handrail wire rope infill - design question
handrail wire rope infill - design question
(OP)
I am designing a handrail that has a 5mm wire rope infill. The wire ropes will be pre-tensioned. The variables are the rope spacing and the span of the rope between the vertical posts.
I have been told that I have to design the wire rope to be sufficiently taut so that a 4" diameter sphere can't be pushed between two ropes. What is the force that I am applying to push this theoretical sphere through the rope? The harder I have to push it, the larger the required rope pretension force will be to prevent the sphere from passing through.
I have been told that I have to design the wire rope to be sufficiently taut so that a 4" diameter sphere can't be pushed between two ropes. What is the force that I am applying to push this theoretical sphere through the rope? The harder I have to push it, the larger the required rope pretension force will be to prevent the sphere from passing through.






RE: handrail wire rope infill - design question
RE: handrail wire rope infill - design question
Typically, the IBC requires a 50# load over a 1 square foot area.... so a 4" dia ball would have approx 4.4lbs of force behind it. Not much, but it's not an easy problem to solve. I found the information here to be helpful:
http://thecableconnection.com/data-on-cable-flex.h...
Good luck
RE: handrail wire rope infill - design question
RE: handrail wire rope infill - design question
Say, I space the wires 3" apart and design for a max opening of 3.5".......this would be a 1/4" deflection in each wire with the other 1/2" as a safety factor.Depending on the span of the wire this could require a significant pretension in the wire and a resulting moment in the last post in the system.This would be an iterative process to get to a pretension one can live with.
The next step is to take that design deflection and translate it into a point load on the wire and then check that point load with the 50# requirement from the codes....using the 3.0" sp as an example,........P=50x3/12=12.5#...so maybe the required pretension will not be as bad as first assumed.
RE: handrail wire rope infill - design question
RE: handrail wire rope infill - design question
RE: handrail wire rope infill - design question
The 4 inch "rule" is a bureaucratic interpretation of the very real need to prevent a baby's head from being trapped between the bars of stairway railing ... Theory is: If a baby can't get her through the bars, the baby's head can't get stuck, the baby won't choke - nor can it get its body through the bars and fall downstairs. A second part of the requirement "against" horizontal bars (wire in your case) is the lesser-know rule that the horizontals can't be used as a ladder by a baby/infant/toddler/small child. Why 4 inch sphere? Its also an approximation: no real head is shaped like that at any age!
So, you need to make a reasonable estimate of how hard a baby can push. Add a conservative factor to that force, then use it as your force. Keep your notes. The code (by itself) is not smart enough to have figured this out already.
RE: handrail wire rope infill - design question
The force applied to the 4" sphere is about 9#.
The procedure is straightforward but intense.
RE: handrail wire rope infill - design question
There must be a starting point.
Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin
RE: handrail wire rope infill - design question
Don't forget to check deflection in the end posts as they may give enough to be significant.
RE: handrail wire rope infill - design question
RE: handrail wire rope infill - design question
While the method may be intense, it is really simple once you write a MathCAD spreadsheet.
RE: handrail wire rope infill - design question
I wish I could find some sort of chart that would make this easier.
Thanks again everyone.
RE: handrail wire rope infill - design question
As for the cables, I use the approach that Sail3 described.
RE: handrail wire rope infill - design question
If I remember right, that sphere size changes to 12" for areas not accessible to the public and to 21" for industrial areas. I would assume in those cases that any specified railing loads were applied directly to the rail and not to a frictionless sphere being forced between the rails.
In certain instances, OSHA allows wire rope toprails, and googling around on the OSHA site shows some requirements of a maximum 3" deflection with the design load in those cases.
RE: handrail wire rope infill - design question
Dik
RE: handrail wire rope infill - design question
RE: handrail wire rope infill - design question
RE: handrail wire rope infill - design question
RE: handrail wire rope infill - design question
RE: handrail wire rope infill - design question
So did I when I was asked to look at a similar project where "cable rails by others" would not fly. In this instance, I passed on the project because I could not do the analysis but became intrigued by the problem. I came across the link above and programed their equations into MathCAD. In all took about 1-1/2 days to do everything (research to programming) of which I was paid for none (I did have to tweak their analysis to get it to work).
Recently I was asked to help another engineer solve this problem. I gave him the link and my MathCAD spreadsheet (we help each other out from time to time) and told him to make sure he charges the appropriate rate to solve the complex problem because someone should be getting paid for the effort that went in.
RE: handrail wire rope infill - design question
"I missed the complexity of this when we gave our fee for designing these cables."
"So did I when I was asked to look at a similar project where "cable rails by others" would not fly."
That is exactly why I HATE "design by others" so much.
