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Re: Crane Design; SE v. ME

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I do not disagree with any of your comments, Christopher.  The majority
of building cranes are in the 5-15T capacity range and 40-60 foot spans,
and I'm not sure that dynamic analysis is needed for these smaller units.
 Assuming the crane-to-building connections hold, damage to the cranes
themselves appears rare, in my opinion.  Once the connections start to
fail, all bets are off.  Top riding crane have additional failure modes
by rail-to-runway connection failures, and by coming off their tracks.

I will try to get the papers out to you this Friday.  For you, this will
be a very simplified approach, but it was intended primarily to open some
eyes to the nature and magnitude of the crane-building interface problem.
 The solution, at least for now, is to get some SE's involved and taking
charge of the total building risk analysis and seismic design.

Russ Nester
rnester(--nospam--at)juno.com
_______________________________________
On Wed, 10 Mar 99 10:18:11 -0600 Christopher Wright <chrisw(--nospam--at)skypoint.com>
writes:
>>Bottom line is that the crane manufacturer needs NO
>>ENGINEERING LICENCES to build and sell a crane.
>This may be an oversimplification of the intent of that wretchedly 
>stupid 
>'manufactured' or 'standard' product clause in most engineering laws. 
>There are two other features of the model law, one defining those 
>areas 
>requiring professional engineering services and the other requiring 
>such 
>services where public safety is an issue. These latter two could and 
>should supercede language slipped in by manufacturers concerned about 
>limits on the shoddy crap they could ship. (BTW, does the Arizona 
>engineering law still exclude the mining industry from its purview?) 
>
>I got involved in a matter once where an electrician was killed when a 
>
>badly designed hoist drive failed. One of the points at issue was 
>whether 
>the hoist manufacturer was practicing engineering unlicensed. Another 
>involved the competency of the AE firm supervising the project to 
>oversee 
>the design and installation of the hoist. It's unfortunate that this 
>case 
>settled so quickly, it might have made the point that engineering has 
>changed some since the days when the engineer was a master builder who 
>
>could sketch and do arithmetic.
>
>>In general, most building cranes will withstand zone 4 seismic 
>loads... 
>> Also suspect might be the runway beams.
>If you mean the specified static horizontal accelerations, 0.3 g 
>doesn't 
>even come close to matching the dynamic loading on a crane structure 
>during a quake. Response isn't confined to a single fundamental 
>frequency 
>and the frequency range of amplified ground motion usually includes 
>one 
>or more of the significant modes. There are also uplift and sliding 
>issues that need to be addressed too. And I've found that runway beams 
>
>stiff enough to be usable (because they're so long) are usually not 
>the 
>problem; if I had to pick just one area I'd say connections.
>
>>The loads you have been supplied by the crane engineer do not include
>>seismic, as you have suspected.
>Don't assume this, either. CMAA doesn't specify the methodology, but 
>that 
>doesn't mean that someone hasn't done a seismic analysis. You just 
>need 
>to be able to assess what you've been given. If it were me and the guy 
>
>handed me a set of reactions based on a static acceleration, I think 
>we'd 
>have a sort chat about dynamics and sufficiency.
>
>I'd be very interested in seing the paper, Russ.
>4903 Royal Oaks Drive, Minnetonka MN 55343 Or email a copy of the 
>document, if that's handier.
>
>Christopher Wright P.E.    |"They couldn't hit an elephant from
>chrisw(--nospam--at)skypoint.com        | this distance"   (last words of Gen.
>___________________________| John Sedgwick, Spotsylvania 1864)
>http://www.skypoint.com/~chrisw
>
>
>
>

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