Source: https://guthlabs.ai/docs/instruments/beam-deflection-fixed-fixed-point-udl/

instrument / verified-with-binding-errata

# Beam Deflection — Fixed-Fixed, Point/UDL

The current ledger marks this instrument verified with errata that must be applied at binding time.

Status: **VERIFIED_WITH_ERRATA**Lifecycle: **verified-with-binding-errata**

## Inspectable records

[01**Overview**Purpose and lifecycle](<https://guthlabs.ai/docs/instruments/beam-deflection-fixed-fixed-point-udl/>)[02**Mechanism**Method and assumptions](<https://guthlabs.ai/docs/instruments/beam-deflection-fixed-fixed-point-udl/mechanism/>)[03**Implementation**Binding and validation](<https://guthlabs.ai/docs/instruments/beam-deflection-fixed-fixed-point-udl/implementation/>)[04**Qualification**Evidence and errata](<https://guthlabs.ai/docs/instruments/beam-deflection-fixed-fixed-point-udl/qualification/>)

## Ledger state

The current ledger marks this instrument verified with errata that must be applied at binding time.

**Area**: Mechanical, Civil & Structural Engineering

**Tranche**: tranche-2

**Evidence ID**: t2-034

**Ledger rows**: 1

No ledger note is attached.

## Review findings

The instrument cannot pass as specified because its UDL maximum-deflection formula is wrong and its claimed reaction outputs lack formulas. The honest label should identify the model as Euler-Bernoulli, linear-elastic theory for an ideal fixed-fixed prismatic beam, with a full-span UDL or a centered point load.

### Formula and scope findings

- The UDL maximum-deflection formula is incorrect: for a fixed-fixed beam under a full-span uniform load, the standard formula is δmax=5wL⁴/(384EI), not wL⁴/(384EI).

- The listed formulas do not provide the reactions required by the claimed outputs. For symmetric full-span UDL, each reaction is wL/2; for a centered point load, each reaction is P/2.

- The point-load formulas are valid only for a point load located at midspan. The point-load position is not represented in the inputs, so the scope must be explicitly restricted to midspan.

- The stated UDL end and midspan moments are correct for a full-span UDL with ideal fixed ends: Mend=wL²/12 in magnitude and Mmid=wL²/24 in magnitude.

### Unit assumptions

- Use a consistent SI system: P in N, w in N/m, L in m, E in Pa (N/m²), and I in m⁴.

- Moments are returned in N·m; reactions are returned in N; deflection is returned in m.

- Mend denotes the magnitude of the hogging moment at either fixed support; the signed value depends on the adopted bending-moment convention.

- The beam is prismatic, Euler-Bernoulli, linear-elastic, and has ideal fixed restraints.

- The UDL acts uniformly over the full span, and the point load acts exactly at midspan.

## Boundary hardening

**BREAK_CLAIMED** · SELF_FLAGGED

An input with E = 0 produces a zero denominator in the deflection formula, so the instrument must reject it or report an undefined result. The specification also leaves reaction sign conventions and signed-versus-magnitude reporting ambiguous.

## Errata and corrections

### Stress-test correction

````
{
  "vector_inputs": {
    "load_type": "central_point",
    "P": 7500,
    "L": 2.7,
    "E": 70000000000,
    "I": 0.0000135
  },
  "wrong_outputs": {
    "left_end_moment": -253.125,
    "right_end_moment": -253.125,
    "midspan_moment": 253.125
  },
  "corrected_outputs": {
    "left_end_moment": -2531.25,
    "right_end_moment": -2531.25,
    "midspan_moment": 2531.25
  },
  "method": "PL/8 = 7500*2.7/8 = 2531.25 N·m; her own working shows the division \"20,250/8=253.125\" — a 10x slip. The deflection field (0.0008136 m) used a separate correct calculation and was unaffected."
}
````

## Inspectable example

4 review vectors are recorded. One source-bound sample is shown below.

````
{
  "inputs": {
    "load_type": "UDL",
    "w_N_per_m": 10000,
    "L_m": 6,
    "E_Pa": 200000000000,
    "I_m4": 0.000008
  },
  "expected_outputs": {
    "reaction_left_N": 30000,
    "reaction_right_N": 30000,
    "Mend_Nm": 30000,
    "Mmid_Nm": 15000,
    "delta_max_standard_m": 0.10546875,
    "delta_max_as_written_m": 0.02109375
  },
  "working": "Reactions: wL/2 = 10000×6/2 = 30000 N each. End moment: wL²/12 = 10000×6²/12 = 10000×36/12 = 30000 N·m. Midspan moment: wL²/24 = 10000×36/24 = 15000 N·m. EI = 200000000000×0.000008 = 1600000 N·m². Correct deflection: 5wL⁴/(384EI) = 5×10000×6⁴/(384×1600000) = 5×10000×1296/614400000 = 64800000/614400000 = 0.10546875 m. Specified deflection: wL⁴/(384EI) = 10000×1296/614400000 = 0.02109375 m."
}
````

## Related workflows

[Beam & Column Structural Benchcase](<https://guthlabs.ai/docs/instrument-workflows/structural-bench/>)

## Sources and evidence

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

- `VERIFIED_LEDGER.json · VERIFIED_WITH_ERRATA`

- `evidence-tranche2/tranche2-results.json`

- `BOUNDARY_HAZARD_CATALOG.json`

- `STRESS_TEST_CORRECTIONS_APPLIED.json`