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Re: Crane Design

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The responsibility for the safe working of the crane and for its integrity rests
with the crane manufacturer.  If I were specifying a crane, I won't care who
engineers the crane for the manufacturer. However, I will include in my specs
that "the crane and its accessories should be in safe operation in the event of
an earthquake, evaluation of forces during the earthquake being determined by
UBC (or ASCE) etc. Devices shall be provided, if necessary, to prevent the crane
from jumping off the runway rails".

As an engineer of record for the building, you will be responsible for the
serviceability conditions of the building columns supporting the crane.  That
is, the column should not experience detrimental deflections at the crane runway
elevation. One of the input data you need for your analysis is the dynamic load
from the crane transferred to building columns at runway elevation. If the crane
manufacturer does not indicate the dynamic loads , you should be able to
calculate it.  I beleieve the crane can be assumed to be a lumped mass.

You may want to put the above in a formal letter to the client.  If the client
does not want to spend the money for extra engineering effort and is willing to
take a risk please have him send you a written reply indicating his decision.
Keep it in your permanent file record.

Rajendran, P.E.

Drew A. Norman, S.E. wrote:

> To all who responded to or followed the recent thread on crane design:
> I forwarded all of the items from the list to my architect client.  From
> this and whatever research he has done independently he says he has
> concluded that (1) the bridge cranes in commercial buildings standard (as
> opposed to essential) occupancy are NEVER designed for seismic loads and
> that (2) such bridge cranes are usually designed by mechanical (as opposed
> to civil or structural) engineers.  He is on this basis taking issue with
> our having specified a design submission including seismic analysis under
> the signature of a structural engineer.  I have suggested that proper design
> of the thirty ton and sixty foot span crane in our building (apx 71 kips
> dead load including rails) requires not only a seismic analysis but a
> DYNAMIC analysis.  My client thinks that I am being overly conservative,
> asking for something that is never done and will cost a lot of money, and
> generally being outrageous.
> Needless to say, my client and I are not seeing eye to eye here.  I have NOT
> drawn the same conclusions from the discussion on the list.  Either he or I
> appear to be misunderstanding the meaning of the posts.  If anyone would
> care to offer a final comment on the subject that might help us to move
> closer together by getting a better grasp on the issues, we would both
> appreciate your efforts.
> Thank you
> Drew Norman, S.E.
> Drew A. Norman and Associates