Thursday, October 28, 2010

December 9th, 2008

St Petersburg, Russia. A saddle jib tower crane that appears to be a Kroll suffered a structural failure that is interesting. I was wondering at first if it was an inner pendant failure. The only pictures that I can find are the ones I've screen captured from the video so they are poor resolution photos. You see how the jib is hanging down but not pointed straight down indicating that it still has support from above. You look at the top chord and you can see the single pendant still under tension. Give it's location in terms of distance from the tower, it's likely that it's a single pendant jib.

Moving back you see that the #1 jib section is twisted and has broken lacings. It really appears that the jib has structurally failed. While that in and of itself isn't something new, take note of the hook and rigging... it's empty. No side loading, no overloading, nothing is written about heavy winds but could it be in the video in Russian?

This accident reported no injuries. It was over, or adjacent to, a medical center that had to shut down as much as possible. Cranes seem to spread out enough of the load that they rarely take out entire buildings, save New York with Massive Favco's coming down on brick structures. But counter weights will punch though multiple floors. if not all of the way to the basement. That being, it's prudent to move as far away as possible.

This may be a clear example of why you should be looking at your crane and walking the jib periodically as the operator. There are good bellman that can do it, but the operator is responsible for a safe crane and I'm here to tell you, riding the trolley doesn't do it. You must see both sides of the jib. You have to look for deformations in the lacings. You have to look at the welds and expose the metal under new paint cracks. If you find them, put primer on them. The primer will crack very quickly if the metal is moving and the metal is likely to move long before it fully fails. That being, I'm pro riding the trolley to review the trolley lines, seeing the load line and knowing how the trolley is performing. The core point being that simply riding the trolley is a lame inspection, and that's putting it politely.

Side note: New FLV downloader, dealing with learning curve. Find full vid and text here. I couldn't find any other stories on accident.

аварии башенного крана, крах башенный кран

Wednesday, October 27, 2010

August 11th, 2010

Sukhumvit Soi, Thailand This story comes from a personal blog and is understood from a translation, but here it goes. A tower crane operator decided that he wanted a energy drink. So he had the guys on the ground put one in a bag for him. The story has describes the operator as agitated or irritable. He sends the hook down without worrying about it being under control. The guys on the ground place the drink in the bag and the operator immediately begins to hoist up. As he was hoisting up, he hung up on some scaffolding. Since the crane was small he soon became overloaded and the jib failed.

With a modern crane, the computer, moment rails and or hoist limits would shut down the crane. The crane being used clearly isn't modern. Likely, it wasn't being maintained properly. So as the operator hoists up quickly, instead of shutting down at 100% of the available load with another 50% before failure should happen, the crane simply failed, and collapsed killing two and injuring 3 others.

The operator was clearly in the wrong. You aren't clear of obstructions, so what are you doing hoisting up? You have people under your hook and you can't give them the courtesy of sending them a stable hook? You didn't pack for the day properly so others must suffer your wrath? What kind of training did this operator have? He knows that he was in the wrong. He ran from the job site and was being looked for by the police. I would think that he would have been safer with the police, but I don't know Thailand. He killed two people over a energy drink. Yikes. Link to blog.

Monday, October 25, 2010

October 23rd, 2010

Cologne Germany What appears to be a Speirings 599-AT5 has suffered a jib failure causing about half of the jib to fall into a tree and dangle from the pendant. No injuries were reported in the accident. The building was struck which will require some repairs.

The Speirings Cranes are mounted to an All Terrain Mobile crane frame. They are very convenient for jobs that don't need a crane full time. If you have a wood frame building maybe you only need a crane a couple days a week. The Speirings Self-Erecting Tower Cranes can drive in, set up in about 30 minutes, make your picks for a few days then be off the payroll while the carpenters frame the floor.

The downfalls to using a crane in this manner come in the form of wear and tear on the cranes. In particular, if you have jibs being folded over and over, what kind of wear are you putting on the connecting pins on these lower chords and through the pendants? Are you looking at them every year or so to be sure that you aren't getting wear that wouldn't be visible without dismantling the connection?

At the end of boxed jib chords you'll find that the male and female pin connections are welded into place. often these welds are ground smooth so it's hard to notice that it's a weld, but it's a weld nonetheless. Cracking can certainly occur there and since it's not an obvious place to look, it can be overlooked in a normal inspection. You have to also be cognizant that you have layers of steel moving at these joints. they can bind on one another or drag also causing undue stress that you may be unlikely to see during the normal crane erection process.

