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Car crash barrier design

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bill8123

bill8123

Mechanical
Nov 14, 2011
23
AU
Hi All

I live on the low side of the street, downhill from a T intersection. The house is cut into the hill, the house is lower than the road. A concern we have is cars losing control around the corner and impacting our house causing injury. A concrete barrier at my boundary isn’t feasible due to the slope of the ground (inadequate footing) and council don’t want to install a barrier. We have room for a double garage between the road and the house. I’m thinking about building a sacrificial steel reinforced solid concrete walled double garage to prevent injuries against a run away car. Please see attached. I have two questions:

1. Do you think this concept could be adequate to bring a 3000kg car traveling at 60km/hr to rest prior to hitting the house?
2. Any ideas on how to calculate the impact loads or could a g factor be used??

Any input is much appreciated

Thanks
 
 https://files.engineering.com/getfile.aspx?folder=f6fb1974-5d1f-42e9-bbcf-0011eb9c87e0&file=2.pdf
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It will be able to stop a car. The question is how much wall deformation you are prepared to accept.

Calculate the energy of the car (1/2 mv^2) and then calculate the work done yielding the walls, ie the plastic resistance of the wall multiplied by the distance it deforms. The walls need to do enough work to absorb your car energy.
 
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Thanks Tomfh. I don't mind if the garage needs to be fully rebuilt after the collision providing the garage does not deform into the house. The primary objective is for the garage to stop the car before it can hurt people in the house.

I might have to hire a structural engineer as I'm mechanical but really interested to hear people's opinions!

I'm now wondering if I'd be better off to go with 275mm thick walls all around. Hmm.
 
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I'd say it's quite feasible. Something you may want to consider: do you just want to protect your house, driver of the car be d@&$#&? If so, then a nice, thick barrier wall should do nicely. For enough money up front, you could probably have it designed so the garage only needs minor repair (and probably replacement of your barrier). That's going to mean bringing the errant vehicle to a stop very quickly, increasing the chances of serious injury or death to the vehicle occupants. If you can live with losing the garage and most of the contents, it becomes a bit easier. The car can come through the first wall, slow down considerable, and then impact the opposite wall and stop. Still won't be fun for the driver, but better chance of survival.

As you can probably guess, the engineering for this won't be cheap. You're probably going to want to find somebody with experience working with the military. Here in the States we call it Force Protection or Security engineering. I've done a bit of it myself. Designing buildings to maintain a certain level of protection for occupants in the case of a bomb blast, or ensuring a structure won't collapse if a particular load bearing element is destroyed by terrorists or other ne'er-do-wells.
 
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If the speed limit for that street is 60km/h then I don't think that those barriers are usually designed for a car travelling at the same speed. My understanding is that they usually take into account some braking by the driver, or they also look at an impact travelling at some diagonal into the barrier. Although given this is your family you probably want something as strong as can be regardless.
 
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In order from the road - Sand/gravel pit/berm, then heavy shrubbery, and a few decent sized trees. No garage.
 
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A formation of water barrels would be a lot cheaper.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"
 
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Is it all downhill to the house?
Would a car actually be airborne?
Is there room for a tall curb near the road?
I have seen people use a very well anchored 10-12" concrete curb to slow down an errant vehicle.
It needs to be deeply anchored (I have seen pipe driven 20' into the ground for this, 4" pipe @12" on centers).
The ides is that it won't stop a car abruptly enough to kill the occupants but the energy involved in tearing the suspension out of the car slows it enough to blunt the impact.
There is a lot of safety barrier technology out there. Keep searching.


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P.E. Metallurgy, consulting work welcomed
 
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Got room for a few Jersy barriers? Just plunk 'em down and done.

The problem with sloppy work is that the supply FAR EXCEEDS the demand
 
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There's some good info on impact loads, load distribution widths, etc. in the AASHTO specs. Section 13 of the LRFD specs. (4th Edition or newer) is where you'd find the most of the relevant information.

Rod Smith, P.E., The artist formerly known as HotRod10
 
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You have about 318,340 ft lb of energy to restrain. The force to restrain it depends upon the distance over which you have to stop the load.
If your barrier is elastic like a giant spring, a 3 ft stopping distance will result in a 32 g force to stop a car going 38 mph. If your barrier crushes plasticly, your
g force will be about half of that.
 
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I agree with the planting ideas of 3DDave and BrianPetersen. Also, can you curb the shoulder higher than the road, so a runaway car will bump into dirt, or slightly flying with reduced speed and heads up. The garage you proposed posses a risk, that the high speed car might touch down on the garage roof, and travel to your house by the remaining momentum, especially in an icy, or raining day.
 
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Bill8123:
Make the lower left (southwest facing) wall of the garage something of an ‘art work’, with some color, so it is obviously seen. Some sort of textured conc. block, with reinforced bond beams every other course, to a height of 4 to 6 feet high, and a few vert. pilasters in the 26’ length of the garage, along with the end returns. Then provide a 4 or 5’ high, by 26’ long, by 3 or 4’ deep (near street to the garage wall) planter for flowers, etc. What you want is something like the planter which absorbs a lot of energy, in the vehicle plowing process through the planter wall and soil, before it hits the garage wall, which is the ultimate backstop, but at a much lower energy level.
 
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Trees and bushes take a while to grow and develop a root system. Construction of a garage takes a while to complete. In the meantime, the danger persists. The Jersey barrier sounds like a good temporary measure, although I'm not sure it would stop a head-on collision.

BA
 
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Around here if there is a barrier that might take a fairly direct impact they have put them on wood posts that are cross drilled. This gives a balance of energy absorption and reasonable G force.
Jersey barriers are designed for glancing impact redirection, not direct impact.

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P.E. Metallurgy, consulting work welcomed
 
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