Macafferri and Geobrugg will sell you an energy-rated fence. That is a different solution than your OP. If you have fencing materials or an existing fence and you want to know the energy rating of your creation (or some legacy fence system), that's a tall order. I'm in the midst of this problem right now.
Here's the trouble - you have an action (the falling rock) and you have a reaction (the fence). To learn about the action, you have to run a rock fall program (e.g., CRSP - the Colorado Rockfall Simulation Program). CRSP's input is topography, rock size, rock morphology and surface hardness. So, if the rock is falling on solid bedrock you'll get a different output than if the rock is falling on soil. Bigger rocks a different result than smaller rocks and cubic rocks different than spherical rocks, etc. When the dust settles (boulders I should say), you end up with a design energy to protect against. Let's say, that you end up with 100 Kj. Well, that's a unit of energy. So, to know the resistance of the fence, you have to know the deflection of the fence - the elastic properties.
Consider the behavoir of the fence. . . Will the fence posts fail (that's deflection)? Will the foundations fail (passive failure and that's deflection too)? How will the fence as a fabric perform? You see, the strand strength of the fence material (6 ga?) may well be 2,100 pounds PER STRAND. You may also know the grade of steel and guess at the elastic properties for each strand. Problem is the fence as a fabric will be governed by other factors. I mean how much strain does the fence have to undergo to mobilize the strand strength? How much strain has to occur until the fence-wrapped boulder encroaches into the travel lanes of the roadway? These are not easy items to determine.
Where's the research? Well, there is some research (old stuff) that relates to border security, airport security and the like. What's the research? It's usually aftermath studies from car strikes and so far I haven't seen any of this convered to energy equations or elastic properties of the fencing fabric.
I'm right at the point of forming my own test to look at the elastic properties of 6-ga chain link fence.
If there is an easy solution to back-calculating the energy rating of an existing "legacy" fence, that was put in place without any engineering calculations, I'd be interested.
f-d
¡papá gordo ain’t no madre flaca!