I prefer to walk the jibs of self erecting cranes after they are folded out. Trust me, I don't like it because the jibs are tiny, not designed to walked on so foot placement is akward, and the bouncing at the tip is interesting at times. But I've found trolley ropes out of their sheaves and other problems that are likely to only be found after folding out. The picture is low resolution, but I'd like to see a close up of the but of the jib section that broke. I really wonder if there might have been pin walk. It's something that I look for. Pins in holes have a tendency to walk in or out during "action". Tie in collars pins are really bad for this. Sometimes tower pins do this as well. Even with a keeper in place, you'll want to see if the keeper is deforming or marring showing that it's under stress during the folding process. Since no obvious structural damage is evident on the lower chords, from the poor picture quality, is it possible that one of the pins simply sheared it's keeper than walked out? Just a final concern and something to watch for.

The likely crane that failed.

Turmdrehkran Unfall

Saturday, October 23, 2010

July 17th 2009

Bellach Switzerland. I got some updated information about a self-erecting tower crane that went over. The internet was kind enough to send me some pictures that really show the story. In the original story I was concerned about the ground and support under the crane. It turns out that was exactly it.

Rather than building up the ground and compacting then using matting, they chose to span over a void to sit on a pre cast concrete vault or man hole. Who made this decision? I find it hard to believe that they could move over 5 feet or even just rotate the base to avoid the void. Sometimes we get focused on doing something one way and we fail to see options. In this case it was to the crane's demise. Was it a $100,000 mistake? I often see self-erectors on buildings. Frankly, if no one were to provide me a engneer"s drawing, I'm out. In this case, I would have required that the void be filled in and substantial matting be implemented. You can't reliably rely on pre-cast with unknown reinforcement.

You have to see one more photo in here too. Not only did they come up with their own bridge design, but they used inferior materials. Look at the quality of this wood at the break. It's split along it's length due to age and at the fracture you can see the dry rot. There were other pieces where the dry rot was clearly evident where there were no fractures. If you are going off the script for what would be sound practices, at least use sound materials. 

Friday, October 22, 2010

December 16th, 2009

Graz Austria A Self Erector fell over with the 49 year old operator in the crane injuring him.

The crane was lifting 1.5 ton concrete tanks at the time of the collapse. Short of making the pick at the tip of the crane, most K type cranes should be fine with this type of weight. Even if the weight exceeded the capacity, it would have to do so by quite a bit to legitimately pull over the crane. Of course I've seen cranes pulled over. We  had one go over here in Seattle a few years back. The crane could not make the pick so a forklift was used to help the crane make the pick. When the forklift was pulled away, the crane gave way. Sadly I cannot find record of this accident and might have to go to the public library to find it.

I share the Seattle story not because I think that this is what happened here, but because a sound self erector just doesn't fall over, just because. You'll notice the luffing rope appears to be intact. You don't see any bends in the tower sections indicating failure. The jib indicates that it's going straight out as if it was not a pendant failure. But the base is overturned. This doesn't appear to be a crane failure but rather a set up failure.

In the reports filed in the inspection in the month prior "defects" were noted (Link to story). My guess is that the defects weren't addressed. Maybe it was a lack of a soils report. Maybe it was poor matting and frankly it might take the majority of a day to fix the problem. Here in Washington State, if I state that there is a defect, it must be addressed prior to continuing or commencing operation. I'm annoyed that we don't have the option for a correction period because there are times where little problems are not going to cause an accident, but it will take time to get parts. Time to reschedule me and the technician and the test weights. Let's say it's a bad sheave that is still functional for example. But if contractors are allowed to ignore the Notice of Deficiencies, and the result is a crane falling, endangering many lives, maybe it's an annoyance that I can live with.

Wednesday, October 20, 2010

August 13th, 2005

Caracas Venezuela A tower crane erected on a cross base (cruciform) that appears to be the manufacturers design tipped over and crashed on to the job site. Two workers were injured can needed treatment. Link to story.

There were two potential causes noted. One was the crane fell out of a plumb condition. It would be odd, but not unheard off. You should always have your soils checked prior to erecting a crane even if it were being installed in the most reliable concrete footing. Through out the job you have to protect the integrity of the foundation as well. I've seen jobs that needed to be shut down due to a dirt contractor becoming over zealous and undermining the crane foundation. The big concrete block doesn't do you any good if it's sitting on air.

