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RE: Factored Load Combinations with Cranes

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> From: "Rich Lewis" <sea(--nospam--at)lewisengineering.com>

> Are there factored load combinations recommended for design in a one
> story building with a crane supported by the steel framing?   IBC

> I ask this for foundation design load combinations.  


> From: "Scott, William N." <William.Scott(--nospam--at)veco.com>

> A crane is an equipment load. The load should not be reduced.

IBC 2003 is very explicit about the application of crane loads including
impact. Crane loads are defined as Live Loads and therefore subject to
the permissible reductions in combinations.

> The loading should be based on crane capacity with impact factors.

I disagree that vertical "impact" loads are a foundation issue for a
typical overhead crane building.


> From: "Rich Lewis" <sea(--nospam--at)lewisengineering.com>

> IBC 2003 states that for occupancy loads of 100 psf or more you can't
> reduce it.  It says for all other live loads it can be reduced.
> ASCE 7-02 basically states the same thing except it infers it is for
> occupancy loads, which is not equipment.

Floor loads are different creatures with different probabilities. IBC
2003 says, "The crane live load shall be the rated capacity of the
crane." Only include impact for certain elements. I don't know where
they include the crane mechanism (bridge and trolley). I think that Gail
needs to chase these guys, too.

> PEMB designers use some different load combination factors for ASD
> design when combining crane with live and wind forces.  Are there any
> PEMB designers out there who can clarify what typical practice is for
> load factor design?

PEMB designers use the same load combination factors that you use, ASD
or LRFD. Those who don't should not be lumped into the generalized group
of "designers." Unfortunately, there are PEMB manufacturers that don't
know a "designer."

Per IBC 2003:
1.2DL + 1.6L + 0.5(Lr or S)
1.2DL + 1.6(Lr or S) + f1(L)
1.2DL + 1.6W + f1(L) + 0.5Lr
etc.
where f1 = 0.5 and L includes crane loads per 1607.12, including impact,
and floor loads (reduced for area or not).
Those are the mandatory combinations (code specific).

ASCE7 is verbatim to IBC 2003 as far as I reviewed. I did note some
inconsequential differences (e.g. f1 is overtly replaced with 0.5). 

NBCC does not permit reductions of crane loads in combination with other
(roof, floor) Live Loads and does require impact in the design load. I
think this is a little conservative.

The MBMA has put together one of the nicest crane-building design
references available, in the Low-Rise Building Manual. The Manual is not
a code but a compilation of MBMA ->member<- manufacturers
agreed-to-be-acceptable design practices ... kind of like AISC manuals.
So, no load combinations, just load development. Nobody has to follow
this guide unless it is in the contract or in a building code.

Also, see the new (free for download, pdf, http://www.cisc-icca.ca)
publication by the CISC, "Guide to Crane Supporting Steel Structures"
and the usual AISE TR-13, "Guide for the Design and Construction of Mill
Buildings."

For those who have read this far, a question:
What "static" load should be used for limiting crane building
deflections, what should be the limiting deflections and why should it
matter? Should we be concerned about lateral building deflection or only
rail separation as a deflection control (P-delta issues aside)? I would
be interested in Christopher Wright's opinions related to the dynamic
effect aspects.

-- 
R. Paul Ransom, P. Eng.
Civil/Structural/Project/International
Burlington, Ontario, Canada
<mailto:ado26(--nospam--at)hwcn.org> <http://www.hwcn.org/~ad026/civil.html>

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