Historic Brick Proof Loads

[Simba13]

Afternoon all,

I am working on a renovation of an existing historic brick building. It's over 100 years old and I'm just not sure how to approach the brick condition/ verifying that the brick can handle the additional loads. The extent of the renovation as far is the brick is concerned are some embeds using the Hilti SC sleeves, these embeds support some floor framing that frames out a new elevator shaft opening. I'm doing the design of the embeds in HILTI and can get them to work but there are a ton of assumptions in the footnotes in the product catalog, one of them being that "minimum masonry strength of 3,000 psi", so my PM has asked that we provide proof loading values to cover ourselves and verify the brick capacity. I've looked through the IEBC appendix where it discusses this but I'm still a little fuzzy on the approach. I've never been involved or worked on proof testing before, how have you all approached this when it comes to older brick masonry?

I feel like I'm starting to go in circles a bit so any direction/help would be greatly appreciated. Thanks.

 

[ANE91]

There’s an ASCE standard with published lower-bound masonry strengths — 41? 34? Something like that. It’s a seismic document but the numbers are sound and potentially appropriate in non-seismic situations. Idk if 3ksi is doable this way.

You could also just physically test the clay masonry. Cut out a few bricks without damaging the mortar and run a prism test. Very few labs know how to do this properly or have the equipment, so call around before you start cutting.

Personally, I would not load a 100yr-old clay masonry wall without knowing its strength.

 

[masonrygeek]

There are a few ways to verify the strength of a brick wall (or do you mean brick unit since you mention 3000 psi?). As ANE91 pointed out you can cut prisms out of a wall. There are ASTM standards that discuss proper removal, but as ANE pointed out, the labs may not be familiar with that. You can also get other specialized equipment called a flat jack that inserts bladders into the bed joints and tests the masonry in situ (ASTM C1196 and C1197). Again, not many firms can do this, but it is a definitive way to determine strength. A good article on the subject is in Structure magazine: https://www.structuremag.org/articl...struction-nondestructive-and-in-situ-methods/.

 

[dik]

3ksi is a pretty large load... are you sure? A 12" brick wall (common old 3 wythe wall) would have a load of 400klf... with whatever safety/load factors are involved.

What you need to do is to remove a representative sample and load test it. This can then be used as a rough idea of what the strength of the assembly is. Any mortar repair should be done using a proper mortar for historic brickwork to avoid 'hard spots'. You want the mortar to fail and not the brick.

 

[XR250]

Can you add more anchors to justify a lower stress?