Interpretation of Rule B3.4.5 "bent tube"

[Jakob]

Hello,

what is the interpretation of bent tube ( I'm not a native english speaker)?

Is the rule only valide when it is an "one-pice" tube witch is bended like in picture A? Or is an assembly of tubes, welded together like in picture B, also considered as "bent tube"?

I would consider B also as an bended tube.


Jakob

http://s14.directupload.net/images/111210/vwnxu3il.png

[Jakob]

Hello,

what is the interpretation of bent tube ( I'm not a native english speaker)?

Is the rule only valide when it is an "one-pice" tube witch is bended like in picture A? Or is an assembly of tubes, welded together like in picture B, also considered as "bent tube"?

I would consider B also as an bended tube.


Jakob

http://s14.directupload.net/images/111210/vwnxu3il.png

[Ben K]

Picture A is a bent tube. Picture B is a cut and welded tube.

Ben

[RobbyObby]

Email the Rules Committee. I wouldn't trust the words of a bunch of amateur forum users at tech inspection.

[Drew Price]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">2012 FSAE Rules - B3.4.5
If a bent tube is used anywhere in the primary structure, other than the front and main roll hoops, an additional tube must be attached to support it. The attachment point must be the position along the tube where it deviates farthest from a straight line connecting both ends. The support tube must have the same diameter and thickness as the bent tube. The support tube must terminate at a node of the chassis. </div></BLOCKQUOTE>


I think this is oddly worded, it's not just you.

Definitely get hold of the rules committee to get your specific situation checked. Even as a native English speaker I cannot make up my mind if the intention of this rule is to prohibit load bearing members from connecting nodes in a straight line, or if it's to prohibit members from having unsupported bent sections rather than unsupported cut-and-welded sections.

I could take a guess as to how I would go about designing about it, but get an official answer from the rules committee before you freeze any designs.

[Michael Royce]

Common sense says that for this rule, if a tube deviates from a straight line between its two end points, it will be considered "bent". In other words, both examples drawn by Jakob are "bent". The reason is that any deviation from a straight line reduces the column strength of the tube and makes it more susceptible to buckling.

Structures 101?

[RobbyObby]

Because I'm nice. Pulled directly from the FAQ document on fsaeonline.com.
It refers to the Front Bulkhead Support but I assume it is meant to applicable to all required structural members.

"Question: Is it permitted to use multiple tubes to
make up each of the required front bulkhead
support members if they are not in a straight line?
What about bent tubes?
Answer: Yes, but the minimum sizes given in the
rules are for single straight tubes. Having non
straight tubes (either multiple mitered tubes or
bent tubes) reduces the strength. A 3
rd
tube is
required in this case per B3.4.5 to carry the
additional load, and it must meet the minimum
structural requirements (1.0” x 0.049”). Other
arrangements and configurations may be
submitted for review through an SEF. Increasing
the tube size for non-straight tubes may also be
submitted as an SEF to avoid additional tubes."

[Z]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">2012 FSAE Rules - B3.4.5
If a bent tube is used anywhere in the primary structure, other than the front and main roll hoops, an additional tube must be attached to support it. The attachment point must be the position along the tube where it deviates farthest from a straight line connecting both ends. The support tube must have the same diameter and thickness as the bent tube. The support tube must terminate at a node of the chassis. </div></BLOCKQUOTE>
Who writes this stuff???

You start with a tube like "A" in Jakob's post, and then fit the "support tube" at its mid-point.

Now you've got TWO bent tubes (ie. either side of the mid-point)! So you have to fit two more "support tubes"!! And so on, until you've got a solid mass of double-walled steel supporting the original bent tube!!!

Maybe that's the idea, because a single support tube (at 90deg to the bend) is not going to add much buckling strength to the bent tube. http://fsae.com/groupee_common/emoticons/icon_rolleyes.gif

Z

[jemartin144]

lol, thats alot of support.

I hadnt really thought to apply this rule to a cut/welded bar. If this rule does apply to cut/welded "bent" tube sections I could ses this getting interesting for some people's designs.

Im especially thinking of the harness' shoulder mounting bar. Ive seen quite a few that looked like jacob's 'b' drawing with braces from the nodes to the main hoop, but not a node, to satisfy B5.4.2. For some of those there weren't nodes very near that joint to trianulate to.

I guess this rules intention is to make those situations safer, and it is the job of those engineers to figure it out.

[Jakob]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by jemartin144:
Im especially thinking of the harness' shoulder mounting bar. </div></BLOCKQUOTE>

Guess what "b" is! http://fsae.com/groupee_common/emoticons/icon_wink.gif

[RobbyObby]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Jakob:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by jemartin144:
Im especially thinking of the harness' shoulder mounting bar. </div></BLOCKQUOTE>

Guess what "b" is! http://fsae.com/groupee_common/emoticons/icon_wink.gif </div></BLOCKQUOTE>

If it is indeed for the shoulder harness bar, make sure you read that section thoroughly, B5.4 IIRC. We were thinking of doing this last year but the Rules Committee were pretty stringent on how to properly brace it, and the gains weren't worth the effort. Just make sure you do your homework.

[Drew Price]

This is how I did the shoulder harness bar for our '08 car to take the bending out:



http://a6.sphotos.ak.fbcdn.net/photos-ak-ash1/v185/179/125/2413466/n2413466_33553920_3346.jpg

http://a4.sphotos.ak.fbcdn.net/photos-ak-ash1/v185/179/125/2413466/n2413466_33553940_489.jpg

http://a1.sphotos.ak.fbcdn.net/photos-ak-ash1/v185/179/125/2413466/n2413466_33553939_123.jpg

[RobbyObby]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Drew Price:
This is how I did the shoulder harness bar for our '08 car to take the bending out:



http://a6.sphotos.ak.fbcdn.net/photos-ak-ash1/v185/179/125/2413466/n2413466_33553920_3346.jpg

http://a4.sphotos.ak.fbcdn.net/photos-ak-ash1/v185/179/125/2413466/n2413466_33553940_489.jpg

http://a1.sphotos.ak.fbcdn.net/photos-ak-ash1/v185/179/125/2413466/n2413466_33553939_123.jpg </div></BLOCKQUOTE>

*Off Topic*
That's the shortest bloody car I've ever seen! Good Lord! Were all your drivers 5'2"? And what was the final weight distribution that year?
*End Off Topic*

[Drew Price]

I believe it was 47/53, 60" wheelbase. Our tallest driver was 6'2" or 6'3", the seating position was pretty upright. That was our first car, it had lots of things that were a little challenged, but we didn't break anything!

[jemartin144]

Being a frame designer, I love looking at old frames and playing the "what on this frame isnt legal anymore" game. That list seems to keep growing every year.

[Drew Price]

Yup. That frame would have had some issues even the year after we built it.