Metal guardrail for low speed roadway

[ywf96720]

Can a W-beam metal guardrail be installed without the end anchorage (concrete block) for a low speed (10 mph) road? The purpose of the guardrail is to protect vehicle from falling off a drop off and lands onto a fuel tank.

 

[thaidavid40]

Are you protecting from the impact of a Subaru, or from a loaded semi-trailer? The anticipated load makes all the difference in you answer. And can the load possibly approach perpendicular to the rail, or can it only impact at an angle? The static equivalent of the dynamic impact load depends on these factors (load, and angle of application). You simply use statics to analyze the moment and shear resistance of the support posts alone, without any tension cable distribution from the anchored cable. I think you will have to crunch some numbers to definitively answer your question.

Thaidavid

 

[ACtrafficengr]

You have a fatal-at-any-speed hazard, so a robust barrier is justifiable. Are you trying to keep costs down, or will anchors be hard to install because of conflicts with utilities, shallow bedrock, or something like that? If it's a cost thing, this isn't a place to cut corners. Go ahead and put in the anchors. You may anticipate low speeds, but if you've read as many crash reports as I have, you'd know not to expect drivers to do what you intend.

If you absolutely don't want anchors, see if box beam railing is available in your area. I think it's used mostly in Wyoming and NY, and may be hard to find outside those states. That system works by bending the box-section railing rather than in tension. Standard deflection is five feet, and minimum run length is 125 feet. It needs to be shop-curved for radii under 725 feet. It's more expensive than heavy-post W beam.

 

[ywf96720]

Thank you all. I was trying to find ways to justify if anchors can be omitted for cost saving purposes (owner's request). It appears that the w-beam guardrails do not come without some type of anchoring system, i.e. concrete block or post system. Thank you for your input.

 

[BigH]

There are studies being done/have been done on the efficacy of guardrails for low volume roads. (See for instance:

http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_638.pdf

) For low speed low volume roads, the costs may outweigh the risk (death - as "bad" as that seems) . . . I know of one road that might have 1 or 2 vehicles a day on it - but guardrails are being put in anyway - the area is mountainous and the road very curvy (Raquel Welsh would be jealous). You might be better just to put in an earth berm that is higher than 1/2 of the normal wheel size . . .