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Re: Cranes and earthquake loads

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Bill ---

This is not an unreasonable approach, if one understands the limitations.
 First, it still may not address directly the weak link - the attachment
of the crane runways to the building. Secondly, the runways may or may
not be supplied by the crane manufacturer (typically not).  The crane
manufacturer is unlikely to have a problem with seismic loads, since the
stress allowables for the crane itself are conservative, and crane damage
is rare.  

Again, the heart of the problem is - who is engineering the attachments
of the crane (runways) to the building, what loads are used for this
seismic design case, and to what standard is this design to be addressed?

When I presented this conundrum to the DOE Committees on Cranes and
Rigging in 1994, I noted that it was difficult to bring a building design
engineer and a crane engineer into the same room together to address this
interface.  Presumably, both are staunchly protecting their scope of
liability.  After the presentation, more than one individual spoke to me
privately stating something to the effect of "I have just such a problem,
and I don't know what to do about it." 

I feel strongly that the Structural Engineer (building EOR) must take the
lead in rectifying this potentially hazardous situation.  Crane engineers
are most likely ME's, and many are not registered.  Most will never
understand the building structure adequately.  The building EOR is much
more capable of understanding the interface problem and enough of the
crane hardware, particularly if he/she works as a team with the crane
engineer.  The best protection of professional liablility is to NOT have
a failure. (My, what a novel concept!)

As a related problem - what do you all do when you review a building with
an existing overhead crane?  How can you assure an industrial owner that
his building is "earthquake safe" if you don't know whether the crane is
safe? You cannot assume that the crane was installed to the level of
safety of the UBC - it was not.   If you exclude the crane from your
review, you have rendered an incomplete, and possibly misleading report
to the owner.  Bottom line - if the crane falls down, someone will beat
you bloody with that report.

Russ Nester
rnester(--nospam--at)juno.com
_____________________________________________________________
On 07 Oct 98 10:00:11 -0400 "Bill Sherman" <SHERMANWC(--nospam--at)cdm.com> writes:
>CMAA 70 for top running bridge cranes states: "Seismic forces are not 
>considered in this design specification.  However, if required,
>accelerations 
>shall be specified at the crane rail elevation by the owner or 
>specifier. 
>The 
>allowable stress levels under this condition of loading shall be 
>agreed upon=
> 
>with the crane manufacturer."  
> 
>I have designed crane runways for the lateral force due to the inertia 
>of
>the 
>crane mass/weight not including the lifted weight.  If the crane is 
>only
>used 
>for infrequent maintenance, a "parked position" can be designated and 
>that 
>position used for the seismic design case (assuming that the 
>probability of
>an 
>earthquake during operational use is quite small.)   

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