Long span catwalk handrail

[dem0001]

First time starting a thread, so forgive me if I'm in the wrong section of the forum.

A structural engineer at my company designed a 67' long, 4' wide catwalk consisting of W21 beams and lateral bracing on the top and bottom flanges. He has since retired, and the catwalk is currently in fabrication. He called me up out of the blue today concerned about the handrail. He showed continuous handrail on the drawings, as is required by code. He's concerned that the handrail will buckle when the W21s deflect under dead and live load. He designed the catwalk for L/360 live load deflection. Handrail is your typical 1 1/2" sch 80 posts with 1 1/2" sch 40 railing connected to the outside of the beam webs.

Are there exceptions in the code to allow for slip connections in the handrail or can we break the handrail into sections? Is this something we even need to worry about? Need to use outriggers to brace the handrail? Any input is appreciated. I can't find anything online about this.

 

[racookpe1978]

If he is concerned about the handrail buckling under compression loads when the W21 deflects, then; Yes, the handrail can be built in two sections - as long as the gap between sections is less than 4 inches. Should be a wide enough gap that no one's fingers can get trapped in a very narrow slot or very sharp-edged notch either.

 

[JStephen]

Expansion joints/ slip connections in the rail are okay, too.

 

[DaveAtkins]

It sounds like he is concerned about the guardrail acting in a composite fashion with the W21. I don't think I would be concerned with this. I am assuming this is an indoor catwalk--if it is outdoor, then thermal expansion/contraction should be accounted for.

DaveAtkins

 

[dem0001]

Thank you for the replies. This is an outdoor catwalk from a boiler building to a stack, so it was designed to "float" on the stack end.

 

[JLNJ]

There is no OSHA requirement for guardrail to be continuous. Build it in manageable sections and don't worry about it.

I'd be more worried about the flexibility of the W21s spanning 67'.

 

[JoelTXCive]

You can do a 'pipe inside a pipe' splice, which allows movement.

Below is a detail from a TxDOT pedestrian handrail.. I've seen this on smaller fall protection rails and it seems to work well.

 

[Bagman2524]

OSHA allows gaps in the guardrail of 19" or less. The 4" gap requirement is per IBC/NFPA-101 for commercial applications where the general public has access.

All I know is P/A and Mc/I

 

[dem0001]

Thank you for the replies and the detail, Joel!

 

[azcats]

Like some others, I would break it into manageable section lengths of 12-15' that bolt to your beams. And if you're really worried about any gaps, put chains in between.

If it were one continuous piece, you'd really be testing the rigidity of your vertical posts and connections in the longitudinal direction. If they had some give, it probably wouldn't be a problem. If they're fairly rigid you'd start putting some axial force into the handrail to push the verticals to stay vertical as the beam deflects into it's shape.

 

[OldBldgGuy]

You're probably too far across this stream to change horses, but it seems to me it's a shame it wasn't designed as 2 trusses with the catwalk grating between them connected to the bottom chords. There are a ton of companies doing pre-eng bridges for trails and using a similar system, the railing becomes as easy as anything to look after and as JLNJ implies, no willies at night about the 67' W21s.

 

[human909]

You're probably too far across this stream to change horses, but it seems to me it's a shame it wasn't designed as 2 trusses with the catwalk grating between them connected to the bottom chords. There are a ton of companies doing pre-eng bridges for trails and using a similar system, the railing becomes as easy as anything to look after and as JLNJ implies, no willies at night about the 67' W21s.

In my experience the cost of a fabricated truss normally exceeds the cost of a couple simple beams for simple walkways up to about 70 feet or so. The other challenge in using the bottom chord of a truss as a walkway is buckling restraint of the top cords. You'd off need fly bracing out riggers or to build a head height truss. It all ends up being cheaper and easier to throw a heavy beam in.

 

[OldBldgGuy]

Oh, I think there are plenty of solutions out there that work quite well. Google "pre-engineered footbridge company" and you'll get 8 or 10 companies in the first 10 listings, and they make their livings at this.