guardrail of wire rope or chain 1

[jenDL]

Has anyone out there designed a guardrail system with wire rope or chain? I'm having trouble reconciling the resulting loads to the posts in a "reasonable" manner. Lets say with two posts and a chain "rail" between, placing the 200 lb. point load at the center, perpendicular to the rail. Assuming a relatively small deflection of the chain, the vector components of the forces pulling inward on the posts gets very large and seems beyond the intent of the 200 lb. point load requirement. Anyone have any ideas on the subject? Thanks.

 

[rowingengineer]

the chain can't be very tight, it must be able to deflect a fair bit since you are relying on canterary effects.

Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that they like it

 

[mijowe]

I have attached a pdf on vehicle barrier cable design. You are probably assuming two small of a deflection, with the cable design an acceptable deflection is pretty big, with a chain that has some sag in it I would assume a fair amount of distance can be expected as well. Anyway the pdf goes through the barrier cable design, the principles will be the same for a handrail.

 

[SlideRuleEra]

This may not be what your are looking for, but cable barriers, for highways, work and are used in some states. In South Carolina they have had some notable success in minimizing vehicle accident damage. See this link for general information:

http://www.fhwa.dot.gov/crt/lifecycle/cable.cfm

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[rowingengineer]

No PDF mijowe, please try again

Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that they like it

 

[mijowe]

Don't know where my pdf got posted, attached is a link with similar content.

http://pti.mountaininternet.com/reportFiles/28-Technote14.pdf

 

[jenDL]

thanks for the info mijowe. my application is only for humans, but that info may come in handy in the future.

 

[Structcon]

What I would do is start by designing the posts for a minimum of 200# at 42". Then I would provide the cables at 4" o.c. (as you would with pickets, per code). Next, I would determine a reasonable pre-tension (or taut-ness), such as 100#, and then calculate the actual cable tension due to a 50psf (or 16.7# at mid-span on each cable) code required load and then verify deflection is less than L/240. This tension should drive the design of the end posts only. Good luck!

 

[JStephen]

Don't attach the cable or chain to each post- run it through a loop on the post. Then when you load it in tension, you're stretching 50' instead of 5' of cable, deflections are larger, and forces are lower.

I'm thinking somewhere, I've also seen a maximum deflection under load- possibly in design of cable handrails on scaffolding.

 

[cntw1953]

I think the key here is "You are probably assuming two small of a deflection" as pointed out by mijowe.

I think you can start with drawing the deflection profile due to chain/cable selfweight alone to determine the angle, then add downward and side push to get maximum forces on support posts. You can also intentionally to produce larger initial sag to minimize the horizontal force components. The analysis is similar to the design for horizontal lifelines, and I remember there is useful guide/doc at SlideRuleEra's web site (see third response from top).

However, I question the application of such flexible guardrail system for human use, can you provide info on location and purpose of this application? Warning: you maybe bombard by responses.

 

[Debaser]

Is it worth asking a manufacturer like Brifen for advice?

http://www.roadtraffic-technology.com/contractors/safety/brifen/