Green Building Forum - Crane collapse

Crane collapse

djh — Wed, 08 Jul 2020 20:57:26 +0100

So the crane collapse in Bow:

https://www.bbc.co.uk/news/uk-england-london-53339296 and lots of other news sites.

Somewhat interesting because it was being used as part of a 'modern methods of construction' using CLT modules.

https://www.swan.org.uk/home/news/swan-housing-association-and-the-mayor-of-tower-hamlets-celebrate-the-delivery-of-modular-homes-to-the-uk%E2%80%99s-first-mid-rise-clt-scheme-at-watts-grove.aspx

"This method of construction dramatically reduces disruption for the surrounding residents during construction"

Interesting to me personally because a friend who lives nearby has been evacuated - the water supply has been knocked out and there's concern about gas leaks and possible structural damage in the surrounding area apparently. Certainly dramatic but if it's a reduction in disruption I would hate to be next to the alternative type :)

What I can't make out is quite how the crane has collapsed. What type of crane is it? Some photos seem to show that its base has come off its mounting pad. The writing on the arm of the crane is upside down as it's now lying which suggests to me that it's somehow fallen up and over the top and fallen on its back????

Failure of the mounting bolts/studs? Or what?

Crane collapse

djh — Thu, 09 Jul 2020 14:53:34 +0100

A bit of information about the crane is at: https://www.wolffkran.com/website/en/gb

The information on there:

"The crane on the construction site in Bow was only 10 years old and was fully erected on a 22 meter tower the day before the incident."

contradicts a report on the BBC site:

"Tower Hamlets Council ...The borough's mayor, John Biggs ...

"Speaking about the crane, Mr Biggs said he understood it was still being erected at the time it fell."

Crane collapse

Mike1 — Thu, 09 Jul 2020 15:07:18 +0100

There's a statement on the Wolff website at https://www.wolffkran.com/website/en/gb that answers some of your questions.

I imagine that the HSE will need to finish their investigation to learn more.

Crane collapse

Paul in Montreal — Tue, 14 Jul 2020 13:26:30 +0100

See also - seems like it was a soil compaction (or lack thereof) problem:

https://www.youtube.com/watch?v=sx3n54duJks

Paul in Montreal.

Crane collapse

djh — Tue, 14 Jul 2020 14:42:55 +0100

Posted By: Paul in MontrealSee also - seems like it was a soil compaction (or lack thereof) problem

Thanks Paul, that looks quite plausible. One of the videos linked from that page suggests that perhaps the underlying ground was extra weak because of WW2 bombing. I also noted in the crane's manual that there is an instruction to never park the crane with the jib in the fully upright position. So there may be a mixture of causes, but it does seem clear that some of the people on site could/should have noticed what was happening at the base of the crane some time before it fell.

In fact, I'll be surprised if there isn't a set of instructions somewhere that says the pads have to be checked regularly. I'm somewhat surprised if the crane itself doesn't have an automatic level sensing mechanism that raises an alarm if the the base stops being level.

Let's hope this gets resolved faster than Grenfell - it appears much simpler.

Crane collapse

revor — Tue, 14 Jul 2020 18:48:49 +0100

When something has not been used for some time or for the first time there is always a risk associated with any disruption to routine. I reckon there will be many many incidents associated with the lockdown arising out of starting things up. Most will be just inconvenient but there will be the odd big event maybe this is an example. More worrying for me would be bringing in an aeroplane into service having been idle for many months. Despite the thorough checks they go through something could be missed with disastrous consequences.
Coming back to the crane I would think there would be some sort of sensors to indicate that the machine was not stable, my cherry picker has outrigger legs with microswitches in the feet and if there is a slight imbalance between all 4 feet it sets off a very loud alarm even though the likelihood of it tipping is remote.

Crane collapse

Paul in Montreal — Tue, 14 Jul 2020 19:35:03 +0100

Posted By: revorComing back to the crane I would think there would be some sort of sensors to indicate that the machine was not stable, my cherry picker has outrigger legs with microswitches in the feet and if there is a slight imbalance between all 4 feet it sets off a very loud alarm even though the likelihood of it tipping is remote.

So the alarm on the crane goes off as one of the pads collapses due to the uncompacted soil it's on ... what do you do at that point? Run like heck probably.

I can see around 15 tower cranes within a 1/2 mile radius of me ... everyone of them is anchored to the ground with a massive concrete foundation - none of them are on pads.

