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Re: Cranes and earthquake loads

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In the USA, cranes are designed by Crane Manufacturers Association Of
America standards, including lateral bracing.  CMAA states in their
standards that earthquake loads are not considered.  Building codes, such
as the UBC are ignorant of this ommission.  The typical result is that
crane engineers design the crane for crane loads only, and pass these
loads onto the SE to design the building.  The SE, not wanting to be
liable for the crane, accepts these loads without question and dutifully
designs the building accordingly.  Not good.  Instrumented readings on
one story industrial buildings in the 1994 Northridge Earthquake revealed
typical peak accellerations at the roof levels to be 1.5 to 2.5 "g". 
Lateral crane loads per CMAA are 10-15% of the moving system, which is
only the trolley assembly.  If the SE uses AISC Code as guidance, the
lateral load for seismic design is still only 15% "g".  I have calculated
typical crane installations with real EQ loads at from 7 to 22 times the
design load. Typical safety factors will not save this situation.

Clearly the codes and standards are disconnected, as is the typical
engineering of crane installations.  In 1994, some of the cranes in Los
Angeles were likewise disconnected and fell to the floor.  To call this
hazardous is an understatement.

Best advice is to brace cranes for, at a minimum, Cp = 0.3x2.0x1.5 = 0.9,
which is a most conservative reading of the latest UBC.  As a procedure,
have the crane engineer address this requirement, then have the SE
review.  Better yet, try to find an SE who knows crane systems and
hardware and address the real loads directly.  Don't hold your breath
waiting for the code writers to close this gap.

I will send a copy of a published article on this subject to anyone who
emails me off line.  I cannot afford to donate the code committee time to
carry this cause forward.  Maybe one of you can.

Russ Nester
rnester(--nospam--at)juno.com
______________________________________________________________________
On Thu, 01 Oct 1998 09:59:44 +0100 Gudrun Olafsdottir <gudrun(--nospam--at)hnit.is>
writes:
>Here goes my first question to the list:
>
>I have been asked whether a crane in a steel-frame building
>we have been designing needs to be designed for earthquake
>loads.  I can't find anything about cranes in our earthquake
>code so I was wondering what is done elsewhere and also if
>anyone has had any experience with this. 
>
>Thanks in advance for any information!
>
>Gudrun Olafsdottir
>
>Hnit Consulting Engineers Ltd.
>Reykjavik, Iceland
>
>
>
>

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