Function
Determine the design code and the special provisions for seismic design (if required) to perform the design or the strength verification for PT Slab design strips according to the following Concrete Design Criteria:
Ultimate Strength Design, the American Concrete Institute (ACI318-19/ACI318M-19)
Note.
ACI 318-19 uses U.S. customary units (ksi, kip, in, ft), whereas ACI 318M-19 uses SI/metric units (MPa, kN, mm, m).
Call
From the Main Menu
select [Post tension] tab > [Design] group > [Design Code Option]
Input
Design Code
Select the design code used for PT slab design and stress verification.
Selfweight Balance Ratio Limit
Min: Specify the minimum allowable selfweight balance ratio.
Max: Specify the maximum allowable selfweight balance ratio.
The inputs verify whether the moment generated by the PT tendon uplift force adequately balances the slab self-weight moment.
The check result can be reviewed in [Post tension] tab > [Design] group > Design Result Dialog > Summary. The requirement is satisfied when:
where Mpt: Moment generated by the PT tendon uplift force, and Msw: Moment due to slab self-weight.
OK: The calculated balanced ratio lies within the specified minimum and maximum limits.
Precompression Level
Min: Specify the minimum allowable precompression stress level in the PT slab.
Max: Specify the maximum allowable precompression stress level in the PT slab.
The input verifies the adequacy of the average compressive stress induced in the concrete section by the prestressing force. This check ensures that the slab section maintains the required level of compression under prestressing.
The check result can be reviewed in:
Design Result Dialog > Summary
Report > Detail Report > Check Minimum Average Compressive Stress for Prestressed Slab
The average compressive stress is calculated as:
where fpc: Average compressive stress at the design section, Fptl: Axial force at the check section due to tendon prestressing force [PTI] (refer to the Design Strip Force Table), and Ag = Gross cross-sectional area of the design strip section.
The requirement is satisfied when:
OK: The calculated average compressive stress lies within the specified minimum and maximum limits.
Allowable Concrete Stress Limit
By Design Code: Automatically calculates allowable concrete stress limits based on the selected design code provisions.
User Input: Allows the user to define allowable concrete stress limits manually.
k: Specifies the coefficient used to determine the concrete compressive strength at the time of initial prestress.
where k is the coefficient applied to the specified compressive strength, f'c is the specified compressive strength of concrete, and f'ci is the specified compressive strength of concrete at the time of initial prestress.
Table
The table displays the allowable stress limits corresponding to each concrete material.
ID: Material identification number.
Material Name: Name of the concrete material.
f'c (kips/in²): Specified concrete compressive strength in the 'Modify material' option.
Allowable (Compression) (kips/in²)
Initial: Maximum allowable compressive stress immediately after prestress transfer.
Sustained: Maximum allowable compressive stress under sustained loading conditions.
Total: Maximum allowable compressive stress considering the total service load condition.
Allowable (Tension) (kips/in²)
Initial: Maximum allowable tensile stress immediately after prestress transfer.
Sustained: Maximum allowable tensile stress under sustained loading conditions.
Total: Maximum allowable tensile stress considering the total service load condition.
OK: Save the design code options and allowable stress limits.
Close: Close the dialog without/after modifying the current settings.