Side intrusion bars

[PeterAllen]

I'm in the process of making new fibreglass doors and while side intrusion bars are not a registration requirement the engineer is recommending I use them. I wholeheartly agree.

I would be very interested to see some photos of how other have installed them and welcome any discussion on their design, material, mounting, cross-section, etc. Thank you.

This is interesting Door anti intrusion bars

[Zedn]

Not a requirement? What state are you in? There are exemptions for side impact testing, but in NSW it is still required. I though this was the case everywhere.

Ask your engineer what size section he wants you to use and then go from there. At the end of the day he wont knock back what he asks for.

[Zedn]

Sorry, just remebered your case is a bit different.

Is your car classed as an ICV or modified production?

Most kits have a couple of pieces of RHS or tube. You need to consider the whole picture though and not just the bars. Consider the load path in the event of a side impact. What you have linked may suit that car, but to other cars may be a lot of weight without improvement. In most cases the front of a car wont fit between the centre of the door and sill so the whole lot doesnt need to be filled in with metal. Also the hinge and latch are the weakest link so introducing more steel in the bars is no good if the striker plate of the door does not mount into solid enough steel.

My gallery has some pics of how it is done in my kit.

[OZCOBRA]

Originally Posted by Zedn

Sorry, just remebered your case is a bit different.

Is your car classed as an ICV or modified production?

Peter said it was" Modified Production."

[PeterAllen]

I've picked up a few configuration ideas from this.

Browser Warning (edit) I don't know why the link has come up with the title but it seems to work fine.

My primary concern is not so much with the bar design itself but rather how it might might utilise the door jamb to stop the whole bar entering the cabin. What's the point of a strong bar atteched to fibreglass.

[AC-460]

My primary concern is not so much with the bar design itself but rather how it might might utilise the door jamb to stop the whole bar entering the cabin. What's the point of a strong bar atteched to fibreglass.[/quote]

Most cobra doors use Ford rear door catches or similar not even designed for side impact in front doors....These catches are only held on with three 1/4 inch bolts. All the side intrusion load comes down to the size of these bolts. Its alright to have big heavy bars in your doors but these bars in the doors will spear straight into you after the three quarter inch bolts have shorn off... In a car the doors carry on past the pillar and in side impact the door carries the load all the way up on the pillar all the load is not exerted on the catch.... unlike a cobra were it is...

[Rob. Smith]

Side intrusion bars are one of the points raised as far as Jap import cars are concerned. (they don't have them)This is one of the many 'issues' that the RTA use to make registration of non-commercial vehicles, very difficult. They are termed grey imports and they are also one of the main reasons for the Dept of Infrastructures decisions on vehicle imports.....a bit of back lash on poor decisions (in-decisions) in the past.

[Outwest34au]

My door bars were quite 1970 standard and didn't inspire a lot of confidence in me in the possibility of a prang. I added 2 x 5/16 flat to them and the engineer was happy enough with my description of the work and style used. The striker plates are bolted through to some 1/2 inch metal and then a leg extends off that block through to the chassis. The weakest link is the bolts holding the striker plate and lock assembly, but that is deemed acceptable it seems.

No doubt my effort isn't as pretty or strong as what others have achieved but it gives me more peace of mind.

[PeterAllen]

Originally Posted by Outwest34au

... then a leg extends off that block through to the chassis...

That sound something like what I want but I just can't figure out exactly what you mean. Could you post some more photos that illustrate the setup. Thanks.

Here is what I have at the moment. I have cut out the inner panel and will replace it with with a sheet of aluminiun with a few rolled ribs. I've made some inner spreader plates for the door hinges and that's about it, so far.

[Zedn]

Originally Posted by PeterAllen

That sound something like what I want but I just can't figure out exactly what you mean. Could you post some more photos that illustrate the setup. Thanks.

Here is what I have at the moment. I have cut out the inner panel and will replace it with with a sheet of aluminiun with a few rolled ribs. I've made some inner spreader plates for the door hinges and that's about it, so far.

