Glulam beams at posts

[dabiz97]

I've never done a commercial space before and I'm doing a pretty standard rectangular CMU building with glu lam beam and purlin roof system in Los Angeles. Most places I have seen have the glu lam travelling past the post bucket with a hinge connector picking up the next beam. Is this solely to avoid bolt holes at the end bearing? I've read the AITC guidelines for drilled holes, but for fasteners do I need to worry as long as I have enough shear capacity without the hole area?

Or is it not advisable to butt glu lam beams together on the same post bucket and use holdowns or purlin cross-ties to drag them together?

 

[woodman88]

You can use smaller sizes for your GLB by cantilevering some over a bearing and supporting another beam at the end of the cantilever, if done correctly. If you (or your client) can afford to use larger GLB's then designing them as simple spans is permited.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[dabiz97]

Thanks for the fast reply, Garth!

 

[hokie66]

Be careful to respect the bolt end distances.

 

[msquared48]

What you are describing is called a "link-span system" and is uesd a lot in commmercial/retail construction.

I suggest that you look into it as it does have it's own design nuances to wtch out for.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[efsinc]

This cantilevered glulam girder systems is commonly utilized to reduce the cost of the overall girder system.

In a typical multi-bay girder line with multiple girders over multiple columns, every other bay will have "double cantilevered" girders, ie, each of the two ends of the girder will cantilever over its supporting column. The other girders will "drop-in" between the cantilieverd girder ends. These "drop in" girders have a significantly reduced simple span, and therefore a significantly reduced section.

The cantilever length is determined as essentially the maximum practical length without increasing the section size....often around 10% of the backspan.... But calc it, and watch for deflections. Since this cantilevered girder experienced tension on the top face of the beam, be sure it is specified properly. If you're not familiar with glulam beam fabrication, look up "balanced" vs "unbalanced" beams. In California, you'll probably be specifying 24F-V8.

The hinge connector is the connection used to support the drop in girder from the end of the cantilever girder. It's a tricky little connector and needs to be well understood to specify properly. If you utilize a pre manufactured connector, which are readily available, they can be specified with "tension bolting" to transfer some lateral loads.