[Shop-talk] weight capacity of aluminum channel

[Jeff Scarbrough]

I haven't done it on 35 years, but at least your equations look familiar.
I find that comforting.

If the capability is questionable, would solid wood blocks of a suitable
height to support the channel somewhere near the center help?

On Fri, Jul 2, 2021, 06:34 Donald H Locker <dhlocker at comcast.net> wrote:

> First oops - I used 10ft length, not 8ft. At 8ft, the numbers look
> better by about 20%
>
> Donald.
> --
> *Plain Text* email -- it's an accessibility issue
> () no proprietary attachments; no html mail
> /\ <https://www.georgedillon.com/web/html_email_is_evil.shtml>
>
> On 2021-07-02 6:16 a.m., Donald H Locker wrote:
> > BIG NOTE: please check my calculations and assumptions; I haven't
> > actually done any of this for nearly 40 years.
> >
> > TLDR: They might not work.
> >
> > The significant supporting bits are the two flanges (3in x 0.5in); the
> > plate across the top adds very little strength.
> >
> > All calculations below in pounds and inches.
> >
> > The maximum stress on the webs (if the weight is perfectly divided
> > between them; more on that later) will be (equation 1-1 in reference 1)
> > with the weight at the center of the ramp. Fb (bending stress in the
> > flange of the channel) must be less than the yield stress of the channel
> > material.
> >
> >   Fb = M*c/I
> >
> > [Ref 2] M for each web: PL/8 = P*120in/8 = P*15in [P is point load, lb]
> > [email] c for each web: 1.5in
> > [Ref 4] I for each web: (b*(h^3))/12 = ((0.5in)*(3in)^3)/12 = 1.125in^4
> >
> >   Fb = (P*15in*1.5in)/1.125in^4 = P*20 lb/in^2
> >
> > For the given situation, p=3840lb, so Fb (max) is 3840*20 = 76800lb/in^2
> > distributed between the two channels, each with two flanges. Since Fb
> > must be less than the material yield stress, 10000 psi for some kind of
> > structural Al, but not high-strength material [Ref 3], this doesn't look
> > very good. Each flange would be loaded to about 19200lb/in^2 if all
> > loads were perfectly distributed. (Note that high-strength Al (e.g.
> > 6061) can have a yield stress of 45000lb/in^2 so looks much more likely
> > to succeed, but I don't know how much I'd trust that.)
> >
> > My biggest concerns would be the division of stresses between flanges
> > (if one channel tilts a little or is not sitting perfectly flat on the
> > trailer or ground, stress sharing will be uneven and one flange make
> > take all stress) and the potential for flange instability (see notes in
> > 1.3.1.5 in Ref 1.) This may not be a problem because the flanges are not
> > particularly deep, but I watched a boat hung from I-beams drop when a
> > structural I-beam twisted slightly from imperfect loading and the entire
> > structure quickly twisted into a totally unsupportive mess.
> >
> > References:
> > 1 Beam stress/strain:
> > <
> https://engineeringlibrary.org/reference/simple-beam-bending-air-force-stress-manual
> >
> >
> > 2 Beam force/reaction:
> > <
> https://engineeringlibrary.org/reference/beam-forces-moments-air-force-stress-manual
> >
> >
> > 3 Material properties:
> > <https://www.engineeringtoolbox.com/properties-aluminum-pipe-d_1340.html
> >
> >
> > 4 Area moments:
> > <https://www.engineeringtoolbox.com/area-moment-inertia-d_1328.html>
> >
> > ATB,
> > Donald.
> > --
> > *Plain Text* email -- it's an accessibility issue
> > () no proprietary attachments; no html mail
> > /\ <https://www.georgedillon.com/web/html_email_is_evil.shtml>
> >
> > On 2021-07-01 10:56 p.m., john niolon wrote:
> >> I'm thinking about using aluminum channel for a set of ramps for my car
> >> hauler.  I have some 'available' that is  10" wide with .50 web
> >> thickness and almost 3" flange... about 15# per ft.
> >>
> >> ramps will be 7-8' long …..  and will go from ground to 17" high trailer
> >> deck...  truck weight is 5300 +/- … with front end weighting 3840.   I
> >> can't find a table telling me weight capacity of
> >> channel with the load traveling up the wide web...   like this   any
> >> ideas on capacity ??
> >>
> >> Image87ABA31D
> >>
> >> thanks
> >> john
> >>
> >>
> >>
> >> _______________________________________________
> >>
> >> Shop-talk at autox.team.net
> >> Donate: http://www.team.net/donate.html
> >> Suggested annual donation  $12.96
> >> Archive: http://www.team.net/pipermail/shop-talk
> http://autox.team.net/archive
> >>
> >> Unsubscribe/Manage:
> http://autox.team.net/mailman/options/shop-talk/dhlocker@comcast.net
> >>
> _______________________________________________
>
> Shop-talk at autox.team.net
> Donate: http://www.team.net/donate.html
> Suggested annual donation  $12.96
> Archive: http://www.team.net/pipermail/shop-talk
> http://autox.team.net/archive
>
> Unsubscribe/Manage:
> http://autox.team.net/mailman/options/shop-talk/fishplate@gmail.com
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://autox.team.net/pipermail/shop-talk/attachments/20210702/3f1bdcfa/attachment.htm>