Floor Joists Supported on Two Adjacent 2"x4" Load Bearing Walls

[gmf]

I am working on a 24 year old three-storey multi-dwelling residential repair project where I have found wood rot in the exterior walls at the basement knee wall and ground floor. The second and third floor walls are in good condition. The building consists of three adjacent blocks separated by fire separations. The fire separation structure consists of two 2”x4” walls individually supporting the floors at interior wall locations. The three blocks are offset from each other by 4 feet.

The basement knee wall is a 2”x6” at 12” o/c stud wall. At the ground floor, the original construction consists of two 2”x4” @ 16” o/c stud walls with an approximate 1-1/2” air space between the walls (I confirmed the same construction at the second-floor exterior wall). Note, only the outer 2”x4” ground floor wall is deteriorated. In addition to exterior wall replacement design, I need to design a repair for the ends of the existing I-joists within the second-floor assembly and the existing 2”x10” @ 12” o/c joists within the first-floor assembly due to some noted wood rot.

As part of my work I started to check the 2”x10” joists for bearing on the two 2”x4” stud walls. When I analyze the continuous 2”x10” joist with two supports 5” o/c apart at one end and a single 2”x4” @16” o/c wall at the other end, I get a shear and bearing issue on the inner 2”x4” wall of the double wall. The joists span 16 feet. Am I analyzing this too literally? Has anyone encountered this situation? Would you assume that the inner 2”x4” wall simply takes all the load?

This situation occurs at the offset between building blocks. It appears rather than build a 2”x6” wall at the 4-foot offset, the original contactor extended the fire separation structure (two 2”x4” walls) out the distance of the offset. The existing joists appear to bear on both 2”x4” walls.

Any assistance/advice would be greatly appreciated.

 

[Stenbrook]

Having the two supports gives you essentially a moment connection, but since they are so close to each other your resulting "moment couple" force becomes quite large which then gives you some shear issues. If I were you, I would check to see if it works using only one support and if it does I would say it was good and move on. Chances are your joist isn't attached to the outermost wall enough to transfer all the uplift that I am sure it is seeing into the wall(let me know if that isn't true).