Hi Charlotte,I suspect that both Grants Commissions are/were trying to say something along the lines of "water course crossings with a span of greater than 6m along the centreline of the intersecting road carriageway should be counted as bridges for the purposes of grants commission reporting, irrespective of whether they are true bridges or multiple culverts laid side by side", and that they coined the term "major culvert" to act as a short hand description of these multiple culverts.As you say there is a big difference between a single 300mm culvert under a road and three 1800mm culverts laid side by side, but the Grants Commissions role is to develop funding formulas so they were probably thinking about the cost of water course crossings, not safety and inspection regimes when they adopted the 6m span to define what should and should not be reported on.Having said all that, the really interesting part of your question for me is, how often terms get used without being properly defined, and how much confusion could be avoided if more terms had proper definitions that everyone across all jurisdictions could agree on and use.The question I guess becomes who should be responsible for getting terms properly defined and where they should be documented.You mentioned the LGAM Knowledge Base and I do my best to document every definition I can find there, but what would be ideal is an "All Levels of Government Wiki" where definitions could be thrashed out and agreed on over time . I believe it would make everyone's lives much easier.Regards,Wayne.
Hi Charlette and Mates,
From my experience, most (if not all) State road authorities in Australia define Major Culverts as structures that have a span, height or diameter greater than 1.8 metres and a waterway area per single cell in excess of three (3) square metres, Austroads suggests 3.4 square metres.
I'm presuming this position has been adopted so that culverts of this size or greater are large enough to:
Any single cell culvert greater than six (6) metres along the centre line of the crossing would typically be classed as a bridge.
Not sure how the Grants Commission would view this approach in light of the "…greater than six (6) metres in length (measured along the centre line of the carriageway)" requirement that local government has to interpret.
Hope this helps.
'major' culverts. i.e. meeting the following criteria:− metal culverts (steel and aluminium): at least one barrel (cell) with span, height or diameter ≥1.2 m, or
−all other culverts: pipes with at least one barrel (cell) with diameter ≥1.8 m, or
rectangular/oval/arch culverts at least one barrel (cell) with span > 1.8 and height > 1.5 m.
stock and pedestrian underpasses
These culverts typically have an opening large enough to:
• access without specialist equipment and are therefore capable of being inspected relatively easily.
• close the road and create a significant safety hazard in the event of structural failure.
I hope this helpsRegardsKevin Chambers
The definition appears to vary depending on context, which is hardly surprising in a local government setting.
Fraser Coast was audited by the Queensland Grants Commission in 2017, specifically including the major/minor culverts and the definition of that. Previously we worked on the general assumption of the 6m of road length as measured in the waterway, i.e if the maximum width of water flowing under the road was 6m or greater it was a major culvert.
For your information, below is the definition as returned to Fraser Coast from the Qld Grants Commission. Our data is now structured to this definition to support generating data for the yearly return.
The key is the last part of the definition we provide in the data collection:
"... Number of major culverts which council has responsibility for, of six (6) metres and over in length, measured along the centre line of the carriageway, from the interfaces where the road approach meets the culvert."
So I've always taken that to mean the length of road that covers the whole structure – i.e. I wouldn't object if they counted the wingwalls on the end of the structure as well.
In the image above, the red line is the 6m length we originally built our data on. The blue line is the 6m dimension we were shown by the auditor to use for the Grants Commission. There are some situations in our network where the headwall distance as shown is quite long, say 20-30m, but only has a couple smallish pipes along it's whole length which wouldn't have flagged for us before.
While this is great for the Qld Grants Commission clarity, it doesn't help me as neatly with doing inspections. Our culvert network is poorly inspected and we have been pushing the level 1 and 2 bridge inspections to also include major culverts in the yearly routine. However, I also took the point of view that major culverts formed of a mass of 375RCPs to be a lower risk asset. At this point in time my yearly major culvert inspections cover all boxes or pipes with a height of 900mm or higher which I take to be a reasonable base level of risk, until each culvert set is assessed for risk in its locality context. I seem to recall when I checked the Qld MRD guide it was a much bigger pipe size before they did inspections, I can't remember if it was 1200, 1500 or 1800, but I took 900 to be enough of a risk as a starting point, considering that they have never been routinely inspected at all in our network.
While so far I'm focused on major culvert inspections, I believe once we move to minor culverts we'll have to also routinely inspect smaller culverts which may be formed of say a single 3x3 RCBC. How small that single culvert is before it comes down to longer inspection processes (3-5 years instead of yearly), I've not really thought too much about, as inspecting lone 900RCPs across the network is pretty onerous.
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Interesting discussion about the definition of a major culvert vs bridge. This may provide some background. The definitions on bridge and culverts were I believe based on traffic loading standards and not waterway capacity.
Firstly, in relation to the Grants Commission definition of 6 metres span for a bridge. Most State Road Authorities had standard drawings for timber bridges and for example the Country Roads Board in Victoria entry standard for a 12-foot-wide bridge to take Class 'A' loading was 16-inch stringers spanning 21 feet. Anything shorter than this was classified as a culvert. The Grants Commission collects data on this to monitor the number of timber bridges and there 6 metres correlates with the old standards for timber bridge construction. My understanding is that the number they collect has no bearing on the actual grant commission formula, however it does assist the National understanding of this deteriorating asset class.
In relation to culverts there is an established Australian Standard AS1597 which is utilised by the precast industry to manufacture "Small Box Culverts" up to 1200mm x 1200mm. Water cross section of 1.44 m2. This equates to a 1350mmm Nominal diameter pipe. For larger span box culverts the State Road Authorities prescribed the design to manufacture utilising traditional reinforced concrete design methods.
The distinction between small and large was largely determined by factory load testing facilities. The smaller culverts were manufactured to performance standards whereas as larger units were to prescription standards.
From an Asset Managers perspective Box Culverts should follow the definition of the Australian Standard as the smaller units were for many years constructed to different standards to those 1500mm span and greater and may have different useful lives.
For simplicity I would classify pipes to 1350mm as small and pipes 1500mm and larger as major. There maybe someone out there with a 1425mm pipe (yes - they did make them). Then make your call although a waterway area of greater than 1.5 m2 would classify them as major.I hope this helps clarify your thoughts.
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