CMU "Arch" Action 1

[BSVBD]

For a running bond CMU wall, i understand the "arch" action above a CMU Lintel.

But, when that lintel occurs at the end of a CMU wall, i consider that the 8"x8" shoulder column is not sufficient enough to consider the arch action above the lintel. However, i can't explain it.

I realize the arch action occurs ABOVE the lintel, but, i feel as though, whenever my bearing is limited to an 8"x8" shoulder column, with no more CMU wall to laterally support it, i feel that that "haunch", or intersection of the lintel bearing on the column, should have the greater integrity of a CMU lintel supporting EVERYTHING above the apex of the triangle.

Any thoughts?

Thank you!

 

[JAE]

Explain - arches need horizontal thrust to "keep the arch up". With 8" of slim CMU you have nothing to provide the necessary horizontal thrust.

Some might argue that instead of an arched load application (ever increasing load from the ends culminating in a maximum load at midspan) you instead might have a triangular shaped load application (zero load at the interior jamb increasing to maximum at the 8x8 column).

Alternatively, you could also assume that the section of masonry above the door is actually cantilevering over the door off the main portion of wall. With that you'd have to ensure that you have adequate reinforcing at the top of the wall and adequate shear capacity for the upper cantilevered portion....i.e. essentially ignoring the 8x8.



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