Top mount hanger vs face mount hanger

[jimtheengineer10]

I need to use a double 1-3/4" x 16" microllam lvl beam to support a floor. The floor joists will be 2x8's. The owner would like to use hangers to support the joists instead of resting the joists on top of the lvl's. Am I correct in thinking that I need to use a top mount hanger instead of a face mount hanger? My thinking is that a face mount hanger will only bear on one of the lvl's.

If I am correct that a top mount hanger is required I just need to make sure the top flange of the hanger is 3.5" wide so it can be attached to the top of each lvl and that the hanger can support the lead of the 2x8.

Thanks in advance.

 

[msquared48]

I would just nail or bolt the LVL's together. I don't think that a standard joist hanger has a top flange large emnough to distribute the load to both joists by itself.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[frv]

You should give the Simpson people a call. They've always been really helpful when I have questions like this. I honestly think it wouldn't matter either way, but give them a call and they can help walk you through it.

 

[woodman88]

Whether top mount or face hanger the load from the hanger will be transferred to just one of the plies.

You will need to connect the plies together to transfer the load equally to each. Some engineers would design the connection for half the load. Others say to design the connection to transfer 2/3 the load. This is to account for critical slip of the connection between the plies. I am between the half and 2/3 the load. But it really depends on the situation.

If you are using a face mount hanger, the nails in the hanger do not count as part of this transfer connection, per most hanger manufacturers. Also you need to note that the connection is to be placed half to each side of the hanger. Also see the attached pdf (a free download from

http://www.strongtie.com/literature/tech-bulletins.html?source=topnav).

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.

 

[dhengr]

Jim:
There are a number of things wrong with your thinking.
1.) The top mounted hanger transfers some (maybe almost all) of its load through the top leg in bearing to the top of the carrying member, true. But, you can’t make the top leg strong (thick) enough to cantilever (2 x 1.75") to really transfer load to the far side LVL. Thus, the LVL’s must be fixed together, to act in unison as one member, to deflect and carry the load together. The top mounted hanger does allow you to use few nails, in shear, into the side of the carrying member, because much of the load is carried in bearing by the top leg. The top mounted hanger works well when the loads are high and the carried members are manufactured so their depth is well controlled.
2.) The 2x8 jsts., sawn lumber, vary enough in depth, that you want the adjustability that face mounted hangers offer, or you end up with a very irregular floor surface elev. With 2x8 jsts. the loads can’t be too high, so this shouldn’t be a problem, and the hangers nailed in double shear would help solve this reaction problem if it existed. Top mounted hangers do not offer this vertical adjustability. Actually, you want to set the tops of the 2x8's a bit higher than the tops of the LVL’s, because the 2x8's will shrink and the LVL’s will not. At least consider this potential shrinkage problem in your detailing.

As I finished typing this and a couple phone calls later, I looked back at your OP and see that Garth covered connecting the LVL’s together very well. So, no need for that para. in my post.

 

[bookowski]

Take a look at the Weyerhaeuser guide for LVL's (

http://www.woodbywy.com/floors/),

they have a section for connections at multi-ply LVL's where they provide capacities for this situation and connection requirements (nailing, through bolts etc.). This table is obviously based on using their LVL's but it might give you a gut check about what's needed to compare to your hand calcs.