The other potential speaks loudly and is much more common. It was indicated that a large I beam may have been hoisted and overloaded the crane. This would be a significant overload of 30% or more. While it's true that some tower cranes don't have scales, an overload of this amount is clearly noticeable to anyone whom has load tested a tower crane. I've been on a crane that was approaching 117% or so and it was flat out uncomfortable. Sadly it took protesting loudly to point out that we were way past what the crane was rated for. This was a case of over reliance on the computers. We had no alarms going off, the display had noted the overloaded condition due to yet the technician wanted to continue on with the test. The next morning they came back and found the problem. That desire to get everything done rather than having to come back literally endangered my life.

Load tests on cranes must be carried out. You must test the limit switches to be sure that they are in good working order and that no overload can happen. Tower Crane operators trust their limits as a habit, good or bad, and we owe it to them to get the limits properly set. Don't scrimp and assume that the limits are still working since the time that the crane was erected.Test the limits properly. Adjust them as needed. Then we can all go home!

Monday, October 18, 2010

August 15th, 2010

St Petersburg Russia. Two Tower Cranes were blown over in windstorms noted as "hurricane's". Considering how often I see the translation to hurricane I wonder if big winds or heavy storm simply translates that way. In both cases the operators were in the cranes and injured. In one the female operator was hospitalized with a brain injury and she suffered a broken leg. Link

The picture of the downed crane appears to be a bottom slewing crane with the machinery at the base, and it's on rails. The failure is structural and in the in the mast. As you look at, what strikes me is that it would appear that the crane was still in operation. The machine deck is opposite of the jib, but it's blow over backwards. The assumption for me is that since the tower doesn't look twisted, it was facing the wind instead of away from the wind. Sometimes operators assume that this is OK because you are getting hit with a crosswind that catches the surface of the jib. But this doesn't take into account the whole picture. Tower cranes weather vane with the jib down wind also because they lean back into the wind when they do so. Imagine walking in heavy winds and leaning backwards instead of forwards to drive through the wind. If your crane is in operation during heavy winds, you are asking it to not only deal with the winds, but lean backwards at the same time. On many cranes the jibs also have positive lift when the jib is unloaded so you also might be losing a portion of the weight of the jib that normally holds it down due to the wind exposure on the bottom surface.

Don't be a hero in the wind. Most tower cranes are to be shutdown by 70 KPH or 42 MPH. Some are sooner. Adhere to it. You may be able to be the guy that runs into the 50's (MPH) for a career, but you only endanger yourself, and everyone else around your crane. There is no warning in structural failure. It will be immediate and unforgiving.  Shutdown the crane, find out what the weather is likely to be doing from a reliable service (In US eg. NOAA, Weather Net) and if it's not looking good and going to get worse, why would you stay in the crane? The climb is not that difficult.

крах башенный кран, аварии башенного крана

Friday, October 15, 2010

Historical Tower Cranes

Liebherr TK8 Circa 1948

I love history. I complain about the safety of the old cranes, but I have to say that I love them. I've operated a Peiner PC 1200 from 1968. No counter swing, controls weren't standardized, single speed trolley that only ran fast due to lack of parts... try threading 10 meter I beams through a doorway with a crane that has only a fast trolley and no counter swing or positive acting brake! While I don't like to see them on sites, I find the history intriguing. Seeing the evolution from small tilt up TK 8's to the massive Kroll K10000 makes me smile like I did when I was a kid getting into my grandfather's old crawler that he had in his junkyard.

Old Portal Crane, Peiner 1200 (US designation), &TK25?

The best website that I know of that has assembled the history of tower cranes is Kran-Info. They have photos of cranes from the 40's with Hans Liebherr's TK8 to the large Wolff portal cranes that began to change how we constructed buildings. Pictures of them in use, pictures of the old controls that may make you scratch your head, and pictures of them being restored. These guys even have a museum that you could visit if you end up in Germany!   

They were kind enough to allow me to promote their site and I thought that some of you may enjoy the site as much as I do. So go check it out. You might be there for a few hours!

Wednesday, October 13, 2010

August 20th, 2010

Nizhny Novgorod Russia, a Hurricane blew through blowing a crane over and into a home damaging it. Also damaged was an apartment building. If you have an event like a hurricane as a once in a life time event for where you are, then maybe the accident is understandable. Clear all humans away from the crane as the storm approaches and if it fails, we can always fix wood.

