Steel Cable Infill for Stair Guardrail
Steel Cable Infill for Stair Guardrail
(OP)
I have a situation where the steel fabricator is using 1/4" diameter steel cables for the infill area of a guardrail for a stair. I have to check the infill for a load of 200 lbs on 1 sq. ft. of area so that people don't fall out the side of the stairs. I'm wondering the best way to check this because it's not like the cable is rigid. I basically don't understand how I'm going to get the side load into a stress in the cable. Off hand it doesn't sound like an easy thing to do.
Thanks.
Thanks.






RE: Steel Cable Infill for Stair Guardrail
1. Say that an 8 ft. length of cable is restrained from horizontal movement at each end (a continuous cable passing though holes in steel post 8 ft o.c., pehaps).
2. A 200 lb. horizontal load is applied to the center of this section of the cable; say that this case say the cable deflects 2 in. (horizontally) because of this load.
3. Since the only way that the 200 lb horizontal load can be resisted is by tension in the cable, draw the force triangle with 200 lb being the horizontal component. Using the Pythagorean theorm, tension in the cable has to be just over 24.02 x 200 lb (or approximately 4804 lb.)
RE: Steel Cable Infill for Stair Guardrail
Of course these calcs are much too precise for the "real world problem". They are offered only to show the geometry for this situation.
RE: Steel Cable Infill for Stair Guardrail
Variables
E, modulus of elasticity
A, cross-sectional area
L, unstretched length of cable
w, uniform transverse load
y, maximum transverse deflection
P, tensile force in cable
Calculate y:
y = L*[(3*w*L)/(64*E*A)]^(1/3)
Calculate P:
P = (w*L^2)/(8*y)
RE: Steel Cable Infill for Stair Guardrail
Cheers
Greg Locock
RE: Steel Cable Infill for Stair Guardrail
I'm not sure where you are located, so I'll give you the IBC 2003 requirements.....
Your setup would not comply with code unless you could assure that the cables are so closely spaced and so taught under load that they would not allow a 4-inch diameter sphere to pass through the space between cables, whether placed horizontally or vertically. This is virtually impossible with cables.
The rules and assessment requirements for handrails were written under the assumption of solid balusters and rails.
The same or similar requirements exist under both the International Building Code and the Life Safety Code (NFPA 101) in the US.
RE: Steel Cable Infill for Stair Guardrail
RE: Steel Cable Infill for Stair Guardrail
However, these folks may be able to offer some insight:
http://www.allformwelding.com/allform_026.htm
RE: Steel Cable Infill for Stair Guardrail
If you took a look at the allform site, practically none of their portfolio meets code for infill.
RE: Steel Cable Infill for Stair Guardrail
Thanks.
RE: Steel Cable Infill for Stair Guardrail
It probably comes from the inspector's childhood.
RE: Steel Cable Infill for Stair Guardrail
Seriously.
"Oh, this guard rail is OK, admittedly there is a 100 ft drop the other side of it, but the code doesn't explicitly forbid horizontal rails in that situation."
Cheers
Greg Locock
RE: Steel Cable Infill for Stair Guardrail
RE: Steel Cable Infill for Stair Guardrail
Hmmm...would that mean that parents are actually supposed to supervise the little buggers?