Bearing on stone wall

[LUGuy]

I am reviewing the addition of a steel column to the top of an existing unreinforced stone foundation. The wall is set with stones that are relatively flat and maybe 2"-3" tall, several inches on the flat. I am approximating that the proportion of stone to mortar/cement is about 2 or 3 to 1. The wall is about 12" thick and 7' tall (exposed height.) The wall is maybe 100 years old.

The wall currently has two similar columns bearing directly on top without problem. The building owner wants to add another column at a different location with 50% greater loadings. Is there any reasonable way to determine the capacity of such a wall for vertical load? The loading is somewhere in the neighborhood of 50 kips.

I have been considering knocking out a 12" deep section 4'-6' long at the top to create a reinforced concrete "beam" to help distribute the forces and provide for installation of anchor bolts. But I haven't assured myself what load should be allowed on a stone wall. This scheme would have forces of about 10,000 lbs / sf at the bottom of the new beam acting on the stone wall.

I am interested to see if others have run into a similar situation.

 

[CSEllc]

I have doine the same thing you are proposing (remove the stone and cast in a concrete transfer beam); however, my loads were not as large.

You might be able to do it.....it really is afunction of the condition of the wall in general and the stones and mortar in the proposed area.

Personally, I would try to avoid it if possible....to much potential risk.

You might want to add a column and transfer beam in the basement to accept the new column. Other options are remove the stone for the full height of the wall and cast in an intergral concrete pier with a new footing or casting two concrete columns (one either side of the wall) with a short concrete transfer beam (the length beam would be the width of the wall). This option woulkd probably require a significant amount of shear reinforcing in the beam.

Good luck with it....

 

[FFIELD]

I agree with CSELLC, 50 kips is a lot of load. Without knowing the condition of the stones and morter in the loaded section of the wall I would not put my License on the line to save a few bucks. New Conc. columns and foundation is the reasonable way to go.