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Reinforcing lighting truss and removing deflection

Reinforcing lighting truss and removing deflection

Reinforcing lighting truss and removing deflection

(OP)
Hello all, I am new to this site and forum.
Looking for help about how to remove deflection and reinforcing truss.

Problem parameters:
We are joining five prefabbed rectangular trusses to span 50' (they come in 10' lengths).
The dimensions of each truss section is 16" x 16" rect @ ~10' long. Weight is 63# each.
http://www.displaysexhibits.com/product-p/qtl3000....

So we are simply using this to move below ground conduit to above ground conduit. We will also mount some gas lines (nitrogen and compressed air) on the span. I don't think we'll go beyond the design spec of 38 lbs/ft for a equally distributed load over a 50' span.

The issue:
There is about a 9" deflection down at the midpoint when we mount this. (that's based on the load data from the mfg)
We want to remove this deflection while stiffening and strengthening the structure. I have attached a rough sketch of the plan.

I'm def not a structural engineer so I'm hoping you guys can help me solve this.

Thanks in advance!

Sifan

RE: Reinforcing lighting truss and removing deflection

I recommend enlisting the help of a local structural engineer. A variety of deviator post heights could work. But, then, the shorter you make the post, the higher the axial load that you'll develop in both the truss and the cables. You'll also want to take care that the deviator post itself is properly stabilized. Off of the top of my head, I feel like about 5' from center of truss to bottom of deviator post should be fairly efficient.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Reinforcing lighting truss and removing deflection

can you separate the 5 panels and rejoin, but adding wedges between each to create a 12" hill over the span ?

another day in paradise, or is paradise one day closer ?

RE: Reinforcing lighting truss and removing deflection

rb1957's idea is a good one. Essentially pre-camber.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Reinforcing lighting truss and removing deflection

(OP)
KootK, rb1957,

Thanks for the posts.
KootK, I'll assume the deviator post is the one in question that extends down. I see your point about length affecting axial load on the support posts and truss itself. Our maintenance guy wanted to use something along the lines of 24" and that seems to be too short.

rb1957, yes, we can detach and reattach the 5 sections. These wedges would essentially act like gussets? Pre-camber is guess is the structural term? They would run the length-wise? Meaning, if we were looking at the entire 50' span, there would be 4 visible triangles/hills from that point of view? I just want to make sure you don't mean between (as in sandwich). Why would we need to detach? Can't we fab the triangles and weld/attach to the truss? Is it a flat triangle or an "extruded" triangle (with depth that spans the 16" depth of the truss)?

again, thanks for the help!

Sifan

RE: Reinforcing lighting truss and removing deflection

Sifan Zhu:
What Rb1957 means is to put shims in the top, end connections btwn. each of the 5-10' truss sections to spread them a bit at the top, w.r.t. their bottom connections. Maybe 1" or 2" thick, and matching the existing bolt pattern. Maybe they would be wedge shaped to fit btwn. the two end pls. on the trusses at each joint. This would cause the sum of the trusses to arch a bit when assembled, or pre-camber. The exact thickness and detail would be a function of your exact truss details and connection means. It would be helpful if you described the trusses, their end connections and the hardware in detail, along with dimensions and sizes of parts and with some photos of same. Koot & Rb, remember, these are stage lighting trusses, made out of double strength tin foil, to be light and handleable. They don’t think much about stability and the like, they blame any problems on acts of God.

RE: Reinforcing lighting truss and removing deflection

god has a lot to answer for ...

another day in paradise, or is paradise one day closer ?

RE: Reinforcing lighting truss and removing deflection

(OP)
dhengr,

Thanks for the clarification.

And to everyone, thanks for the help! I have discussed with my team the ideas I have learned from this thread.

Sifan

RE: Reinforcing lighting truss and removing deflection

There are several issues not discussed, such as the potential for collapsing in the horizontal direction. You may find the ideas you have won't work unless there is a lot of reinforcing. I'd not go with any ideas expressed here and go only to a structural engineer. The full details of what you have are not shown here. It also likely requires a P.E. since failure may injure someone.

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