EQUATION:

f'dc = (DIF) f'c

(33)

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.

3.

DYNAMIC DESIGN OF BEAMS.

a.

General.

(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.

b.

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:

EQUATIONS:

Mu = As fdy (d - a/2)

(34)

and

As fdy

a =

(35)

0.85b f'dc

where,

Mu

=

ultimate moment capacity, in-lb

As

=

total area of tension reinforcement within the beam, in2

fdy

=

dynamic yield stress of reinforcement, psi

d

=

distance from extreme compression fiber to centroid of

tension reinforcement, in

a

= depth of equivalent rectangular stress block, in

b

= width of beam, in

f'dc = dynamic ultimate compressive strength of concrete, psi

The reinforcement ratio, p, is defined as:

As

EQUATION:

p =

(36)

bd

2.08-71