Tuesday, December 29, 2009

December 28th, 2009

Shenzhen China What is being reported as a crane collapse has killed five and injured one yesterday in China. The accident doesn't specify if it's a tower crane and details are sometimes hard to come by out of China. If I find more I will post.

Thursday, December 17, 2009

November 21, 2009

Update to the Hawaii self-erector tip story. News in Hawaii isn't what I'd call complete. I wouldn't characterize US news in general as good as it's based on popularity. I asked around and got the story. You might say that this is the rumor mill, but it's reliable.
The model was an IGO 21 and not a 50. It's a little crane with only 3900 lbs capacity in tight. This explains the Jeep;s roll bar having the ability to shield the tourists from being crushed. As you might recall, two ladies were sitting in a Jeep when the crane fell over them, but the roll bar saved their lives.
The reason for the collapse is so shocking it's funny. To be clear, I don't know who was who here, or who was doing the work. The crane was purchased in the not too distant past. The assertion was that this was the first job for the crane. They are going to dismantle the crane. Instead of reading the manual and making a step by step checklist and putting someone who knows the process in charge, they just started working. (These manuals are very detailed, use great drawings and the steps are numerically ordered. For the most part, you don't even have to know how to read.) The first thing they did was remove the counterweight. The second thing they did is yell "No, No, No!" and watch some ladies luckily live.
This is one of those stories that leaves me feeling incredulous. Maybe I've just been spoiled, but I don't know what goes through someone's head that leads them to make these types of decisions. What would make a person pull the counterweight on a crane with 80 feet of boom standing out there? It's stories like this that must be shared, simply so that it can be prevented and we can be encouraged to do things right the next time.

Saturday, December 5, 2009

December 4th, 2009

Dongguan City, China A Tower Crane from somewhere near the 50th floor of a planned 68 floor building. 3 people were killed with 5 injured. The story that I've found so far on it reports it as a "quality problem" with the crane already.
The Chinese cranes that I've seen here in Washington have reasonable workmanship. During a foundation load test, I was even concerned that maybe they were too strong, or underrated from the factory. You could see little deflection sighting up the tower. The tie-ins were very loose with pin play from the collar to struts as much as 11 mm from centerline. The response I got to this condition was that it was "acceptable" where as a German manufacturer only allows 1.5 mm for the same connection. There were many design issues with the crane such as having slewing gears inside the turntable (occupied space during climb) with no gear covers. The hook had no rating or data available to reference it's size or measurements. The wedge and socket had not markings on them to reference size of rope or manufacturer. There was an article in 2007 about dangerous steel from China being used in tower cranes. All of these things are required here in the US. I had other questions as well.
We can only hope that China continues to improve for the safety of it's people and anyone whom buys their cranes. If anyone gets more details, please share them.

Edit : Today reports are that the "power arm" broke. It's not clear to me if the mean the counterjib or jib. They speak about the counterweights breaking away, but it's lost in translation I believe.There are tremendous stresses behind the pendants of some counter jibs, of course depending on design. On some you have a lot of weight cantilevered out and counterweight placement is critical. it's not much more of an answer, but it's jib related either way. Link

Wednesday, December 2, 2009

December 1, 2009

Warsaw Poland, The Poles are building a new National Football (read soccer in North America) Stadium in Warsaw. They have multiple cranes both Mobile and Tower throughout the job site. Yesterday two workers died when they fell 50 feet in a elevator car attached to the crane. Story

This is a first for me. I've never seen an elevator on the side of a crane. For us in the US, the idea of an elevator is one of those mystical winged horse ideas. I've climbed over 600 feet of tower on a suspension bridge. I do think that it's a decent idea for getting tools onto the crane and for any rescue operations that may need to happen. But since I've never seen one of these elevators, I have to make some assumptions. If I'm wrong about their construction, please let me know. I'd love to learn about these.

I assume that the elevators were are talking about are similar to regular Construction Hoists that fall under ANSI A10.4 here in the US. A rack and pinion, electric (potentially hydraulic) drive system held to it's track by guide rollers. (For come quick background, in my part of the world, the crane erector often erects both the crane and Hoist as a package deal. I was a licensed Elevator Mechanic in Washington State and now inspect them as well as Tower Cranes.) Most modern (last 15 years) elevators have three electric motors on the car. The point is not just power but also redundancy. If all three were to fail, then there is an overspeed governor that should kick in at 125% of the cars rated speed. The old style is a cable driven clamp system that squeezes the tower legs until it grinds to a stop, and the new is essentially a brake on a gear that gets tighter as the car travels further, after it's engaged of course. The system should be tested after the install. The overspeed governors should be swapped out every four years or so. They do have dates on them. I wouldn't expect to see a counterweight system because they you are added load to the top of the crane whether the is at the top or bottom.

I certainly don't know what caused this accident. I bring up common designs just for understanding of how they work. I would suggest that if your operator is taking an elevator, he isn't inspecting his crane, so who is? Guys hop in elevators and run them because they are easy. Installation and maintenance of elevators is dangerous and important work. It should only be done with a very experienced supervisor involved.