Steel Bearing Plates For Lintels in CMU Walls

[Gopher13]

I have a question about bearing plates for steel lintels over openings is cmu walls. Should the bearing plate sit on the face shells or should it just sit on the grouted core? In my case, they will be cutting an opening is an existing cmu wall. I am requiring them to grout three cores below each bearing point. If the bearing plate is sized so that it only bears on the grout then I am relying on the bond between the grout and the mortar to hold up the lintel (this seems worrisome to me), however if I size the lintel to bear on the face shells there will not be a full bed of mortar.

All comment would be helpful. Thanks in advance!

 

[calvinandhobbes10]

This is a decent question about a standard detail.
Size your bearing plate an inch below nominal (7 inches for 8-in masonry) so it catches over half of the face shells. Also check that the load isn't too heavy.
If you're over 150 psi I'd say look closer at the load path.

 

[KootK]

I'd concentrate your efforts on getting a clean grout bed under the plate and not sweat whether or not you're catching the face shells. Consider:

1) You probably need to bear on the grouted core no matter what to achieve bearing so it's not as though you're eliminating the need for grout/block bond anyhow.

2) Face shells sometimes pop off as they aren't really all that secure in the first place. This is particularly the case when invasive work is being done near by. The last thing that I'd want is for most of the bearing to be inadvertently taking place on the face shell because the grout bed is shoddy.

I've always wondered about the grout/block shear transfer mechanism myself. And the bearing condition once you get to the bottom of that. I'm afraid that I don't have a definitive answer. Maybe just assume 0.25 MPa-ish bond?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.