aluminum DOM

Here is the long answer...take 1.9 in od pipe .145 wall r is. 626

For ASD...the easy stuff

KL/r is 1*48/.626 is 76.67 which is less than 200 so it is not slender

Cc is sqrt((2*pi^2*E/Fy) is 126

Fa is ( (1-(76.67)^2 / (2*126^2))*36)/(5/3 + ((3*76.67)/(8*126)) - ((76.67^3)/(8*126^3))

Equals 15.71 ksi * .75in^2 is about 12k!

Got it? Lol


Read up in AISC ASD Chapter E.

So...there is way more to it than just critical buckling load....this does not buckle before it is overstressed so to speak...plenty of safety factor in there.

Got to go back work....was on phone...sorry about the typing...but my dick does feel bigger now.
 
Xlr8r...you are an artist with words! Lol

Torsion doesn't really directly apply...kinda sorta similar...but not exact.
In simple terms..the amount of material and the distance from the members
center matter more in resisting buckling than the material properties.

Hence why wood makes pretting good columns but not so good beams...

It obviously is way more complicated than that....but simple in general theroy.

If you single member "compression strut" traction bars are fixed at the axle...you have shot a hole in your foot....they are no longer compression only and have become an element in bending...which is bad bad bad for all of the size shaped we have discussed.

Later...
 
Lazersmith Bars are a great example of how to make them...

Tapered ends in multiple steps as needed to get from a thicker wall small diameter near the rod end insert to a larger diameter thinner wall for the center section (should be 60% of total length).

IMHO they don't need to be longer than 48 to 56 range...but I wont argue with sledpullers opinions.
 
One could model these in FEA and see that they could resist even higher forces that critical buckling values....BUT

The designer needs to be realistic in all conditions, end fixities, tolerances....etc.

Model that same tube in compression with an 1/8 in of side deflection and watch those numbers come crashing down to values much more similiar to empirical methods.

FEA is way cool...but mucho dangerous in the wrong hands.
 
cquestad said:
If you single member "compression strut" traction bars are fixed at the axle...you have shot a hole in your foot....they are no longer compression only and have become an element in bending...which is bad bad bad for all of the size shaped we have discussed.

Later...
Click to expand...


That is a good point.
 
Thanks Christian... and LazarSmith has 2 "a"s. :)

Torsion doesn't apply directly - as in a driveshaft - but it is an element of the buckling mechanism for a slender column... and considering traction bar design from that viewpoint reconciles intuition with mechanical engineering, IMO.
 
Leaf sprung rear axles have more than enough strength forward/rearward at the point where the axle is connected to the spring. Tracion bars...aka compressive struts are all that is needed to keep the axle from rotating. Using a ladder bar in this application is just a waste of wieght and space because the size and strength that is required for them to work is already partially redundant with the leaf spring system. If somebody had a weak flexible trailing arm or three link rear end...a ladder bar system might be the way to go...

For us...a properly designed "minimalistic" traction bar is best. A obvious case of where less is MORE!
 
cquestad said:
Lazersmith Bars are a great example of how to make them...

Tapered ends in multiple steps as needed to get from a thicker wall small diameter near the rod end insert to a larger diameter thinner wall for the center section (should be 60% of total length).

IMHO they don't need to be longer than 48 to 56 range...but I wont argue with sledpullers opinions.
Click to expand...
A side note. Most the pulling bars aren't long for strength. They're long because the 2nd gen dodge frame bends if you put the frame attachment point behind where the frame boxing ends. I think it was Teddybear (Josh) that posted pictures of his truck bent in a U shape after a season and short bars.
 
I guess we haven't discussed their are appropriate and inappropriate aluminums? Anyone consider titanium?

Ladder bars are for more than help in locating the housing, as was implied.

I was under the impression that the length was determined by frame failure areas (boxed v nonboxed) and also arc of travel compared to ds.
 
Last edited:
I think i would have strengthened the frame...then ran shorter bars...lol. Boxed it!

The aluminum tube or pipe you will be able to find will only be 6 or 7000 series. You will be fine. Titanium will make you broke.
 
joefarmer said:
Most the pulling bars aren't long for strength. They're long because the 2nd gen dodge frame bends if you put the frame attachment point behind where the frame boxing ends.
Teddybear (Josh) posted pictures of his truck bent in a U shape after a season and short bars.
Click to expand...

cquestad said:
I think i would have strengthened the frame...then ran shorter bars...lol. Boxed it!
Click to expand...

Traction bar length affects anti-squat & weight transfer more than anything else... the infamous photo shows how not to install the front heim: continuous perimeter welding & inadequate bracket design.

2nd Gen Rams can have the front heim mounted anywhere from the rear arch up to the tranny output shaft - our brackets direct the bending moment from bar thrust to the frame rail's strong side.
 
cquestad said:
If you single member "compression strut" traction bars are fixed at the axle...you have shot a hole in your foot....they are no longer compression only and have become an element in bending...which is bad bad bad for all of the size shaped we have discussed.
Click to expand...


If I say anything about this, are ya just gonna get all pissy again?
 
That is funny...

How about as long as you don't say anything silly I wont throw a hissy and refuse to help anymore...


Smart Ass...
 
cquestad said:
Before I do that explain to the world how you get a moment through a pinned connection?
Click to expand...

Driving/pulling/racing is dynamic. The movement of the truck, bouncing, for example, causes the bar to flex. At that point the bar is no longer totally in compression. Just sayin'... :smileglasses:

I won't argue the material or formulas, or what works from experience, etc. I do have a question, though. Why not mount the rear of the bar above the axle (as has been mentioned in this thread) so the bar is in tension under accelleration?
 
cquestad said:
Before I do that explain to the world how you get a moment through a pinned connection?
Click to expand...

Driving/pulling/racing is dynamic. The movement of the truck, bouncing, for example, causes the bar to flex. At that point the bar is no longer totally in compression. Just sayin'... :smileglasses:

I won't argue the material or formulas, or what works from experience, etc. I do have a question, though. Why not mount the rear of the bar above the axle (as has been mentioned in this thread) so the bar is in tension under acceleration?
 
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