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Crane Design; SE v. ME

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Thanks to everyone who has taken the time to respond to my post about the
bridge crane design (ME v. CE).  I have replied to several of you off list,
but thought it appropriate to respond to a few items where everyone could

Bill Sherman asked for clarification on a couple of points.  In response:

1.  The runway beams in this installation are designed by the manufacturer,
as are the bolts which connect them to fixtures at the bottoms of hangers
designed by our office for crane reactions the supplier specified.

2.  Our design drawings are clear.  The crane is specifically identified as
a "structural component" and our notes indicate that the design of such
components and their connections to the structure illustrated in our
drawings shall be performed by an SE employed by the contractor.

Chris Wright, commenting on Russ Nester's reply, noted, "CMAA doesn't
specify  ...  but that doesn't mean ... someone hasn't done a seismic
analysis. ... If it were me and the guy  handed me a set of reactions based
on a static acceleration, I think we'd have a ... chat about dynamics and

The (preliminary) calculations we have seen to date include NO seismic
analyses whatsoever.  I had a "chat" with the ME for the supplier this
morning.  He asserts that dynamic forces created by the crane starting and
stopping under load are generally greater than any which might occur in an
earthquake, but I think agreed to submit a seismic analysis (under ME, not
CE or SE signature) to prove it.  It was reasonably clear to me however that
we are talking about a simplified static rather than a dynamic analysis -- I
don't think response spectra are in this company's repertoire, and he is NOT
planning on hiring an outside consultant to help him with this.

Resolution of the issues on this particular project may be complicated by
the fact that it is being done as a design-build.  Contractually, our firm
is structural consultant to the architect, who is working for a general
contractor.  Even though our design documents are clear, if what we are
asking for exceeds the minimum standards of governing code we may be asked
to defend them to the contractor, who is after all our client's customer.
It is for this reason that my client and I are particularly interested in
(a) relevant legal, building code and/or safety requirements, (b) standards
of practice (what is everyone else out there doing), and (c) experiences
anyone out there might have had with problems due to improperly designed
bridge cranes (particularly in re their performance in earthquakes).

Drew Norman, S.E.
Drew A. Norman and Associates