What about replacing those spreader plates with a piece of 5mm x 50mm flat bar extending across both hinges. Bend the 5mm bar to follow the contour of the door, then butt weld 2 pieces of 32mm x 4mm steel tube running as the intrusion bars. Add a gusset welded at 90deg to the 5mm flat bar to brace the butt joint. Then do similar on the other end for the latch to attach to. (just an opinion, no responsibility taken!)

John Wilson recommends 32x4 tube on his website:
Newsletter

Does it use the datsun frame for the hinges and striker plate to mount to?

[PeterAllen]

Thanks for the input.

I would be concerned that in joining the two hinge spreader plates I would limit the ability to align the door properly.

If I read John Wilson's comments correctly the requirements are that an intrusion bay should NOT engage the pillars/jamb as it may inhibit the function of the hinges and the latch?

Originally Posted by Zedn

...Does it use the datsun frame for the hinges and striker plate to mount to?

Yes.

[Outwest34au]

Originally Posted by PeterAllen

That sound something like what I want but I just can't figure out exactly what you mean. Could you post some more photos that illustrate the setup. Thanks.

Sorry for the dodgy pics, just saw your message and didn't have time (feel like) pulling the seats out in the cold and dark.
I hope they explain it a bit better for you than I could in words.





I still have to see how the engineer wants part A connected to part B. I have my ideas, he may have different.

[AC-460]

the strength comes down to those bolts holding you striker plate.....

[Outwest34au]

Originally Posted by AC-460

the strength comes down to those bolts holding you striker plate.....

I believe you.

Can you show other designs or alternatives? I'm open to change.

[Zedn]

Originally Posted by AC-460

the strength comes down to those bolts holding you striker plate.....

You will need bloody good tyres to resist the amount of force to shear off those bolts even at 1/4" grade 5. Hence why manufacturers use this design.

[AC-460]

Whats tyres got to do with a vehicle coming at you from side on.....

[Zedn]

Originally Posted by AC-460

Whats tyres got to do with a vehicle coming at you from side on.....

What stops your car from moving sideways in the direction your hit? Considering the car as a free body diagram, there is an external load applied from the other car minus the load applied from friction in tyres. If the impact load is higher than the traction the body is not in equilibrium and moves in the direction of the impact. So the bolts dont have to resist the load of the car, they have to resist the friction of the tyres .

If you are hit from behind and your foot is on the brake it will do much more damage than if you didnt have your foot on the brake.

[PeterAllen]

Originally Posted by Zedn

What stops your car from moving sideways in the direction your hit? ..

A tree, e.g. '0.05'.

[xlr8tr]

Originally Posted by PeterAllen

A tree, e.g. '0.05'.

well said- or a guardrail, or wall, or.....

[Zedn]

Originally Posted by xlr8tr

well said- or a guardrail, or wall, or.....

I think we are talking about different things. Im talking about side impact from a vehicle.

That may happen if you slid sideways into a pole or similar. If you are in this position then the bolts will be least of your worries. For that sort of collision you actually want the side intrusion bars to deform a bit to absorb energy.

First of all you are assuming that the side impact is a very narrow object that only impacts the door. In reality this is very unlikely to happen due to the size of cobra door (or ferrari).

If a car is hitting you from the side you are in most cases going to be crossing an intersection where you are both crossing paths (such as someone running a red light). In this case there will not be trees or walls in that direction, there will be road. If it is a T intersection it will be very unlikely they will t bone you. You will t bone them or run up the back of them.

This link will show you why i talk about tyres. Select tab for side impact test and press play. Notice what the car does when tested. The impact is absorbed by both the friction of the tyres and crumple zone of the front of the other car.
ANCAP - Crash Testing Explained.

You also need to consider what is going to happen to the driver. In a cobra, the top edge of the door is quite low. When the car is hit from the side the driver will be whipped towards the incoming car. If it is a 4wd it may go over the bars.

There is much more to crash science than a point load in the middle of a side intrusion bar. The shear capicity of each bolt in the striker is several thousands Kgs. The full impact is also not applied only on the bolts it is also carried by the hinges and any other part of the car that is hit.

There is also the thicknes of the striker plate/latch to consider as it is probably less than the bolts