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RE: bridge crane runway beams

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Mike, The lateral load must be taken by 1/2 of the Iy of the crane girder.
The cap channel is an option; however, the cost of the material may not be
the issue.

The least cost solution will likely be a rolled shape (i.e., a W24x104)at 26
cents per pound. vs. beam with cap channel (at 26 cents per pound plus 10
plus shop hours at $50.00/hour. That $500 plus can buy a lot of material in
lieu of potential headaches.
When adding a cap channel, there are several additional costs beyond the
material.
	1. Shop fitting and welding raises the quality level of the fabricator
	2. Maintaining the straightness of the girder during the welding operation.
Welding will add heat to the top flange, causing reverse camber or sweep
which must be corrected
	3. Over time the welds between the channel and the edge of the top flange
are likely to crack with load cycles of 500,000 of more.
	4. Under severe service(Class D cranes)  these same welds must be
continuous
	5. During the welding operation or subsequent to the installation; the web
of the channel may bow away from the flange of the girder; which generates
additional stresses within the welds and  web of the channel. Subsequently,
cracks will appear. This can be eliminated by cutting slots in the channel
web and fillet welding through the slots to the top flange.

All of these items add cost and increase the risk for the owner. Use the
W24x104 based on your preliminary numbers.

David I. Ruby, S.E.

President, Ruby & Associates, P.C.
30445 Northwestern Hwy., Suite 310
Farmington Hills, MI 48334-3102

Phone:            (248) 865-8855
Fax:              (248) 865-9449
Cellular:         (248) 514-2677
E-mail:           druby(--nospam--at)rubyusa.com

--
> -----Original Message-----
> From: Michael Hemstad [mailto:mlhemstad(--nospam--at)yahoo.com]
> Sent: Thursday, December 28, 2000 12:12 PM
> To: seaint(--nospam--at)seaint.org
> Subject: bridge crane runway beams
>
>
> I'm designing a bridge crane runway.  The owner's
> specifications require adherence to CMAA 74, which in
> turn requires that lateral deflection be held to less
> than L/400 based on 10 percent of maximum wheel load
> without impact.  Does anyone know the intent of this?
> What section properties are expected to be used?
>
> I assume that I should check the runway beam for
> bending based on this same lateral load in conjunction
> with the full vertical load.  Does anyone have a
> comment on this?
>
> In my particular case,  I have a 40 foot runway beam
> span (only a 2 ton crane). I find that a W21x83
> wideflange is adequate by itself, with vertical
> deflection of about L/1100 and lateral deflection of
> L/640. The lateral deflection is based on the 10
> percent of vertical moment acting laterally on the
> full beam Iy; i.e., I pretend that the lateral load is
> at the centroid of the beam instead of maybe 6 inches
> above the top flange.  Alternatively, I can weld a
> channel on top of a lighter wideflange, saving not
> very many pounds of steel but increasing lateral
> stiffness a good deal.  This is what I'm used to
> seeing, but I can't see a reason to do it here.  Am I
> missing something?
>
> Any help or comments would be appreciated.
>
> Mike Hemstad, P.E.
> TKDA Inc.
> St. Paul, Minnesota
>
>
>
>
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