The bending plates are installed in foundation frames flush with the pavement surface. Recesses for the frames are 50 mm deep in the bearing area and about 100 mm in the centre for cables and drain. One weighing threshold with three small plates is 3775 mm wide and two large plates are 3525 mm wide. Both measure 650 mm in the driving direction.
In single threshold applications the speed is usually measured with two induction loops, one on each side of the threshold. The induction loops are 2000 mm wide and 4000 mm long, spaced 1000 mm (cut is 175 mm on either side of the frame).
The maximum unevenness of pavement level under a 6 m straight edge is 3 mm. This is checked with a disc 150 mm in diameter and 3 mm thickness. ASTM-E1318 recommends a certain procedure for starting and progressing with the straight edge. The disc should not pass under the straight edge within 60 m before and 20 m after the scale. The most critical point of the check is 20 m before the scale. At 50 m the impact of unevenness is about 1/10 of that at 10 m. Grinding high spots is preferred over filling of depressions. ASTM-E1318 also suggests marking pavement sections 'pass/fail'; however, it is more useful to state the actual unevenness in mm using a special gauge.
Sufficient personnel with a team of three construction workers and a specialist from the supplier should be scheduled for the installation of one WIM lane with bending plates per day (or night). A group of six experienced people can install two lanes per shift of eight hours. Personnel for traffic control are additional.
Planning and coordination with installation teams for power and phone is mandatory. A digger who could dig and lay the duct for the sensors at the same time is required. The digger can move more freely and save cost on additional shoulder closure with the lane on the cabinet side closed for sensor installation.
The following equipment is required for the installation of the bending plate:
- Construction equipment and tools as per the installation manual for a bending plate include: concrete saw, jack hammers, compressor, rock drills, propane torch, putty knives, trowel, mixing paddle, torque wrench 19 mm, buckets, brushes, industrial vacuum cleaner, set of electrician tools, fish tape and small water tank. A digger may be required for the trench to the cabinet as well as lifting equipment for the cabinet.
- All WIM equipment including two or three frames completed, bending plates, electronics, cabinet, power supplies, modem and surge protection.
- Installation material: two-component epoxy, silicone sand filler, silicone sealant, premixed mortar, ground cable and connection terminals, loop wire and sealant, ducts.
Complete installation procedures are available from the manufacturers.
The following briefly outlines the procedure:
- Recess for the frames, drain and cable duct are marked, cut with a concrete saw and broken out with jack hammers.
- Anchor holes are drilled with 25 mm rock drills.
- After the pit is cleaned and checked small walls are built to retain the grout (epoxy) in the bearing area until it has hardened. Then the two-component epoxy (plus filler) is mixed and poured into the bearing area.
- The frames, suspended at the correct height, are lowered into the pit. Anchors are inserted and excessive epoxy is removed. Epoxy is heated up to about 45 degrees for faster curing.
- Ground connections are made between frames, ducts for cable and drain are laid, and recesses over ducts filled with cold mix and compacted.
- Once the epoxy is cured, bearing rails are inserted. Weigh pad cables are pulled in and weigh pads lowered into the frame. Levels are checked and height adjusted if necessary with thin shims.
- Fastening rails are inserted and fastened with lock nuts. Any gaps are filled with silicone.
- Parallel to the weigh pad installation the loops are cut, laid and sealed.
- The lane can be opened for traffic.
The figures below illustrate a pavement cutting area for bending plate installation, and a bending plate site before and after installation.
Figure: Pavement cut for bending plate installation
Source: TMR 2008a.
Figure: Bending plate site before and after installation
Source: TMR 2008a
PAT DAW 100 bending plate installation and operation
International Road Dynamics 2007, ‘Operational manual Australia PAT DAW 100’, International Road Dynamics, Saskatoon, SK, Canada.
EastLink bending plate installation, operation and maintenance
Electronic Load Weighing Co. of Australia 2008, ‘Operational and maintenance manual for Eastlink Victoria PAT DAW100 weigh-in-motion system’, Electronic Load Weighing Co. of Australia, NSW.
Electronic Load Weighing Co. of Australia 2008, ‘Eastlink, Victoria weigh-in-motion system installations: installation and commissioning manual’, Electronic Load Weighing Co. of Australia, NSW.
Electronic Load Weighing Co. of Australia 2008, ‘Installation instructions stationary weigh pad and 69’’/1.75 M frame’, Electronic Load Weighing Co. of Australia, NSW.