# Codemap: concentric-footing

Hybrid (Typst + Python) structural calculation that checks a square, concentrically loaded reinforced-concrete spread footing per ACI 318-19: soil bearing, one-way shear, two-way (punching) shear, flexure, minimum steel, and concrete bearing. `calc.py` is the single source of truth; `footing.typ` presents only.

Generated: 2026-08-21
Files indexed: 13 (all deliverables present)

## Layout

```
calcs/concentric-footing/
├── calc.py                         [logic]    — ACI 318-19 footing checks; Pint YAML → compute() → results.json; CLI --input/--output/--stdout.
├── input.yaml                      [config]   — Pint-quoted quantities; Blavatnik defaults (Ps, Pu, qa, Bf, Df, cover, fc, fy, lambda, column_width, base_plate_width, N, rebar_size).
├── results.json                    [state]    — last calc output: {tool, version, project, prepared_by, values, checks}.
├── test_concentric_footing.py      [test]     — pytest lock of corrected ACI 318-19 benchmark (12 tests); imports calc.py:compute via importlib.
├── footing.typ                     [logic]    — Typst presentation sheet; imports lib/sheet.typ + results.json, derives loads, emits <concentric-footing-loads>/<concentric-footing-results>.
├── generated/footing.pdf           [doc]      — compiled artefact (~204 KB).
├── CONCENTRIC-FOOTING.pdf          [doc]      — reference: Blavatnik square footing 36in×36in×12in, 3000 psi, 4-#4 (contains known 68in vs 92in perimeter typo).
├── PROJECT_STATE.md                [doc]      — architecture, pinned equations, units, tolerances, corrected benchmark, known limitations.
├── TASKS.md                        [doc]      — 5-task plan (001 numerical core, 002 pytest lock, 003 Typst sheet, 004 docs, 005 review).
└── tasks/
    ├── 001_calc_and_input.md       [doc]      — numerical core spec (calc.py + input.yaml + results.json).
    ├── 002_numerical_tests.md      [doc]      — pytest lock spec (test_concentric_footing.py, compute() only).
    ├── 003_typst_sheet.md          [doc]      — Typst presentation spec (footing.typ + compile + metadata query tests).
    ├── 004_docs_refresh.md         [doc]      — README + codemap refresh spec.
    └── 005_review.md               [doc]      — reviewer pass spec (engineering + deterministic evidence + simplify).
```

(footing.typ and generated/footing.pdf are now present on disk — see layout above.)

## Hot Spots

- `calcs/concentric-footing/calc.py` — single source of truth for all six ACI 318-19 checks; any equation change must be reconciled with `test_concentric_footing.py` and the benchmark in `PROJECT_STATE.md`.
- `calcs/concentric-footing/PROJECT_STATE.md` — pins every equation, unit, tolerance, and the corrected benchmark; the builder must not invent behavior beyond it.
- `lib/sheet.typ` (in worksheets root, external) — shared `calc-line` / `check` helpers used by `footing.typ`; changing them breaks every sheet's PDF.

## Conventions

- Hybrid Pint pattern: `input.yaml` (quoted quantity strings) → `calc.py:compute()` → `results.json` {tool, version, project, prepared_by, values, checks} → `footing.typ` (presents only, no recomputation) → PDF compiled with `--root .` from `worksheets/`.
- Load determination (DL/LL, tributary area, column self weight) is derived in Typst and emitted as `<concentric-footing-loads>`; Python reads checked `Ps`/`Pu`. The test suite reconciles them.
- Pin one hand-calculated example in `pytest.approx` before treating the tool as stable; correct reference typos in the Scope note rather than reproducing them.