Machine Foundation Mass & Static-Pressure Worksheet
Convert a documented project/OEM mass-ratio assumption into a consistent concrete mass, volume and block thickness. Also calculate average static contact pressure and 1× operating frequency. The worksheet does not choose the ratio or certify foundation adequacy.
Document the preliminary geometry
Select units before entering values. US customary inputs use international feet, avoirdupois pounds mass, pounds per cubic foot and pounds-force per square foot. Changing the unit selector reinterprets—not converts—numbers already typed.
Foundation target mass
Concrete volume
Required block thickness
Total supported static mass
Average static contact pressure
Pressure ratio / 1× frequency
Equations and units
| Quantidade | Equation in SI working units | Significado |
|---|---|---|
| Preliminary foundation mass | mf = k mm | k is a user-supplied project/OEM assumption,not a value selected by this worksheet. |
| Concrete volume | V = mf/ρ | Mass divided by mass density. |
| Block thickness | H = V/(L W) | Selected rectangular plan;dimensions remain exactly consistent with V. |
| Average static pressure | qmédia = (mm + mf + madd)g₀/(L W) | g₀=9.80665 m/s²;uniform full-contact gross average. |
| Pressure ratio | U = qmédia/qpermitir | Shown only if a positive project value is supplied;no pass/fail label. |
| 1× frequency | f1× = n/60 | RPM-to-hertz conversion only;not a natural frequency or resonance check. |
Internal calculations use kilograms,metres,cubic metres and kilopascals. Exact definitions used for US customary conversion: 1 lbm = 0.45359237 kg and 1 international ft = 0.3048 m. At standard gravity,1 psf = 0.04788025898033584 kPa.
Why the former “sizing calculator” was removed
The old page selected 3:1 for rotating machines and 5:1 for reciprocating machines without a cited project criterion,claimed that mass “absorbs vibration energy”,and implied that more mass always reduces vibration. Mass changes inertia and natural frequencies;damping dissipates energy. Added mass can move a mode toward or away from an excitation frequency,so monotonic improvement is not guaranteed.
The old geometry also contradicted its own mass result. It multiplied one cube dimension by 1.5 and rounded all dimensions upward,but continued using the smaller target mass for soil pressure. The displayed block could therefore contain much more concrete than the pressure calculation assumed. This worksheet instead requires L and W and solves H exactly from the target volume.
Universal claims for minimum concrete grade,depth as a multiple of machine width and reinforcement mass per cubic metre were removed. These are structural/geotechnical design decisions,not consequences of machine mass alone. Defaults,pump/compressor/fan presets,silent density/bearing fallbacks and prefix-tolerant parseFloat input were also removed.
Dynamic-design scope and sources
ACI PRC-351.3-18, Report on Foundations for Dynamic Equipment is the current ACI Committee 351 report listed in the 2025 ACI Collection. Its official contents cover static and dynamic loads,supporting-medium impedance,rigid/flexible modeling,frequency and forced-response analysis,acceptance criteria,concrete,reinforcement,anchorage,seismic and fatigue considerations. The official preview says it supersedes ACI 351.3R-04 and applies to rotating,reciprocating and impact/impulsive machinery.
ACI identifies the document as a committee report for competent users,not a mandatory contract specification. This page does not attribute a universal 3:1,5:1,concrete grade,depth or reinforcement rule to ACI. Exact preliminary-sizing recommendations and clause-level requirements require the licensed report and project context.
NIST SP 811 Appendix B,updated August 2025,provides the exact foot and pound conversion basis and published conversion examples used to validate the SI/US implementation.
Minimum information still needed for design
- Machine and OEM loads:static weights,unbalance,reciprocating forces/moments,torque,piping/nozzle loads,transients,upset and maintenance cases.
- Excitation frequencies and harmonics over run-up,normal operation,coast-down and variable-speed ranges.
- Foundation geometry,centres of mass/force and resistance,rotary inertia,structural stiffness,anchors,grout and fatigue demands.
- Soil/pile dynamic stiffness,damping,embedment,layering,groundwater,settlement and soil-structure interaction.
- Natural frequencies,mode shapes,forced response amplitudes,acceptance criteria and field verification.
