Residential Foundation--Bracing Sidewalls

[sjhgeotech]

A builder is concerned about the transfer of lateral pressures from then end-walls of a house foundation (9-foot pre-cast walls) to the floor system. The foundation walls that run perpendicular to the floor beams transfer load directly to these beams, so those walls aren't a concern. However, the end-walls that are parallel to the floor beams are the concern. Should bridging be tied perpendicular between each floor beam to transfer the load?

Thanks!

 

[PEinc]

It's possible (but not probable) that the end walls span horizontally between the front & back walls. Someone should ask the designer about the end walls and their ability to support the backfill.

 

[scottiesei]

Is there sheathing on the floor system and connection to a ledger board or other member at the parallel walls? Depending on the floor system,i.e: sawn lumber, trusses, etc. their are some requirements for blocking at the end of floor diaphragms. Also, do not forget the wind load from the wall above will also be acting at that location.

 

[sjhgeotech]

The floor system is comprised of I-joist with 3/4" plywood. The I=joist run parallel to the end walls. The bottom of the end wall is essentially simply supported by the 4" slab at the bottom, but the top is free with the first I-joist basically nailed to the top of the wall. I think that the Contractor is going to install blocking (2x6's) at the bottom flange of the I-joist. I am unsure of how far this blocking should continue out into the floor system.

Thanks.

 

[scottiesei]

Check to see what brand of I-joist was used. Different manufacturer's spec different requirements but for an example: BCI joists get blocking at 6'-0" for the first 3 bays. There are also connection requirements with strapping for the blocks. The critical connection is at the wall/joist. If there is a sill plate, you may be able to add some clips to help transfer the load.

 

[scottiesei]

Also, the blocking is usually small segments of I-joist, to make a "full depth" block, not just "rat runs".

 

[sjhgeotech]

So for a 60 foot long wall, you would install 16" (I-joists 16" on centers) of I-joist at 6-foot centers, for the first three bays? It seems like this would cause a torque in the I-joist unless they were continous through every bay? I will check with the manufacturer. Thanks.

 

[scottiesei]

I think the idea is by the third bay, the load has distributed itself into the diaphragm above sufficiently. They just don't want to rely on the first joist or two for load transfer from the wall to the diaphragm. But yes, please do check with the manufacturer and the EOR as well.

 

[DaveAtkins]

Blocking, as described above, will not cause torque in the floor joists, IF the floor sheathing is attached to the blocking, and IF there are joist hangers or some kind of nailing connecting the blocking to the floor joists (you can work out the statics).

DaveAtkins