truss deflecting over time?

Dagger · May 10, 2022

This is structure I saw . Goal post 34 ' span. LED Wall 54 panels at 30 lbs per panel.

First day there was only a slight smile in truss Day by day I noticed the truss smiling a little more. By day 4 it was quite noticeable. Day 5 I noticed someone putting a genie super tower in the back raised and put in the center of the truss. Someone must have noticed as well and put it there as a precaution.

My questions are

1 )is it normal for a truss line to deflect over time?

2 ) IF I am reading the christie lites truss chart correctly,

Wasn't the strucutre overloaded to begin with.??

Image 1 of structure. Image 2 is truss chart.

Image 1 . 34 ' span and 54 panels at 30 lbs per. = 1620lbs.

Image 2 : uniform load 32' span is 800 lbs.

Help much appreciated. Thanks.

RonaldBeal · May 11, 2022

Disclaimer: This is not professional rigging advice.
Kinda sorta/not really. On a flown truss, we may see deflection increase a little as the rigging "settles in" A bridle on a slight angle may shift, spansets under load may tighten or shift a little etc...
On the shown ground support, I would think the only way for deflection to increase is if the base of the legs have slid farther apart (even less than an inch can induce deflection.) or something is loose, allowing the shift... definitely investigate further.

RonHebbard · May 11, 2022

Dagger said:
This is structure I saw . Goal post 34 ' span. LED Wall 54 panels at 30 lbs per panel.

First day there was only a slight smile in truss Day by day I noticed the truss smiling a little more. By day 4 it was quite noticeable. Day 5 I noticed someone putting a genie super tower in the back raised and put in the center of the truss. Someone must have noticed as well and put it there as a precaution.

My questions are

1 )is it normal for a truss line to deflect over time?

2 ) IF I am reading the christie lites truss chart correctly,

Wasn't the strucutre overloaded to begin with.??

Image 1 of structure. Image 2 is truss chart.

Image 1 . 34 ' span and 54 panels at 30 lbs per. = 1620lbs.

Image 2 : uniform load 32' span is 800 lbs.

Help much appreciated. Thanks.

@Dagger Are you certain your truss is smiling rather than sneering? (Some are a devious combination of cunning and cunniving.)

egilson1 · May 11, 2022

1) That looks narrow to be a 34' span.
2) Deflection over time like you describe is unusual, and could mean that the truss is overloaded just enough to slowly bring the material to its yield point, then failure.
3) The solution of using a genie lift with a capacity at BEST of 650lbs was woefully ignorant of fact that you would instantly be overloading said lift.
4) I think the number of panels is not correct. There are 10 lift points on the wall. I would assume they are half meter wide panels, so you would then end up with 5.4 panels per column. Something doesn't line up there.
5) Yes you were reading the load chart correctly. Do you KNOW that that is Christie truss and not some other manufacture?

Amiers · May 11, 2022

The truss is 2 5 5 10 10 with 2 corner blocks. So technically 34’ span if you want to include the corner blocks.

The wall looks roughly 18’ x 10’ so depending on the size and brand of each panel it could be between 54 and 60 panels.

I would venture to say your diagonal pipe was helping push the legs out that we not weighted properly and the weight of the wall assisted in that compounded with that wall according to you being the weight it is.

1 : Yes and no
2 : according to you based on the facts yes.

This is one of those posts with not enough information to give a definitive answer though.

But fun to speculate

Edit:
I would of built it 10 5 2 5 10 as the loads for the smaller truss are much greater according to your chart in the cliff notes

MNicolai · May 11, 2022

Just to comment on the make/model of the truss -- whether it's overloaded or not is definitely subject to whether that's actually the truss you think it is and if the panels weigh what you think they weigh. Tomcat's Light Duty 12x12 plated truss, for example, has roughly 175% the capacity of what Christie is publishing, at the 30-40ft spans. Not all 12x12 trusses are created equal.

egilson1 · May 12, 2022

Amiers said:
The truss is 2 5 5 10 10 with 2 corner blocks. So technically 34’ span if you want to include the corner blocks.

