Masonry Magazine April 2002 Page. 11
Strength design was added to the MSJC to improve the other masonry provisions for allowable stress design, veneer criteria, empirical design, prestressed design, and glass unit design. The rationale for including strength design was to provide for an improved model for inelastic system performance, especially for earthquake-induced loads. The rationale includes a better compatibility with the inelastic load criteria put forth by the ASCE 7-98 (Minimum Design Loads for Buildings and Other Structures) and the IBC documents.
In addition to the inelastic material and system criteria, the new masonry strength design chapter also includes strength provisions for flexure, shear, bond, anchorage, and other system components. Criteria are provided for cross section design properties, including maximum strains and other material provisions. Strength for maximum bending and the associated shear and bond criteria are included. These strength design criteria have been correlated to the latest version of the ASCE 7 load criteria.
Seismic Design Requirements
Prescriptive seismic design requirements in the MSJC have been substantially revised to be compatible with both the IBC and ASCE 7-98. Many of the changes to the seismic requirements were needed to update terminology. Previously seismic design requirements were applied to various seismic zones based on where a building was located. Later, seismic requirements were applied to buildings based on their assigned Seismic Performance Category (SPC) that was based on both the location of the building relative to areas of known seismic activity and on the importance of the building. Recently that term was abandoned by the seismic design community, and it has been replaced by a more accurate descriptor of Seismic Design Category (SDC), which is based on the location of the building, its importance, and the soil conditions supporting the structure. To recognize the change in terms, the MSJC requirements have been updated to now apply to the various Seismic Design Categories (SDC). SDC A, B, C, D, E, and F rather than the previously used Seismic Performance Categories (SPC A, B, C, D and E).
In addition, shear wall definitions consistent with the those in ASCE 7-98, Appendix A.9.11 and the IBC have been have been added into the Code. These limitations allow designers to coordinate the prescriptive detailing and design requirements of the MSJC with the Response Modification Factors (R Values) and other seismic coefficients from ASCE 7 or the IBC. Because of the higher risk associated with moderate to high SDCs, restrictions are placed on the use of some shear wall types in specific SDCs. In addition, minimum reinforcement requirements are established in areas of moderate to high seismic risk. Phillip Samblanet describes some of these shear wall types in TMS Responds Volume 1, No. 1 as related to the IBC. The following also briefly describes each shear wall type:
• Empirically Designed Shear Walls - As the name implies, empirically designed masonry shear wall