huangyhg

bearing on old brick
fellers,
i have a 110 year old brick exterior agriculture building being remodeled into commercial space. we are removing a few interior timber columns and spanning a w18x55 steel beam on the exterior brick wall consisting of 3 wythes of brick. the brick is in good shape and is supporting the timber framed second floor. the architect wants to support the end of the steel beam in the brick wall, the end reaction is about 10 kips. is this a good idea? i'm not sure what capacity i can figure for brick this old?
old brick is extremely variable in its properties. i've seen old brick vary from a few hundred psi in compression to several thousand psi. further, the interior of old brick is generally lower in strength than its exterior faces due to the manner in which brick was fired in those days. the makes the brick less capable of withstanding point loads.
i would be careful with supporting a steel beam with a 10 kip load on it. it would be much better to provide a concrete or steel column. you could remove the existing brick, fashion a column, then replace a veneer of the brick to maintain "the look".
i think, ron, you meant the term "interior" of the brick was the interior (middle) wythe of the 3 wythe wall, not the brick on the interior of the building...correct?

if the foundation is a strip footing, using a new column may require a pad footing placed under the strip footing.
if you assume a bearing pressure of 100 psi, you could use a 10 x 10 or 8 x 14 baseplate on top of the wall. to ensure the beam reaction gets into the center of the wall, you could use a square bar centered on the baseplate and on the wall. both bar and plate should be sized on the assumption of uniform bearing pressure. if the old brick appears to be in good shape, that does not seem like a bad idea.

ba
jae...i meant the physical interior of a brick unit. i just recently cross-sectioned several bricks of this age and found the exterior 1/2 inch or so was much stronger than the interior of the brick. i have seen this before as well old brick.
fairly often, due to water intrusion and wetting/drying, the interior wythe of a three-wythe coursing will actually be a bit stronger than the exterior wythe. the middle wythe can be like either, depending on the depth of water intrusion, the chemistry of the brick, and the workmanship.
also, most mortar from that timeframe is lime putty mortar, not portland cement. it is greatly more friable and generally has lower strength.
i agree with ba. i have seated plenty of beams on old brickwork using 125 psi bearing. ba's 100 psi sounds conservative enough to me. bearing is not the only issue, but i wouldn't worry about supporting 10 kips on a 3 wythe wall.

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