CMU Wall Design 2

[tft2001]

I am working on a project that has an interior CMU wall system that is supporting 12" deep steel joists spaced on 24" centers for a mezzanine floor. These walls intersect into other CMU walls that do not support joists. As suc, the elevations are established. The joists ends are to bear on embed steel plates. The question is whether the embed plates are to be flush with the CMU or raise the plates out of the CMU by say 1/4" to avoid any direct contact of the joist ends with masonry? Any thoughts or design guidance document recommendations would be appreciated.

 

[firai]

We usually detail the plates to be on top of the CMU. In other words, the bottom of the plate is flush with the top of grout/CMU, and the joist seat is raised above the masonry by the plate thickness. SJI has a requirement for the bearing to be equal or less than 1/2in. from the face of the wall, so the masonry has to be notched at every seat to meet that requirement if the top of the plate is flush with the top of CMU.

I hope that helps.

Structural Design Engineer
New York, NY

 

[a2mfk]

Agree with firai. Also a 1/4" gap would allow for slight joist rotation once it is loaded and deflects into the top of the CMU. With no gap the rotation would cause some edge loading in the CMU, probably the same reason for the minimum firai gave.