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 where [alpha] is the angle between inclined stirrup and longitudinal axis of
the member.
Shear reinforcement in walls shall be spaced so that every 45 degree line
extending from mid-depth (db/2) of a wall to the tension bars, crosses at
least one line of shear reinforcement.
(c) Cell reinforced masonry walls essentially consist of solid
concrete elements. Therefore, the relationships, for reinforced concrete as
presented in Section 5-3 of NAVFAC P-397, may also be used to determine the
ultimate shear stresses in cell reinforced masonry walls. Shear
reinforcement for cell reinforced walls may only be added to the horizontal
joint similar to joint reinforced masonry walls.
(4) Dynamic Analysis. The principles for dynamic analysis of the
response of structural elements to blast loads are presented in Section 1 of
this manual. These principles also apply to blast analyses of masonry
walls. In order to perform these analyses, certain dynamic properties must
be established as follows:
(a) Load-mass factors, for masonry walls spanning in either one
direction (joint reinforced masonry construction) or two directions
(combined joint and cell reinforced masonry construction) are the same as
those load-mass factors which are listed for reinforced concrete elements of
Section 6-6 of NAVFAC P-397. The load-mass factors are applied to the
actual mass of the wall. The weights of masonry wall can be determined
based on the properties of hollow masonry units previously described and
utilizing a concrete unit weight of 150 pounds per cubic foot. The values
of the load-mass factors, KLM, will depend in part on the range of
behavior of the wall; i.e., elastic, elasto-plastic, and plastic ranges. An
average value of the elastic and elasto-plastic value of KLM is used for
the elasto-plastic range, while an average value of the average KLM for
the elasto-plastic range and KLM of the plastic range is used for the wall
behavior in the plastic range.
(b) The resistance-deflection function is illustrated in Figure
2. This figure illustrates the various ranges of behavior previously
discussed and defines the relationship between the wall's resistances and
deflections as well as presents the stiffness, K, in each range of behavior.
It may be noted in Figure 2, that the elastic and elasto-plastic ranges of
behavior have been idealized forming a bilinear (or trilinear) function.
The equations for defining these functions are presented in Section 5-16 of
NAVFAC P-397.
(c) The ultimate resistance, ru, of a wall varies with a) the
distribution of the applied load, b) the geometry of the wall (length and
width), c) the amount and distribution of the reinforcement, and d) the
number and type of supports. The ultimate resistances of both one- and
two-way spanning walls are given in Section 5-10 of NAVFAC P-397.
(d) Recommended maximum deflection criteria for masonry walls
subjected to blast loads is presented in Table 28. This table includes
criteria for both reusable and non-reusable conditions as well as criteria
for both one- and two-way spanning walls.
2.08-208
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