GDE collapses onto Barton Highway

johnboy 17 August 2010 128

[First filed: Aug 14, 2010 @ 15:54]

Bridge collapse

The Canberra Times brings word of a new and sorry twist in the tail of the Gungahlin Drive Extension with a major collapse of the new work over the Barton Highway:

Firefighters have freed a man trapped under a section of the Gungahlin Drive extension that collapsed this afternoon. Stage two of the extension has collapsed onto the Barton Highway while construction work was underway around 2pm.

Everyone on site at the time of collapse has been accounted for. The Emergency Services Agency said paramedics treated 15 people at the scene, and 10 would be taken to hospital in stable conditions.

More as it comes in. If you have pictures please send them in to images@the-riotact.com

UPDATE: The ESA has this to say:

3:10pm Saturday 14 August 2010 – Update two – no serious injuries 15 people being assessed on scene by intensive care paramedics with up to 10 to be transported to hospital in a stable condition.

No critical injuries at this time.

2:35pm 14 August 2010 – Update person freed One person confirmed trapped on scene has been freed by firefighters.

2:15pm Saturday 14 August 2010 – Report of construction collapse ACT Ambulance Service and ACT Fire Brigade responding to reports of a construction collapse on the Barton Highway Gungahlin.

Update to follow

FURTHER UPDATE: This grim warning on the traffic implications from the ESA:

4:10pm Saturday 14 August 2010 – Final update on partial bridge collapse ACT Ambulance Service has transported a nine patients to the Canberra Hospital in a stable condition with minor injuries following a partial bridge collapse on the Barton Highway Gungahlin.

The section of bridge that collapsed was under construction adjacent to an existing bridge.

The injuries range from limb to suspected spinal.

A total of 15 patients have been assessed on scene by intensive care paramedics.

One man was trapped for around 15 minutes until he was rescued by firefighters.

The ESA was alerted to the incident just before 2 o’clock.

The road is expected to remain closed for quite some time.

ANOTHER UPDATE: The ABC has word from roads supremo Tony Gill:

“Our initial advice is that it could take up to two weeks before we are in a position to remove the debris and get the road open for public use,” he said.

“We are getting an independent engineer’s report just to get an understanding of how the bridge collapsed and secondly we need to engage a demolition contractor to remove the debris.

“But we also have to make sure it is safe for that demolition contractor to go in and remove the debris.”

ONE MORE UPDATE FOR THE ROAD: The TAMS websites has this morning (16 August) put up a statement dated 14 August on the road closures (file data says it was created this morning):

The ACT Government wishes to advise motorists and other road users that Barton
Highway, at its intersection with Gungahlin Drive, is closed (in both directions) until further
notice.

Barton Highway (Northbound): All northbound traffic will be detoured via Gungahlin Drive, Ginninderra Drive, Baldwin Drive and William Slim Drive to reconnect with Barton Highway.

Barton Highway (Southbound): All southbound traffic will be detoured via Gungahlin Drive, Sandford Street roundabout, and Gungahlin Drive to reconnect with Barton Highway.

Gungahlin Drive (Southbound off-ramp): Right turn onto Barton Highway will be closed.

Traffic will be able to turn left from Gungahlin Drive onto Barton Highway towards the city,
however people are encouraged to detour via Mitchell.

Detour signage has been erected to alert people of the closure and to direct traffic.

The ACT Government apologises for any inconvenience caused.

For up-to-date information on road closures please call Canberra Connect on 13 22 81.

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128 Responses to GDE collapses onto Barton Highway
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pete74au pete74au 9:02 pm 02 May 11

I know its a bit late – But I still admire that pre-emptive monument that JS built in advance of the foul up and bridge collapse – very astute don’t you think.

BrassRazoo BrassRazoo 1:02 pm 26 Aug 10

Contractors have trouble securing the flaps on roadworks speed limits signs or forgetting to change them. Not surprised they have problems building a bridge.

screaming banshee screaming banshee 4:29 pm 24 Aug 10

I-filed said :

clearly the “dodgy practice” was of enough concern for him to attempt to raise it officially.

Yeah, but to raise it with his boss in his APS IT job. His boss was probably sick of him daydreaming and staring out the window all day. Did he raise it with his wife…I bet she told hime to shut the **** up too.

junkett junkett 9:40 pm 23 Aug 10

Growling Ferret said :

When is the next ACT election? The next 6 months of traffic chaos getting out of Gungahlin might be enough to change a Government if enough residents are pissed off with the ACT ALP

Naah, mate – out of luck. Still subject to the mindless drones in the pubic service who are largely laborites. Nohope will ride again.

JC JC 4:47 am 23 Aug 10

gooterz said :

In the US and other places they make the bridge offsite and then place it over the span. Miminal distruption and it takes a few hours to install (not including the supports!)

