Removable diagonal design check

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KeithBoden
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Removable diagonal design check

Post by KeithBoden »

I am working on a removable diagonal for my existing roll bar. I believe the design provides reinforcement to the main hoop that is comparable to a fully welded diagonal, and the simulation studies seem to agree. Would a tech inspector be willing to take a look and agree or disagree with the strength of the design? I did the simulations without modeling the rear braces, roof braces, or the additional points that the main hoop is attached to the unibody just to get a feel for the strength of the diagonal connections.

Details:
Clevis - 3/4" shank, 1/2" pin hole diameter
Bolts - grade 8, 1/2-13 with grade 8 nut
Tube adapters - turned out of cold rolled bar stock, light press fit into the tubing and fully TIG welded
Connecting plates - 3/8" cold rolled steel
Diagonal tube - 1.75" x .120
Attachments
Design and analysis of diagonal.jpg
Rich Rock
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Re: Removable diagonal design check

Post by Rich Rock »

Keith,

The GCR shows diagrams of what SCCA accepts for design of removable braces. Somewhere around page 115-120. If you want to try and get your design accepted, you will need to contact the folks at the National office.

Or you could get around the requirement for a diagonal in the plane of the main hoop by adding another rear brace going from the top of the main hoop behind the driver to the bottom of the rear brace on the passenger side.
SteveTC
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Location: Hunlock Creek, PA 18621

Re: Removable diagonal design check

Post by SteveTC »

Hi Keith,

That is an interesting concept and definitely one we have not seen before as we generally never see a removable cross brace. The GCR does have guidelines for a removable brace, and is on page 118 of current GCR.
Though your concept could be strong enough, it does not meet the GCR guidelines. The concern also is that the single tab may want to pierce the tube if it is really needed.
Is there a chance you can just do a diagonal to the rear brace and have it not removable?

Steve Marsh
PHA Tech Inspector
KeithBoden
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Re: Removable diagonal design check

Post by KeithBoden »

Thanks for the feedback guys! I'm hoping to run SM (http://www.pahillclimb.org/phpBB/viewto ... f=1&t=3151) and was banking on the "Removable roll bars and braces must be very carefully designed and constructed to be at
least as strong as a permanent installation." clause of the hill climb rules. If my car is ok with just a roll bar, I'll still strongly consider just welding the diagonal in - I'd rather not compromise the safety or be surprised and fail tech.

I guess I need to really nail down my car class first. Is there a Tech Inspector in the Harrisburg area that wouldn't mind taking a look at the car? I'll drive to wherever you are and at a time that suits.
Rich Sweigart
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Re: Removable diagonal design check

Post by Rich Sweigart »

I believe Autopower makes a bolt-in rollbar with removable dia. braces that is legal for hillclimbs. :shock:
Rich Sweigart
Rich Rock
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Re: Removable diagonal design check

Post by Rich Rock »

Keith,

Any chance you can bring the car to the PHA meeting this Saturday in Reading? I'm sure there will be at least a couple people there who will be happy to look at the car.
KeithBoden
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Re: Removable diagonal design check

Post by KeithBoden »

Rich Rock,

That sounds like a good idea, I'll get there!
Rick Kase
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Re: Removable diagonal design check

Post by Rick Kase »

As a general rule, our tech inspectors can approve any roll structures that are shown in the rule books as to the standard type.
Any time something comes along that is different than is shown or is of a non standard material or design Must be approved by National. It is a very hard procedure to show National that what you are doing meets their standards.
If you do something not shown the tech is required to refer it to National.
Fritzler
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Re: Removable diagonal design check

Post by Fritzler »

I'm not sure about the classes you're interested in but in the world of sports racers and formula cars, the SCCA won't even consider an alternative to what they show in the GCR unless you have calculations signed and stamped by a registered professional engineer saying the design meets certain criteria spelled out in the GCR.
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