Extending a floor joist/beam to act as a rim board under braced wall line 1

[met33]

I have a braced wall line in a single family home that spans from interior to exterior. I'm using a 3.5" x 14" LSL beam under the interior portion of the braced wall (spanning points 2-3-4 in the diagram below). This beam runs parallel to the floor joists. I'm considering extending this beam continuously to serve as the rim board under the exterior portion of the braced wall line (points 1-2 in the diagram).

The benefit would be that the beam can serve as a collector to deliver loads to the concrete foundation wall between points 1-2, although this isn't strictly necessary for the overall design to work.

The drawback is that tying the floor system to the rim board could result in undesirable interactions between the two. For example, under patterned loading, there will be a significant uplift force in the rim between points 1 and 2. On the other hand, there is a roof truss girder above this wall that lands 7" to the left of point 2. Therefore, the roof dead load will counteract some of this uplift, but will not entirely negate it, and wind loading could shift the balance in the wrong direction.

I think the answer is to split the beam at point 2, so that section 1-2 is a "standard" rim board and section 2-3-4 is a "standard" continuous interior beam. But I wanted to see if others have encountered this situation and how you handled it.

 

[phamENG]

at that length, breaking it into 2 or even 3 spans would be good for consructability. But do you need a collector to run through the entire diaphragm at that point? The answer should be yes if you have engineered shear walls. In that case, continuity is required. But it can be accomplished with straps.

 

[XR250]

Might want to sharpen you pencil on the patterned loading and consider what is realistic. Likely not an issue in reality. I have never considered wind load in a situation like this.

 

[met33]

Good point about constructability. A 40-ft 3.5" x 14" LSL weighs about 600 lbs. A crane will be on-site.

Straps are an option. After working on it some more, I'm leaning toward leaving it as a single piece.

As mentioned, the uplift force might not be a practical issue. Either way, it's small enough to handle with anchorage to the foundation if necessary.

 

[driftLimiter]

A splice at point 2 and a strap back to blocking or a continuous rim seems like a good option. I try not to have a continuous beam go over a wall like that for the uplift concern as well.