Expert: Roger Zona - 4/19/2010

Question
Roger,
I am a contractor who specializes in installation of industrial cranes. In addition to the cranes themselves, I am often asked to install the runway beams, rails and columns that support the cranes. Some of these systems are totally self supporting and others are hung from the building structure or have their own columns, but are braced to the building for lateral and longitudinal support. I generally am not responsible for the design of any of this, however if a system that I installed were to fail I'm sure that I would be held as one of the responsible parties (e.g. get out the checkbook to pay either the lawyer or the plaintiff, or both) I have been asked to install a crane system that is braced in one side to a concrete block wall with a recommended method of connection being angle tied to the crane column and welded to a plate that is bolted to a plate, attached by anchor bolts (either wedge or epoxy type)into the concrete brick. What I know about the bricks (or as some people call them cinder blocks) is that they break fairly easily. I anticipate the lateral load will be about 1400 pounds. Can you tell me the tensile strength of this material and your opinion of attaching to them?

Answer
Hello Ted,

I think the risk is much too high considering the conditions.  You know - the weakest link, etc.!  The block is most likely concrete block (not cinder block) which is not a particularly strong unit.  The design strength can vary depending on the length of time the block was cured and the amount of cement used.  They are usually hollow core which means they are only as strong as their weakest point.

I have used tower cranes many times but I always had a Structural Engineer determine the method of attachment. You are taking a great risk without the backup.  The cost is minor compared to the risk.

As for the strength of the concrete block, you, or the General Contractor, should ask the supplier for a test report on their block.  Normally they test their product periodically and should have a report on hand.

Let me tell you about an experience I had.  Building a 16 story condo, the exterior walls of concrete block were being installed.  At a height of about three stories there was a failure and a whole section of wall collapsed.  Upon investigation, it seems the manufacturer had mistakenly used a fly-ash aggregate and their was little strength in the blocks.  Fortunately it was a limited number of blocks and we were able to rebuild the wall.  It cost the manufacturer but we also lost time on the job.  I've never had a tower crane failure but I have seen other types of cranes have problems - but usually from overloading.

You are aware of the consequences if a failure should occur.  Ask your insurance agent what the results would be.  Ask your attorney how he would defend a failure.  Ask the Building Official what is required.  I'm surprised your G.C. doesn't require an Engineer's opinion.  That being said, please take the necessary safety precautions.

Good luck

Roger
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