[simonrobb]

Unreinforced masonry is weak in tension because of the weak binding interface between the masonry unit and the mortar. The reason masonry is used in wall construction and not in, say, a suspended floor, is precisely because walls don't typically experience tensile forces. Any tensile force resulting from e.g.: wind loading on the entire structure is typically overcome by the self-weight of the masonry.

If there is a special case where tensile forces are expected, for example a retaining wall, or a mid-rise structure, or earthquake load, the engineer will specify the the masonry is reinforced with steel and then it can resist tension through the unit/mortar interface just fine.

It is a poor structural engineer who tells the architect masonry isn't an option because tension.

[abduhl]

The tension is resisted via the steel, not the CMU/mortar interface. Masonry behaves similar to concrete (that’s what the C in CMU stands for...) and suffers from the same issue as concrete re: lack of tensile strength. It is not the mortar interface which makes masonry a problem for tensile loading conditions but the structure of the masonry and mortar itself. They simply are not amenable to carrying tensile load at a microscopic level.

I don’t know what structural engineering you’ve done or what jurisdiction it’s in, but for practical purposes on the west coast in America, structural masonry isn’t an option beyond maybe 3 stories because of tension (due to seismic demand) and any structural engineer that says otherwise is looking to get sued for negligence.

Elsewhere in America this is less true but still most modern engineering doctrines would lead you quickly away from masonry for anything substantial, although cost and schedule is obviously a key factor in masonry’s favor.

Everything else about the use of masonry in walls I generally agree with, although the move away from allowable stress has impacted it as described above. Except maybe I would quibble about the use for retaining walls. CMU can be particularly cost effective for some geometries of retaining walls when used with steel.