apesteel

name

apesteel

description

apeSteel is a composition-based, strictly-typed Python library implementing AISC 360-22, AISC 341-22 (seismic), and AISC 358-22 member-level steel design (plus EN 10365 IPE/HE shapes). Use this skill whenever the user is writing, reading, debugging, or reviewing code that imports apeSteel: building Element composites (section + SteelMaterial + Bracing + construction), running AISC checks via the Element facade (classify_flexural, classify_axial_compression, classify_seismic, flexural_strength_F2/F3/F4/F5, shear_strength_G2, compression_strength, combined_strength_H1, torsion §H3), the BeamCheck facade (run_full_beam_check), pulling shapes from AISCv16Catalog / EuropeanIPECatalog, working with frozen Report dataclasses and AISCClauseReference citations, the canonical N-mm-tonne-s baseUnits convention, the geometry classes (DoublySymmetricISection, SinglySymmetricISection, ChannelSection, RectangularHSS, RoundHSS, TeeSection, DoubleAngleSection, SingleAngleSection, RectangularBar, RoundBar), and BeamColumnConnection seismic checks (panel-zone shear, column-flange tension, doubler/continuity plates per AISC 341 §E3.6e and 358). Covers apeSteel's own idioms — composition spine, pure-function vs Element facade, AISC clause-cited Reports. For AISC code theory and worked examples see the aisc-steel-design skill; for FEM modeling that consumes these checks see apegmsh-helper.

apeSteel helper

apeSteel is a composition-based, strictly-typed Python library that implements AISC 360-22, AISC 341-22 (seismic), and AISC 358-22 member-level design. Every calculator returns a frozen, AISC-cited Report; every Element check is a method on a composite of (section, material, bracing, construction).

This skill teaches apeSteel's vocabulary and idioms — the composition spine, the units rule, the report contract, and which method to call for which AISC chapter. It does not re-explain AISC equations; for code theory and worked examples reach for the aisc-steel-design skill.

Repo: C:\Users\nmora\Github\apeSteel. Public surface: everything is re-exported from the top-level apeSteel package — from apeSteel import … is always correct.

---

1. Mental model

1.1 The one immutable rule: units

apeSteel runs in a single canonical base:

N-mm-tonne-s (force = N, length = mm, stress = MPa, moment = N·mm, mass = tonne).

Every dataclass attribute, every function argument, every return value inside the library is a float already in this base. Multiply on the way in, divide on the way out — baseUnits (the companion package) supplies the multipliers.

import baseUnits as u
assert u.BASE == "N-mm-tonne-s"

300 * u.mm        # → 300.0
4.0 * u.m         # → 4000.0
345 * u.MPa       # → 345.0
1.2 * u.kN * u.m  # → 1.2e6 N·mm (a 1.2 kN·m moment)

There is no compound kN_m symbol in baseUnits — build a moment unit by multiplying (u.kN * u.m) and divide by the same product to display.

There is no Quantity wrapper. The float you store is the canonical value. To display a result, divide by the matching constant:

phi_Mn_kNm = report.phi_strength_LRFD / (u.kN * u.m)

baseUnits lives at https://github.com/nmorabowen/baseUnits and is pulled by the [dev] extra of apeSteel. If anyone switches the base system, every apeSteel module asserts on import and fails fast.

1.2 Three primary domain objects + a composite

Every analysis is the same chain:

SectionGeometry  →  SteelMaterial  →  Bracing  →  Element  →  Report
   (or catalog)                                  ← .method() ←

Primary object	Role	Notable instances
SectionGeometry	pure shape (no Fy)	DoublySymmetricISection, SinglySymmetricISection, ChannelSection, RectangularHSS, RoundHSS, TeeSection, DoubleAngleSection, SingleAngleSection, RectangularBar, RoundBar
SteelMaterial	grade & expected-strength factors	A36, A992, A572_Gr50, S275, S355, S460 (or build your own)
Bracing	Lb_top, Lb_bot, Cb	per-element
Element	the composite that owns every check	built via section.element(...)

Element is @dataclass(frozen=True). Rebind a single field with the with_* builders — section properties are cached and don't get recomputed:

e2 = element.with_material(S355)
e3 = element.with_bracing(Bracing(0.001*u.m, 1.5*u.m, lateral_torsional_buckling_modification_factor_Cb=1.2))

1.3 Every calculator returns a Report

Each calculator returns a @dataclass(frozen=True, slots=True) subclass of Report. Universal attributes:

• cited_clauses: tuple[AISCClauseReference, ...] — every spec/section/equation/page touched
• governing_limit_state: str — e.g. "yielding", "inelastic_LTB", "web_elastic_buckling"
• phi_LRFD, omega_ASD — both factors, always
• nominal_strength — in base units
• phi_strength_LRFD, omega_strength_ASD — design strengths in base units

Plus the AISC-symbol-suffixed intermediate quantities (limiting_length_plastic_Lp, web_shear_strength_coefficient_Cv1, …) so every step is introspectable without rerunning the math. Never print inside the engine; Report.format() is the only renderer.

