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RE: Crane Design

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I have not followed this thread (not for lack of interest, only time!)

Here's an Australian perspective:

We as engineers design cranes and crane structures, such as that referred to
here.  Whether that be mechanical or structural is not as clear - but in any
case to approve the design requires us to meet the requirements as laid out
in the occupational health safety and welfare act and regulations, and
therefore be competent in the application and understanding of the
appropriate codes and standards.

Often, the crane supplier provides the design of the bridge crane (crane
code compliance), and the runway beams are designed separately (crane code
and steel code compliance), using the loads provided by the crane supplier
on the vendor drawing.  The crane supplier usually uses a structural (or
mechanical) engineer to provide this.  Irrespective of whether a mech or
structural engineer does the calcs and certifies the design, it must meet
relevant Australian Standards (Crane code) and government acts (mines
department or occupational health).

That a mechanical engineer normally does the design, and that a seismic
design is never done, are irrelevant issues if the standards or acts require
it (seismic design).  The bottom line is that a bridge crane, its immediate
supporting structure and the building which houses it will be affected by a
seismic event and demands as much attention as any other structure or piece
of equipment supported on a structure.  In my experience, the major issues
regarding equipment from a seismic point of view are that the connections
are able to withstand the likely seismic forces applied to them and that
overall stability is maintained.

Having accepted that a seismic design is necessary in a location which
requires consideration of seismic loads, the method (static or dynamic) is
chosen depending on the structure type etc, and the applicable code.  In New
Zealand and Australian codes, there are rules to define what can and can't
be designed using static analysis, irregular structures for example usually
require a dynamic analysis - engineering judgement plays a part.  I expect
if the person employed to do this work knows the issues (and he should),
there shouldn't be an argument as to the approach to this problem and the
method used.

Perhaps your architect could give you *sound* reasons why you are
over-specifying, and not his two reasons that you quoted below.  I hate the
expression "we've never done that before" as a reason not to do something.


Dave Meney
Structural Engineer
Yenem Engineering Services
phone		08 9257 2695
fax		08 9257 2264
mobile	0417 949 374
e-mail	yenem(--nospam--at)

-----Original Message-----
From: Laurence B. Oeth III [mailto:viacalx(--nospam--at)]
Sent: Thursday, 18 March 1999 11:23 am
To: seaint(--nospam--at)
Subject: Re: Crane Design

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
> 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
> drawn the same conclusions from the discussion on the list.  Either he or
> 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
I assume the original question relates to the crane itself, and not the
runway.  Runways definitely require design to resist seismic
forces/deflections including the crane DL (but not payload mass).

If your bridge crane operates in an occupied structure, and/or is cab
operated (i.e. - occupied space as a part of the crane), and you are
under UBC jurisdiction, it appears hard to exempt those "occupied"
spaces from the seismic provisions of the Code.  What does your local
building official say?

I think a dynamic analysis is probably not warranted unless there is odd
geometry with a high likelyhood that the crane's behavior will effect
the response of the structure (your judgement).  Vertical acceleration
components (@ 2/3 of horizontal +/-) are usually less than the impact
factor crane mfr's use.  Also, low allowable stresses due to fatigue
considerations also enhance overall strength, at least for most of the
crane's life.

If you spec seismic analysis/design for the crane, I would suspect the
mfr can see that seismic loads are less than typically designed for
against normal use.  Forcing them to spend money retaining an outside
structural engineer seems a likely cause of friction and negative
feedback THROUGH the architect.

Perhaps a compromise:  Discuss design loadings with the engineer of
record for the crane mfr (mechanical or structural) and convince
yourself that seismic loads either will or will not control the design.
This should take less than one hour of your time.  If odd conditions
exist, you and the crane designer will uncover them, and this will
provide a justifiable reason for additional that the
architect and HIS client can buy into.

Also, a mfr's certification that the crane is designed to resist
specified loads may provide the owner with better protection than an
engineer's seal obtained under duress.  If a problem later arises, he
will have a deep pocket to collect from.

Creeping commercialism vs. professional responsibility.  Try to solve
with a smile.  Good luck.

Larry Oeth