Have need for shelves to hang on tilt-up concrete (not block) wall. Must be
sturdy, but don't want supports at the corners. I'm thinking about some kind
of triangular bracket anchored either from above (which holds a plank inside
the bottom of the triangle) or from the back side (for which a plank would
sit on the top of the inverted triangle):

|\
| \
| \
| \
=======
-------
or
=======
-------
| /
| /
| /
|/

(key: = is the plank)

Haven't been able to locate such locally (want to do this over the weekend
upcoming).

Basically I want no forward supports, just wall attachments with some kind of
diagonals.

Other ideas?

Thanks,
--
John English