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.
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.
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?
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.
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).
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.
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.
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?
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.
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).
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.
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.
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.