The wall looks roughly 18’ x 10’ so depending on the size and brand of each panel it could be between 54 and 60 panels.

I would venture to say your diagonal pipe was helping push the legs out that we not weighted properly and the weight of the wall assisted in that compounded with that wall according to you being the weight it is.

1 : Yes and no
2 : according to you based on the facts yes.

This is one of those posts with not enough information to give a definitive answer though.

But fun to speculate

Edit:
I would of built it 10 5 2 5 10 as the loads for the smaller truss are much greater according to your chart in the cliff notes

Based on the diagonals those are 8’ sections. 3 of them. And a 2’. So 26’
Also the bumper eyes are on half meter spacing, so that wall is just over 16’ wide.

Amiers · May 12, 2022

egilson1 said:
Based on the diagonals those are 8’ sections. 3 of them. And a 2’. So 26’
Also the bumper eyes are on half meter spacing, so that wall is just over 16’ wide.

Second glance I could agree with that. 2 4 4 8 8. I would still have done 8 4 2 4 8. With 3 of those sticks according to the chart rated the same as 8’ sticks this does change what the truss can handle.
Regardless I stand by my statement that the legs were not weighted properly or possibly built properly which we can’t see soooooo who knows.

Dagger · Jun 19, 2022

I found the following confirmed infos:
- truss chart applies to the truss being used.
-the build is
Cornerblock , 2', 8 ' , 8' , 8' and corner block = 26'
- the wall is 10x6 = 60 panels
weight of 1 panel = 18.4lbs = 1104 lbs

Based on the truss chart Uniform load at 24' is 1128"lbs

The legs were built in an "upside down T shape" 16 feet high plus the legs truss going downstage 8ft +4ft and going upstage 8 ft +4ft . ⊥ ( upstage legs were sandbagged. ( roughly 375lbs of bags)

So everything was within allowable load limit. I guess I was just wrong about seeing the truss deflecting.

there are 4 10' pipes attached on truss as braces.

can someone explain the reason behind needing those braces?

RonHebbard · Jun 19, 2022

Dagger said:
I found the following confirmed infos:
- truss chart applies to the truss being used.
-the build is
Cornerblock , 2', 8 ' , 8' , 8' and corner block = 26'
- the wall is 10x6 = 60 panels
weight of 1 panel = 18.4lbs = 1104 lbs

Based on the truss chart Uniform load at 24' is 1128"lbs

The legs were built in an "upside down T shape" 16 feet high plus the legs truss going downstage 8ft +4ft and going upstage 8 ft +4ft . ⊥ ( upstage legs were sandbagged. ( roughly 375lbs of bags)

So everything was within allowable load limit. I guess I was just wrong about seeing the truss deflecting.

there are 4 10' pipes attached on truss as braces.

can someone explain the reason behind needing those braces?

@Dagger Were your 4 x10' braces at an angle to minimize lateral movement or vertical to minimize sag?
Toodleoo!
Ron Hebbard

cbrandt · Jun 20, 2022

Dagger said:
I found the following confirmed infos:
- truss chart applies to the truss being used.
-the build is
Cornerblock , 2', 8 ' , 8' , 8' and corner block = 26'
- the wall is 10x6 = 60 panels
weight of 1 panel = 18.4lbs = 1104 lbs

Based on the truss chart Uniform load at 24' is 1128"lbs

The legs were built in an "upside down T shape" 16 feet high plus the legs truss going downstage 8ft +4ft and going upstage 8 ft +4ft . ⊥ ( upstage legs were sandbagged. ( roughly 375lbs of bags)

So everything was within allowable load limit. I guess I was just wrong about seeing the truss deflecting.

there are 4 10' pipes attached on truss as braces.

can someone explain the reason behind needing those braces?

26' is more than 24', so the load rating would be less. You've got the weight of the panels, but do you have the weight for any of the rigging or cabling included? That is also the load rating for brand new, not abused truss.

truss deflecting over time?

Dagger

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