Masonry Wall Anchorage
Masonry Wall Anchorage
(OP)
I'm anchoring a masonry wall to a flexible diaphragm. I've calculated the anchorage force per ASCE 7-10 Section 12.11.2.1 as 0.4SDSIekaWp = 5.4 kip. If these were concrete anchors, ACI would require either: (1) a ductile failure mechanism, or (2) design for the amplified seismic load (a.k.a. overstrength). The masonry code does not hold me to any such requirements with regard to anchor design. The IBC does not either. Should this connection be designed for overstrength?






RE: Masonry Wall Anchorage
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
www.americanconcrete.com
RE: Masonry Wall Anchorage
RE: Masonry Wall Anchorage
I'm looking at the 2015 IBC, and Section 1905.1.8 gives an exception for wall out-of-plane anchorage, but only for anchors loaded in tension. Anchors loaded in shear don't get the same exception. Did the 2012 IBC allow the exception for anchors loaded in shear? This seems like a possible oversight in the new code. My anchors are on top of the wall, loaded in shear.
RE: Masonry Wall Anchorage
From FEMA P-1026 Seismic Design of Rigid Wall-Flexible Diaphragm Buildings:
"In ASCE 7-10, Section 12.11-1 and 12.11-2, ka and Lf account for diaphragm flexibility. If a diaphragm is rigid, Lf equals 0 but if it is flexible, Lf equals the span length. For many buildings with rigid walls and flexible roof diaphragms, the diaphragm span between supporting walls or frames will be longer than 100 ft so ka will often be equal to 2.0. For diaphragms in which ka equals 2.0, the acceleration parameter used to compute the out-of-plane wall anchorage force is 0.8SDS, which is 80% of the maximum design spectral acceleration parameter. The intent is that the wall anchorage force is resisted elastically for a force level computed using the maximum design spectral acceleration. The 0.8 factor is included to recognize that some connection and member overstrength may be relied upon to resist the top of wall anchorage force [SEAOC Seismology Committee, 1999]."
RE: Masonry Wall Anchorage
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.
RE: Masonry Wall Anchorage