Rule T3.5.5 - Bent tube (or member consisting of multiple tubes not in a line)

[Don Nguyen]

Hey everyone, I'm from the University of Arizona.

"If a bent tube (or member consisting of multiple tubes that are not in a line) 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, terminate at a node of the chassis, and be angled no more than 45 degrees from the plane of the bent tube."

I'm having a lot of trouble visualizing what this rule is requiring. I submitted a frame to the rules committee and was told that the main roll hoop supports don't satisfy the 45 degree angle specified, and I'm seeking a better understanding of the rule.

The frame in question was:

A possible solution I came up with what I think the rule is stating is:

This thread is nothing personal against the rules submissions, but they haven't been going into detail to the extent for me to get an idea.

Thanks everyone.

[TiJei]

Hi Don,

I don't see why you refer to the "bent tube rule". However I think your main roll hoop bracings violate rule T3.13.7.

Regards
Timo.

[Don Nguyen]

Timo, it was the only one pointed out to me when I submitted to the rules committee, but more details weren't really specified.

[Mitchell]

Don't forget T3.13.6

"From the lower end of the braces there must be a properly triangulated structure back to the lowest part of the Main Hoop and the node at which the upper side impact tube meets the Main Hoop."

I feel like they have referenced the wrong rule. Your initial harness bar satisfies T5.4.2 as far as I understand it.

[TiJei]

@ Mitchell: I think we are reffering to the same rule. Maybe from a different document status. Your wording sounds like 2014 Rules. Anyway we mean the same thing.

@ Don: I think I don't understand what is meant by "main roll hoop supports". Maybe you could post the original reply from the RC? The only bent tube in your initial design is the shoulder harness bar, however I agree with Mitchell that this should be rule compliant. To overcome this you could redesign it from 5 straight tubes. However the only rule deviation I can see from the pictures is that the main roll hoop bracings are not connected to the lowest point of the main roll hoop.

My first comment was maybe a bit short, however I sent that from a smart phone with bad internet connection.
Apologies for that.

Regards

[onemaniac]

I see what RC is referring to. It's the front hoop bracing that is in multi pieces.
Your front hoop bracing support (meaning tubes that 'supports' the bracing) that connects the 'cut' and the upper side impact structure node is forming an angle greater than 45 degrees from the tube plane.
I may be wrong, but that's how I would interpret.

[Don Nguyen]

This was exactly the only thing specified to me when I submitted my frame.

The main hoop brace support structure does not appear to satisfy included angle requirement of T3.5.5.

There was nothing else detailed and he didn't offer a visual solution, so I really am confused. I think they're talking about these two tubes not-in-line:

[troot]

Sounds more like 3.14.4 and from the image that seems to make more sense, the mount you have circled should not be considered a structural tube as it relates to bracing or impact structure eg what the ses looks at.

[Adam Farabaugh]

I think they're most likely referring to this (highlighted in orange):


This is a "bend" in the sense that the brace support which could go straight from the bottom of MRH brace -> upper SIS is actually made of two tubes which are not in a line.

Now I can't pretend to understand the 45-degree thing, from the first time they put that language in I was confused.

[slicktop]

I agree with Adam. I interpret the 45 bend rule as this: If you have a tube that has a bend or has multiple pieces that form a bend, then that tube will form a plane. The plane is defined by the two endpoints of the tube and a point in the bend, to where the entirety of the bent tube is parallel to and on the plane. Then, this tube must have a support tube that terminates at a node of the chassis, and the support tube must not make an angle of more than 45 degrees with the plane.

It seems that your left and right MRH bracing supports tubes are different from side to side, if I am seeing it correctly. To me it looks like the left side does not satisfy T3.13.7, as Timo pointed out. Also, on the right side, the horizontal tube pointing rearward off the MRH (the one attached to the same node as the harness bar) I believe would need to meet the MRH bracing support thickness requirements as it is needed for triangulation, if it does not already.