Paul in Montreal.

Crane collapse

djh — Tue, 14 Jul 2020 19:50:18 +0100

Posted By: revorWhen something has not been used for some time or for the first time there is always a risk associated with any disruption to routine. I reckon there will be many many incidents associated with the lockdown arising out of starting things up.

This had nothing to do with lockdown. The crane had only just been installed, while building sites have been open for ages.

Crane collapse

djh — Tue, 14 Jul 2020 19:54:17 +0100

Posted By: Paul in MontrealSo the alarm on the crane goes off as one of the pads collapses due to the uncompacted soil it's on ... what do you do at that point?

I would expect a sensor to be able to detect the gradual movement that was described by the chap in the video you posted. If it was indeed sudden then why has the other rear pad sunk?

Posted By: Paul in MontrealI can see around 15 tower cranes within a 1/2 mile radius of me ... everyone of them is anchored to the ground with a massive concrete foundation - none of them are on pads.

AIUI, that's a big difference between tower cranes, which must be bolted down, and luffing jib cranes, which can be stood on a good surface and ballasted. This design is ten years old and has a proven history, I believe.

Crane collapse

Paul in Montreal — Tue, 14 Jul 2020 20:56:52 +0100

Posted By: djhI would expect a sensor to be able to detect the gradual movement that was described by the chap in the video you posted. If it was indeed sudden then why has the other rear pad sunk?

Perhaps both pads sunk slowly but one suddenly cracked and failed?

Posted By: djhAIUI, that's a big difference between tower cranes, which must be bolted down, and luffing jib cranes, which can be stood on a good surface and ballasted. This design is ten years old and has a proven history, I believe.

Ah, right! Obviously you need a stable surface though, which seems to have been the problem here.

Paul in Montreal.

Crane collapse

djh — Tue, 14 Jul 2020 22:53:03 +0100

Posted By: Paul in MontrealPerhaps both pads sunk slowly but one suddenly cracked and failed?

Indeed so, but any pad movement is very bad news, so a sensor that raised the alarm whilst they were sinking slowly (i.e. sometime during the preceding <24 hours) would have been useful.

Crane collapse

tony — Wed, 15 Jul 2020 11:32:23 +0100

I canâ€™t see any evidence of pads sinking in the pics

Crane collapse

djh — Wed, 15 Jul 2020 11:57:53 +0100

Posted By: tonyI canâ€™t see any evidence of pads sinking in the pics

Opticians are open

Crane collapse

djh — Sat, 18 Jul 2020 16:05:25 +0100

Hmm, the more I see the more I smell ....

I went looking to see if any initial reports or anything had been published (apparently they haven't moved the crane yet and as a result people are still not allowed to access their homes or cars) and didn't find any, but I did find some a rather worrying news analysis piece:

https://www.insidehousing.co.uk/insight/deadly-accidents-a-timeline-of-recent-crane-collapses-in-the-uk-67131

and following from that:

http://news.bbc.co.uk/1/hi/england/london/3269061.stm
https://www.constructionnews.co.uk/news/knowledge-news/crewe-deaths-lead-to-calls-for-new-tower-crane-regs-29-06-2017/
https://unitelive.org/there-must-be-no-delay-in-crane-accident-investigation/
https://www.britsafe.org/publications/safety-management-magazine/safety-management-magazine/2020/bow-crane-collapse-protest-laws-must-change/

I don't know what the problems were with the national register legislation, but it seems we need to beef up the quality control requirements somehow. Anybody know what other countries do? Germany, Switzerland?

We also need to arrange that there is guaranteed adequate finance to pay penalties and compensation (insurance, or liability passed to holding companies or whatever).

More construction regulations that aren't fit for purpose.

Crane collapse

Jonti — Sat, 18 Jul 2020 18:11:06 +0100

djh,

I don't know the details of legislation covering construction cranes in Switzerland but know that there is a national set of laws covering them which is then beefed up by county laws. Two big differences however are that in Switzerland construction companies can only work in the county they are based in and to a lesser extent in neighbouring counties. If a company is sloppy everybody knows and they get no work.

Also, there are effective controls undertaken by the county and town councils.

Having said that accidents do still happen. Last year a large transport crane went over into Lake Luzern and sank to a depth of 30m (100ft). Luckily no one was hurt as the two labourers helping load the barge managed to jump clear and swim back to shore and the crane driver also got out in time. It was an impressive show getting the crane back out of the lake though.

