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  • 1.  Concrete T-Joints- Dowel Orientation

    Posted 05-09-2017 11:01 AM

    In the case of a concrete cantilever wall, I have seen details of the hooked bars from the vertical wall reinforcement turned inward and also outward (see attached images). Documents on CRSI's website claim that turning the hooked bars outward do not develop the total moment in the wall, but highway standards and even ACI details show the hooked bars turned outward.
    Could anyone offer their opinion or experience on which is the correct way to detail this connection?

    John Carlyle EIT, S.M.ASCE
    Structural Design Engineer
    Baltimore MD

  • 2.  RE: Concrete T-Joints- Dowel Orientation

    Posted 05-10-2017 09:56 AM

    In the example you show, the tension steel in the wall stem is on the left. By turning the hook outward-to the left-you would be putting the hook in a portion of the footing that is in compression.  This is preferable.  The wall reinforcing on the right side of the stem is for crack control and the orientation of the hooks really doesn't matter.

    Edwin Phillips P.E., M.ASCE
    Greeley & Hansen, LLC
    Richmond VA

  • 3.  RE: Concrete T-Joints- Dowel Orientation

    Posted 05-10-2017 09:57 AM

    I don't claim to be an expert in retaining wall or concrete design as I am only starting to learn both myself, but I can make a few observations and give my opinion.

    First off, the vertical rebar in the stem of the wall that is on the opposite face of the applied pressure appears to be necessary.  That face of the stem is going to be acting in compression.  Think about how and in what direction the stem is going to want to bend; the rear face is going to be stretched, while the front face is going to be compressed.  Concrete is good for compression.  Steel is added for tensile strength.  Because the front face is going to be acting in compression; the rebar on the front face appears to be unnecessary.

    For similar reasons, in my opinion, the vertical rebar on the "rear" face of the wall should be hooked "inwards" (i.e., towards the front of the wall), as shown in the "Hook Bars In" drawing that you provided (minus the other vertical bars, as I discussed above).  Again, think about how and in what direction the toe is going to want to bend.  It is going to want to bend "upward" so that the bottom face of the toe will be acting in tension and the top face in compression; therefore, the rebar is needed in the bottom.

    Here is an example of a detail that we use when designing retaining walls.  Note that we the top steel extends into the toe in the attached drawing only for holding the longitudinal steel, not for its strength.
    Sample detail of a cantilevered stem wall
    Therefore, to answer your question, I believe the hooked bar (singular) should be turned "inward."

    If I am wrong in any of my observations, someone please let me know for both mine and Johns benefit!

    Read Plott P.E., M.ASCE
    Civil Engineer
    Mocksville, NC