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Re: Crane Design

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          In order to provide you with a good reply there are a few 
          things which would be nice to know:
          What type of loads are being lifted (i.e., are they 
          hazardous types of material) ?
          Is the area directly beneath the crane normally occupied by 
          workers or is it a vacant area with restricted access ?
          By the 1997 UBC, what required type of analysis is dicated 
          for the building (static or dynamic) ?
          The answers to these questions would provide some of the 
          intangibles in the decision on what type of analysis to 
          require.  I know you may be in a strong position 
          contractually (because you put the requirements in the 
          construction documents), but as you noted, sometimes you 
          have to prove that what you're asking for is reasonable and 
          Risk is a function of two parameters, probability of 
          occurence and consequences of the event.  Defining what 
          rigor of analysis would be required is dependent upon what 
          type of "risk" one wants to accept.  I think you're two 
          options is a full response spectra analysis or allowing them 
          to provide a equivalent lateral approach.  Once I know the 
          answers to the questions above I can provide you with a more 
          informed recommendation.
          Robert C. Rogers, PE

______________________________ Reply Separator _________________________________
Subject: Crane Design
Author:  seaint(--nospam--at) at Internet
Date:    3/16/99 11:14 PM

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