({}^{\circ}\)38\({}^{\prime}\)12.5\({}^{\prime\prime}\) N 85\({}^{\circ}\)31\({}^{\prime}\)46.8\({}^{\prime\prime}\) W. The bridge was built in 1970, and it consists of 11 spans, eight of them are reinforced concrete, and the remaining three are steel girders. The total width of the bridge is 13.28 m, and its total length is 132.6 m. Figure 2 presents the side view of the instrumented bridge. The utilized measurement system was a portable bridge weigh-in-motion (B-WIM), of which more information about it can be found in [28]. The B-WIM was installed and calibrated on the bridge, and the scheme of the B-WIM installation is shown in Figure 3. The B-WIM is measuring set consisted of the following elements: ten strain transducers ST-503, one temperature sensor STS-13, two distributor collectors (spiders) SSP-83, one external router EXR-03, one camera, one equipment cabinet with an SPU-23 processor unit equipped with SAM-43 amplifiers, CTU-03 control unit, GCP-33, and SPS-23 power supply, 12 V battery with charger, and one power cell cabinet with an ethanol power generator. The sensors were installed in a tension zone of the slab and beams. The strain transducers ST-503 were equipped with four strain gauges. The deformation from the extensometer was transformed into an electrical signal and sent through the distributor manifold SSP-83  
Figure 1: Considered truck weigh systems: (**a**) overview, (**b**) specific locations ([[https://www.bing.com/maps](https://www.bing.com/maps)]([https://www.bing.com/maps](https://www.bing.com/maps))). to the SAM-43 amplifiers. The amplifiers were installed in the SPU-23 processing unit. The signals were continuously recorded during the measuring period of three days, and the signal offsets occurred due to the extreme amplification of signal and temperature effects. If offset exceeded predefined thresholds, the signal was nulled. A STS-13 temperature sensor was used during measurements. The weight of a passing vehicle was calculated based on recorded deformations adjusted for the thermal material deformations; the calibration was necessary to set the specific material parameters and arrange a sensor suitable for a particular bridge structure. The layout was adjusted for two lanes and selected girders (Figure 4a,b). Figure 3: Scheme of the measuring apparatus arrangement. Figure 2: Side view of the bridge. The ST-503 sensors located under the girders measured the weight of individual vehicle axles, while the sensors situated directly beneath the deck measured the number of axles and vehicle speed. A simplified measurement scheme is shown in Figure 5. The strain transducers were bolted into steel anchors on the bottom surface of selected elements. Six sensors were attached to all beams and four directly to the bottom side of all beams (6 sensors). The whole measurement process was fully automated and worked almost maintenance-free. Thanks to the use of batteries and power generators, it could also operate in areas where it is not possible to connect it to a stationary electrical supply. The power generator was automatically started when the battery power decreased below the defined minimum level to recharge it. As a result, the service consisted almost exclusively of periodic refueling, every 20 days, for the power cell, which in this case ran on ethanol. For remote transmission and access to a collected data, the measuring set was also equipped with an external router EXR-03. It enabled data transfer and constant control over the system.