Uplift on brick wall: connector choices
Last Post 26 Jul 2014 12:52 PM by Keith Winston. 0 Replies.
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Keith Winston
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26 Jul 2014 12:52 PM
    I have to look over engineering analyses of uplift of beams attached to the top of a brick wall. The wall is 12" wide multiwythe unreinforced solid brick, the uplift force is typically between about 300 and 1000#. I'm not an engineer but my physics background helps me follow the reasoning and calculations involved.

    I have looked at many dozens of these, stamped by many different PE's. Far and away the most common method of attachment is a bolt or threaded rod embedded in the top of the wall 6-10" with Hilti HY70 ro equivalent epoxy. In looking into this further, I've realized that the HY70 ratings are for mounting into the side of the wall, not the top, and require a 16" distance from edges, obviously not possible in the top of a 12" wall. Some other approaches include essentially the same but with anchoring cement in the hole, or threaded or mechanical expansion devices (typically with fairly shallow embedment, 2-4").

    I've talked with engineers at Hilti, and they basically said they have no tests or reliable way of determining the best way to do this. I've done a fair bit of web research. I've talked with several experienced structural engineers. I have found no solid information, nor really anything that could justifiably be called "best practices".

    The reason this came to a head was that one PE, undertaking an analysis of his own, concluded that the embedment of the 3/8" threaded rod required for the uplift had to be embedded 50". If you understand how these are installed, you'll know that's impossible, or at least practically so. And yet, he's actually the only engineer that didn't improperly apply the load tables.

    Now there are real problems with the issue to begin with: unreinforced brick walls are inherently suboptimal for uplift. And yet, the problem needs to be solved. So I'm looking for something that I can have some faith in, research towards that end, or any help towards a "best practices" solution. Thanks for any help.