f'm for masonry wall at wide flange bearing point

[Forensic74]

I'm looking to verify the capacity of an existing bearing point where a wide flange is bearing on the edge of a CMU wall corner. Due to the way the wall is coursed and lack of bearing plate, there are several vertical head joints that I think would significantly reduce the capacity of the connection.....therefore I don't think I can blindly use a f'm of 2000 psi

I think the big question here is how to establish f'm for use in the TMS equations for bearing. If any of you have dealt with a situation like this, I welcome all thoughts. I'm almost thinking that a tested mockup is the only way to establish a reasonable f'm.

And no, there is no danger to life safety at this time.

 

[wannabeSE]

NCMA TEK 18-1C, Evaluating the Compressive Strength of Concrete Masonry, has information on taking prisms from existing buildings. I assume you are evaluating the axial capacity of a wall with a concentrated load rather than bearing strength at a connection.

 

[Forensic74]

I'm not so concerned with the bulk axial strength of the wall as I am with how the concentrated load from the beam ( over 30 kip ASD combo reaction) flows into the wall. I am most concerned of how the head joints immediately beneath the concentrated load will act as shear planes.

If the beam were in the central area and perpendicular to the wall, it would be less of a concern, but again, this is right on a corner. And I dont think i mentioned previously, but there is a control joint where the perpendicular wall abuts (other leg of the wall corner). So there really isn't any good load distribution outward from the bearing point.

I've seen that NCMA TEK, but the prisims it describes really dont seem to address localized conditions but rather bulk strength of the wall.

 

[JLNJ]

If the masonry is reasonably uniform you should be able to use the specified f'm.

It sounds like the question might be more about load distribution through the bearing area. If the beam lands right on a corner and doesn't properly extend onto the wall, then you might have some spiked bearing stresses. I've seen it where the masonry wants to crack at these points of high stress right at the edge of the clear opening.

In my mind, there is always a question as to how well the beam flange or bearing plate distributes (or spreads out) the bearing force onto a wall.

A sketch would help elicit better responses.

 

[Forensic74]

Yes! this is a question about load distribution through the bearing area. How do you define "reasonably uniform" and "proper extension of beam into the wall"?

The way the mortar joints lay out, I question what f'm value to utilize in the bearing equation.