The crane was being disassembled. Normal procedure is to remove large (about 2 1/2" in diameter) pins on the top section that hold the ends of the four crane legs firmly into slots on the identical section below it, while a smaller portable crane provides upward tension to enable the pins to be removed and secures the section. The top section being removed is always firmly attached to the smaller crane which lowers it to the ground after pin removal. After the topmost section is removed the portable crane is reattached and the next section has the pins removed on that section in the same manner. In the Seattle accident ALL THE PINS ON EVERY OTHER SECTION were removed at once so that only the weight of the sections with end tabs of the legs in the slots of the section below were holding the sections in place. Add in an unusually strong wind and the crane blew over. There were several crane companies involved and nobody spoke up.
Note pins installed on top left, missing on top right
Witty Banter
Apr 30, 19 11:37 am
I admittedly know absolutely nothing about proper crane disassembly but its unfortunate that from your description this was easily avoidable.
Quentin
Apr 30, 19 11:44 am
Always marveled at how they put those things up and take em down. Sad stuff here.
chigurh
Apr 30, 19 11:58 am
that description is terrible...diagrams would help.
Non Sequitur
Apr 30, 19 12:01 pm
Contractor tried to cut corners and save time on crane disassembly by skipping steps. At least that's how it's been explained from a few of my FB acquaintances in construction.
tduds
Apr 30, 19 12:02 pm
Is there a source for any of this besides that photo and your own conjecture?
Peter Normand
Apr 30, 19 10:00 pm
This is, thankfully, not a Chicago problem. This seems to happen too frequently in New York. Hopefully we learn the names of the crane contractors and steer our clients away from those who take unnecessary risk.
Everyday Architect
Apr 30, 19 11:41 pm
I've seen various news articles citing the possibility that they removed the pins prematurely. They all seem to be quoting the same experts though so it is probably premature to definitively say it was the case.
I worked on a mid rise project in Metro DC a few years ago (18 floors) where the 250 foot tall crane collapsed and landed on 7 townhouses on adjacent property. Fortunately no one was seriously hurt....miraculously the crane operator survived the fall and sufferred only 2 broken ankles......as the crane twisted while falling -dinged into the building under construction , damaging slab edges on 6 or more floors(which slowed down the fall) and the boom (arm of the crane ) twisted further on its way down and crushed the wooden roof trusses of 7 adjacent town houses. The accident happened at 7:45 AM and in DC most workers have left home at the time so no one was home nor injured in the town houses. The crane operator was fortunate because the cab of the crane landed on one of the few grassy areas of the construction site. The crane operator eventually healed, the town houses were repaired and the homeowners were compensated and the findings of the investigation concluded that the cause of the incident was metal fatigue where the tower was bolted down into the massive concrete tower crane base within the building’s foundation.
Amazing!!!!!
Volunteer
May 3, 19 7:05 am
From the Engineering News Record, May 2, 2019:
"It is obvious that all the pins to every other mast section (including the cab / slew-ring) were removed from the Seattle tower crane. This made the vertical mast vulnerable to a wind pressure that would have never toppled any tower crane if the pins remained in place. Maybe this time, my whistle-blowing will be recognized by the tower crane industry as valid, instead of dismissed.
Terry McGettigan is a tower crane specialist and operator. He has over 40 years of experience in the industry, running his first tower crane in 1978. Formerly certified as a crane inspector by both Washington State's L&I and California's Cal/OSHA, he is also a factory-trained tower crane technician with all the leading manufacturers. He has documented past crane accidents on his website www.towercranesupport.comwhich can be viewed here. He is currently based in Seattle, Wash. "
Non Sequitur
May 3, 19 7:37 am
Interesting that this guy runs a site on this topic. This confirms the chatter I’ve read elsewhere. I wonder how common this is.
betonbrut
May 3, 19 4:03 pm
In my limited experience... what occurred in Seattle is very common. Most masts are 10' sections and are erected and disassembled in 20' sections; the reason being speed.
