Out-of-Plan Seismic Loading on Masonry (CMU) Wall

[DJYork]

I have a load bearing masonry wall with a parapet. When determining the out-of-plane pressure on the wall I utilize ASCE 7-05, Section 12.11.1 (Structural Walls and Their Anchorage: Design for Out-of-Plane Forces). The argument arrived that the out-of-plane forces should be design per 13.3.1 (Seismic Demands on Nonstructural components: Seismic Design Forces). I disagree, because this is a load-bearing masonry structure. However, it did make me think about the parapet being loading. Technically, it does not provide any structural value, so should it be designed per 13.3.1, because the structural wall calculation does not give any increase for a parapet. What loading do you utilize for out-of-plane loading? I am designing the wall, and not the anchorage.

Thank you for any input.

 

[epitome1170]

Personally, I design the masonry walls as a continuous wall segment (similiar to metal studs, I do this since the wall is built as a continuous unit) in which the parapet and the wall is loaded with the 12.11.1 design load.

The only reason I would even think of using the 13.3.1 section on parapets would be if there was an actual "break" in the wall (i.e. to support a floor slab and then the masonry continues).

Hopefully that made some sense. If not, I would have to draw pictures.

 

[WillisV]

The portion of wall from base to roof should be designed for 12.11.1 and the parapet for 13.3.1 (so you have two different load magnitudes applied over the height of the wall).