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Re: Crane Design; SE v. ME

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> 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).

Standards of practice are usually inadequate to ferret out anything
except the most obvious. Nobody has time/budget to check the other
supplier except for back-of-the-envelope level. Often, this is covered
up by notes disclaiming responsibility. So, if you can show that you are
expecting numbers in one range and are receiving numbers that are an
order of magnitude different, or don't provide the correct infomation
(e.g. static values aren't any good if you are asking for time dependent
loads), you can make an easy case .

There are many examples of improperly designed ANYTHING. Whenever I
encounter resistance to a request for good engineering analysis the
final result tends to be inadequate. Maybe, not coincidentally, that is
what I felt prior to asking the question, anyway. Frequently this is
covered up by some phrase such as, "we've been doing it that way for
years and never had any problems." This is REALLY scary when spoken by
an engineer.

Beware manufactured products, for the suppliers are the worst offenders.
Their engineers have rarely had the incentive or support to fully
understand the product and how it fits into any individual total design.

My experience with MEs is that they do not have a good appreciation for
the way that building codes work and how a structural engineer has to
deal with the information that they provide. So, when you tell them that
they have to meet the building code they will always disagree, but, if
you rephrase it and explain the dynamic effects that you need to model,
they may be more open to assisting. Avoid the ME/SE segragation during
the technical discussion until everybody agrees on what type/level of
analysis is actually required.

You have the law behind you despite the fact that the customer is
standing between you and good engineering practice. You may need to get
some muscle from the building authority to indicate that the crane
system, as a significant attachment to the building, must meet the
dynamic response requirements of the total structure. At that point,
everybody might agree that an SE is required.

Paul Ransom, P. Eng.
Burlington, Ontario, Canada
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