While my own experience is primarily with mobile cranes rather than the tower variety, I still fail to understand why or how anyone would remove pins so far ahead of the mobile crane removing the mast sections. I have designed and assembled several strandjack gantries in the past. Installing pins during assembly, and removing them during demob, was specialized work that few knew how to do well. In order to place or remove pins, the mobile crane hoisting the mast section would have to slowly hoist millimetres up and down as the first pins were tapped gently. A good ironworker knew the sound that the pin would make when it was aligned, and would quickly drive the pin with one swing. Any attempt to drive the pin before proper alignment did nothing but wreck hammers. Each mast section was flown up with come-alongs already in an X pattern at the pin elevation, to help facilitate in pulling the components into alignment. Despite good European fabrication and tolerances, variations in the mast dimensions meant that a bit of pulling was often required to get everything aligned. Those mast connections can't be sloppy, or the crane would wobble all over the place under operational loads.
All that said, my point is that it's surprising that:
1) it would be common practice to remove pins so far ahead of the dis-assembly
2) there is even a way to remove pins in the mast chords with so much dead load above, and connection "pre-stress" forces caused by the variations in mast shape
Not to lay blame on the crane manufacturer here, but suppose that the pin connections carry little compressive load, and that instead, the individual mast chords are designed to transmit compression by bearing, with the pins carrying tensile loads only. I see a potential re-think of that design in the future, where pins carry gravity loads and therefore cannot be removed without first hoisting up on the mast section.
Another way to put what is being eluded to that the pins may have been removed - would you erect the crane using a similar method, only putting in the pins once the tower and cab is in place... I think not.
I really hope it was something else, because it just seems like such a 'don't do it' thing to remove the pins ahead of the immediate removal of a section and an avoidable accident ultimately if this is the contributing factor. Especially removing pins at the base where it started to topple would have been wholly unnecessary as the base connection appeared to be accessible from the roof
I've designed quite a few crane bases (piled solutions and large foundation pad solutions), for some reason they make me quite nervous compared to other work, watched too many crane fail compilations on YouTube I guess!
Without supporting any theories, I remember winds off Lake Union. I worked at the foot of Pine Street and on certain days, walking around a tall building corner in that neighborhood would walk you right into a blast of wind.
Newspaper here is saying every alternate set of bolts/pins was out and this was contrary to manufacturers recommendations for dismantling.
Hmm.
I am 80 miles west of Seattle out on the coast, we did have gusty winds here on the day of the collapse. Wind/gusts here show up in the Seattle area a few hours later.
If they move an oil platform or hoist big things or run tunnel borers or upright cruise ships driven onto rocks by thoughtless idiots, they always have an agent from the insurance underwriter present. NOTHING happens without their approval or they're released from their responsibilities. Check lists are always run, everything is planned. No-seat-of-the-pants-moves. If something unexpected happens the insurance guy is experienced enough to agree with any correction moves.
I hope the underwriter for this crane accident is bankrupted as I hope the crane owner is also by the likely $100M in claims. I also hope that all crane underwriters respond by requiring a skilled agent to be present during all assembly, take-down, and repairs of these cranes in the future to guard their interests from incompetent, cheap, lazy, ignorant, and careless operators.
If even a paper-pushing agent with a certified (by the crane maker) take-down list had been present this entire disaster would not have occurred. One person. There for a week... Pathetic.
I personally would think it best to have 4 lines / cables up on what ever section is below the section to be removed and of course attached to a solid points at the roof of the building. Would it add a bunch of extra time yes, but at least there is not a huge unsupported sail in the sky to fall.
If the tower can be free standing when actually working as a crane it can clearly be free standing when being dismantled - PROVIDED that only one section is unbolted at a time, and that section is already pre-supported by the removal crane before being unbolted.
Tieing it back with guy lines seems a little over the top.
'Totally avoidable': 3 firms fined in Seattle crane collapse
By GENE JOHNSON | Thu, October 17, 2019 04:33 EDT
TUKWILA, Wash. (AP) — Washington state on Thursday fined three companies a combined $107,000 for their roles in a crane collapse that killed four people in Seattle last April, with officials calling the accident "totally avoidable."
The Department of Labor and Industries released the results of its investigation Thursday. It found, as experts suspected, that the crane toppled in a wind gust because the workers who were disassembling it prematurely removed pins securing sections of the crane's mast, contrary to the manufacturer's instructions. The practice appears to have been common in the industry, even though it had led to fatal collapses before, investigators said.
The collapse occurred April 27 in the booming tech neighborhood of South Lake Union, where the crane had been used in the construction of a Google office building. Sections of the crane landed on the building and on traffic below, striking six vehicles. Two ironworkers on the crane were killed as were two people in cars. Four other people were injured.
"The incident that occurred was totally avoidable," department Director Joel Sacks said at a news conference. "If the companies on site had followed the rules, the crane would not have fallen."
Regulators issued the biggest fine, $70,000, to Salem, Oregon-based Morrow Equipment Co., which supplied the crane to general contractor GLY. GLY was fined $25,000, and Northwest Tower Crane Service Inc. was fined $12,000.
Morrow was most culpable because it was the expert on site and should have known and ensured the manufacturer's instructions were followed, regulators said, while the other companies were cited for not having a supervisor present, inadequate training or other violations.
Two other companies that were investigated were not responsible, officials said.
The companies have 15 days to appeal. Morrow did not immediately return an email seeking comment. In an emailed statement, GLY President Ted Herb said the Bellevue-based company was deeply concerned by the collapse, cooperated with investigators and had already made changes.
Herb said the company will "do everything possible to protect our workers and the community."
Brian Haight, crane program manager with the department, said that the manufacturer's instructions say the crane should be dismantled in sections. As a secondary crane is attached to the top of the section being removed, workers pull the pins for that section only, leaving the rest of the tower secure. The pins are about 16 inches (40 cm) long and weigh 26 pounds (11.79 kilograms).
At the crew's pre-task meeting that morning, they did not review the manufacturer's instructions for crane removal, Haight said.
That afternoon, the secondary crane couldn't function because of high winds. So the disassembly crew, while waiting for the winds to die down, decided to remove the pins up and down the tower crane and to loosen the bolts attaching the tower to its concrete base. When a gust of around 50 mph (80 kph) hit, the crane swayed and collapsed.
Early pin removal was blamed after a tower crane mast collapsed during disassembly in Dallas in 2012, killing two workers. Terry McGettigan, a tower crane specialist in Seattle, wrote a paper after the Dallas collapse warning about the danger of taking shortcuts.
Following the April collapse, the department issued a hazard warning that was shared among the crane industry internationally. It also asked crane companies in Washington to notify them of assembly or disassembly of any tower cranes, so that the department can send an auditor to inspect the crane and ensure proper procedures are followed.
It is also re-examining its rules for crane operations and is considering making that notification request mandatory instead of voluntary.
The $70,000 fine issued to Morrow was the maximum allowed under state regulations for a single, willful violation of workplace safety rules, unless a company has a prior history of such actions before, said Anne Soiza, the department's assistant director.
David Beninger, a Seattle lawyer who plans to sue on behalf of one victim's family, said the state's investigation had explained how the collapsed happened, but not why.
"That's what the civil litigation will try to get at," he said. "We know procedures were broken, but how often, and why? This is a fairly widespread practice of cutting corners, and that's a concern."
