1Flexure Behavior

318-05

Ce 572

10.3.2 BALANCED STRAIN CONDITION

fy /Es (or 0.002)

0.003

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210.3.3-4 STRAIN CONDITIONS

tdc

Compression-Controlled

Tension-Controlled

Transition

c 0.003 = 0.003

t 0.002 t0.002 0.005< < t 0.005

0.003

c c

tc 0.6d tc 0.375d

99/02 DUCTILTY COMPARISONS

0.4

0.6

0.8

1.0

0.002 0.004 0.006 0.008

b0.50

t =0.004t =0.005

t =0.0075

318-02

318-99

1.0 2.0 3.0 4.0

b0.75

b

(- )

tNet Tensile Strain,

t yDuctility , /

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39.3.2 VARIATION IN

Spiral

OtherTransition Tension -

ControlledCompression-Controlled

0.90

0.700.65

t = 0.002 t = 0.005

9.3.2.7 MODIFIED FACTOR

9.3.2.7 Flexural sections in pretensioned members where strand embedment is less than the development length as provided in 12.9.1.1:

(a) From the end of the member to the end of the transfer length . . . . . . . . . . . . . . . . . . . . 0.75

(b) From the end of the transfer length to the end of the development length shall be permitted to be linearly increased from 0.75 to 0.9.

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49.3.2.7 MODIFIED FACTOR

Where bonding of a strand does not extend to the end of the member, strand embedment shall be assumed to begin at the end of the debonded length. See also 12.9.3.

12.9.3 Where bonding of a strand does not extend to end of member, and design includes tension at service load in precompressed tensile zone as permitted by 18.4.2, ld specified in 12.9.1 shall be doubled.

FIG. R9.3.2.7(a) VARIATION OF

Free End of Strand

End of Development Length

End of Transfer Length

bse d

3000f

ldEnd of Memberand FreeEnd of Strand Distance From Free End of Strand

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5FIG. R9.3.2.7(B) VARIATION OF

End of

DebondingEnd of

Development Length

End of Transfer Length

bse d

3000f2

End of Member

Distance From Free End of Strand

* ld as Determined by Eq. (12-4)

0.5

Free End of Strand

2ld*DebondedLength

0.6

0.7

0.8

0.9

1.0

18.0 - NOTATION

fdc = decompression stress. Stress in the prestressing steel when stress is zero in the concrete at the same level as the centroid of the tendons, ksi

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6DECOMPRESSION STRESS fdc

Stress

Strain0.030.020.010

fdcfse

fpsSteel Stress at Service Load From Cracked Section Analysis

DECOMPRESSION STRESS fdc

fdc = fse + fc x Eps/Ecwhere fc is the Concrete Stress at Level of

Steel Under Dead Load and Prestress

fdc May Be Conservatively Taken as fse

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7Flexural Strength

Bonded Approximate approach using Eq. (18-3) Strain Compatibility and Equilibrium

Unbonded Approximate method using Eq. (18-4) and (18-5) Strain compatibility and Equilibrium

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