Friday, February 24, 2012
Picture from RMF24.pl
Rzeszow, Poland. A tower crane with the classic Potain Arrow on the counter jib suffered a structural failure between jib section #1 and 2, possibly exclusively on jib section #2. The cause of the failure is not noted. Fortunately no one was injured in the accident. I find it incredibly important to note that the operator was "sober" as noted in the article. (I find this amusing as if drunkenness would be normal or a likely cause of a crane accident as if he were driving on snow. Not that it's likely as a cause, but I suppose a lapse in judgement has been known to occur during alcohol consumption.)
This is an interesting accident. The pendent is fully connected still. Jib section #1 is still aloft. Yet when you look at the end of it, you can see that the chord splices have ripped, presumably at their welds or just adjacent to them. Chord construction is commonly large angle iron pieces welded together for form a square member. At the ends, the splice connections, be they male or female, are welded on. If the welds at this point were not looked at since they are not obviously noted as welds in a cursory glance, a strong load sitting on this splice could easily cause a fracture of the lower chord splice welds which would then rip the top chord, as it has done, and the trolley would be missing from these pictures as nothing would be present to hold it up to be visible. Additionally, note the cables (ropes) appear to be broken near the weld failures indicating trolley placement.
Certainly wind could have played a role, as well as side loading. Side loading is less likely to be a cause this far in on the boom as leverage is severely reduced and the slewing motors would have a difficult time causing this damage at a 10 meter radius. Wind is also commonly caused with the trolley farther out. See this South African accident as an example.
I feel confident that this was simply a structural failure. We have an older model of crane and I would ask, who is looking at this crane? When they inspected the boom, did they look at those welds, especially underneath the chords? Normally these jibs are flat on the ground and a mirror would be necessary to do this. Inspect your welds regularly. I have my jib walked monthly at a minimum. We spend an hour going through the jib, trolley and ropes. Obviously I look that the easily reachable items daily. You too should take the time to look over each weld. You'll find nothing 99 times, but that 100th time you may save your own life.
Posted by Gaytor Rasmussen at 9:58 PM
Friday, February 17, 2012
New York City, NY Imagine a empty dump truck falling from the sky at near terminal velocity. It virtually happened. One of the Favelle Favco tower cranes at the World Trade Center suffered a load line failure while hoisting 3 girders weighing up to 40,000 lbs around 40 stories. The load came crashing back down on to the truck it had been hoisted from. No one was reported as injured.
For me, this is a mind blowing accident. Favco's can hoist 40,000 lbs on a single line pull, depending on the model. Not only that, but at a rate of 190 meters per minute. I'm on a pretty short crane right now because we are on a two crane site, but I'm feeling pretty certain that even with a empty hook, it doesn't move at 190 meters per minute, let alone with it's maximum load. The point being, it's a horse. Both a Clydesdale and a Quarter horse in one. So what could the cause be?
NYDailyNews.com is reporting that the crane had a rope rubbing a bolt in October of 2011. Simple rubbing is not a cause for replacement. Flattening of individual wires to 2/3 their original diameter is cause for counting the wire as broken. Crown breaks would be another cause to count them as broken and then the rejection criteria according to manufacturer of the crane and the rope would begin to be sorted out. So did the company replacing the cable not deal with the rub problem root cause? Maybe, but not likely. The crane would have been inspected since then, and likely beyond the daily operator inspection. Not that this rules out error.
Another cause that occurs to me is the potential for the wrong rope to be installed. Tower crane load lines are to generally designed at a 5:1 ratio. So if you have a 40,000lb capacity on a single line pull, you need a 200,000 capacity rope. What strikes me is the potential for a incorrect rope installation. While this would be stunning, would it be more stunning than not properly addressing a bolt rub? Think about it, if you have a non-rotating rope, you have a swivel at the attachment point. If you have a rotating rope, you have a fixed attachment point. You can also have right hand or left hand lays depending on the drum rotation and attachment side that can affect the design and installation. Were one of these detail missed in the October rope replacement? I was talking with a friend about it this morning and he wondered about a rope defect. After some consideration, I thought, If you have a 37x7 rope, you have 259 individual wires. What are the odds that you would have multiple failures within one rope? While it can't be ruled out, it doesn't seem likely. I have to lean toward the wrong rope being installed. You can't have left a potential known rub point as a problem... right?
