On a steel engineering structure the checks are three and distinct: how much material is left in the members, whether the weld beads are sound, and how hard the bolts of the connections are really pulling.
- ✓ Remaining thickness of the members measured through the paint
- ✓ Inspection of the weld beads with angle beam probes
- ✓ Measurement of the actual load of the connection bolts
- ✓ Readings stored and comparable between successive inspections
Road and railway structures work under cyclic loads for decades, in aggressive environments and often with difficult access. Knowing the real condition of the structure comes from repeatable measurements, taken at the same points years apart, not from occasional surveys.
Thickness measurement quantifies the loss of section of the members, even through the protective coating. It is the figure that feeds the structural check: without the actual remaining thickness, the calculation rests on the design geometry, which after thirty years in service no longer describes the real structure.
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On bolted connections the ultrasonic measurement of elongation makes it possible to know the actual load of each bolt, and to recognise a loosening in progress by re-checking the same element over time. The condition is having the reference reading with the bolt unloaded, recorded at assembly.
The checks on a steel structure
| Element | Check carried out |
|---|---|
| Beams, chords and diagonals | Remaining thickness, even through the paint |
| Weld beads of the joints | Search for cracks and lack of fusion |
| Bolted connections | Actual load and uniformity of tightening |
| Areas where water stagnates | Localised corrosion under the coating |
| Bearings and restraint areas | Loss of section at highly stressed points |
Repeatability over time
The value of an inspection on an engineering structure lies not in the single campaign but in the series. For the series to mean anything the points have to be identified in a stable way: numbered, marked and called up in the same order, so that today’s reading is comparable with the one from five years ago.
The grid files of instruments with a data logger preserve this structure, and DakMaster™ compares the campaigns, producing the document to be attached to the structure’s file.
Recommended instruments
| Instrument | Typical use |
|---|---|
| Dakota CX8-DL | Remaining thickness of the members with data logger |
| Dakota FX70-DL | Inspection of weld beads in the field |
| Dakota BT1-DL MiniMax | Measurement of the load of the connection bolts |
| Dakota MultiMax | Continuous monitoring of connections under observation |
Frequently asked questions
Yes, with instruments fitted with Echo-Echo mode, which exclude the coating layer and return the thickness of the steel alone.
Only if the reference reading with the bolt unloaded was recorded at assembly and if one end of the bolt remains accessible. Without the initial reference the elongation cannot be derived.
The interval depends on the maintenance plan of the structure and on how aggressive the environment is. What matters from the instrumental point of view is repeating the readings at the same identified points, so that the campaigns remain comparable.
Back to Construction and Infrastructure, or write to us from the Contacts page: describe the structure and the inspection plan foreseen.
Further information and contacts
Systems division and sensor integration partner : www.roder.it
More information about RODER SRL : about us
Contact for general information : info@roder.it
Contact for information about these products : info@roder.it
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