It all depends upon the bridge. For example the GDE bridge over Gininderra Drive was built kinda this way.

Deref Deref 4:21 pm 21 Aug 10

CraigT said :

Yeah, but we got homosexual marriages, so at least he’s getting the really important things right.

No. We haven’t.

Deref Deref 4:10 pm 21 Aug 10

“Biggest and best disaster man”? Stanhope can’t hold a candle to the unmitigated catastrophe that was Kate Carnell. We’ll be paying for her incompetence for generations.

I-filed I-filed 12:14 pm 21 Aug 10

DJ, no need for a flame, and no, not a “I once had a friend” story, but a first-hand account of what I was told by a colleague. I’m not in a position to post detail as I don’t recall the engineering exactitude of the problem. What I do recall was that the colleague was distressed at his supervisor’s reaction, sat at a window overlooking the construction site, and was a qualified engineer. And yes it is a worry, as clearly the “dodgy practice” was of enough concern for him to attempt to raise it officially.

DJ DJ 9:31 pm 20 Aug 10

I-filed said :

This is a worry. Seven years ago a colleague who was an engineer (albeit working in an IT job for the APS) observed some really dodgy practices going on with the construction of an office building in Allara St – one he was due to move into once completed. He raised his concerns with his supervisor – and was told to shut the **** up or risk his job. He shut up. I wish I had more detail. To this day I don’t know what the faults were, but I haven managed to avoid stepping inside that particular building myself!

Is this a “I once had a friend…” story? I prefer the Penthouse version that starts with “I never thought it would happen to me, but…”

Surely you can come up with some details about the ‘dodgy’ practices? Unless you can, it’s not really a worry is it?

martyo martyo 7:20 pm 20 Aug 10

flashback friday – must say I almost turned around at the prospect of this site on beclo way this afternoon…..http://farm5.static.flickr.com/4118/4910039224_fd2cec000c_b.jpg

I-filed I-filed 4:46 pm 20 Aug 10

This is a worry. Seven years ago a colleague who was an engineer (albeit working in an IT job for the APS) observed some really dodgy practices going on with the construction of an office building in Allara St – one he was due to move into once completed. He raised his concerns with his supervisor – and was told to shut the **** up or risk his job. He shut up. I wish I had more detail. To this day I don’t know what the faults were, but I haven managed to avoid stepping inside that particular building myself!

Aeek Aeek 4:08 pm 20 Aug 10

Best thing for Glenoch for over a year.

shadow boxer shadow boxer 3:35 pm 20 Aug 10

So that’s 7 days now, surely enough time to minutely photograph and examine the mess, can we clean it up and re-open the road please

Madashell Madashell 10:15 am 20 Aug 10

Fall is 3% oneway so no need to speculate futher on that point a) that’s how it looks b) the beams all fell in one direction c) (and most importantly)I know some people in low places at Roads ACT who have confirmed it.

Arthur says “P-delta effects are not a feature of flexural beam design in this case, they are primarily associated with axially loaded members such as columns in large heavily loaded sway resistant frames and are not relevant.”

Why the big deltas get all the big press when the little deltas can be just as important I’ll never know (Leonhard Euler would be most unimpressed). Firstly I’d suggest that P-Delta effects are relevant to all columns depending on exactly how you want to define your delta (could cite thousands of techical articles but I won’t). For what its worth a lateral buckling failure of a beam is directly analogous to a column failure in the sense that the compression flange is esentially failing by buckling sideways. As to whether P-delta may be relevant in this case. If you consider that the delta is the offset nature of the load to the neutral axis of the steel beam then I would suggest it is (although largely from an academic perspective).

The other technical point of interest is which beam has the heaviest load? Now intuitively many are going to say that that’s easy the ones under the voids have a lighter load (hmm maybe not). If you consider for a second the fluid nature of the concrete you might think no, wait a second the void tie downs will transfer uplift away from that area so they may in fact have the heaviest load.

By the time you have slept on it you might even think that depends on the slump of the concerete or the relative time to initial set, whether it is currently being vibrated, what temperature it is at now, what temperature was it batched at, whether there are any set retarders or superplasticisers in it or indeed who the Captain of Hawthorn is this year. Fortunately there is always some ironing out of this effect by the timber joists but my point is that like most things that look dead simple, they are not necessarily as simple as they first appear.

Arthur McKenzie Arthur McKenzie 11:33 pm 19 Aug 10

If you have a look using Google Earth you will see that the existing bridge and immediate approaches are straight and level so there would be no, or very little need for lateral camber of the bridge. Each sweeping bend ends well before the bridge abutments are reached. Lateral camber would be unnecessary to provide ‘extra traction’ for vehicles. It appears the existing bridge is fairly level longitudinally as well. Of course the bridge road surface (hotmix) would be ‘cambered’ to achieve adequate raindfall runoff and drainage. I doubt the new bridge would be any different.

