Cable tension for railing guard 3

[shobroco]

Does anyone have a good way to calculate the tension required on a 3/16" cable that is acting as part of a guard at a stair opening? The cables are 3 1/2" apart and run vertically from the 1st floor to the 2nd floor ceiling, passing through sleeves in the end of each tread & the second floor. The maximum length of cable with no lateral support is about 7', & the spacing must be less than 4" to meet code requirements for a guard. This means they must be tight enough that they can't be pushed more than 1/4" sideways. The biggest problem is that all this tension is loading a new steel beam at the second floor ceiling level & I have to size that beam & carry that load down to the foundation. It is a renovation of an existing dwelling.

 

[rb1957]

to keep people off the cables, i suggest barbed wire (maybe razor wire) ... it'll also help in keeping people from going through the wire (creating several hanging up opportunities) !

 

[shobroco]

We set up a test cable today & at 500lb pre-tension 10lb lateral force deflects a 7' cable about 3/4". 3/16" stainless rod was almost exactly the same.

I just talked to the architect again, he really doesn't want visible posts, so closer spacing seems to be our best option. The 4" spacing is to prevent children getting through it or stuck in it, the load that the guard has to carry is unrelated to the force required to push a 4" sphere between the cables. The cables will easily carry the required lateral load directly, although our code (Ontario) like IBC does not have any value for the force on the sphere.

For rb1957, the 1/4" deflection is the amount that adjacent cables have to deflect to pass the 4" sphere. Maybe your razor wire is best. I don't think I'd push on it with 8.7 lb force.

 

[shobroco]

Boo: the links are great, & will probably lead to over-analyzing as flgulfcoasteng says he has done. Thanks to everyone for their input.

 

[boo1]

Since we cant find any code requirement for the force on the 4" opening, ducument you engineering judgement using an industry recommended force as your standard. I would use the documents attached as a guide for the engineering file.

 

[Compositepro]

One option that hasn't been considered is that you don't necessarily need posts to keep the cables from spreading apart. You only need links between cables. These could be aesthetically designed.

 

[shobroco]

Compositepro: Thanks for the good suggestion, I'll try that on him.

 

[shobroco]

It didn't take long to get a response: our code does not permit any horizontal member between 140 and 900 above the walking surface that will facilitate climbing. If links at 900 vetical spacing won't work I guess razor wire would still meet that requirement.