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Calcimator

Prestressed Concrete Calculator

Estimate prestress losses (elastic shortening, creep, shrinkage, relaxation) and effective prestress for pretensioned concrete members.

Inputs

MPa

ACI 318: max jack 0.80×fpu=1488 MPa; at transfer 0.74×fpu=1376 MPa; low-relax strand fpu=1860 MPa

mm²

ASTM A416 Grade 270: 12.7mm strand 98.7 mm²; 15.2mm (0.6") 139.4 mm² (most common)

strands
mm
ft
MPa
mm²
mm³

Results

Initial Prestressing Force

2,343,600 N

Total Prestress Losses

233.93 MPa

Effective Prestress

1,161.07 MPa

Elastic Shortening Loss36.52 MPa
Creep Loss38.56 MPa
Shrinkage Loss117 MPa
How to Use This Calculator
  1. Enter the beam span, cross-section dimensions, and concrete strength at transfer and 28 days.
  2. Input the prestressing steel area, initial prestress force, and eccentricity.
  3. Set the superimposed dead load and live load in kips per foot.
  4. Review the Prestress Losses, Net Prestress Force, and the Cracking Moment.
  5. Check that stresses at transfer and service remain within ACI 318 permissible limits.

How the result changes with Initial Prestress (fpi)

Initial Prestress (fpi)Initial Prestressing ForceTotal Prestress LossesEffective Prestress
6501,092,000 N171.48 MPa478.52 MPa
1,0251,722,000 N202.92 MPa822.08 MPa
1,4752,478,000 N240.64 MPa1,234.36 MPa
1,8503,108,000 N272.07 MPa1,577.93 MPa

What each input means

Initial Prestress (fpi)
Initial prestressing stress in the strand per ACI 318 §26.10.2. Max jacking stress: 0.80×fpu for low-relaxation strand (fpu=1860 MPa); 0.75×fpu at transfer; ACI limits initial fpi ≤ 0.74×fpu immediately after transfer.
Area per Strand
Cross-sectional area of a single prestressing strand per ASTM A416. Grade 270 low-relaxation: 9.53mm (⅜") ≈ 54.8 mm²; 12.7mm (½") ≈ 98.7 mm²; 15.2mm (0.6") ≈ 139.4 mm² (most common); 15.7mm ≈ 150 mm².
Number of Strands
Total number of prestressing strands in the member.
Strand Eccentricity
Distance from the centroid of strands to the centroid of the concrete section.
Member Length
Total length of the prestressed concrete member.
Concrete Strength (f'c)
28-day compressive strength of the concrete.
Gross Section Area
Gross cross-sectional area of the concrete member.
Section Modulus (bottom)
Section modulus at the bottom fiber of the concrete section.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Initial Prestress (fpi) = 1395, Area per Strand = 140, Number of Strands = 12, Strand Eccentricity = 200 = 8 input(s) provided
  2. Calculate Initial Prestressing Force
    Initial Prestressing Force
    2343600 = 2343600
  3. Calculate Total Prestress Losses
    Total Prestress Losses
    233.93 = 233.93
  4. Calculate Effective Prestress
    Effective Prestress
    1161.07 = 1161.07
  5. Calculate Elastic Shortening Loss
    36.52 = 36.52
  6. Calculate Creep Loss
    Creep Loss
    38.56 = 38.56

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