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Re: Factored Load Combinations with Cranes

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Rich,

I am not familiar with the code you are referring to, Rich. I am, however, familiar with crane usage. I can show you service type operations and factories running two shifts with service cranes. These people would not like to be told that they can not use their cranes when they have a full snow load on the roof!

If your code permits the load reduction combination factors you have listed it may be legally correct to do so. But I would suggest that you think carefully about the crane service before you do.

I would personally not use reduced load combinations factors if I were designing a new facility. For upgrading a crane, or for adding a crane where none existed before, you do what you have to do; but make sure that you have your disclaimers clearly stated and that your client and the local building authority are on side.

Regards,

H. Daryl Richardson


----- Original Message ----- From: "Rich Lewis" <sea(--nospam--at)lewisengineering.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Friday, January 14, 2005 4:32 PM
Subject: RE: Factored Load Combinations with Cranes


I'm not sure if you have looked at the load combinations lately.

Eq. 16-2 has 100% crane and 50% roof.
Eq. 16-3 has 100% roof and a reduce live of 50%
Eq. 16-4 has 100% wind and a reduce live of 50%
Eq. 16-5 has 100% seismic and a reduce live of 50%

I think the crane load is accounted for in Eq. 16-2

Rich Lewis
Lewis Engineering



-----Original Message-----
From: Daryl Richardson [mailto:h.d.richardson(--nospam--at)shaw.ca]
Sent: Friday, January 14, 2005 12:36 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Factored Load Combinations with Cranes

Fellow engineers.

       Do not reduce crane loads as part of load combinations!!!  Crane

operator very often overload the cranes; in some cases substantially.

       About two years ago I was called on to check out a Five (5) Ton
crane because "it broke and they dropped the load".  Fortunately they
were
lifting a dumpster of scrap metal; and, even more fortunately they
didn't
drop it on anyone or on anything of value.

       They were pretty upset.  They had been disposing of the scrap
metal
this way for years and nothing like this had ever happened before!  (But

then we have all heard the "We always done it that way before."
argument,
haven't we?)

       The final failure was a broken cable.  I also recommended that
they
strip it down and check the bearings, several sets of which needed
replacement.

       The real cause of failure: the dumpster weighed ELEVEN (11)
TON!!!!

Regards to all,

H. Daryl Richardson
----- Original Message ----- From: "Paul Ransom" <ad026(--nospam--at)hwcn.org>
To: <seaint(--nospam--at)seaint.org>
Sent: Friday, January 14, 2005 10:00 AM
Subject: RE: Factored Load Combinations with Cranes


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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