If you scroll down there are some interesting photos in the news item below.

https://www.luzernerzeitung.ch/zentralschweiz/nidwalden/goliath-ein-monster-und-der-pneukran-so-spektakulaer-lief-die-bergung-in-beckenried-ab-ld.1189071

Crane collapse

djh — Sat, 18 Jul 2020 19:33:10 +0100

Thanks, Jon.

Posted By: JontiTwo big differences however are that in Switzerland construction companies can only work in the county they are based in and to a lesser extent in neighbouring counties. If a company is sloppy everybody knows and they get no work.

Interesting. Are counties in Switzerland similar to those here? I imagine that if you tried to bring in such a law here, it would be criticised as too parochial/ restrictive of trade. But maybe that's a good thing?

Crane collapse

Jonti — Sat, 18 Jul 2020 21:23:38 +0100

djh,

the whole political system is the opposite in Switzerland to that here in the UK. The town council is the most important part when it comes to planning, enforcement and tax. The county is the second most important followed by the national government in third. Even if the national government approves something such as a motorway and the county says yes. If the town council says no then it isn't happening.

Crane collapse

Rex — Thu, 30 Jul 2020 13:35:43 +0100

Whilst I am hardly any sort of expert on tower cranes, there is one feature that I cannot understand.

Obviously, any crane works as a sort of balance; to counteract the working load, there is usually a weight on the other end. Given that this weight on tower cranes seems to be generally non-moving and X tons of concrete blocks, how does the crane stand upright when there is no working load?

Crane collapse

tony — Thu, 30 Jul 2020 14:19:55 +0100

Centre of gravity inside the base footprint or anchored feet

Crane collapse

Peter_in_Hungary — Thu, 30 Jul 2020 14:29:05 +0100

IMO the X tons of concrete blocks on the back of the crane is a counterweight not a balance. The structure of the cranes (box girder(ish) upright will take a given amount of stress applied by the load on the horizontal arm and It is my understanding that the counter weight will 'counter' the lifted load and so allow a greater working capability.

The counterweight on the back will be within the stress limits of the upright without a load on the front so the crane should not fall over backwards. The ground anchorage also needs to be secure enough to avoid being torn out by the turning moment applied by either the counterweight on its own or a combination of counter weight plus lifted load.

Just my thoughts

Crane collapse

Rex — Thu, 30 Jul 2020 16:29:07 +0100

Agreed, counterweight is a preferable word. But the no-load stress on the tower and the relevant fixings in the ground must be immense. Obviously, because the average crane does not fall, it is all within the design limits, but surely if something goes wrong, it all goes wrong very, very quickly?

Crane collapse

Mike1 — Fri, 31 Jul 2020 01:41:06 +0100

86 known incidents world-wide in the 20 years to 2009, it seems: http://www.hse.gov.uk/Research/rrpdf/rr820.pdf

34% during Erection/Dismantling/Extending, 33% uncertain cause, 18% bad weather...

Crane collapse

djh — Fri, 31 Jul 2020 10:43:32 +0100

Posted By: RexBut the no-load stress on the tower and the relevant fixings in the ground must be immense. Obviously, because the average crane does not fall, it is all within the design limits, but surely if something goes wrong, it all goes wrong very, very quickly?

Note that for this crane and other similar ones there are no fixings into the ground, just ballast weights on the base.

How quickly you think it falls depends on the mechanism and when you start measuring. If it was left parked with the jib too high and a strong gust of wind blew it over that would be quick. But normally there is warning of strong winds. If the ground slowly collapsed under the back two pads then nothing much would seem to happen until it overbalanced, but when did it start falling? So I don't think it's a very useful question.

Crane collapse

djh — Fri, 11 Sep 2020 22:21:30 +0100

Just to update:

It seems that progress is very slow (surprise, surprise!)

The crane has not yet been removed; there's not even a timescale for it yet.

HSE has released no information about the cause of the accident.

Residents are likely to be unable to reside in their properties for many months to come.

It seems to me that 'the system' is completely broken, much like 'the system' as it applies to building regs, planning etc. Is there actually anything that can be done?

https://www.towerhamlets.gov.uk/News_events/2020/September_20/Update-Bow-crane-collapse.aspx
https://www.constructionenquirer.com/2020/08/24/union-demands-answers-over-bow-crane-collapse/
https://www.bbc.co.uk/news/uk-england-london-53890146