Page 521 - Design of Reinforced Masonry Structures

SHEAR WALLS 7.83

10. Special reinforced masonry wall: A masonry shear wall designed to resist lateral
forces while considering stresses in reinforcement and satisfying special reinforce-
ment and connection requirements. Permitted in all seismic design category structures
(A through F).
11. Special reinforced prestressed masonry wall: A prestressed masonry shear wall
designed to resist lateral forces while considering stresses in reinforcement and sat-
isfying special reinforcement and connection requirements. Permitted in all seismic
design category structures (A through F).
12. Empirically designed shear wall: A masonry shear wall designed under Provisions of
Chap. 5 of MSJC-08 Code and assigned to Seismic Design Category A structures.
Of the above list of 12 types, only 6 (listed as No. 2, 3, 6, 9, 10, and 12) were covered
in MSJC-05 Code; all other types are new to the MSJC-08 Code, and are not referenced
in ASCE 7-05 for use as shear wall building systems. 2009 IBC (Section 2102) recognizes
eight of types of shear walls (listed as No. 2, 3, 4, 6, 7, 9, 10, and 11).
Discussion and design of prestressed masonry and AAC masonry walls are outside the
scope of this book. Pertinent design provisions for these types of walls can be found in
MSJC-08 Code Chap. 4 and App. A, respectively. A brief description, design methods,
and requirements of the above described shear walls types, and pertinent seismic design
categories can be found in the Commentary to the MSJC-08 Code (Table CC-1.17.3.2:
Requirements for Masonry Shear Walls Based on Shear Wall Designation).
In general, classification of shear walls is based on their ability to act as parts of SFRS
for buildings in seismic regions. Table 7.5 lists various building systems in which these
different types of shear walls are permitted or not permitted to act as lateral force–resisting
elements in buildings assigned to various seismic design categories (B through F, discussed
in the next section), pertinent height limits, response modification factors (R-factors), sys-
tem overstrength factors (D ), and deflection amplification factors (C ).
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The relevance of this classification lies in the fact that when used as parts of SFRS in build-
ings, they are subjected to certain restrictions and height limitations as listed in Table 7.5 as
well as certain mandatory detailing and reinforcement requirements for the purposes of seis-
mic design (MSJC-08 Section 1.17). The intent is for the shear walls to have adequate capac-
ity for inelastic response and energy dissipation during a seismic event. They are assigned
different values of seismic response modification factors, R, and overstrength factors, W . The
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ductility levels of various types of shear walls are indicated by values of their seismic response
medication factors, R (Table 7.5). The higher the value of R, the greater the ductility of shear
walls; consequently, the smaller the design seismic forces they are required to resist.
Regardless of the type of shear walls used as parts of SFRS in a building, a designer
must provide proper load path for transmission of seismic forces from diaphragms or other
parts of a building to shear walls. Load path connections and minimum anchorage forces
should comply with the legally adopted building code. When a legally adopted building

code (e.g., 2009 IBC) does not provide minimum load path connection requirements and
anchorage design forces, designers should use provisions of ASCE 7-05 Section 12.11.
Ordinary plain masonry walls are simply unreinforced masonry walls that are permitted to
be used as SFRS elements in SDC A or B structures. These walls are assigned an R value of 1½,
and are designed in accordance with the requirements specified in MSJC-08 Section 2.2 or 3.2,
for allowable stress design (ASD) and strength design (SD), respectively. The tensile strength
of masonry is taken into account and walls are so designed that tensile strength of masonry is
not exceeded, and thus preclude the possibility of cracking.
Detailed plain masonry shear walls are masonry walls designed to comply with the
requirements of MSJC-08 Secs. 2.2 or 3.2 for ASD and SD, respectively. These walls are
assigned an R value of 2 and an overstrength factor W = 2.5, and are permitted to be used
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