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Author Topic: Mount 12" box truss to confer block wall  (Read 1737 times)

Rob Spence

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Re: Mount 12" box truss to confer block wall
« Reply #50 on: October 18, 2017, 02:57:28 pm »

One thing the OP needs to understand is that with the fastening means he has mentioned , he isnít including the ratings or expected loads.
I said the grout is the weak point in a block wall. I did not say you canít use it. I have no problem hanging pictures in my house from fasteners in the grout because, first, the load is light and well within the specs and load is mostly a vertical sheer load on the fastener. Not much tension on the grout.
All of your methods, Nathan, are common and usable IF USED WITHIN THEIR DESIGN SPEC.
One problem with grout lines in addition to what was mentioned above is that it was installed by an unknown (to an engineer) person while the block may well be made to a verified spec.



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David Allred

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Re: Mount 12" box truss to confer block wall
« Reply #51 on: October 18, 2017, 04:40:30 pm »

?..which says nothing about the orientation.  Butt to the wall?  Parallel to the wall?

But I guess that happens these days where appearance trumps substance...

Really?  One end mounted to the wall, and the other end floating  magically in the air?  If you thought that or didn't understand, you should have sought clarification. 

Nothing wrong with looks as an important factor in the decision.
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Nathan Riddle

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Re: Mount 12" box truss to confer block wall
« Reply #52 on: October 18, 2017, 10:31:59 pm »

One thing the OP needs to understand is that with the fastening means he has mentioned , he isnít including the ratings or expected loads.

I haven't? [and no i'm not trying to 'play dumb' or be sarcastic, I'm really questioning my experience here]

Ratings? Meaning of the hardware? Is the below quote of myself not sufficient? [seriously not trying to be an a$$ about this, i'm actually questioning the validity of my statements as 'proof' of the ratings/expected loads]
 
36lbs + 1x sharpy (35lbs) + cables <= 100lbs [limit]

When using a 3/8" anchor with 3" depth I have a tension force of 3229 lbs or with a 5:1 safety factor 645.8 lbs per wedge anchor.

That means a total force of 5166.4 lbs could be pulled out of the wall straight (sheer forces would be more, but the force will be a combination of the two [simple to calculate, no real need as the forces always be much less]. The truss max loading is: 5746.5 lbs. Thus both the truss and the wall would fail at the same time roughly with a safety factor of 5:1 for concrete anchors (unknown on trussing).

In the end, yes I over engineer because I know the end user will probably exceed any initial expectations as they are uneducated fools.

I never said I would only make the trussing safe to 100lbs I would make it safe to 5000lbs with a max load sticker of 100lbs (make it 300lbs so they can have more) if necessary.

That's enough to make it both safe for the '300lb kid who wants to do pull-ups' and any other idiotic things they wish to do.

At the end of the day I've accounted for ALL pieces of hardware in the install and made sure it was safe. Rather than running away because it is a liability for my company. (I would rather accept the minimal risk from my over engineering than them doing it wrong and hurting/killing someone).

https://www.confast.com/products/technical-info/thunderstud-anchor.aspx

Also, was the 100-300lbs not enough info? Should I be specifying torque?

Again, I am NOT trying to be sarcastic. I want to know so that if/when* I talk to an engineer about specifications for loading truss on a wall in the future (because it WILL happen again) I want to not sound like an idiot...

I said the grout is the weak point in a block wall. I did not say you canít use it. I have no problem hanging pictures in my house from fasteners in the grout because, first, the load is light and well within the specs and load is mostly a vertical sheer load on the fastener. Not much tension on the grout.

Agreed, tension isn't good. But I was willing to calculate the tension given the torque (moment) on the truss from a perpendicular loading at a distance away from the wall rising to sheer force down & compression on the bottom of the truss and tension along the top.

Giving rise to 6x clamps along the top (unistrut being found to be a better material in-between truss and wall for allowing expansion/compression) & 2 along teh bottom (because they will be under compression less is needed.

