Hanging Glulam Beam

[eric294yz]

I have a situation in a building we are designing in which the architect would like to hang a glulam beam (used for the ceiling framing) from a W beam above used for the roof framing. Are there any code limitations to utilizing a bolted connection to hang the glulam from the W beam. It was proposed by someone to use an inverted U-bucket welded to an HSS to hand from the W beam, and then use thru bolts through the glulam. Are there any code restrictions that anyone is aware of that will not allow this type of configuration. It seems to me as though you would be placing the laminations below the bottom row of bolts in the glulam into tension which is not a good idea.

Your thoughts?

Thanks

 

[hokie66]

Through bolts to glulam beams is common practice, and your timber code should give you values to use.

 

[dhengr]

Eric:

You leave a lot to the imagination as you describe your problem, a few sketches, loads and dimensions would really help to get the picture across. Your concern is partly right, in that cross grain tension from bolt bearing can be a problem if not handled properly. Proper attention to details, bolt hole end distances, bolt hole edge distance where only a few plies have cross grain tension, and code allowable bolt loadings, etc. usually takes care of this as Hokie suggests. In your case you don’t want the bolt holes to close to the end of the glulam or to near the top few plies of the glulam, either will cause splitting when loaded. Why not put a ‘U’ shaped saddle under the glulam? Then your hanger system can be anything you want, welded or bolted to this saddle. Alternatively, two side plates on the glulam, bolted or shear plates if needed, or some such, in the bot. 2/3's of the glulam, then again, any hanging system.

 

[TXStructural]

Also, if the glulam is heavily loaded, I would consider a strap under the glulam connected to a tab or angle off the wide flange. This also allows flexibility as the glulam deflects. If the load is substantial, and you are connecting to the bottom flange, consider a partial-depth stiffener on the wide flange connecting the web to the bottom flange, rather than relying on bending across the bottom flange.

 

[eric294yz]

hokie66 thank you for your reply. I am aware of the values for bolted connection in the NDS however I am a bit concerned about the proposed connection configuration. Perhaps the attached sketch will help clarify the situation. I have two glulams spliced at the center of the connection shown. I am concerned about the 4 kip reaction force being perpendicular to the laminations in the glulam. Are there any code restrictions against such a configuration?

 

[JAE]

I don't see a problem with your sketch. It is simply bolt shear through the GLB - typical bolt double shear design.

I would second the concerns of dhengr above about proper bolt spacing, etc.

 

[ToadJones]

you could use the same saddle but bolt down through the top of it, then your bolts would be in tension and compress the plies of the glulam...countersink the bolt head or all-thread washer in the bottom of the glulam and plug it so it is hidden. The top of the fasten on top of the saddle will probably be invisible.
The Arch will love the connect since it wont show any fasteners!!!!

 

[hokie66]

Your connection type is fine with proper attention to bolt spacing, end distance, edge distance etc. as others have noted. I think your concern was that the glue would fail, but in glulam beams, the glue bond is typically stronger than the wood in the cross-grain direction.

 

[msquared48]

Your connection is OK, but I would go one step further.

I like glulam beams to bear on more than just bolts - just my gig - no code requirement here. I would install two vertical threaded rods from the plate above to another bearing plate below. The rods are at the center of the glulam, welded flush to the plate below, and tightened with bolts above the top plate.

Mike McCann
MMC Engineering

 

[wannabeSE]

The AITC has a publication on connections that may be helpful. While the publication does not have a detail for hanging beams, the concepts are the same.

http://www.aitc-glulam.org/shopcart/Pdf/aitc_104_2003.pdf