masonry basement walls 2

[jdbpe]

The BOCA Code calls for an engineered design (needs rebar) for a 8" basement cmu wall that supports more that 4 feet of fill. If the wall supports less than four feet of wall than reinforcement is not required (empirical design). I have a residential project where the existing 8 inch wall with no reinforcement supports 5'-4" of fill. The owners want to put a 2nd floor on and the building dept is requesting an analysis of the wall. Without reinforcement the wall is overstressed when supporting 5'-4" of fill.How do you reinforce the wall so that it can support the fill and meet code?

 

[JAE]

You can specify the following:

From the inside of the basement, you can cut away the face shell of a single, vertical line of masonry to expose an open cell shaft. Insert a vertical rebar in the cell at an appropriate location and fill the cell with grout or small aggregate concrete. The grout would extend out to the face of the wall to replace the missing face shell as well. Do this at whatever the required bar spacing is for the wall.

Alternatively, you could install small vertical beams to the wall, bolting to the wall along the beam length to add flexural strength.

Either case should be properly engineered to account for the existing axial loads, new axial loads and lateral earth loads. You may want to consider removing the earth from the wall temporarily as the initial stresses on the block may be too large to begin with.

 

[wiktor]

You can also analyse the wall. Adding another floor will increase axial load, while your bending moment remain the same, so your tensile stresses be lowered.
As for existing overstress check the wall with the all loads applied, i.e. earth pressure, self weight and weight of supported floor.
Assuming that the wall is supporting the building, the floor will also act as a strut, providing horizontal support at the floor level.

 

[jheidt2543]

My existing single story home is 30+ years old and has an unreinforced 8" block basement foundation wall that is 7'-0" high. Exterior backfill is 6'-6" high against the wall on three sides of the house with the fourth side exposed to the backyard. There are no cracks in the wall. The Masonry code is very conservative when you use the emperical method (as it should be).

My point is the same as wiktor's, analyize the wall with all design loads to see if it really needs reinforcing. JAE's method of reinforcing the wall will certainly work but, it is very messy and very expensive. There might be other viable solutions.

 

[haynewp]

I would double check with the building department. They may end up wanting you to bring the wall up to code, regardless of whether the unreinforced wall with the additional vertical load will work. IBC requires bringing up to current code under certain situations. CHeck with your code.

Check if BOCA requires at least #4 vertical bars at 48" o.c.