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Calcimator

Offshore Platform Design Calculator

Estimate foundation sizing, bearing capacity, and stability ratios for gravity-based offshore platforms under combined dead, live, and environmental loads.

Inputs

Results

Total vertical load (kN)

20,500

Required base area (m²)

205

Overturning FoS

2.21

Equivalent diameter (m)16.16
Overturning moment (kN·m)75,000
Sliding FoS4.1
Actual bearing pressure (kPa)150
How to Use This Calculator
  1. Enter dead load (kN), live load (kN), horizontal environmental load (kN), and vertical environmental load (kN).
  2. Enter overturning arm (m) — lever arm from seabed to environmental load centroid.
  3. Read total vertical load (kN) and overturning moment (kN·m).
  4. Check sliding and overturning unity check ratios — values < 1.0 indicate a stable platform.
  5. Use load combination results to size jacket legs and seabed foundation elements.

How the result changes with Dead load (kN)

Dead load (kN)Total vertical load (kN)Required base area (m²)Overturning FoS
100,000105,5001,05525.78
350,000355,5003,555159.45
650,000655,5006,555399.23
900,000905,5009,055648.18

What each input means

Dead load (kN)
Permanent structural and equipment weight.
Live load (kN)
Variable loads: personnel, consumables, stored materials.
Horizontal env. load (kN)
Combined wave, current, and wind horizontal force.
Vertical env. load (kN)
Vertical environmental load component (wave slam, buoyancy change).
Overturning arm (m)
Lever arm from seabed to centroid of horizontal environmental load.
Allowable bearing (kPa)
Allowable seabed bearing pressure from geotechnical investigation.
Soil friction coefficient
Foundation-soil interface friction coefficient for sliding check.
Safety factor (FoS)
Global safety factor applied to bearing capacity check.

What each result means

Total vertical load (kN)
Sum of dead, live, and vertical environmental loads.
Required base area (m²)
Minimum foundation footprint area to satisfy bearing capacity with FoS.
Equivalent diameter (m)
Diameter of a circular base with the required area.
Overturning moment (kN·m)
Moment about the base from horizontal environmental forces.
Overturning FoS
Ratio of restoring to overturning moment. Should exceed 1.5.
Sliding FoS
Ratio of frictional resistance to horizontal load. Should exceed 1.5.
Actual bearing pressure (kPa)
Bearing pressure at factored foundation area.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Dead load (kN) = 15000, Live load (kN) = 5000, Horizontal env. load (kN) = 3000, Vertical env. load (kN) = 500 = 8 input(s) provided
  2. Calculate Total vertical load
    Total vertical load = deadLoad + liveLoad + envVertical
    20500 = 20500
  3. Calculate Required base area
    Required base area = (totalVertical * safetyFactor) / bearingCapacity
    205 = 205
  4. Calculate Overturning FoS
    Overturning FoS = restoringMoment / max(1, overturningMoment)
    2.21 = 2.21
  5. Calculate Equivalent diameter
    Equivalent diameter = sqrt((4 * requiredArea) / π)
    16.16 = 16.16
  6. Calculate Overturning moment
    Overturning moment = envHorizontal * overturningArm
    75000 = 75000

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