The operator was killed in the collapse. How could an operator be killed in a hurricane? What was he waiting for? If it were a Tornado with much less warning, as soon as you saw it coming wouldn't you cut the load free, weather vane the crane, get down and get away from the crane? Are you really hoping to make a pick or two when the eye of the storm passes over? I don't understand it. Link

аварии башенного крана, крах башенный кран

Tuesday, October 12, 2010

August 9th, 2010

Salvador, Brazil A crane collapsed with three workers on it killing two and burying one whom was rescued and appears to have survived. The employees are employed by the crane erector whom was also responsible for the operation of the crane. Unfortunately nothing indicating a potential learning moment crops up from the story.

The crane appears to be a small top slewing crane and from the two pictures that I've found I don't see any mast, yet both the tip and the counter jib of the crane. It should be safe to say that the entire super stucture has dismounted the tower. There are a number of things that can cause that. Old technicians have told me uncomfortable stories about testing the slewing brakes on the old cranes. On some of the old cranes you'll see "toppling hazard" stickers in reference to closing the brakes without slowing the swing. Well, that used to be a method of testing the brakes on some cranes. You closed all of the brakes simultaneously and timed the braking. Fortunately I've never seen that... intentionally. I've seen a faulty bearing cause an immediate stop and I don't ever want to see that again. We had five of us up top and before we swung a second time, three of us were below the turntable... of course we were just listening and not terrified... right? We dismantled that crane and installed a new bearing.

The crew may have been inspecting the crane to determine what the problem was. Bearings and broken welds are often difficult to determine. We often hear noises in our cranes and we should pay attention to them. Having a second set of eyes is critical to seeing the whole picture. I had a crane on a cross base once that was fracturing the counter weights because the base was flexing excessively. Age and slop on the pins? I don't know. We welded in some beams that ran horizontally and stiffened the structure. The popping stopped when the beams were added and I ended up being safe. Is it possible that they were searching for a problem and were too late in finding it?

colapso do guindaste de torre

Monday, October 11, 2010

October 6th, 2010

Seoul Korea, I think that we have at least two cranes involved in an accident with two people dead. I have found video of the site, but it only leaves me with questions. The Video is slow to load at this site, but it will get there. This screenshot, at the top of the blog, is from another video that I couldn't get to load and it shows a crane that appears to have collapsed at the turntable. Assuming the timing of the videos are similar, and they are according to the dates loaded, it would seem that we must have had one crane collapse at the turntable, fell, and in the process struck the other tower crane boom.

The immediate reports are that this is a Comedil flat top crane and the Cat Head bolts are to blame. The suggestion according to the translation of the article is that the bolts should be periodically replaced. There seems to be questions about the type of bolt used and the manufacturing of them. Admittedly, this is from a terrible translation. You can read the article here.

I don't have a Comedil manual on hand to verify whether or not those Cat Head to Turntable bolts must be changed out each time. If they do, well, you should, obviously, change them out. The type of bolt that I'm used to seeing is of the same finish and visually appears to be the same material used in the tower bolts. I don't know if they are tightened to their yield, but I doubt it because they are tightened with a torque wrench if  I'm not mistaken. Either way, follow the manufacturers plan on bolts and do not skimp on what bolts to purchase.

UPDATE: This is a copy from a translation of a Japanese story on the Korean Collapse. The short version -TLDR: Cat Head bolts were changed out to a smaller and weaker version. Link to story

