Source: https://guthlabs.ai/docs/instruments/footing-size-calculator-preliminary/mechanism/

instrument mechanism / verified-clean

# Footing Size Calculator (Preliminary) mechanism

The inspectable method record for Footing Size Calculator (Preliminary), kept separate from implementation and qualification.

Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**

## Model scope

The algebra is correct for preliminary sizing under a centered axial load, positive allowable pressure, compatible units, and a square footing assumption. Verdict is NEEDS_REVIEW because the specification leaves the load basis, gross-versus-net pressure convention, unit contract, and applicability constraints ambiguous. The existing honest label is appropriate but should explicitly state that self-weight, eccentricity/moments, settlement, shear, stability, code minimums, and constructible rounding are excluded.

- A_req=P/qallow is the standard preliminary formula only for a concentric axial load and a uniformly distributed allowable bearing pressure; the specification does not state those constraints.

- The formula does not account for footing self-weight, overburden, eccentricity, moment, shear, settlement, sliding, overturning, or code-required minimum dimensions and rounding.

- The square-footing dimension formula is valid only when a square plan shape is explicitly selected; rectangular footing dimensions are not determined by the provided formulas.

## Units and conventions

- P and qallow must use compatible force units, with qallow expressed as force per unit area.

- Examples using kN and kPa rely on 1 kPa=1 kN/m², so P/qallow produces m².

- Examples using N and kPa require converting qallow from kPa to N/m² before division.

- The calculation assumes P is the load basis appropriate for comparison with the stated allowable soil pressure, but the specification does not identify whether P is service, factored, net, or gross load.

## Inspectable vector

One of 4 source-bound review vectors:

````
{
  "inputs": {
    "P": 600,
    "P_unit": "kN",
    "qallow": 200,
    "qallow_unit": "kPa",
    "shape": "square"
  },
  "expected_outputs": {
    "required_area": 3,
    "required_area_unit": "m²",
    "square_side": 1.73205,
    "square_side_unit": "m"
  },
  "working": "1. Since 1 kPa=1 kN/m², qallow=200 kN/m². 2. A_req=P/qallow=600 kN ÷ 200 kN/m²=3 m². 3. Square side=√A_req=√3 m=1.73205 m."
}
````

## Failure boundary

**BREAK_CLAIMED** · SELF_FLAGGED

The plain formula has no stated input validation or load-sign convention. Zero or negative allowable pressure can cause division-by-zero or invalid negative areas, zero load produces a nonphysical zero footing, and a signed compressive load can produce an undefined square root.

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/footing-size-calculator-preliminary/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/footing-size-calculator-preliminary/implementation/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/footing-size-calculator-preliminary/qualification/>)

## Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

- `VERIFIED_LEDGER.json`

- `evidence-tranche5/tranche5-results.json`

- `BOUNDARY_HAZARD_CATALOG.json`