Nizhny Novgorod, Russia Tower crane collapses onto an adjacent apartment building collapsing the entire apartment killing a mother and child. Ten others were injured in the collapse. The crane is an older self erecting type. The base appears to be stable and the failure appears to have happened in the mast. Self-erectors like this use cables to tension pendants that pull the top of the back to create back moment. If you look at the rest of this crane, the rest of the maintenance doesn't look good. Corrosion on the tower makes me wonder about how the rest of the crane was maintained. If that tensioning cable breaks, this would be the result. There are certainly other possibilities, but given stable ground, the failure point, and poor maintenance, it's my first guess. These things need to be inspected regularly. It won't 100% prevent this, but it saves lives even if there isn't a way to quantify it.
Thursday, March 12, 2009
NYC, New York a report is out as of yesterday officially blaming the first tower crane collapse (May 30th 2008) on improper rigging of the tie - in collar. The report is 339 pages and I certainaly have not read it. I'll give you a synopsis from a dozen different stories over the last year.
The collar is installed in halves. One side is brought in and the rigging is transferred from the crane to come alongs attached to the tower itself. The the same process is done to the other side. The crane manufacturer requires that four attachments per half are used, In the case of the accident only two were allegedly used per half. This would be very common for a multitude of reasons such as only having to adjust one comalong per corner to adjust the elevation and level of the collar, less equipment, less time wasted, etc. Four points is how most manufacturers specify the work be accomplished. however, most crane collars do not weight 11,000 pounds either. Most are in the neighborhood of 4 to 6,000 lbs.
Another claim made is that the rigging used was old, flat straps (Nylon Webbing) both UV infiltrated and having suffered nicks in the edge of the eyes and noted prior to use. With flat straps it's important to not used them twisted or bunched up. The eyes failed and a common cause of this is that the eyes are used with the same size hooks and shackles wearing over and over in the same points. A single nick is important to evaluate and realize that 50% of the breaking strength may be gone. I have flat straps in my personal truck for pulling that are nicked, but would never used them for hoisting.
The attorney for the rigger who has been charged in this case claims that the reports claim that one broken strap would not cause the failure of the otehr three is either lawyering or plain ignorant. As the collar is adjusted to the proper elevation and level, the stresses are virtually never equal. As we all know, when rigging something off of four points, you should only calculate the rigging for three points as at any given moment one leg is seeing minimal load. Add in adjusting one corner at a time and often a corner or two comes slack. If you had a rigging failure at this point, you will not only see shock loads doubling and quadrupleing intended loads, you would likely see a zipper effect as the load transferes in milliseconds from corner to corner until the final failure. It would not be a sudden drop evenly onto all three straps in which case the attorney would be correct.
The cures are... Use the eight pick points specified by Favco when installing their massive collars. Currently many companies still aren't doing this. Use the proper rigging for the job. When bunching up or breaking over a sharp edge, do not use flat straps. you can use wire rope, endless round nylons, or grade 80 or 100 chains designed for rigging.
It's unfortunate to hear that people died and the ignorant union leadership hasn't ensured that their membership is kept safe and are using the best practices possible. Maybe that's not fair... where is the DOB on this, general contractors, crane owners... pull your heads out boys and learn from the mistakes. Somebody lead the way.
Posted by Gaytor Rasmussen at 10:32 AM
Monday, March 9, 2009
Jalan Bangsar Utama, Malaysia A crane working on the 22nd floor suffered a load line failure causing the crane to fall and two workers were killed. http://www.nst.com.my/Current_News/NST/Sunday/Frontpage/20090308220153/Article/index_html
The story doesn't specifically state that this was a tower crane nor does it show a picture of a crane. Given the 22 stories and the planned continuing to 38 stories I am inferring that we are talking about a tower crane. Hoist cables are complex machinery and need to be inspected. regularly. The sentiment that it "suddenly" failed is often not the case unless it was the wrong cable in the first place. I've spoken to many operators whom have never even been on the jib of their crane. How are they lubing the rope from the tip back? How are they inspecting the rope? On a hammer head riding an available trolley basket is the easiest way to get a decent view of the rope. Often to inspect a jib I'll have the operator trolley to the tip, then I can walk the structure reviewing it, the trolley ropes as they sit, and verify outer trolley limits. Then I'll ride the basket back slowly so that I can see the loadline as close as possible since it normally sags up to 15 feet down.
Inspect your ropes. 20 minutes can save a life.
Posted by Gaytor Rasmussen at 7:01 AM
Saturday, March 7, 2009
New York NY
News story out of New York about crane inspectors used there. I would suggest that the problem with a governmental inspector in general is that they focus on semantics and miss the real issues. For example ASME B30.3 requires a 110% foundational overload test. Manufactrers often prohibit this test and limit it to 100% of the rated capacity. If the city (such as NYC) requires it so they'll look past the manual and say that it's required here, so do it. At that point everyone's ass is hanging out on the line because you have ignored the manufacturer. But the law says...
Another example is load testing a four part crane. You need to get into the line pull limit and the moment curve of the lad chart. Some manufacturers suggest doing so in two part operation. Yet some city inspectors will focus in on load testing the crane to it's maximum capacity. You can accomplish this in two part operation but they want to see four part operation and don't fully understand that you don't prove anything as the cranes are not limited by structural in tight, but by line pull factors such as the transmission, brakes, or staying within rope safety factors. Most independents know what the intent of the rules are and don't hang up on the minusha of language that distracts buearucrats from seeking corrections on real safety items. I have never seen a governmental inspector walk a tower crane jib in seven years. They aren't even verifying bent keepers or weld integrity then.
Just my two cents.
Posted by Gaytor Rasmussen at 6:56 AM
Wednesday, March 4, 2009
Jeddah, Saudi Arabia
A tower crane collapsed in Jeddah yesterday for unknown reasons. The jib of the crane stretched accross a street and struck two cars. Two were taken to the hospital and there were no reports of death.
The article (linked below) notes that the crane was anchored at the 4th floor (tie in or base anchored on a elevated base?) and was only three years old. They suggest that it was old or overloaded but I would suggest that there are many other potential causes. Towers touching floors cause fulcrum points. Was a collar installed properly? Where is was "tied in" was it properly engineered for the loads intended? Tower cranes have limits installed and are intregal to the crane. On most PLC (primary logic controlled) cranes found on virtually all 3 year old cranes it would be difficult to overload them. Design criteria for cranes mandates that they be designed to handle loads of 150%. To overload a modern tower crane, you'd have to have a shock load, load the crane with another piece of equipment while the load is suspended, intentionally bypass the limits, or have a limit failure. I've been on a crane that was overloaded around 115 to 120% of capacity due to computer fault and poor judgement. It's an ugly event and any experience would tell you to get that load off of the crane. I don't buy the overload and would suggest that design or other failure occured.
Since most of the articles were in Arabic, does anyone else have anything to add? And a number of you had this story in hand yesterday. I noticed my statcounter picked up a surge of hits. I looked for a crane accident yesterday and was unable to find one. I'm using Google alerts. Does anyone have a suggstion for your better options.
Edit: Good pictures found Here
انهيار رافعة برجية
انهيار رافعة برجية
Posted by Gaytor Rasmussen at 6:42 AM