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Tower crane collapse -- Downtown Seattle
2

Tower crane collapse -- Downtown Seattle

RE: Tower crane collapse -- Downtown Seattle

Sadly that's like 'The Annual' big city crane fall.

Apparently they were in the process of dismantling it. I'm sure there are probably instability points in that process where it comes down to crossed-fingers that a wind gust doesn't show up at exactly the wrong moment. There are reports that a large gust and high winds did occur at the time of the failure.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Tower crane collapse -- Downtown Seattle

(OP)
Well, a little better than crossed fingers... we usually set weather windows (20mph or sometimes 30mph) beyond which no jumping or dismantling should take place. How that gets implemented... varies.

----
The name is a long story -- just call me Lo.

RE: Tower crane collapse -- Downtown Seattle

Based on the photos it's pretty hard to see why the bits are separated but spread all over the place. The bit of the hammerhead bit are on the roof of a building while the cab and one tower section are on the street separated. I assume the crane fell towards the building on which the hammerhead pieces are sitting. Still I'm struggling to make sense of how the bits seem to be so far away from each other?

RE: Tower crane collapse -- Downtown Seattle

Saw that last night on the local news. Not a pretty sight - 4 dead. Investigation will take 6 mo to a year.

Mike McCann, PE, SE (WA)


RE: Tower crane collapse -- Downtown Seattle

Looks to me like the crane rose from the center of the building. It did not appear to have jib, counterjib or tower peak attached anymore. And it just tipped over from the roof line. Probably moving pretty fast by the time it hit 90° and pushed the top tower section and the cab into the street below.

Quite a few photos here: https://komonews.com/news/local/crane-falls-on-mul...

RE: Tower crane collapse -- Downtown Seattle

Those photos make it a lot clearer to see how all the bits came down. What I thought was the cross arm is just more tower on the roof!

Seems odd that it fell over if the cross arm was already removed (unsure if the mobile crane shown lifting the cross arm is what was removing it, or if it is cleaning up the debris)? But it seems like it was removed given its on the opposite side to which everything else fell. Something must have seriously gone pear shaped.

Theres some pretty serious holes in the concrete pavement where something impacted giving an idea of the force involved (photo 22).

Given there doesn't seem to be a whole lot of damage like block shear or bearing failures on the tower connections (of the one lying in the street) I guess either the bolts/pins sheared or there were no connectors present (a scary thought).

RE: Tower crane collapse -- Downtown Seattle

Wonder if the pins were out and that other big crane was there to disassemble the remaining parts when it was tipped by a wind gust. I have no experience w/ tower crane assembly/disassembly.

RE: Tower crane collapse -- Downtown Seattle

My understanding is that the tower crane was being disassembled at the time.

RE: Tower crane collapse -- Downtown Seattle

Yep.., just as 20 to 30 mph winds hit the area from the north.

Mike McCann, PE, SE (WA)


RE: Tower crane collapse -- Downtown Seattle

Seems like about every single section of truss separated from every other one.

The building took some serious damage too. Note the huge compressor bank that got knocked over and partially smushed holes in the roof.

What a story that lady and kid in the car have. That cross piece crushed the car between the mom's head and the kid in the back seat kiddychair. Probably a few inches either way would've X'ed one them out.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Tower crane collapse -- Downtown Seattle

Anyone know the standard protocol for dismantling one of these cranes? Is it SOP to remove securing connectors at the tower joints prior to the crane being hooked up?

RE: Tower crane collapse -- Downtown Seattle

For the record, in the videos posted by JAE, the tower is falling to the south across Mercer Street, consistent with wind from the north.

Mercer Street is a main east-west arterial that connects to I5 1/2 mile to the east of the incident. The dash cam is looking to the west.

Driven thru the area many, many times in the past. They don’t call it the “Mercer mess” for no reason. Lots of standing traffic most times during the day.

Mike McCann, PE, SE (WA)


RE: Tower crane collapse -- Downtown Seattle

Not sure on standard practice regarding removing all the pins, but it sure looks like none were present the way it slowly tipped from the base and separated on impact?

If the base pins sheared I would have thought it gets to some extreme deflection point and they break and it goes much quicker. It seemed to just go slowly without any evidence of the shock of connections giving way that I'd expect (look at videos of cranes collapsing while carrying loads for this effect).

RE: Tower crane collapse -- Downtown Seattle

Just arm-chairing this with my colleague.

It looks like pins were removed from alternate sections all the way up so that the sections could be removed in pairs by the secondary crane and then transported by truck. You can see that the pairs of sections came apart cleanly in the overhead shots.

Apparently this is common practice as referenced by a Seattle Times story.
https://www.seattletimes.com/seattle-news/investig...

Quote:

A crane’s vertical mast is composed of 20-foot sections that are generally removed by another crane, two at a time because a tractor-trailer can carry a 40-foot load.

“It’s just a matter of unbolting the tower sections and lifting them down,” Ritchie said. “Some people like to remove the bolts ahead of time.”

The sections are bolted together, usually with two or four bolts or pins at each of four corners. Sometimes, Ritchie said, crews will remove most of the bolts from multiple sections at the same time, leaving only two bolts, at diagonal corners, connecting each section.

RE: Tower crane collapse -- Downtown Seattle

I bet that two things will change regardless of the cause of this accident.

That only one segment at a time is unbolted and that the fall zone around a crane is cleared during assembly and disassembly.

Have crane crews just been that lucky all this time? I can see that the fewer trips the workers have to make up and down to remove pins the less likely they are to be injured, but this may shift the schedule.

RE: Tower crane collapse -- Downtown Seattle

So irritating when they hack the videos and slow them and never show you the full speed or the entire video.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Tower crane collapse -- Downtown Seattle

MUCH better! Thanks charliedalphabravo.

Dang. So that was entirely just the vertical part of the crane! That's the part I'd have thought was the least problematic to remove.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Tower crane collapse -- Downtown Seattle

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.

RE: Tower crane collapse -- Downtown Seattle

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!

RE: Tower crane collapse -- Downtown Seattle

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.

RE: Tower crane collapse -- Downtown Seattle

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.

RE: Tower crane collapse -- Downtown Seattle

TV said 35 at time of collapse. We’ll see...

Mike McCann, PE, SE (WA)


RE: Tower crane collapse -- Downtown Seattle

Human error? More like gross negligence.

RE: Tower crane collapse -- Downtown Seattle

Agreed Spartan. No one needed to die.

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.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Tower crane collapse -- Downtown Seattle

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.

RE: Tower crane collapse -- Downtown Seattle

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.

RE: Tower crane collapse -- Downtown Seattle

Videos show sections of the crane separating cleanly all the way down to the pedestal.
From the pictures cab its looks like a Liebherr crane

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