Bridge collapse on M20

[scz4]

Must have been a low speed impact, the truck, or rather the digger, doesn't look to have traveled more than a couple of metres from where the front of the boom would have made contact.

[phil-sti]

There will be an insurance company having kittens when it returns Tuesday.

[ATTAK Z]

dandarez said:

Still puzzled why the need for a concrete structure for narrow pedestrian use, and why no central support?

There were lots of RC structures when the motorways were built ... less long term maintenance ... RC construction seems to have been out of fashion for quite some time now ... RC structures are built in situ whereas steel bridges can be fabricated off-site by machines ... maybe due to the demise of experienced tradesmen in the construction industry

Edited by ATTAK Z on Saturday 27th August 21:20

[cahami]

Is it possible that the dump truck was loaded on the high part of the trailer above the fifth wheel? And if so assuming it's a 6 ton swivel dump truck it would be about 3m high, how high is the bed on top of the fifth wheel? And even if this was the case it would only have been the roll bar that dislodged the bridge you would have thought it would just bend.

[greygoose]

ATTAK Z said:

dandarez said:

Still puzzled why the need for a concrete structure for narrow pedestrian use, and why no central support?

There were lots of RC structures when the motorways were built ... less long term maintenance ... RC construction seems to have been out of fashion for quite some time now ... RC structures are built in situ whereas steel bridges can be fabricated off-site by machines ... maybe due to the demise of experienced tradesmen in the construction industry

Edited by ATTAK Z on Saturday 27th August 21:20

The M20 is a bit odd for UK motorways as lots of the actual roadway is made of concrete rather than Tarmac, parts have been resurfaced with Tarmac around the towns due to the extra noise vehicles on concrete produce.

[JumboBeef]

I'm just glad the white hgv was a truck and not a coach, could have killed many.

[Elysium]

ALawson said:

I expect no central support due to "risk" of vehicle collision from 3rd lane, to be honest if it can span why would you put another support in.

The photo of the end of the broken section shows almost a fresh broken concrete colour in the top right section, the other 3/4 looks different.

Exactly right. If a central pier had been constructed it would need to be designed as a highway structure, with impact resistance, vehicle barriers etc. Far better from an engineering and value perspective to avoid it all together.

The photos showing the joint pre-collapse have a lot of staining so water has evidently been allowed to run through it. The end post-collapse shows some clean concrete, lots of efflorescence where the salts have reacted with the water and some ripped grout / mastic.

It's a true movement joint so there was no mechanical connection between the two halves.

Edited by Elysium on Saturday 27th August 21:32

[Vaud]

phil-sti said:

There will be an insurance company having kittens when it returns Tuesday.

I doubt it. They will have it factored into their costs. This is a bridge, and a couple of vehicles - no-one can claim holiday costs, etc - nor are we talking about life long rehabilitation costs for a school bus full of kids.

If they haven't factored it in then they are in the wrong business.

[powerstroke]

Dogwatch said:

General Price said:

It looks like the dumper hit it and got pushed back into the digger.

Certainly looks that way. If the artic had hit the undamaged bridge you would expect the trailer roof to have been scraped back right across whereas on the nearside it is almost complete.

Why was the truck on the hard shoulder ? I would say it was going slowly and the load caught the bottom of the bridge knocking it off ?? the other truck was in lane 1 and going faster hence the damage to its trailer???

[phil-sti]

Vaud said:

phil-sti said:

There will be an insurance company having kittens when it returns Tuesday.

I doubt it. They will have it factored into their costs. This is a bridge, and a couple of vehicles - no-one can claim holiday costs, etc - nor are we talking about life long rehabilitation costs for a school bus full of kids.

If they haven't factored it in then they are in the wrong business.

Factored in somebody taking a bridge down? I doubt that's even thought about, bridge strike yes, bringing a bridge down I doubt it

[Vaud]

phil-sti said:

Factored in somebody taking a bridge down? I doubt that's even thought about, bridge strike yes, bringing a bridge down I doubt it

Insurance factors in much worse cases.

Life long medical treatment for just one young person is massively higher. I think ~£20M is the highest single person payout that is publicly disclosed.

[Elysium]

powerstroke said:

Why was the truck on the hard shoulder ? I would say it was going slowly and the load caught the bottom of the bridge knocking it off ?? the other truck was in lane 1 and going faster hence the damage to its trailer???

I think it was probably queuing for the exit. Lots of people seem to use the hard shoulder for that these days.

[Flipatron]

Looks to me like the dumper truck (on the low loader) has caught under the bridge at low speed. The dumper truck then tilts, lifting the bridge off it's foundation. The forward motion of the truck then moves the bridge a few meters clear and then collapses onto the low loader. There seems to be no clear evidence of an impact big enough to push it off its foundations.

[greygoose]

Vaud said:

phil-sti said:

Factored in somebody taking a bridge down? I doubt that's even thought about, bridge strike yes, bringing a bridge down I doubt it

Insurance factors in much worse cases.

Life long medical treatment for just one young person is massively higher. I think ~£20M is the highest single person payout that is publicly disclosed.

I should think rebuilding a bridge and closure of a motorway will be in the millions pretty quickly. It is just fortunate there weren't multiple vehicles crushed and a pile up due to people braking as the bridge fell.

[hornetrider]

General Price said:

It looks like the dumper hit it and got pushed back into the digger.

That's the money shot. Wonder why it was on the hard shoulder not the main carriageway?

[don'tbesilly]

Elysium said:

powerstroke said:

Why was the truck on the hard shoulder ? I would say it was going slowly and the load caught the bottom of the bridge knocking it off ?? the other truck was in lane 1 and going faster hence the damage to its trailer???

I think it was probably queuing for the exit. Lots of people seem to use the hard shoulder for that these days.

The footbridge is quite a distance from the slip road leading onto the M26 and I've never encountered queues to join the M26 from the M20, so I don't think that's why the truck was on the hard shoulder.

[saaby93]

Anyone taking best bets on how long it takes to lift a lump of concrete off a truck and re-open a motorway?

[The Nur]

Tuesday?

[ATTAK Z]

Flipatron said:

Looks to me like the dumper truck (on the low loader) has caught under the bridge at low speed. The dumper truck then tilts, lifting the bridge off it's foundation. The forward motion of the truck then moves the bridge a few meters clear and then collapses onto the low loader. There seems to be no clear evidence of an impact big enough to push it off its foundations.

To me it looks like the section of the bridge that collapsed is simply supported by the cantilever sections of the structure ... a common design concept for this type of bridge, which allows for thermal movement (which someone alluded to earlier in the thread) ... as such the supports do not allow for a great deal of lateral loading

[oobster]

Jeez, I haven't seen ITV news for quite a while, they REALLY like to over-dramatise things don't they!