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?

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.

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.

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.

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.

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.

Posted By: tonyI can’t see any evidence of pads sinking in the pics

Opticians are open

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

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.

Centre of gravity inside the base footprint or anchored feet

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?

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.