What likely occurred here was the support crane had been released and too many pins had been removed... they got ahead of themselves... As a GC here in Seattle (not involved in this project or working for any company involved in this incident) I can confidently say what occurred was not due to cutting corners to increase profits. It was likely human error that led to this tragic event.
The crane was being disassembled. Normal procedure is to remove large (about 2 1/2" in diameter) pins on the top section that hold the ends of the four crane legs firmly into slots on the identical section below it, while a smaller portable crane provides upward tension to enable the pins to be removed and secures the section. The top section being removed is always firmly attached to the smaller crane which lowers it to the ground after pin removal. After the topmost section is removed the portable crane is reattached and the next section has the pins removed on that section in the same manner. In the Seattle accident ALL THE PINS ON EVERY OTHER SECTION were removed at once so that only the weight of the sections with end tabs of the legs in the slots of the section below were holding the sections in place. Add in an unusually strong wind and the crane blew over. There were several crane companies involved and nobody spoke up.
Note pins installed on top left, missing on top right
I admittedly know absolutely nothing about proper crane disassembly but its unfortunate that from your description this was easily avoidable.
Always marveled at how they put those things up and take em down. Sad stuff here.
that description is terrible...diagrams would help.
Contractor tried to cut corners and save time on crane disassembly by skipping steps. At least that's how it's been explained from a few of my FB acquaintances in construction.
Is there a source for any of this besides that photo and your own conjecture?
This is, thankfully, not a Chicago problem. This seems to happen too frequently in New York. Hopefully we learn the names of the crane contractors and steer our clients away from those who take unnecessary risk.
I've seen various news articles citing the possibility that they removed the pins prematurely. They all seem to be quoting the same experts though so it is probably premature to definitively say it was the case.
https://www.usatoday.com/story/news/nation/2019/04/29/seattle-crane-collapse-human-error-likely-experts/3623629002/
https://www.cnn.com/2019/04/30/us/seattle-crane-collapse-experts/index.html
I worked on a mid rise project in Metro DC a few years ago (18 floors) where the 250 foot tall crane collapsed and landed on 7 townhouses on adjacent property. Fortunately no one was seriously hurt....miraculously the crane operator survived the fall and sufferred only 2 broken ankles......as the crane twisted while falling -dinged into the building under construction , damaging slab edges on 6 or more floors(which slowed down the fall) and the boom (arm of the crane ) twisted further on its way down and crushed the wooden roof trusses of 7 adjacent town houses. The accident happened at 7:45 AM and in DC most workers have left home at the time so no one was home nor injured in the town houses. The crane operator was fortunate because the cab of the crane landed on one of the few grassy areas of the construction site. The crane operator eventually healed, the town houses were repaired and the homeowners were compensated and the findings of the investigation concluded that the cause of the incident was metal fatigue where the tower was bolted down into the massive concrete tower crane base within the building’s foundation.
Amazing!!!!!
From the Engineering News Record, May 2, 2019:
"It is obvious that all the pins to every other mast section (including the cab / slew-ring) were removed from the Seattle tower crane. This made the vertical mast vulnerable to a wind pressure that would have never toppled any tower crane if the pins remained in place. Maybe this time, my whistle-blowing will be recognized by the tower crane industry as valid, instead of dismissed.
Terry McGettigan is a tower crane specialist and operator. He has over 40 years of experience in the industry, running his first tower crane in 1978. Formerly certified as a crane inspector by both Washington State's L&I and California's Cal/OSHA, he is also a factory-trained tower crane technician with all the leading manufacturers. He has documented past crane accidents on his website www.towercranesupport.com which can be viewed here. He is currently based in Seattle, Wash. "
Interesting that this guy runs a site on this topic. This confirms the chatter I’ve read elsewhere. I wonder how common this is.
In my limited experience... what occurred in Seattle is very common. Most masts are 10' sections and are erected and disassembled in 20' sections; the reason being speed. What likely occurred here was the support crane had been released and too many pins had been removed... they got ahead of themselves... As a GC here in Seattle (not involved in this project or working for any company involved in this incident) I can confidently say what occurred was not due to cutting corners to increase profits. It was likely human error that led to this tragic event.