1.4 Pure-function form and Element-facade form are both first-class

For every AISC equation, there is a free function (compute_flexural_strength_F2_compact_doubly_symmetric, classify_flexural_compactness_B4_1b, compute_shear_strength_G2_doubly_symmetric, compute_combined_strength_H1_1, …). The Element method is a one-line wrapper over it. They stay in sync; pick whichever fits the workflow:

• Element facade — interactive design, member-level reports.
• Free functions — parametric studies, FEM post-processing, porting from procedural spreadsheets.

from apeSteel import (
    classify_flexural_compactness_B4_1b,
    compute_flexural_strength_F2_compact_doubly_symmetric,
)

props = section.compute_section_properties()
flex_class = classify_flexural_compactness_B4_1b(props, A992, construction="welded")
F2 = compute_flexural_strength_F2_compact_doubly_symmetric(
    section_properties=props, material=A992,
    unbraced_length_Lb=4.0*u.m,
    lateral_torsional_buckling_modification_factor_Cb=1.0,
)

1.5 Verbose names + AISC symbol suffix

Public attributes are spelled out, followed by the AISC symbol so the spec link is unmistakable:

section.flange_width_bf                          # bf
section.web_thickness_tw                         # tw
bracing.unbraced_length_top_flange_Lb_top        # Lb_top
bracing.lateral_torsional_buckling_modification_factor_Cb  # Cb
report.limiting_length_plastic_Lp                # Lp
report.nominal_flexural_strength_Mn              # Mn

Inside short calculator bodies the bare AISC symbol (Lp, Mp, Fy) is allowed — that's what the code citation says.

---

2. Building an Element — the canonical example

import baseUnits as u
from apeSteel import (
    A992,
    Bracing,
    DoublySymmetricISection,
)

# 1. Three primary domain objects (each its own node in the model graph).
section = DoublySymmetricISection(
    flange_width_bf     = 300 * u.mm,
    flange_thickness_tf = 22  * u.mm,
    web_clear_height_hw = 350 * u.mm,
    web_thickness_tw    = 12  * u.mm,
)
material = A992
bracing = Bracing(
    unbraced_length_top_flange_Lb_top = 0.001 * u.m,   # slab-braced
    unbraced_length_bot_flange_Lb_bot = 4.0   * u.m,
    lateral_torsional_buckling_modification_factor_Cb = 1.0,
)

# 2. Compose into an Element (the section method is the canonical builder).
element = section.element(material=material, construction="welded", bracing=bracing)

# 3. Run any AISC member-level check as a method.
flex_class = element.classify_flexural()                  # 360 §B4.1b
axial      = element.classify_axial_compression()         # 360 §B4.1a
seismic    = element.classify_seismic("highly_ductile")   # 341 §D1.1
F2_both    = element.flexural_strength_F2_both_flanges()  # 360 §F2 LTB

print(F2_both.governing_flange)
print(F2_both.governing_report.phi_strength_LRFD / (u.kN * u.m), "kN·m")
print(F2_both.governing_report.governing_limit_state)

Gotchas

• Never pass Lb = 0 for a slab-braced flange — use a small positive value (0.001 * u.m). The F2-5 regime check expects Lb > 0.
• construction is "welded" (default) or "rolled". It drives the plate-element compactness limits in §B4.1b and the residual-stress factor in §F3.
• Element.bracing may be None at construction. Classification methods (classify_flexural, classify_axial_compression, classify_seismic) do not require bracing. LTB methods do; calling flexural_strength_F2_* with bracing=None raises ValueError.

---

3. The Element check methods (cheatsheet)

The full ISO-mapped surface — Element.<method>() → AISC clause → free-function equivalent. Doubly-symmetric I is the default; SS I has F4/F5 (DS-only methods raise NotImplementedError on SS).

