Table 28

Deflection Criteria for Masonry Walls

Wall Type

Support Type

Support Rotation

Reusable

One-way

0.5deg.

Two-way

1.0deg.

Non-Reusable

One-way

1.0deg.

Two-way

2.0deg.

(e) When designing masonry walls for blast loads using response

chart procedures of Section 1, the effective natural period of vibration is

required. This effective period of vibration when related to the duration

of the blast lading of given intensity and a given resistance of the masonry

wall determines the maximum transient deflection, Xm, of the wall. The

expression for the natural period of vibration is presented in Equation (1),

Section 1, where the effective unit mass, me, has been described

previously and the equivalent unit stiffness, KE, is obtained from the

resistance-deflection function. The equivalent stiffness of one-way beams

is presented in Table 7 which may be used for one-way spanning walls except

that a unit width shall be used. Methods for determining the stiffness and

period of vibrations for two-way walls are presented in Section 6-8 of

NAVFAC P-397.

(f) Determining the stiffness in the elastic and elasto-plastic

range is complicated by the fact that the moment of inertia of the cross

section along the masonry wall changes continually as cracking progresses,

and further by the fact that the modulus of elasticity changes as the stress

increases. It is recommended that computations for deflections and

therefore, stiffnesses be based on average moments of inertia, Ia, as

follows:

EQUATION:

Ia = In + Ic

(130)

2

where,

In = the moment of inertia of the net section, in4

Ic = the moment of inertia of the cracked section, in4

2.08-209