The lesson for us is daily inspection. Don't show up early and take a morning nap in the cab. Go through the crane. Look at the rope on the drum. It's not complete, but it's better than putting your feet up and setting the alarm. Make sure that we are going through our ropes against the horizon regularly and monthly have the bell man wrap it with a towel as we hoist up or down as appropriate. I've seen 9 month old ropes birdcaging off the drum with the hook at the lowest point. If I hadn't simply walked back to the drum, who knows what would have happened. Look at all of the rope. Make it a habit. Think of the ride this operator must have went through losing 40k and the fear that he might have just had a death under his hook Take that thought with you. It's what should be motivating you daily because you never know unless you inspect.
Posted by Gaytor Rasmussen at 8:37 PM
Saturday, January 28, 2012
College Green, NSW A man named Fen Joyce fell from a 45 tower crane jib at 12:30 AM after having been at a party. His friends are mourning the loss and note that he was a fun person to be around. You can read more in a newspaper article in the Manly Daily
It's not that uncommon for people to climb cranes at night. I've seen pictures show up on photo sites that are of people sneaking around. People have been passed out in cabs only to be found by the operator in the morning. Talk about a hang over. I've had the hook of my crane tangled in trees after fraternity pledge week near the University of Washington. I've even heard stories of people climbing cranes to steal power cables for their value in copper wire. One of those stories also involves two heel marks being drug out to a car due to apparent electrocution. One of my favorite stories involves a local operator whom decided to retire to his cab after going out with the iron workers on site to enjoy some brews. He awoke with lasers on his chest from police shooters and the cell phone ringing with the job superintendent on the other end asking him for any information about how to get into the cab.
We should take measures to keep people from hurting themselves. I'm back to running a crane after our long economic slow down. I'm working in a University District so I have the base walled off with razor wire at the top of the wall. Additionally there is a set of hatch doors on the tower that would force someone to crawl outside of the tower to continue up (top of second tower section). If they get to the top, the door to the cab is locked, but they could certainly access the jib. Short of positioning a MMA trained security guard on the tower, I'm not sure what else we could do to deter this behavior. In the crane being used on this job, a solution may have been simply locking the lower hatch door on the cab which would prevent a person from getting further than the turntable.
People are sometimes just determined to do what they want to do. We can't protect everyone from themselves, but we could do our level best with some efforts as simple as a pad lock.
Posted by Gaytor Rasmussen at 8:05 AM
Saturday, December 24, 2011
Essex England. The boom of a luffing crane suffered a structural collapse and has been left hanging while crews assemble to disassemble the structure and make the site safe. At this time, high winds are expected so the nearby flats have been evacuated. Given the fact that the crane is not likely to weather vane properly, this seems like a prudent move.
I have only found one picture on BBC's website. Link The details are sparse at this point but it seems clear that the boom is being supported by the pendant. The cause of this accident could be varied. Structural failure due to weld failures. A pin backing out at a splice connection. Side Loading. Operating in high winds. It's a wide open until more details are released.
Posted by Gaytor Rasmussen at 7:49 AM
Monday, February 21, 2011
Stuttgart, Germany A Tower Crane collapsed inside of a 40,000 seat stadium. The crane was a mere 14 meters high, and the cab of the crane was dislodged in a way that it seapartated from the wreckage which allowed the 31 year old operator to clear himself from the cab with broken ribs. He was immediately taken to the hospital.
The crane appears to have broken away at the Cat Head to turntable connection. Sometimes these connections are made with through bolts. We have seen a number (1, 2)of Comedils come down due to poor bolting and bolts that have never been changed out after being torqued. I have personally found loose bolts on similar connections. I'm not familiar with the particular crane in use here so I can't really know what type of connection it is that we are talking about. Is it a pin that maybe had a keeper missing? A set of shouldered bolts that were not tightened due to being forgotten?
You should be putting your hands on the bolts of your cranes. I can't tell you how often I find hand loose bolts that should be tightened well beyond my physical ability to loosen them without a tool, let alone by hand. This is how we can prevent these problems from getting to the point of failure. Daily Checks should be done prior to each shift. Don't take the extra time your employer gives you to just go up in the crane and get yourself set up, walk that jib. Look at those pins. Put hands on those bolts. It's your life that we might be talking about.
Kran Unfall Stuttgart
Posted by Gaytor Rasmussen at 9:25 PM
Saturday, February 19, 2011
Plymouth, Devon, UK A man in his 30"s fell from a tower crane. The fall was about 200 feet in length and resulted in death.
