Tuesday, July 28, 2009

July 28th, 2009 Mother of all Near Misses

Blue Cross/Blue Shield in Chicago was adding 24 floors onto their existing 33 story building downtown Chicago. The building was entirely being constructed out of structural steel sans concrete core. The hoisting was being done by two Potain MR605’s which are big luffing tower cranes. One of those cranes nearly came tumbling down from over 600 feet. Great decisions prevented that from happening. This is the story of the nearest miss I’ve ever seen. And I’ve seen a few.

The crane operator had an unloaded hook. He’s running the crane when he hears a loud bang and feels movement from what feels like the tower. He stops to assess what has caused it. The Bellevue crane that survived in the above story, Same thing. Unusual noise and shutter… stop and go see what that was. The crane that collapsed in Bellevue it happened during the crane erection, but we couldn’t get anyone to believe that it was a problem. I had an intermittent popping in a cross base once that wasn’t showing what the cause was. Eventually my ballast started spalling on the frame and cracks were developing in the concrete. We decided that it was torsional loading causing the base to flex. We called in an engineer to design a stiffening method and the problem went away. The commonality… stop and assess.

The towers are connected by pins. The upper section is hollow (with reinforcing) angles with holes milled to accept a set of pins, and from the tower below, a dowel of sorts also milled to accept the pins. It’s a tight positive connection. This dowel which cannot be viewed once the tower is connected is what failed. A crack caused a full separation in the leg connection. This crane was effectively three legged instead of four at this point. Private discussions that I’ve had with some that were there claim that engineers familiar with the equipment said that the engineering numbers showed that the crane should not be standing.

The crane was secured by welding a box frame to the outside of the tower leg. The project was nearly finished so the other tower crane was used to dismantle the nearly fallen tower crane within a few days. Since then all of these towers have had their connections reviewed and NDT tested at a cost to Manitowoc. The Technical Service Bulletin asks that pitting corrosion, cracking, and even scratches in the paint in this dowel area are cause for further review. This article has some decent pictures of what to look for.

So what caused the problem. There is a hypothesis that has been developed. The building was again made of structural steel. Structural steel flexes quite a bit. A job in Portland years ago had a Liebherr 630 tied into it’s structural steel building. In order to plumb the building, they had to balance out the crane first to remove it from pushing or pulling the entire building around. If you have two tower cranes tied into structural steel and don’t have all off the steel as rigid as possible, including diaphragm, then you raise the crane, and add more steel which you will make plumb and rigid, you are likely to add loading to the crane’s mast by pushing it around, and out of plumb. Additionally you have two cranes pushing that steel back and forth on each other adding loading that is unintended in the tower design. We may never know 100% why, as it could have had inclusions in the steel, Porosity, pitting, etc… we can only learn from the potential problem and seek to prevent it in the future.

I applaud the operator for his wise decision making. I’d name him, but I’m not sure that he wants that kind of attention. Dogging everything off and finding that problem was exactly the right answer. Potentially hundreds of lives were saved. To gasp the scope of this… the crane is 600 feet up with 160 feet or so of jib. The break is 20 meters of tower down. So if the crane fails entirely, you have about 250,000 lbs of steel and concrete coming down from 600 feet 230 feet long into a busy street an hitting occupied buildings. Locals 1 Ironworkers and Local 399 Operating Engineers proper training saved lives even though most never knew about it.

Sunday, July 19, 2009

July 17th, 2009

A Self-Erecting Truck Tower Crane toppled this week in Switzerland. Storms and heavy rains were reported and the ground does appear to be wet. I also look at this photo and see poor soil conditions for setting up a crane. The ground clearly isn’t level, but I can only assume that the properly leveling of the crane was addressed. Something that simple isn’t happening is it? I wish that the picture was taken from a little further back so that we could see if there was good cribbing (dunnage, mats) or not.

It’s not often that we see Self-Erecting Truck Tower Cranes go over. They are a great piece of equipment, but the operators need to be aware of all of the same problems that come on both the tower cranes and truck cranes.

There were no reports of injuries in this accident.

I found the last two stories on www.Vertikal.net. It's a great site and magazine (Crane and Access) that keeps track of trends in the industry. Based in Europe, they sometimes find stories that my normal alerts miss.

July 17th, 2009

Oetwil, Switzerland A self-erecting tower crane that appears to have been well set up had tipped over while being used in a concrete pouring operation. !5 workers were on site but fortunately no one was injured.

The immediate thought given the clear stability of outriggers and number of counterweights is the limits. Is it that the limits were never tested or set up? Usually self-erectors limits are contained and once set up for the crane, they won’t need to be re-set unless the configuration of the crane is different. In Washington State the cranes are treated as tower cranes and the limits must be retested during each crane erection. Under the not yet released ASME B30.29 (new self-erector standard) the cranes also must be tested after each crane erection. Of course this is the US standard and even that is voluntary… at least until you have an attorney in a deposition asking you why you didn’t follow it as he stares at your wallet. Then it doesn’t feel so voluntary.

Self-erectors are a great tool, but they need to be operated by competent people. Running it rough and not catching loads near the limit can lead to problems. Imagine trying to run fast on an older crane. You are trolleying out and not paying attention to how heavy the load is or the load chart. From top trolley speed the over-turning moment limit goes off and stops the trolley instantly. The load has 60 feet of line out and now it just stopped at 100% of its capacity. The load swings out 20 more feet before stopping which is now at the toppling capacity due to dynamic loading. I personally think that this is the type of thing that causes most self-erectors to topple. Just an opinion.

Thursday, July 16, 2009

July 16th, 2009

Chattanooga Tennesse. A 41 year old Tower crane operator suffered a medical emergency while in the crane. From 105 feet the fire department had to rescue the operator and lower him to the ground using a ladder truck with a man basket on it.

