02.06.2008

A tower crane letter

In this morning’s batch of emails, we had a correspondence from the USA, prompted by the tower crane accident in New York on Friday.

Ordinarily we would have held off publishing this immediately while we considered the pros and cons and the potential repercussions. The last thing we want to be doing at this time is a scaremongering in what is for the most part a reasonably safe industry.

But given what it covers and that it adds a highly important point to the debate we are publishing an abridged version with the full letter going into the June issue of Cranes&Access.

We have not published the correspondents name at this time, nor named the correspondent, as we do not have his permission to do so, due to the time difference.

"Don't put off till tomorrow, what you should do today"!

Before going to work at 5:15am I watched the news on the most recent NY crane accident and it was immediately apparent to me that the Slew-ring assembly had failed.

The first thing I did when I got to the top of the 450ft (136m) of 2003, tower crane was check the slew-ring bolts with a 2lb beater using minimum force. There are two rows of bolts, each row having 59.

With the crane balanced off, I started with the top row ( slew bearing ) and when I struck the third bolt it moved ( loose ), I continued checking and when I came to the 28th bolt it broke in two! I then went back to the bolt that had movement and decided to remove it for inspection, which revealed a severe crack at the same location as the one that sheared off.
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The nut from tghe broken bolt

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The broken bolt

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The loose bolt with crack

Because of finding two bolts with a similar failure and the likelihood that there could be many more, I immediately put the crane out of operation. The manufacturer has been contacted and we're trying to arrange for a "Factory Engineer" to come out and thoroughly examine ALL the bolts, and if needed oversee the replacement of ALL slew-ring bolts. Which is the only certain solution!

I will admit that if not for this most recent event, I would not have gone through the extra effort / procedure needed to properly inspect a slew-ring. The typical way it's done by operators and inspectors is either just a "visual" while climbing through the slew-ring, or just a tap with a carpenters hammer, relying on your sense of sound to hear a difference between bolts.

The problem with this is that without balancing off the crane to ensure that the load on the bearing is distributed equally, you can't get a true sense that the bolts are equally tightened and torqued to the proper specifications. And that goes for mast bolts too!

Bottom line, it just doesn't tell the whole story, especially considering the potential for loss of life and property damage. These common, time-saving methods are just not enough for what's at risk. Like the old saying goes,” don’t put off till tomorrow, what you should do today"!

This is a good example of why tower cranes should be thoroughly examined, and more then just once or twice a year. Tower crane examinations require time and contractors are going to have to get used to it.

I was recently talking to a third party tower crane Inspector and he boasted that he can inspect a crane in three hours, easy money! In general a good tower crane thorough inspection should take at "least" six to eight hours (depending on configuration). And with all due respect to OSHA and others, "they are the Jack of all trades and master at none", and cannot be expected to have detailed knowledge of tower cranes.

Name withheld pending request to publish it.