Vertical wire balustrading tensioning

[D Walter]

Hi, we have a ground floor to roof stairwell/atrium and are looking to diverge from the plans and construct an L shaped walk-on glass floor at first floor level bisecting the atrium, leaving the area above treads 5-15 and part of 1/2 winder 4 open (see sections of plans attached) for access up the stairs.  The glass floor will be constructed of four approx. 1m square 31mm panes of laminated glass supported on steel frames and will have a steel handrail.  The stairs themselves will have open risers and will appear as if cantievered from the wall but will in fact be of steel construction, bolted into the structural concrete wall, and clad in elm plywood.

 

We did not want to use the more traditional steel or glass balustrading for the "cantilevered" staircase so our plan is to use vertical 5mm stainless wire for balustrading, 3 per tread spaced at approx 75mm.  The wire will be tensioned at the top at the handrail level (approx 1m above first floor level), will pass through a steel eyebolt or hole in the structural steel frame at first floor level and tensioned at the bottom underneath each tread.  We are thinking of using swage stud threaded terminals for tensioning top and bottom, rather than bottle screws, both to save money and have a cleaner appearance (see attached pic).  The maximum length of wire will be approximately 3.5m, at tread 4/5. 

 

I don't know if anyone on the forum has any experience in this area but I would welcome any thoughts or suggestions, including on whether we will be able to maintain sufficient tension using the swage stud threaded terminals.

Swage Stud Threaded Terminal.docx

[ProDave]

I suspect building control will not pass this.

 

I know someone that tried it, and they could not get enough tension to satisfy building control that they would not push apart, and so fell foul of the "100mm sphere will not pass through"

 

They ended up putting an additional handrail, which oddly enough seemed to disappear again after the building was signed off.

 

I recall seeing the same issue on a Grand Designs house, there they inserted polycarbonate sheet between the wires, and I suspec that sheet did not stay long either.

[D Walter]

Thanks ProDave.  That is exactly my concern.  Flexion of 12.5mm in two adjacent wires would result in a 100mm gap.

[Mr Punter]

I can't be much help but to say we had raking wire balustrade on a commercial stair. Must have been 2m centres and it did not flex much even if I climbed on it.

 

You could ask the wire company to do some calcs and worst case you may need a link between a few of the longest ones to limit deflection.

 

The 100mm sphere is supposed to represent a baby's head so you don't need to factor in excessive force.

[Temp]

Perhaps I misunderstand but..

 

2 hours ago, D Walter said:

The wire will be tensioned at the top at the handrail level (approx 1m above first floor level), will pass through a steel eyebolt or hole in the structural steel frame at first floor level and tensioned at the bottom underneath each tread.

 

Why tension the wires at both ends?

 

2 hours ago, D Walter said:

I don't know if anyone on the forum has any experience in this area but I would welcome any thoughts or suggestions, including on whether we will be able to maintain sufficient tension using the swage stud threaded terminals.

 

If I've understood correctly that's going to be limited by the upward force you are allowed to apply to the end of the "cantilevered" stair treads (before they start bending upwards). You might need to run the wires down to the ground and anchor them there, using a double ended adjuster at tread level. But then how much tension can you put on the top end/handrail?

 

I think you need to get this properly designed.

 

I doubt the strength of the swage is an issue. Google finds...

 

http://www.ybw.com/forums/archive/index.php/t-270417.html

If it's done properly, a swage results in a cold weld between the two metals - basically they are compressed together so hard that the crystals merge and you have one continuous metallic structure. The same holds for aluminium terminal scrimped onto copper wire, which is why crimped connections work so well.

 

http://www.cruisersforum.com/forums/f116/strength-of-cable-terminations-wire-rope-grips-vs-swaged-131788.html

According to LOOS & WESCO:
“The swaged connection will exceed the rated breaking strength of the wire rope or cable when properly applied.”

[D Walter]

Thanks Temp.  Your question as to the reason for tensioning at either end is apt.  The only reason I can give is the very unlikely risk (provided the installation is set up optimally in the first place) of running out of thread to tension the wire as it stretches over time.