Grade beam reinforcement requirements 1

[AaronMcD]

I've searched the web and the ACI and can't seem to find any direction for stirrup/closed tie requirements for grade beams bearing on soil. This is a high seismic area, usually SDC D. Since there does not seem to be any code direction, I tend to ask for closed ties at d/2, with longitudinal bars restrained per the requirements similar to columns or special moment frame beams - in other words restrain all longitudinal bars with cross ties or stirrups unless they are closer than 14" apart, in which case every other bar is restrained.

I have a project where the contractors miserably failed to get the reinforcement placed per drawings, and do not want to install the additional several hundred crossties. I said I'd dig into the code and see what I could find, but I can't seem to find anything. What do you all do, and is it based on a source or based on typical practice? My beam is primarily bending, transferring load from concrete shear walls and moment frames into the soil.

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[AaronMcD]

Looking into it closer, the foundation seismic section of ACI indicates foundation should remain essentially elastic. Also I design these things as transfer beams with overstrength. However, There is a section 18.13.3.3 that refers to special moment frame detailing if columns impart moments into the grade beam. One could argue that the end of a concrete wall imparts a moment similar to the way a column does and it should be detailed similarly at wall ends.

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[r13]

Grade beam is a beam happens to getting in touch of soil. However, the soil has never been allowed/trusted to provide support. So reinforce it as a beam.

 

[AaronMcD]

Then what would you call a foundation which bears on soil but acts as a beam to transfer seismic loads?

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[r13]

Grade beams are supported on piles, pile caps, or spread footing pedestals. Are you talking about the turn down in the mat foundation?

 

[slickdeals]

Look at ACI 318-11, 21.12.3.2