Example Problems -Cont. - dm2_080266

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(11) Determine maximum deflection from Figure 6-7 of NAVFAC
P-397; check criteria.
(12) Calculate ultimate shear stress from Equation (127)
(13) Determine required area of shear reinforcing using
Equation (128)
(14) Find rebound shear at support and required area of anchor
reinforcing.  Use Figure 6-8 of NAVFAC P-397.
Calculation:
Given:
(1) Clear span between columns, 150 inches
(2) Pressure-Time loading as shown in Figure 68a.
(3) Maximum support rotation, 0.5 degree
Solution:
(1) Use 12-inch wide hollow concrete masonry units and ladder
type reinforcing with No. 8 gauge side rods and No. 9
gauge cross rods 16 inches on center.  Assume db = 10
inches for this type of reinforcing.
(2) Reinforcing steel in tension or compression:
fdy
=
fy x DIF
= 70000 x 1.10
= 77,000 psi
Concrete in shear
f'dm
= f'm x DIF
= 1350 x 1.00
= 1,350 psi
(3) Use one layer of reinforcing between every masonry unit
joint, therefore 8 inches on center.
As = .0206/8
= .0026 in2/in
Mu = Asfdyds
= .0026 x 77,000 x 10
= 2002 in-lb/in
2.08-249

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