Also, thorough bolts were determined to be the best, inwhich case when mounting the unistrut would be much safer and could get away with only 2. But if using wedge lag bolts then 6 along the top would probably be better off. Albeit much harder to get straight and make the truss mount correctly.

All of your methods, Nathan, are common and usable IF USED WITHIN THEIR DESIGN SPEC.
One problem with grout lines in addition to what was mentioned above is that it was installed by an unknown (to an engineer) person while the block may well be made to a verified spec.

Agreed. I thought I was stating my case well and providing the design specs of the hardware in question. I now believe that assumption to be incorrect given Mr. Rees's questioning of the layout.

This flows into my next thought.

I have mishandled stating my case clearly. Sorry all.

Sometimes you have the design in your head and it's too simple to forget others don't. I try to think about that when posting on a forum, but I'm not perfect...

Hopefully the attachment work.
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Nathan Riddle

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Re: Mount 12" box truss to confer block wall
« Reply #53 on: October 18, 2017, 10:34:12 pm »

OK.  I assumed truss was being proposed to span the stage, not bolted flat to the wall and chosen because it "looks cool".
Aesthetic issues don't really rank as the decider for me, I guess.

Hopefully the above image helps to clear things up.

The horizontal truss is what they want to do in three places across the stage without the truss 'risers' so they 'look' like they float.

And aesthetics might not be a decider for you. But it is probably #2 right next to the BIG #1 (budget) for Churches.  ;)
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David Allred

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Re: Mount 12&quot; box truss to confer block wall
« Reply #54 on: October 19, 2017, 08:00:44 am »

I haven't? [and no i'm not trying to 'play dumb' or be sarcastic, I'm really questioning my experience here]

Ratings? Meaning of the hardware? Is the below quote of myself not sufficient? [seriously not trying to be an a$$ about this, i'm actually questioning the validity of my statements as 'proof' of the ratings/expected loads]
 
Also, was the 100-300lbs not enough info? Should I be specifying torque?

Again, I am NOT trying to be sarcastic. I want to know so that if/when* I talk to an engineer about specifications for loading truss on a wall in the future (because it WILL happen again) I want to not sound like an idiot...

Agreed, tension isn't good. But I was willing to calculate the tension given the torque (moment) on the truss from a perpendicular loading at a distance away from the wall rising to sheer force down & compression on the bottom of the truss and tension along the top.

Giving rise to 6x clamps along the top (unistrut being found to be a better material in-between truss and wall for allowing expansion/compression) & 2 along teh bottom (because they will be under compression less is needed.

Also, thorough bolts were determined to be the best, inwhich case when mounting the unistrut would be much safer and could get away with only 2. But if using wedge lag bolts then 6 along the top would probably be better off. Albeit much harder to get straight and make the truss mount correctly.

Agreed. I thought I was stating my case well and providing the design specs of the hardware in question. I now believe that assumption to be incorrect given Mr. Rees's questioning of the layout.

This flows into my next thought.

I have mishandled stating my case clearly. Sorry all.

Sometimes you have the design in your head and it's too simple to forget others don't. I try to think about that when posting on a forum, but I'm not perfect...

Hopefully the attachment work.

Does that drum shield have a ceiling? :o 
What about the drummer supporting the middle section like a Carmen Miranda hat.  Would definitely require a chin strap.  Talk about a mover. 8)
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Nathan Riddle

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Re: Mount 12&quot; box truss to confer block wall
« Reply #55 on: October 19, 2017, 11:44:06 am »

Does that drum shield have a ceiling? :o 
What about the drummer supporting the middle section like a Carmen Miranda hat.  Would definitely require a chin strap.  Talk about a mover. 8)

Haha, yes it does.

And if you look closely you'll see the hard edges, where I cut and pasted the left truss image to show a center one's placement.

Though the guy who supports the center truss is rather buff ;) He does a squat, gets it over his head and then holds it there for both services and practice. It's impressive!
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