Feedback on this "riser"

[AudJ]

A group that uses my facility has been asked to replace their 18" riser
set because the old ones have become unstable. They use the space when I am not there, and this riser was set up, as an example, to replace the total of 4- 4x4 risers. They are used to as a set to hold up 7 brass players so this design is making me nervous. The manufactured support frame seems good, but there are 9 points supporting a 4x4' 3/4" plywood. 8 of the points are drilled through the plywood with no fasteners. There is almost 3' between supports diagonally.

I would like opinions, but more importantly, any hard facts I can use to get them to purchase a safer deck. These people have "been here a lot longer" than me, and "know a lot more" than I do about these things, so it will be a tough conversation without something to back me up. I am most afraid that they will continue to use these, and just not tell me. Maybe I'm wrong, but if these risers are unsafe, I may need to scare them a little to get them to comply.

 

[Van]

Actually, looks like a pretty decent design with the exception that I would want a better grade, 7 - 9 ply material and perhaps 2, 1 x 2 'stringers' on the underside. Have them run the same direction as the kick rail on the US side, and centered between the DS and Mid and Mid and US areas.

 

[RCDVS]

Correct me if I'm wrong, but what I see is a 4'X4' panel of 3/4" plywood supported at each corner and at the middle of each side as well as the middle of the panel. Like you said, it has nine support points. There is only a lateral distance of 2' between the support points. The only thing which might bother me about this structure is if the riser "wobbles" side to side or corner to corner. I have been building 4'X4' risers for many years with support only around the perimeter, no support in the middle. A 4'X4' panel of 3/4" plywood can easily support the weight of a couple of brass players unless they get up and jump up and down in unison. Even then it would probably just crack, not collapse.
With that said, if the framework does "wobble" then fastening the posts to the panel would make the entire structure extremely strong and stable. I don't think this is what you were hoping to hear but I don't think these risers are the least bit dangerous. One thing to think about. This looks like a commercial product. I doubt the manufacturer could sell this design if it wasn't safe.

 

[AudJ]

Excellent - Thank you for some good insight. I feel better about it. They purchased the frame (which seems good), and home-made the top. My concern is that the 3/4" does give a bit when walked/stood on. And there really isn't much material left where the holes are. But I am used to the traditional riser, and appreciate learning from those who know.

I'll make the suggestion that they add a few stringers underneath, and see where it goes.

Thank you so much!

 

[Footer]

Excellent - Thank you for some good insight. I feel better about it. They purchased the frame (which seems good), and home-made the top. My concern is that the 3/4" does give a bit when walked/stood on. And there really isn't much material left where the holes are. But I am used to the traditional riser, and appreciate learning from those who know.

I'll make the suggestion that they add a few stringers underneath, and see where it goes.

Thank you so much!

Even some angle iron on the edges would do it. Just something to beef up the ply. I never like to see floating ply.

 

[BillConnerFASTC]

Load then up - an actual load test. Lay bags of sand or cement or gravel to equal 150 psf. That should assure a sufficient design factor for what its used for. 4 X 4 = 16 sq ft = 2400 pounds or 48 bags? Just carry one to Lowes or Home Depot and do it there.