Vertikal reports the story as a man whom climbed over a security fence then climbed the crane without authorization. When he reached the turntable he found that he couldn't get any higher and then fell or jumped to his death.
The picture shows what appears to be a Liebherr 420 (US designation). These cranes have a hatch door from the turntable to cab transition. If you are the operator, you can place a lock that would prevent a person from getting past this area. The height of the cab and it's sheer sheet metal face would make it impossible to climb around without setting up ropes.
This is one of those things that we in the industry often endeavor to prevent, but it seems like a uphill battle. I've seen cranes with 10 feet of plywood walls built with razor wire at the top. The crazies still get by. People stealing copper show up to take the large power cords that feed 480v with a 200 amp service up to the crane. Operators will show up and find the cord gone. We've seen it where they've just taken bolt cutters and cut right through the live wires. I've heard a story about it happening at a crane service yard where they found drag marks as if the person who did it was injured and couldn't walk out. Sorry, I find that hilarious. Sometimes justice moves at the speed of light.
You should do what you can to prevent people from getting themselves hurt, but if they are jumping fences, clearing plywood walls while getting through razor wire, they are determined and short of putting a couple of trained pit bulls on the second mast landing, we can't save these people from injuring themselves. Even at that, they would certainly sue here in the US for the bites that they would receive, and sadly they'd often win.
Posted by Gaytor Rasmussen at 7:58 AM
Monday, February 14, 2011
Buenos Aires, Argentina (Palermo Las Canitas) A tower crane on a specially designed pedestal collapsed killing no one. It fell over four buildings, destroyed the ceiling of one apartment, which would have likely killed the occupants if they were in that spot, but everyone walks away from this one.
Looking at the design, I've never seen anything like it. It's a large concrete footing on top of four concrete pillars. At first my thought was that that they were trying to make it easier to finish the building at the end of the job. Normally you would pull the tower sections out, then go back and fill in the 3x3 meter holes in the floors that allowed the crane through. But if you had four concrete pillars close together like that, what could you put in that area of the building? So ease of removal couldn't have been the case. It actually looks like it would make it 100 times worse because you would have to remove all of that concrete. The only thing even remotely close to this that I've ever seen is a crane that was anchored to a large structural concrete beam that then had Aluminium Screw Jack Shoring for the next two floors down.
Looking at the base, I just don't like the way it's set up. You have a crane that is sitting on top of this large concrete block as if it's a raised footing. Then you have two floors of concrete columns. It would be one thing if the concrete portion had something to resist the torsional loading, but I don't see much that would resist that. I see some wood, but a compression or two on soft wood and you simply have wood sitting there and providing no resistance. We've all felt concrete floors move under us when a car drives by in a parking garage, and frankly a crane being loaded and torquing up to swing is doing the same thing to concrete. Since even flexible concretes are terrible in shear, what is stopping this concrete from moving? In the case of the crane on the large structural beam that I've seen, it was all tied into the floor of a building with enough mass to resist it. Here, there is little mass, and the mass that is there, only makes it worse because it's so top heavy.
For us in the field, this strongly points out the need to inspect your cranes, daily, and prior to your shift. Get out that flash light and look for concrete cracks. Don't show up to your crane and just run up the ladders. You might get the odd person whom doesn't understand. But here is the reality. That concrete, it didn't crack overnight. It was moving, and those cracks could have been seen. The same is true with most weld cracks. They spend a while moving and tearing just a bit more each time until enough of the weld has failed that it can't take the stress at all and let's go. Dig around, look. One other important thing, notice that the failure is on the side that would normally be considered loaded because the limited size of the jobsite on that side of the crane? The counterweights load that side of the crane nearly as much as the maximum pick on the jib side. So be sure to look at all sides of your crane thoroughly.
This story was brought to my attention by another blogger. Gustavo with Gruas y Tranportes (Cranes and Transports) alerted me to the story as it was in his home town. He has written a few blogs on it and there is some more information that can be found there. Thank you Gustavo.
This morning a video from inside one of the apartments came out on this website. Can you imagine the fear of watching TV while sitting on that couch! If you were under it, it might be deadly. I also found it interesting to see so clearly where the rebar was helping the concrete hold together.
Colapso de grúas en la Argentina
Posted by Gaytor Rasmussen at 7:35 AM