Crash Barriers

[Glenn]

How do crash barriers on the sides of roads work? How are they supposed to deform in a collision? Is there any shock absorption material / device between the barrier and the upright posts that support it?

This is for an A-level physics project - joy of joys!

Thanks

[sddsddean]

Have a look at this. It details most sorts of barriers

http://www.hill-smith.co.uk/barrier.htm

 

The most common one, the corrugated tensioned crash barrier (TCB), is as its name implies tensioned. However, due to expansion and contraction due to temperature, there is a formula as to how much you tension it on a given day. You can regularly go along a  TCB and find all the tension bolts are loose. A TCB works by acting as a giant rubber band which deforms around the front of the vehicle which effectively stops it rebounding into the road. The posts which hold it are purely to support it at 610mm above the road surface. If you look at the bolts you will see that sections of barrier are held together by 8No 32mm bolts, but the barrier is held up by just one 10mm bolt per post.

[ianess]

Great for stopping vehicles but bl**dy dangerous for motorcyclists.

I have a relative who hit a steel post on the type that has steel tensioned rope as the barrier when he was flung off his bike.

I suppose being permanently disabled was better than being run over by a vehicle on the opposite carriageway but he suffered horendous injuries.

Is there any ongoing research?

[Octavius]

Concrete barriers, when impacted, are designed to safely control the direction of the errant vehicle along the line of the barrier, with the crumple zones of the modern vehicle providing protection to the driver and passengers. Concrete barriers control and so prevent the vehicle from breaching the reservation and hitting on-coming traffic. Furthermore, unlike other barrier systems, they do not have to be replaced if a vehicle has collided with them. Concrete barriers are built to last for at least 50 years.

 

The steel barriers are intended to bend/move with the vehicle whilst reducing the speed & impact (in theory).