Span direction of grating on walkways

[J1D]

I realized recently this is specified differently among my colleagues.

There is no standard for the spanning direction of grating mats on platforms, walkways, etc. But for an elevated walkway or catwalk it is preferred in some client specs to have the bearing bars perpendicular to the walking direction, mainly to block the view through the grating to feel safer.

Technically the structural performance is slight different from my view. For grating spanning longitudinally (say Option A) needs transverse beams at say every say 5ft, while for grating spanning transversely (say Option B)will have no transverse beams but we still use some to provide lateral restraint to the support channels (stringers). When we have grating welded to the support beams the two options may give different capacities.

For non-removable grating we typically say "to be welded to support members with 2" long 3/16" fillet welds at eighth bearing bar maximum spacing". This means:

For Option A, grating is welded to the transverse beams, no connection between grating to the stringers

For Option B, grating is welded along the stringers. The actual welding will be from the banding bar (required in this case) to the stringers.

I think in this case Option B will not only look safer but be stronger as well.

What is your practice and opinion on this?


Thanks,
J1D

 

[msquared48]

Better traction and less chance of slippage if the grating span is normal to the direction of travel.

And as for rollover, with the edge channels and "J" bolts, I have never found it to be a problem.

Mike McCann
MMC Engineering

 

[Ron]

Most bar grating is galvanized. If you cut the pieces transverse to the direction of travel, you have a labor intensive operation and a lot more corrosion potential.

Weigh the extra cuts and protection necessary with the substructure costs..

 

[shobroco]

I'm with Mike on bearing bars normal to travel direction, mostly for traction. Around here, interior grating is seldom galvanized, & exterior is almost always galvanized, but the fabricator typically cuts (& bands if removable) the grating to size before galvanizing.

 

[J1D]

We used pre-painted black even on the exterior grating for years, no issues.

As per Fisher & Ludlow, the grating mats are supplied in 3'x24' standard size. The bearing bars are in the 24' direction. If we have a 3'x24' walkway Option A needs only one panel. The price is about $770/lot. To change bearing bars to be transverse (Option B) the standard size will be cut into 8 pieces and the banding will be much longer. The price is $200 more. But bear in mind this option can save some transverse beams, the difference is not that bad.

I like Option B for sure, but I don't know if it is always preferred or not, even other way around.

 

[TLHS]

I'm going to go off on a tangent!

Just as a comment to adding beams for lateral support on a platform even if you're spanning the grating the other way, I'd suggest you take a close look at that. Depending on the span, you may be using a lot of steel and labour to add capacity that you could have added by just upsizing the main beams a size. You still need to support it laterally at the vertical support points, but providing periodic lateral support to the beams in this kind of scenario is not always the most economical.

This is especially true when you're in a situation where you may be upsized already for constructability (things smaller than 200mm or *maybe* 150mm can be a bear to connect so you often have a minimum depth despite not needing it in short spans) or deflection (longer spans). I know in the back of my mind there's a little voice saying "lateral support! lateral support!" all the time, but it's not always what you want to do.

As a secondary point, I personally wouldn't worry about which direction allows the grating to add more strength to the system. You generally see grating in industrial locations. These are also the locations where you're most likely to have someone come along and cut a hole square in the centre of the grating in the future so they can run a pipe or cut out a panel to install equipment and then replace it without securing it properly. As such, I just design connections so that they'll hold the grating in place and neglect any possible diaphragm action or lateral support the grating may provide.

For deciding the span direction, it generally just depends on the geometry. Long and skinny you probably want to span with the direction of travel. Shorter spaning walkway and fat (maybe up to needing three or maybe four panels) it might make sense to span against the direction of travel if it saves you a couple of beams.