Out-of-plane anchorage for wood truss to CMU wall
Out-of-plane anchorage for wood truss to CMU wall
(OP)
I have a building with a wood roof bearing on a CMU wall. Conventional construction in the area connects a wood top plate to the top of the CMU wall with the pre-fabricated trusses bearing on the top plate.
ASCE 7 12.11.2 requires a "direct connection" capable of resisting an out-of-plane wall force for the connection of the truss to the wall.
Some engineers have suggested that the interpretation of "direct connection" would prohibit the use of a top plate, and that the pre-fabricated wood truss would need to connect directly to the CMU wall.
I'm just curious about what others are doing for this scenario.
ASCE 7 12.11.2 requires a "direct connection" capable of resisting an out-of-plane wall force for the connection of the truss to the wall.
Some engineers have suggested that the interpretation of "direct connection" would prohibit the use of a top plate, and that the pre-fabricated wood truss would need to connect directly to the CMU wall.
I'm just curious about what others are doing for this scenario.






RE: Out-of-plane anchorage for wood truss to CMU wall
BA
RE: Out-of-plane anchorage for wood truss to CMU wall
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.
RE: Out-of-plane anchorage for wood truss to CMU wall
RE: Out-of-plane anchorage for wood truss to CMU wall
I appreciate your response because I agree that the top plate should be considered a direct connection, and I see that others feel the same way.
RE: Out-of-plane anchorage for wood truss to CMU wall
RE: Out-of-plane anchorage for wood truss to CMU wall
I think you are dealing with someone who is reading the code too literally.
DaveAtkins
RE: Out-of-plane anchorage for wood truss to CMU wall
That's what Simpson embedded masonry anchors are for, with the trusses sitting on a wood or steel ledger and the anchor nailed to the truss and embedded into the CMU wall.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Out-of-plane anchorage for wood truss to CMU wall
RE: Out-of-plane anchorage for wood truss to CMU wall
RE: Out-of-plane anchorage for wood truss to CMU wall
I don't see the LTA2 clip being sufficient to satisfy the out-of plane anchorage requirement. I don't have a Simpson catalog with me right now but per IBC, isn't the connection subject to a 280plf minimum load? Depending on your truss spacing, I don't think you can get there with just the LTA2 clip. If I'm not mistaken, there are Simpson connectors available for top of wall condition.
Also, if you're relying on the top plate instead of direct connection to the CMU, the top plate needs to be checked just like a ledger including the bolt spacing.
How much do you need to design the connection for? The required anchorage force would really dictate how you're going to detail the connection as trusses bearing on top plate would have a lower capacity compared to putting a ledger to the side of the wall.
RE: Out-of-plane anchorage for wood truss to CMU wall