No offense to anyone here (okay, maybe a little if you're guilty of doing this) but if some is hired to design something, DESIGN IT! Passing it onto "others" (usually the contractor) is great for your fee or deadlines but only hurts everyone else. "Others" usually means the contractor who then has to hire another engineer to design something.
If the contractor is smart he'll catch this "by others" bit and drop a big fat question mark into his bid which raises the cost of the project. If not, he then has to scrounge to fit an engineer's fee and design into his costs and time schedule (or he farms it out for cheap and gives a substandard product). THEN if it turns out that the design is much more complicated than anyone anticipates the contractor gets pissed at the "by others" engineer who gets pissed at the original EOR engineer and the client is pissed at everyone for either cost overruns or delays.
A while back we got hired to do a design for some steel pipe handrails for a post office. REALLY basic stuff but it was in the drawings as "handrail design by others" and the EOR required a stamped calculation submittable for them. It was only a few hundred bucks of design fees IIRC but the contractor hadn't budgeted for it and only caught the "by others" note last minute so they had a day of delays. DON'T DO THIS!
Then who becomes responsible for the design? For example if the EOR specified horizontal wires and told you to do the structural design only you would have to fill your design full of caveats that you're not responsible for anything but the structural scope. Legal battles would be fun for those I'm sure; lots of finger pointing. We had some concrete stairs to design the other day for a commercial building. 7.5" rise (vs 7" maximum allowed by IBC). We gave them lots of notes regarding how that's wrong but we're not responsible. Fun. I'm pretty sure it went in at 7.5" rise. DON'T SPECIFY "BY OTHERS"!
...
Sorry, huge pet peeve of mine. Interesting topic here.
Maine EIT, Civil/Structural.
RE: handrail wire rope infill - design question
Go ahead and design everything on a building yourself while your competition charges the same and "calls out design by others" :>
RE: handrail wire rope infill - design question
For example, say you're hired to design a multimillion dollar underground concrete sewage structure where probably about 1/4 of the design work is structural and your fee is based on being hired to do that work. You should not be dumping that onto the contractor who may or may not have read all 3,000 pages of your specification with a magnifying glass during the bidding phase. A specification which has multiple "hidden" sections that relate to the structural design spread throughout the spec. A specification that has a clause stating that after 3 reviews by the EOR they can start charging for reviews. A clause which can get very abused and cost the contractor almost $100,000 and who still hasn't been paid for this work.
My boss and everyone in our office provide fair, honest, no BS work for the jobs we're bidding on and are hired to do. Sure we lose out, I know of a couple of jobs I'm sure it cost us the bid. Doesn't matter, it's not right and sooner or later clients will (hopefully) wise up to the fact that this can and does happen because, in the end, they're the ones who really lose.
Maine EIT, Civil/Structural.
RE: handrail wire rope infill - design question
Maine EIT, Civil/Structural.
RE: handrail wire rope infill - design question
RE: handrail wire rope infill - design question
But back to the original post: Consider this loading: Little Kid A weighs 40 lbs and stands on that bottom cable. Littler Kid B then sticks his 4" head between the cables. That is probably much more likely to happen than an actual infant forcing his frictionless head through the cables with 9 lbs force.
RE: handrail wire rope infill - design question
If they were vertical I'd look at placing them 3 1/2" on center with a reasonable pretension and see what the force would be cause 1/2" deflection. I bet you will get more than the 200# and you'd be in the free and clear.
Horizontal rails seem like a bad idea to me. Period.
RE: handrail wire rope infill - design question
Maine EIT, Civil/Structural.
RE: handrail wire rope infill - design question
http://eng-tips.com/viewthread.cfm?qid=273157
RE: handrail wire rope infill - design question
RE: handrail wire rope infill - design question
RE: handrail wire rope infill - design question
RE: handrail wire rope infill - design question
It seems like a very logical requirement, but I don't recall seeing a similar requirement in the US Codes.
RE: handrail wire rope infill - design question
And off topic but honestly how do you guys even use those codes, the NBCC is full of the legal mumbo jumbo stuff but at least I can find useful information relatively easily. Both of the IBC and IRC are a hell of a lot tougher to manage than the NBCC. Granted I'm biased because I solely use the NBCC so I have lots of experience reading through the junk to get to the meat.
RE: handrail wire rope infill - design question
The Michigan LARA (Building Codes) regulators have changed their horizontal cable rails guidelines1
http://www.michigancodes.com/module11.html
It does appear that the "words" they use do seem to be a sales guide to the railing cables, but ....
RE: handrail wire rope infill - design question
Like anything else you get familiar with it. I find the IBC ok, but the IRC is a disaster.
RE: handrail wire rope infill - design question