June 10, killed two西橋dong (Inc.) GS GS survey construction tower crane accident in question involved the construction of the outsourcing company.
This accident investigation committee, the National Institute of Scientific Investigation, Korea Occupational Safety and Health Authority under the Ministry of Labour, (stock) to participate in Korea Occupational Safety. The only private research organization of these (strain), Korea Industrial Safety, GS outsourcing company that has itself as an institution per year utility construction inspection. So construction union "has been the case study happens to leave the outrageous murderer" has been criticized.
Moreover, the construction union member organizations other than the State Department worried that the investigation of the case as it hides all interested parties. Industrial Safety and Health Authority, was passed by the tower crane design approval of an improved type of low strength bolts.
The tower crane accident happened CTT 561-1A is, CTT equipped modified after being imported into the country 516 models are equipped, they were equipped with low-grade deformed bolt type type type from the pin. However, occupational safety and health corporation on September 17, 2004, approved the design of this equipment grated pass.
Oh Hiteku construction union chief external relations, "features a thin bolt is true, from a pin method / 3 about the weak" and "accident happened in 1997 was broken bolt so well," he explained. Tower cranes are used in particular crash site, which currently is running 10 in the nation, adding that the situation can not exclude the disaster.
Despite the structural flaws of the equipment, occupational safety and health approved by the corporation and thus inspection, GS will be participating in the Korea Occupational Safety and Accident Investigation of construction contractors, the survey results were unbelievable. Construction union said: "We can expect comedy and transparent investigation" and that "this field study is likely to be concealed as bad management of equipment suppliers," the statement said.
In addition, the investigation into the accident that eliminated many trade union advisory experience in the field, see the construction union can not cover up the incident because the suspect] has been refuted. Oh Hiteku director, "the union could not accept requests to join the investigation continued," and "on the tower crane accident in a foreign country is not too hard, but must also resolve the fundamental problem we will of Not enough, "his voice raised.
Currently, the union construction tower cranes on a frequent accidents "are mushrooming hundreds of equipment leasing company, from maintenance and repair of equipment are not investing in the competition by dumping blood" has been said.
Since construction equipment management law in 2007, has been designated as one reason to be delegated to private bodies entrusted inspection from the Land.That the rampant money because loose testing private inspection organizations in the field.
For this construction union "of the Land, the test should be leaving any time of the accident-prone company and get to present a comprehensive management plan for the introduction of a demerit system," he said.
Translation / censure: Yasuda (Yu) 
Use of copyrighted material, pursuant to authorization fromsharing license version 2: 

타워 크레인 붕괴

Sunday, October 10, 2010

September 13th, 2008

Turin Italy, An apparent tower crane operator found himself hanging from his load line by his knee. The fire department managed to rescue him by repelling down to him then continuing down to the ground with the operator. This might be the closest to a Darwin Award recipient I've seen on a crane.

The article doesn't seem to indicate how he got there. One thing is certain, he was on the jib without being tied off or secured if you will. I suppose if he thought that he saw a problem with the load line and leaned down to see what it was and lost his balance, the accident becomes plausible. Paint oxidation on lacings can make the cranes slick to walk on. The day does look like there maybe moisture in the air. If condensation has built up on a tube lacing and he's crossing in the middle, it's another way that you can slip. I have to say, after 8 years of walking crane jibs, I'm as uncomfortable on a wet oxidized lacing as I am on a icy or snow covered one. To make matters worse, it looks like he's wearing rubber boots. If you don't have the proper foot wear, being a flat bottomed, firmly supported, yet soft rubber soled boot, leather upper boot, what are you doing there?

The weight of the block is likely to be the thing that saved this man's life. As his load would have been added, the block would have been raising at a relatively slow rate decelerating him. The block weighs more than he does so as it came up due to his added weight, it prevented a sudden shock from the fall and must have been the difference between him being able to hold on during the deceleration and not being able to hold on. He's very lucky and this is a clear reminder to tie off at all times. Enjoy the video

Friday, October 8, 2010


Heidelberg Germany Maybe the earliest photos of a tower crane accident. I've hesitated in posting this accident before because I'm not sure of what this crane is that is down. It's clearly from 1955 and from the Heidelberg Water Authority. It's clearly a bottom slewer on rails. The rails are not secured against the torsional moment induced by the crane because they have slid all over the place. But from the pictures, I can't tell if this is technically a derrick or a tower crane. If the boom mounts at the base, I'd call it a derrick. if it mounts up above, I'd call it a tower crane. Either way, it's very early and the crane in the background appears to be a Liebherr TK10 on the same rails.
As a learning note, the rails should be secured well enough to resist the torsional (twisting) moment of the crane. These rails shifted significantly indicating that this was a serious problem, if not the cause of the accident. Interesting photos either way! Link to the orignial.

Turmdrehkran Unfall

January 30th, 2010

Starnberg Germany, A Self Erecting Tower tipped slowly enough that all of the construction workers except for one managed to get to safety. One of the workers was caught and suffered a renal contusion (bruise of the kidney). The cause of the accident is not listed. Could it be an over load? Were the appropriate counter weights installed? Was the base set level within 1% of level? Was the soil reviewed prior to the installation? These are some of the major issues to address and watch for in dealing with Self-Erecting cranes besides the obvious boom rope which clearly performed well in this accident.  

