f'dc = (DIF) f'c
For the recommended reinforcing steel having a static yield stress fy =
60,000 psi, the dynamic design stress fdy = 66,000 psi. While for the
recommended concrete compression strength f'c = 4,000 psi, the dynamic
design stress f'dc = 5,000 psi.
DYNAMIC DESIGN OF BEAMS.
(1) The design of beams is performed in a manner similar to that
given in NAVFAC P-397 for slabs. The most significant and yet not very
important difference in the design procedure is that in the case of a slab,
the calculations are based on a unit area, whereas for a beam, they are
based on a unit length of the beam.
(2) Beams are primary support members and as such are generally not
permitted to attain large plastic deformations. In fact, the ultimate
support rotation of beams is limited to 2 degrees. Consequently, the
maximum stress developed by the reinforcement will be within its yield
range. The reinforcement is not stressed into its strain hardening region.
Ultimate Dynamic Moment Capacity.
(1) The ultimate dynamic resisting moment, Mu, of a rectangular
beam section of width, b, with tension reinforcement only is given by:
Mu = As fdy (d - a/2)
ultimate moment capacity, in-lb
total area of tension reinforcement within the beam, in2
dynamic yield stress of reinforcement, psi
distance from extreme compression fiber to centroid of
tension reinforcement, in
= depth of equivalent rectangular stress block, in
= width of beam, in
f'dc = dynamic ultimate compressive strength of concrete, psi
The reinforcement ratio, p, is defined as: