1. NOTATION
fps = stress in prestressing steel at service loads less decompression stress, ksi
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2. 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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3. DECOMPRESSION STRESS fdc
Strain
0.03
0.02
0.01
fdc
fse
fps
Steel Stress at Service Load From Cracked Section Analysis
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4. DECOMPRESSION STRESS fdc
fdc = fse + fc x Eps/Ec
where 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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5. NOTATION
s = center-to-center spacing of flexural tension steel near the extreme tension face, in. Where there is only one bar or tendon near the extreme tension face, s is the width of extreme tension face
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6. 18.1.3 – CODE SECTIONS EXCLUDED FROM CHAPTER 18
The following provisions of this code shall not apply to prestressed concrete, except as specifically noted: Sections 7.6.5, 8.4, , , , 8.11, , , 10.5, 10.6, , and ; Chapter 13; and Sections 14.3, 14.5, and 14.6, except that certain sections of 10.6 apply as noted in
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7. 18.4.2 – PERMISSIBLE STRESSES (’99)
(c) Extreme fiber stress in tension in precompressed tensile zone …
(d) Extreme fiber stress in tension in precompressed tensile zone … based on transformed cracked sections …………………………
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8. – NEW CLASS C
Prestressed Flexural Members Are Classified as Follows:
Condition
Class
Stress Condition
Uncracked U
Transition T
Cracked C
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9. 18.3.3 – PRESTRESSED FLEXURAL MEMBERS
Classes U, T, and C Are Based on the Computed Extreme Fiber Stress ft at Service Loads in the Precompressed Tensile Zone
Precompressed Tensile Zone is that Portion of the Member Cross Section in Which Flexural Tension Occurs Under Dead and Live Loads
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10. 18.3.3 – PRESTRESSED FLEXURAL MEMBERS
New Class C Permits Design Using Any Combination of Prestressing Steel and Nonprestressed Reinf.
Classes U, T, and C Apply to Both Bonded and Unbonded Members, Except …
Prestressed Two-Way Slab Systems Must Be Designed as Class U
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11. TABLE R18.3.3 – SERVICEABILITY DESIGN REQUIREMENTS
Assumed Behavior
Prestressed
Class U
Uncracked
Class T
Transition
Class C
Cracked
Nonprestressed
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12. TABLE R18.3.3 – SERVICEABILITY DESIGN REQUIREMENTS
Section Properties for Stress Calculations at Service Loads
Prestressed
Class U
Gross Section (18.3.4)
Class T
Class C
Cracked Section (18.3.4)
Nonprestressed
Not Required
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13. TABLE R18.3.3 – SERVICEABILITY DESIGN REQUIREMENTS
Tensile Stress at Service Loads
Prestressed
Class U
Class T
Class C
No Limit
Nonprestressed
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14. TABLE R18.3.3 – SERVICEABILITY DESIGN REQUIREMENTS
Deflection Calculation Basis
Prestressed
Class U
Gross Section ( )
Class T
Cracked Section ( )
Class C
Nonprestressed
Effective Moment of Inertia, Ieff
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15. TABLE R18.3.3 – SERVICEABILITY DESIGN REQUIREMENTS
Prestressed Concrete Members with Tension Not Exceeding Are Class U, and a Cracked Section Deflection Analysis is Not Required
In ’99 Code, a Cracked Section Deflection Analysis Was Required for Members With Tension Exceeding , but the Section Was Not Assumed to be Cracked Unless the Tension Exceeded
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16. TABLE R18.3.3 – SERVICEABILITY DESIGN REQUIREMENTS
Crack Control
Prestressed
Class U
Uncracked
Class T
No Requirement
Class C
Modified by
Nonprestressed
10.6.4
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17. TABLE R18.3.3 – SERVICEABILITY DESIGN REQUIREMENTS
Computation of fps or fs for Crack Control
Prestressed
Class U
Uncracked
Class T
No Requirement
Class C
Cracked Section Analysis
Nonprestressed
M/(As x Lever Arm), or 0.6fy
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18. TABLE R18.3.3 – SERVICEABILITY DESIGN REQUIREMENTS
Side Skin Reinforcement
Prestressed
Class U
No Requirement
Class T
Class C
10.6.7
Nonprestressed
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19. 18.4.4 – SERVICEABILITY – CLASS C
For structures subject to fatigue or exposed to corrosive environments, special investigations and precautions are required.
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20. 18.4.4 – SERVICEABILITY – CLASS C
Use and Eq. (10-4) to Compute Spacing s (for Crack Control), Except:
For Tendons, Use 2/3 of Spacing “s” Required by Eq. (10-4)
With Combination of Nonprestressed Reinf. And Tendons, Use 5/6 of Spacing “s” Required by Eq. (10-4)
(3) Use fps in place of fs in Eq. (10-4)
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21. 18.4.4.1 – SPACING REQUIREMENT In 10.6.4 As Modified by 18.4.4
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22. – STEEL STRESS
fps = Stress in Tendon at Service Load Less Decompression Stress fdc
Stress at Service Load is Based on a Cracked Section Analysis
fdc May Be Conservatively Taken as the Effective Prestress fse
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23. 18.4.4.3 – STEEL STRESS fps Shall Not Exceed 36 ksi
If fps  20 ksi, Spacing Limits Do Not Apply
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24. – SKIN REINFORCEMENT
If Effective Depth > 36 in., Skin Reinforcement Must Satisfy
Area of Skin Reinforcement, Ask, Includes Both Nonprestressed Reinforcement and Tendons
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25. 18.8.1 – REINFORCEMENT LIMITS
Previously in Appendix B of ’99 Code
Limits Are Based on Net Tensile Strain, t
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26. 18.8.1 – REINFORCEMENT LIMITS
Per and , Prestressed Concrete Sections Are Classified as:
Tension Controlled
Transition, or
Compression Controlled
 Factors Given in 9.3.2
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Ex. 24.3

27. R18.8.1 – REINFORCEMENT LIMITS
Net tensile strain limits for tension-controlled sections given in may also be stated in terms of p as defined in the 1999 and earlier editions of the code
The net tensile strain limit of corresponds to p = 0.32b1 for prestressed rectangular sections
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28. 18.8.2 – MINIMUM REINFORCEMENT
No Technical Change
Was in ’99 Code
Total Reinforcement Must Satisfy:
 Mn  1.2 Mcr
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29. – FLEXURAL MEMBERS
Place Part or All of the Bonded Reinforcement Close to Extreme Tension Fiber
Reason: Control Cracking Under Full Service Loads or Overloads
See 18.9 for Members with Unbonded Tendons
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30. 18.9 – MINIMUM BONDED REINF.
— For two-way flat plate slab systems, minimum area and distribution of bonded reinforcement shall be as required in , , and
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31. 18.10.4 - MOMENT REDISTRIBUTION
Moment Redistribution Permitted If Bonded Reinforcement Is Provided At Supports
Redistribution Per 8.4 Applies Equally to Prestressed and Nonprestressed Concrete
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