"Road Plate" - H-20 Rated - Type of bolt connection needed? 1

[aalver2]

Hello,
We have a concrete structure (basically four walls which are beneath grade) who's top slab is supported by walls and sits flush with existing grade. This slab has been designed to take H-20 loading. We have now been asked to add a "trench" to our slab, in order to fit and store electrical cables. We have decided to cover this trench, which is 5 ft in length, with a 1" steel plate (H-20 rated). This plate must be removable in case the maintenance crew needs to get to the cables (I've read these are often called road plates). We are unsure how to bolt this down or what connection system to use. I would appreciate if someone could point me to some reference I could look at, or some standard detail...
Thanks,

Alex.

 

[bridgebuster]

Are you replacing the top slab in its entirety with a plate or are you cutting a "trench" in the slab and covering it with a plate?

In either case, you can bolt the plate down with post-installed anchors. However, you would need to determine a horizontal force to apply to the anchors.

If you are replacing the slab in its entirety you could construct a cast in place slab and add an access hatch. Go to Bilco's website; they have hatches rated for HS-20. I used one for a similar situation.

 

[TLHS]

How much traffic is it? If it's just occasional access I might not bolt it down at all. I'd make sure it was inset into the slab so that top of plate approximately equaled top of slab and then let it butt up against the slab. I'd also make sure the bearing surface (top of trench wall or brackets or whatever you come up with) and edge of slab had steel plate or an angle there so that the surface you're bearing on and where the plate might hit the edge of slab is properly armoured.

This is what I'd do for a trench with grating over an industrial area with occasional traffic.

If you're going to bolt it, you'd want to machine things so that the bolts end up countersunk. For forces, look to the bridge code. It's got things like assumed lateral loads for traffic and similar items. I'd still armour everything assuming the plate is jumping all over the place, because I figure there's a pretty good change that the maintenance guys don't bolt it up completely after the first time they pull it.

Also, have you considered heavy duty grating? It's going to be significantly lighter for the people trying to remove this thing, and a lot less material.

 

[aalver2]

Bridgebuster: Thanks for the response and recommendations. We are just cutting a trench into a portion of the slab and covering with a plate.

TLHS: I don't expect much traffic will be going over this thing. I guess you could say it is on an industrial site, not a public road or anything designed for regular vehicular traffic. But occasionally we could expect a few vehicles going over it. Like you mention, we were also thinking of adding an angle and letting it sit on the slab edges which will support the plate. The question is whether to bolt it down or not, and if we did, which would be the best way to have the bolts counter sunk as to not have any bolt part extruding from the top of plate/top of slab plane level (or is this not even an issue?). We cant use heavy duty grating since we need a solid cover to keep most water out of the trench.

 

[thaidavid40]

Pre-drill and tap holes in the anchor frame on which this sits. Put a compressible filler under these holes to keep concrete out of the way, and allow the bolts to protrude through the frame below (to ensure full thread engagement). Counterbore the plate and use flat hex-head cap screws (don't use socket head cap screws - they fill up with grit and the hexes strip out). If your horizontal loads are low (as they should be, since the plate is constrained within its frame) then one, 5/8" bolt every 24" on-center should work adequately.
Dave

Thaidavid

 

[Lomarandil]

I wouldn't be too worried about a bolt head on the surface of the plate -- but you're right to be thinking along those lines.

I can't find the news story anecdote, but you do need to be careful that your bolts don't pop up and puncture tires. As I understand it, this can happen for adhesive anchors if you don't get a good bond. Also, it can happen if the span is long enough to cause the plate to deflect and pry the bolt over hundreds of cycles.