Scoreboard Mounting to Ceiling 1

[CBSE]

As part of a new build/TI for a school I need to figure out how to mount a new center hung scoreboard to the ceiling of the existing gymnasium. It's a wood structure with arched glulams and 4x12 purlins. I have checked the capacities and both are sufficient for the added load. The weight of the scoreboard is 1,020 lbs...so not really that heavy.

My question is...how does a person mount this to the ceiling? I was originally contemplating an eye bolt attached to a plate screwed into the bottom of the purlins, but that doesn't seem like a good idea due to the possibility of the bolts getting wiggly over time from crushing the wood (maybe?).

My other idea was to do a u-shape bracket around the purlins, (2) total as that is how many cables come off the scoreboard, and then weld an i-bolt to the bottom of the bracket. Thoughts?

 

[Ron]

Your scoreboard would kill anyone under it if it fell. Take than into account. Further, I would provide redundancy in such an application with cable suspension as a secondary "catch".

 

[KootK]

I'm fine with either connection so long as:

1) The connection/lag screw extends far enough into the member that a tension perpendicular to grain failure is precluded.
2) The load does not have a significant component that would induce cross grain bending in the purlin.

#2 worries me frankly. Any chance you could run a pair of HSS between the glulam arches and suspend your thingy from that?

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.

 

[jayrod12]

I would be saddling it and bolting through. This isn't something you lag screw in a permanent state of tension if you ask me.

 

[Ron]

jayrod12...exactly. In addition, I would provide a cabling redundancy for safety. Overhead is nothing to play with and lag screws/bolts are not always made of better steel.

 

[BUGGAR]

Quote from drawing: "The optional floor is not to be stepped on".

 

[CBSE]

Thanks everyone. Here is the detail I have come up with so far. I'm adding a new 5-1/8" x 12" glulam (a bit overkill), with a 1/4" bent saddle, with additional saddle welded to it and i-bolt.

What are your thoughts about the welding of an additional saddle to the system as shown? I was trying to figure out something better than welding the i-bolt. I suppose I could probably just show the bent plate dropped below the beam and have no welding at all.

Jayrod, I do like the idea of through bolting, and will probably move that route, I'm still contemplating the Simp. SDS screw idea.

 

[KootK]

I'm adding a new 5-1/8" x 12" glulam (a bit overkill), with a 1/4" bent saddle

Does this mean that the loads will be applied in the plane of the glulams? Or will there still be a component of the load transverse to the member?

What are your thoughts about the welding of an additional saddle to the system as shown

It seems fine but perhaps unnecessary when you could just have the eye bolt cleanly shop welded to your hardware. There's stuff like this too: Link

Graphically, your screws look to be rather low on the section for my liking. It's much better to grab the section above the centroid to keep from tearing the lower half of the beam away from the rest via tension perpendicular to grain. This is one of the reasons why I'm fine with the underside lag bolt connection. From the perspective of the wood, it's the same tension problem whether you use the lag bolt or the saddle (un-flanged). And really, a deep lag is likely to grab more of the section than the bolts through the side anyhow.

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.

 

[jayrod12]

From the perspective of the wood, it's the same tension problem whether you use the lag bolt or the saddle (un-flanged). And really, a deep lag is likely to grab more of the section than the bolts through the side anyhow.

Except, you have to worry about pull-out capacity and proper pre-drilling etc.

I was thinking you extend the saddle to near the top of the purlins and bolt through up there. I would probably be ok with a series of SDS screws as well as opposed to a bolt, but they would be significantly closer to the top than CBSE's detail shows.

 

[KootK]

Except, you have to worry about pull-out capacity and proper pre-drilling etc.

Worrying about the pullout capacity seems to be just a choice that we make for some reason. Wood design is very much a statistical thing and lag bolt withdrawal values get tested and established using the same reliability principles as everything else. The Germans, and gradually we Canadians, are migrating towards all manner of nifty wood screw applications that put lags in permanent tension and they seem to test and perform just fine.

As for the quality of the install, I'd get around that by utilizing some the cool self tapping varieties that are available: Link

I actually prefer the underside lag in this situation because:

1) As I mentioned above, the cross grain tension issue is the same for both connections.
2) A long ASSY lag would engage the entire section and draw it together snugly.
3) In the presence of the a transverse load component, the screw would actually act as reinforcement to help with cross grain bending.

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.

 

[azcats]

Regarding the eye bolt - if you're going to have some fabrication performed anyway, why not just weld a padeye to the bottom of the bent U and use a bolt type shackle? The lock washers and tack welds on your detail give me pause.

 

[MotorCity]

Assuming the numbers workout, I am sure your concept would work. That said, I would be inclined to simplify it because it looks like a overly complicated load path (many parts and places where something could go wrong).

My first preference would be to locate the saddle on top of the glulam. This would mean that the ceiling or roofing might have to be lifted a little to squeeze a plate in there but it could be done. Probably not an option, but just a thought.

Next I would look at using a bottom saddle as you have shown, but using through bolts instead of screws or lag bolts. Just my own preference, makes the connection look a little more robust.

What about replacing the eyebolt with a vertical plate with a hole in it for attaching the rigging?

 

[CBSE]

I hadn't thought about a Padeye with a shackle. What makes me nervous about welding an eye-bolt to the plate is the horizontal stress on the weld. It just doesn't "feel" right to me. And maybe it just doesn't feel right because I haven't used that type of scenario before. I am looking at removing the additional "U-shape" at the bottom and having the contractor auger out a small area in the wood so that I can connect directly to the bottom of the u-shaped bent plate.

 

[CBSE]

Here is my final detail. It's a bit over designed, but I feel very comfortable with it.