Source: https://guthlabs.ai/docs/instruments/unit-weight-self-weight-load-calculator-structural-members/mechanism/

instrument mechanism / verified-clean

# Unit Weight / Self-Weight Load Calculator (Structural Members) mechanism

The inspectable method record for Unit Weight / Self-Weight Load Calculator (Structural Members), kept separate from implementation and qualification.

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

## Model scope

NEEDS_REVIEW because the exact ambiguity is whether the input is mass density ρ or weight density γ, and because g is unspecified for the ρ formulation. The honest label should explicitly state accepted units, the selected formulation, the gravity constant, the assumption of uniform member properties, and that the output is a downward distributed load.

- The formula w=ρ·A·g is correct only when ρ is mass density, such as kg/m³, A is in m², and g is in m/s²; the formula w=γ·A is correct only when γ is weight density, such as N/m³ or kN/m³.

- The input description 'material density/unit weight' is ambiguous because mass density ρ and weight density γ are different quantities and require different formulas.

- The specification does not state that the member is prismatic or that density and cross-sectional area are uniform along its length; otherwise w may vary with position.

## Units and conventions

- For the density formulation, ρ is mass density in kg/m³, A is cross-sectional area in m², g is gravitational acceleration in m/s², and the result is w in N/m.

- For the weight-density formulation, γ is force per volume in N/m³ or kN/m³, A is in m², and w has corresponding units of N/m or kN/m.

- Test vectors use g=9.80665 m/s² unless another value is explicitly provided.

- The resulting self-weight load acts downward in the direction of gravity.

## Inspectable vector

One of 4 source-bound review vectors:

````
{
  "inputs": {
    "density_rho": 7850,
    "density_unit": "kg/m³",
    "area_A": 0.01,
    "area_unit": "m²",
    "g": 9.80665,
    "g_unit": "m/s²"
  },
  "expected_outputs": {
    "w": 769.822025,
    "w_unit": "N/m",
    "w_kN_per_m": 0.769822025
  },
  "working": "w=ρ·A·g\n=7850 kg/m³ × 0.01 m² × 9.80665 m/s²\n=78.5 kg/m × 9.80665 m/s²\n=769.822025 N/m\n=0.769822025 kN/m"
}
````

## Failure boundary

- Reject or clearly handle negative, non-finite, or missing density, weight density, area, and gravitational acceleration values.

- A zero area produces zero self-weight and should be accepted or explicitly defined as an invalid geometry boundary; negative area must be rejected.

- Do not apply g to γ because γ already includes gravitational acceleration.

- Unit mismatches, especially mm² versus m² and N/m³ versus kN/m³, can cause errors by factors of 10⁶ or 1000.

- The calculator should identify the load direction as downward and should not imply that the scalar magnitude alone fully defines a structural load.

- No division-by-zero operation is present in the stated formulas, but any later conversion or derived calculation must guard against zero denominators.

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/unit-weight-self-weight-load-calculator-structural-members/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/unit-weight-self-weight-load-calculator-structural-members/implementation/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/unit-weight-self-weight-load-calculator-structural-members/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`