 Turmdrehkran Unfall

May 6th, 2010

Tubize France, A Tower Crane lost one of it's counterweights while operating. The weight crashed through a school that the weight was suspended over going through the roof, through the floor and into what appears to be a parking structure. One counterweight remained attached. The combination of the trolley being all of the way in and apparently no load being on the hook and the weight remaining attached may have been the difference between collapse and remaining standing. Had the second weight dropped off suddenly I have a hard time believing the crane would stand. On the other hand, it's certainly happened a number of times where one jib of the other has collapsed and the crane remained vertical. If you've ever been on a crane while being erected or dismantled, you'd no doubt be with me and not understand how that can be. Link to original story with more pictures.

July 22nd, 2010

A blogger posted some pictures of a 33 story tower crane that suffered a collapse in the superstructure. It's not clear if this is a pendant failure or the tower top, but the whole superstructure is totaled and they report at least two dead.
The location of the accident isn't clear. I found the blog with Traditional Chinese but Google Maps brings up a Chhang Road in Cambodia. I unfortunately don't have a clear understanding of where this accident took place.

August 16th, 2010

Inner Mongolia, A tower crane being climbed down for dismantle failed in the mast. Four workers were present on the crane during the climb and three were thrown from the crane receiving injures such as broken backs. The fourth was trapped in the mast, pinched on his leg by the collapsed structure.

The rescuers can be seen in the picture. It really shows the standards of safety required. We have rescuers wearing no fall protection up 20 meters and fully exposed. no High-vis, No work boots... PPE is non existent here.

The man that was trapped was released after 40 minutes and taken to the hospital. Link to story with more pictures.

August 31st, 2010

Changchun City, China A tower crane collapsed killing 4 and injuring 1. Link No details are really given and the pictures don't share enough to see the exact cause, but one picture is worth 1000 words.

The tip of the crane in the accident shows that the Load Line is improperly terminated. Normally you would see the wedge and socket running to a swiveled connection that would allow the rope to spin out and prevent the block from ever twisting up and allowing the rope to work as a non-rotating rope. These applications vary, but look at the termination closely. It appears that the rope is simply ran around the tip, turned into an eye, then three wire rope clips have been added. Even the tip of this rope appears to not be secured from fraying. The strength of the rope is compromised to an assumed 75% of capacity with the clamping method since it includes the live end. The bending of a rotation resistant rope around a boxed tube puts it well outside of the D/d ratio allowed further weakening the rope. The prevention of the rotating of the rope will only lead to the twisting of the block and potentially core failure. This may well be the dumbest, or at least equal to the dumbest, thing that I've seen an erector ever do. I can only dream what the actual cause of the failure is. Homemade mild steel nuts on the mast bolts?  


August 11th, 2009

Nanchong, China I found a second crane Nanchong that collapsed in August of 2009. Link No notes were available on the number of injured involved.
The crane was clearly recently installed and being climbed to it's working height. You can see the climber, the tower hanging from it, and the additional towers on the ground. It's not a common practice to use a small crane to erect a tower crane then climb it later. In the US, most of the cranes are erected to the needed working height and climbing is a less common practice except when the height of the crane will be beyond the maximum free standing height.
Two things stand out to me in this picture. first and foremost, the tower doesn't appear to be plumb. Is that an illusion? I hope. Was the soil not adequate? Was it built out of plumb, I don't know but the appearance is that the mast failed on the side that it's leaning to. That could all be a coincidence.
The other thing that stands out points back to my last post, also about Nanchong and Climbing accident. The hydraulic ram is visible and partially extended. It's on the opposite side of the apparent structural failure. So if the ram is pushing up, the rollers at the bottom of the climber are not tight, and the climber and super structure are allowed to lean too far out of plumb, then you have loading beyond the engineers intention and the point loading (fulcrum) on the side of the tower at the bottom rollers exceeds the design strength and you have a failure just like this one. Add in the potential of the crane being out of plumb to begin with and it's a recipe for failure.


June 22nd, 2010

Nanchong, China A tower crane collapsed killing two and injuring one. Link The accident appears to have been a climbing accident where the mast failed. When I zoom in on the picture (certainly is grainy as I don't have CSI enhance capability) I see what appears to be a gap between the mast and the turntable with a climber in between.
Generally when you climb a crane, it's to be balanced. There is a rocking back and forth as the hydraulics push at a slight angle on most models. but the amount of overturning moment induced on the tower should be minimal and certainly not enough to cause the tower to buckle. It should be vertical loading almost exclusively.
The cause of the buckling, being unbalanced, wind, or improperly adjusted rollers (some older models had rollers that had to be adjusted on each climb) are my primary suspects here.