Page 192 - Civil Engineering Formulas

128 CHAPTER FIVE

TENSION DEVELOPMENT LENGTHS

For bars and deformed wire in tension, basic development length is defined by
the equations that follow. For No. 11 and smaller bars,

0.04A b f y
l d (5.30)
f c
2
2
where A area of bar, in (mm )
b
2
f yield strength of bar steel, lb/in (MPa)
y
2
f c 28-day compressive strength of concrete, lb/in (MPa)
However, l should not be less than 12 in (304.8 mm), except in computation of
d
lap splices or web anchorage.
For No. 14 bars,
f y
l d 0.085 (5.31)
f c
For No. 18 bars,
f y
l d 0.125 (5.32)
f c
and for deformed wire,
f y 20,000 A w f y
l d 0.03d b 0.02 (5.33)
f c S w f c
2
2
where A is the area, in (mm ); and S is the spacing, in (mm), of the wire to be
w
w
developed. Except in computation of lap splices or development of web rein-
forcement, l should not be less than 12 in (304.8 mm).
d
COMPRESSION DEVELOPMENT LENGTHS
For bars in compression, the basic development length l is defined as
d
0.02 f y d b
l d 0.0003d b f y (5.34)
f c
but l not be less than 8 in (20.3 cm) or 0.0003f d .
d
y b
CRACK CONTROL OF FLEXURAL MEMBERS

Because of the risk of large cracks opening up when reinforcement is subjected to
high stresses, the ACI Code recommends that designs be based on a steel yield
strength f no larger than 80 ksi (551.6 MPa). When design is based on a yield
y
strength f greater than 40 ksi (275.8 MPa), the cross sections of maximum
y