Something that we don’t talk about much on tower cranes is how to rescue operators, and sometimes others, when they suffer a medical emergency. On a tower crane 300 feet in the air it becomes difficult and time consuming for figure out on the fly. As an erector we always had long ropes for tag lines and if one of us were injured, we would get them down via rope immediately. It would violate everyone’s policy to do so, but sometimes common sense and Bureaucracy don’t mix. I’m gonna save someone’s life and worry about the consequences later.

Contractors should develop rescue plans and talk about it. Materials such as good climbing ropes, possibly a block, harness, carabineers, should be available. If you don’t have a rescue plan in place, you may find yourself with a man in trouble and a fire department trying to figure out how to get someone down as they are literally dying. In the US these emergencies happen 3 or 4 times a year. With some simple planning, this problem if figured out ahead of time might save a life.

Additionally, something that I’m an advocate of is Trauma Suspension Straps. If you fall into your harness and are waiting for the Fire Department to rescue you, you might be killed by your harness due to heart failure (low blood pressure) Worse, the blood that pools in your legs cannot circulate and if you hang for too long, the cells will have de-oxygenated and become poisonous. When you are taken out of your harness, you have the potential to die anyways. For guys like me working on my own, that’s a miserable prospect. The straps roll up in a small packet and remain on your harness. If needed you unzip the packet, connect the straps into a loop and they allow you to stand taking the pressure off of the leg straps allowing the blood to flow and preventing a heart attack or toxic blood. $20 might save your life one day.

Saturday, July 11, 2009

July 11th, 2009

The Liverpool tower crane that collapsed is being removed.
It's a good showing of what it takes to remove these
cranes after collapse. They have a self erector to suspend
the workers cutting the crane apart. There is a 500 ton
crane assisting the 800 ton crane. Clean up of this
magnitude can easily approach a million dollars. I was
involved with the clean up for the Belleve crane collapse
and the cutting apart of the crane and it is a long drawn
out process to figure out weights, closest center of gravity
for rigging, and methods of cutting that will prevent the
shock loading on the crane. It's dangerous work for certain.

Monday, July 6, 2009

July 6th, 2009

Seoul, Korea A Luffing tower crane collapsed in Seoul Korea killing the operator. No one else is reported as being injured. The 50 meter crane collapsed while hoisting 300 kilo items. Those of us in the crane world know that luffers are capable of much more capacity than that. Even a shock load of that magnitude would not take down a structurally sound tower crane.
It was noted in the article that the cause of the collapse appears to be in the tower. My first inkling would be to look at the clearance of the tower to the floors or formwork. I often run across jobs that have formed so close to the crane that the crane moves into forms. When you do this you create fulcrum point over a small area that isn’t designed to take these forces. Nearly everyone knows that you can’t touch the boom of a crane to any fixed object. The same is true for tower crane masts. Carpenters or other workers don’t know this, then you have operators climbing on to cranes at the top floor and not inspecting as they climb. The result is the guy at the base of the crane can kill you out of simple ignorance. Climb your crane daily. If it’s too hard, that’s all the more reason to be doing it. It not just about the belly, it might just help you from becoming a carbon copy of this operator. Additionally dislodged connecting members and lacing failures are items to be looking for during those climbs.
The crane crashed across a rail line and caused major traffic problems as well. That’s two collapses and one lost load in two days. We must be vigilant in continuing to improve.

타워 크레인 붕괴

July 6th, 2009

Liverpool, England A luffing (assumed to be a Wolffkran from the design) tower crane has collapsed backwards into a apartment building adjacent to the jobsite. The operator was thrown from the cab onto the building and is in stable condition. No one in the apartment or jobsite is reported to be injured other than the operator.

Possible reasons for this collapse are numerous off of the one picture. No limits on the boom allowing the boom to be taken past 86 degrees or so can cause this. Poor soil conditions giving way under a base can cause this. Structural failure in the tower would be obvious given more pictures. Shock loading due to poor rigging or load line failure also can cause loss of rear overturning moment.

The crane is an obvious loss. The project will be at a stand still. The apartment next door may have to be evacuated long term. We can’t say what the cause is from the one photo, but preventing it looks awfully cheap now.

Saturday, July 4, 2009

July 4th, 2009

Melbourne, Australia. A crane hoisting drywall lost the load at about 15 stories causing a near miss accident. The load narrowly missing striking a car as you can see in the picture. The article isn't clear about how the accident happened outside of the claim that the load must have "snapped".
Rigging failures due to improper rigging are not uncommon. New York had one that permanently disabled a architect late in 2007. Many others happen that we don't hear about. The US is finally getting testing on national rigging standards that will allow for standardized testing. It should be helpful in making sure that loads are more secure and this happens less often. Having a qualified rigger in charge of attaching a load is critical because often an operator can't see the load. I picked a load in the blind once using four way rigging with self closing hooks. The rigger on the ground could not get the hook in the picking eye. He chose to close the hook with the load resting on hinged portion of the clasp. The load was 180 feet in the air before I could see what he had done and my only recourse was to have everyone stop and clear out until the load was safe again.
Another instance was a guy using a chain for rigging put a lock in the chain instead of finding the right rigging. That was the jobsite foreman. A rigger in the blind with no education or supervision can endager the entire jobsite and the public.
Another point, you shouldn't be hoisting over the public. You really need to find another way and this is accident is a great example of why.
Make sure that you have someone educated rigging your loads. If you are in the states or Canada look into NCCCO certification. Unions, Crosby puts on good classes. Call your rigging supplier and I'm sure that they can point you in the right direction