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 SECTION 5.
OTHER STRUCTURAL MATERIALS
1.
MASONRY.
a. Application. Masonry units are used primarily for wall
construction. These units may be used for both exterior walls subjected to
blast overpressures and interior walls subjected to inertial effects due to
building motions. Basic variations in wall configurations may be related to
the type of masonry unit such as brick, clay tile or solid and hollow
concrete masonry units (CMU), and the manner in which these units are laid
(running bond, stack bond, etc.), the number of wythes of units (single or
double), and the basic lateral load-carrying mechanism (reinforced or
non-reinforced, one or two-way elements).
(1) In addition to their inherent advantages with respect to fire
protection, acoustical and thermal insulation, structural mass and
resistance to flying debris, masonry walls when properly designed and
detailed can provide economical resistance to relatively low blast
pressures. However, the limitation on their application includes a limited
capability for large deformations, reduced capacity in rebound due to
tensile cracking in the primary phase of the response as well as the
limitations on the amount and type of reinforcement which can be provided.
Because of these limitations, masonry construction in this Manual is limited
to concrete masonry unit (CMU) walls placed in a running bond and with
single or multiple wythes. However, because of the difficulty in achieving
the required interaction between the individual wythes, the use of multiple
wythes should be avoided.
(2) Except for small structures (such as tool sheds, garages, etc.,)
where the floor area of the building is relatively small and interconnecting
block walls can function as shear walls, masonry walls will usually require
supplementary framing to transmit the lateral forces produced by the blast
forces to the building foundation. Supplementary framing is generally
classified into two categories (depending on the type of construction used);
namely flexible type supports such as structural steel framing and rigid
supports including.reinforced concrete frames or shear wall slab
construction. The use of masonry walls in combination with structural steel
frames is usually limited to incident overpressures of 2 psi or less while
masonry walls when supported by rigid supports may be designed to resist
incident pressures as high as 10 psi. Figures 51 and 52 illustrate these
masonry support systems.
(3) Depending on the type of construction used, masonry walls may be
classified into three categories: a) cavity walls, b) solid walls, and c) a
combination of cavity and solid walls. The cavity walls utilize hollow
load-bearing concrete masonry units conforming to ASTM C90. Solid walls
use solid load-bearing concrete masonry units conforming to ASTM C145 or
hollow units whose cells and voids are filled with grout. The combined
cavity and solid walls utilize the combination of hollow and solid units.
Masonry walls may be subdivided further depending on the type load-carrying
mechanism desired: a) joint reinforced masonry construction, b) combined
joint and cell reinforced masonry construction, and c) non-reinforced
masonry construction.
2.08-197
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