In December 2009 we discussed deletion of the minimum 280 pound per linear foot (plf) requirement for wall anchorage in 2009 International Building Code (IBC) Section 1604.8.2. This article will address the wall anchorage requirements for structural walls as it relates to seismic design.
Section 1613.1, in both the 2006 and 2009 IBC, references ASCE 7-05 for seismic design requirements. ASCE 7-05 Section 12.11, Structural Walls and Their Anchorage, sets forth seismic design requirements for anchorage of structural walls. This section is intended to mitigate the significant hazards posed by walls separating from floor or roof diaphragms, which provide lateral support, during an earthquake. The provisions have evolved over the years, notably changing after each major earthquake. Structural walls and related terms are defined in ASCE 7-05 Section 11.2, under the heading WALL, as follows:
Structural Wall: Walls that meet the definition for bearing walls or shear walls.
Bearing Wall: Any wall meeting either of the following classifications:
1)Any metal or wood stud wall that supports more than 100 plf of vertical load in addition to its own weight.
2)Any concrete or masonry wall that supports more than 200 plf of vertical load in addition to its own weight.
Shear Wall: A wall, bearing or nonbearing, designed to resist lateral forces acting in the plane of the wall.
In order to better understand the application and scope of ASCE 7-05 Section 12.11, Table 1 summarizes the requirements of this section.
S.K. Ghosh Associates Inc., is a structural seismic, and code consulting firm located in Palatine, Ill., and Aliso Viejo, Calif. President S.K. Ghosh, Ph.D., and Susan Dowty, S.E., are active in the development and interpretation of national structural code provisions. They can be contacted at firstname.lastname@example.org and email@example.com, respectively, or at www.skghoshassociates.com