What that means is the secondary effects referred to above would be negligible or non existent. P-delta effects are not a feature of flexural beam design in this case, they are primarily associated with axially loaded members such as columns in large heavily loaded sway resistant frames and are not relevant. The beams on the GDE falsework here would be required to carry negligible axial load. The only substantial source would be (non-existent vehicle braking forces or highly restrained temperature effects, equally non-existent) and secondary effects which would normally be carried by a bracing system. Effects due to imperfections are taken into account in the Perry-Robertson based design formulae in the steel structures code and are not directly taken into account in engineering calculations. Along with residual stresses in the steel these effects are irrelevant.

While not impossible it also is very unlikeley that a designer of this falsework would need to, or be bothered with wasting time, utilising finite element analysis. Either way the modelling method is of no consequence.

The failed falsework beams all tipped over to one and the same side because they were laterally unstable. The rest followed.

Madashell Madashell 9:42 pm 19 Aug 10

Russ said

“So if I understand correctly, the middle beam would have been plumb, but beams either side out from the centre would be increasingly (slightly) out of vertical? “

Road alignment over must be a sweeping bend because the deck has a oneway fall, underside has a parallel oneway fall and the beam supporting the ones that fell over has a parallel one way fall. So all the beams all lean in one direction. Might only be 2 or 3% but you can see the varying heights of the props on the adjacent spans. Probably not all that relevant in this case but sometimes such subtleties can be the straw that gave the camel an awful heria.

Russ Russ 8:15 pm 19 Aug 10

Thanks for the responses Arthur and Madashell.

Madashell said :

The other interesting point is that they are leaning in sympathy with the road camber which adds a P-Delta effect to the usual buckling phenomenom lowering the load capacity still further.

So if I understand correctly, the middle beam would have been plumb, but beams either side out from the centre would be increasingly (slightly) out of vertical? What I don’t understand is where this camber derives from, given I’d have thought the underside of a bridge can be dead flat.

Or do you mean the camber being formed on the poured and screeded concrete imparts differing masses to each beam (ie. the load is heavier in the middle than the edge), causing them to respond in this manner?

Madashell Madashell 6:09 pm 19 Aug 10

Yep I’d also say Russ is right so if that was one of your lighter 760UB’s with top loading and only partial lateral restraints at the supports (look at the ones still standing)then they’d only be good for about 20% of their fully restained capacity (assuming they span 11-13m). The other interesting point is that they are leaning in sympathy with the road camber which adds a P-Delta effect to the usual buckling phenomenom lowering the load capacity still further. The buckling equations in the code are independent of these torsional effects so some poor structural engineer is no doubt sitting around rederiving the code buckling equations from first principles to account for that effect.

I know you are probably all thinking that they could just build a finite element model (like on CSI) but that’s not really the same thing as the equations are trying to account for ‘out of straightness’ and residual stresses etc. You can also throw in a modecum of biaxial bending if you want to be really pandantic I guess, but the bottom line is that the lateral restraint was not as comprehensive as it should have been so it fell down. Everyone makes mistakes but when structural engineers make them they are very public affairs so I feel for the structural engineer in this case. Lesson learned for life I am sure but a dam hard way to learn it.

BTW someone was asking if the pump had concrete in the lines and I do not know but the hopper had been cleaned out so I expect that the answer is no.

Arthur McKenzie Arthur McKenzie 10:39 pm 18 Aug 10

Russ said :

So the critical failure was that the I-beams were able to twist when they should have been braced to prevent this?

It looked like that to me!

The only point I would differ on is the top flange splice plates and bolts were missing from the beams I saw. Somebody above mentioned they were replaced with a weld because the plates were removed to avoid fouling with the formwork. That would be consistent with what I saw.

Russ Russ 10:20 pm 17 Aug 10

Just to clarify from the experts as to what *might* have happened.

From what I understand, there were a series of 760UBs (universal beams, or I beams) that spanned the gap over the road. These were there only as a temporary support for the concrete formwork, and the lengths of beam were joined with plates on the top and bottom flange and on the vertical web, bolted each side.

On top of these beams were some intermediate elements, then sheets of glossy black formply, then a criss-cross network of steel reinforcing bars along with large hollow steel tubes that would create hollow voids through the concrete span.

They began pouring concrete using that Schwing pump that seems to be marooned there, and at some point, the increasingly heavy “deck” of freshly poured concrete caused the supporting the I-beams to twist and rotate, losing their strength from the vertical part of the “I” and thus bending, collapsing the support structure and bringing everything down that was above it, including the poor workers.

So the critical failure was that the I-beams were able to twist when they should have been braced to prevent this?

Also, seeing that pump sitting there now – does anyone know whether the operator was able to flush the concrete out of the rams and piping?

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