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,

(5.30)

whereAbarea of bar, in^2 (mm^2 )
fyyield strength of bar steel, lb/in^2 (MPa)
28-day compressive strength of concrete, lb/in^2 (MPa)

However,ldshould not be less than 12 in (304.8 mm), exceptin computation of
lap splices or web anchorage.

For No. 14 bars,

(5.31)

For No. 18 bars,

(5.32)

and for deformed wire,

(5.33)

whereAwis the area, in^2 (mm^2 ); and Swis the spacing, in (mm), of the wire to be
developed. Except in computation of lap splices or development of web rein-
forcement,ldshould not be less than 12 in (304.8 mm).

COMPRESSION DEVELOPMENT LENGTHS

For bars in compression, the basic development length ldis defined as

(5.34)

butldnot be less than 8 in (20.3 cm) or 0.0003fydb.

CRACK CONTROL OF FLEXURAL MEMBERS

Because of the risk of large cracks opening up when reinforcement is subjected to
high stresses, the ACI Coderecommends that designs be based on a steel yield
strengthfyno larger than 80 ksi (551.6 MPa). When design is based on a yield
strengthfygreater than 40 ksi (275.8 MPa), the cross sections of maximum

ld

0.02fydb

fc

0.0003dbfy

ld0.03db

fy20,000

fc

0.02

Aw

Sw

fy

fc

ld0.125

fy

fc

ld0.085

fy

fc

fc

ld

0.04Abfy

fc