Element method	AISC	Free function
classify_flexural()	360 §B4.1b	classify_flexural_compactness_B4_1b
classify_axial_compression()	360 §B4.1a	classify_axial_compression_B4_1a
classify_seismic(ductility, Ca=0.0)	341 §D1.1	classify_seismic_compactness_341_D1
flexural_strength_F2_top_flange() / _bot_flange() / _both_flanges()	360 §F2 (compact DS)	compute_flexural_strength_F2_compact_doubly_symmetric
flexural_strength_F3_*_flange[s]()	360 §F3 (non-compact / slender flange)	compute_flexural_strength_F3_noncompact_or_slender_flange
flexural_strength_F4_*_flange[s]()	360 §F4 (DS noncompact-web, SS compact/noncompact web)	compute_flexural_strength_F4*
flexural_strength_F5_*_flange[s]()	360 §F5 (slender-web plate girder, DS & SS)	compute_flexural_strength_F5_slender_web_plate_girder
shear_strength_G2(transverse_stiffener_spacing_a=None)	360 §G2	compute_shear_strength_G2_doubly_symmetric
compression_strength(Kx, Lx, Ky, Ly, Kz, Lz)	360 §E2–§E4 (DS I)	compute_compression_strength_from_K_L
phi_Pn_vs_length(lengths_L, Kx=1, Ky=1, Kz=1)	E capacity curve	compute_phi_Pn_vs_length
combined_strength_H1(Pr, Mrx, …)	360 §H1.1	compute_combined_strength_H1_1
connected_to(column)	builds BeamColumnConnection	—
run_full_check()	dispatches B4.1b → F2/F3/F4/F5 + G2	run_full_beam_check
compute_deflection_*	serviceability	compute_deflection_*

For non-I shapes, use the free-function facade under apeSteel.checks — it routes channels, HSS, tees, angles, bars, unsymmetric shapes to the right §F chapter automatically:

from apeSteel import (
    compute_flexural_strength_channel,           # F2 major / F6 minor
    compute_flexural_strength_rectangular_hss,   # F7
    compute_flexural_strength_round_hss,         # F8
    compute_flexural_strength_tee_or_double_angle,  # F9
    compute_flexural_strength_single_angle,      # F10
    compute_flexural_strength_bar,               # F11
    compute_flexural_strength_unsymmetric_F12,   # F12
)

---

4. The BeamCheck facade

run_full_beam_check(element) (also Element.run_full_check()) is the "one call, full member" entry point. It:

1. Classifies via B4.1b.
2. Routes to F2 / F3 / F4 / F5 based on web + flange compactness and section symmetry.
3. Runs both flanges through the routed engine and picks the governing one (lowest phi*Mn).
4. Runs G2 web shear (DS only at present).
5. Returns a BeamCheckReport aggregating everything.

It does not run seismic compactness or axial / combined — those need extra inputs the caller must supply explicitly.

from apeSteel import run_full_beam_check
report = run_full_beam_check(element)

report.routed_flexure_chapter        # "F2" | "F3" | "F4" | "F5"
report.governing_flexural_flange     # "top" | "bot"
report.governing_flexural_phi_Mn / (u.kN * u.m)
report.shear.phi_strength_LRFD / u.kN

---

5. Catalogs — when not to build plate-by-plate

Two catalogs ship in apeSteel.sections:

from apeSteel import AISCv16Catalog, EuropeanIPECatalog

aisc = AISCv16Catalog()
ipe  = EuropeanIPECatalog()

Three adapters per catalog:

• get_row("W24X94") — the raw CatalogRowAISCv16 (or …EuropeanIPE) for any of the 2 299 shapes (W/M/S/HP/C/MC/L/WT/MT/ST/HSS/Pipe).
• get_section_properties("W24X94") — universal SectionProperties for downstream calculators. Today only W/M/S/HP adapt cleanly; channels/angles/HSS raise SectionTypeNotAdaptableError.
• get_doubly_symmetric_i_geometry("W24X94") — a plate-built DoublySymmetricISection reconstructed from (bf, tf, h, tw). Useful for verification (compare plate-built Ag, Ix, J, Cw against the AISC published values) or anywhere a calculator needs raw plate dimensions.

Fuzzy matching. Typos trigger a RapidFuzz fallback at similarity ≥ 80/100. The match is returned with a logging warning; below 80 a SectionNotFoundError is raised with the best candidate attached for debugging.

props = aisc.get_section_properties("W24X94")
element = section_from_plates.element(material=A992, construction="rolled", bracing=bracing)

---

6. Singly-symmetric I-sections — the sharp edges

SinglySymmetricISection is a full citizen of the ISection union, but F2 / F3 / G2 assume doubly-symmetric geometry and will raise NotImplementedError on it. The canonical SS flexure interface is F4 (compact / non-compact web) or F5 (slender web) — AISC §F5 covers DS and SS. Use flexural_strength_F4_* / flexural_strength_F5_*.

Section properties for SS sections depend on which flange is in compression. The Element exposes both views:

props_top_comp = element.section_properties_for("top")
props_bot_comp = element.section_properties_for("bot")

element.section_properties is the cached "top"-compression case.

---

7. Combined forces & torsion — Chapter H

Full Chapter H is shipped (§H1.1, §H1.2 with Cb amplification and Pey, §H1.3 single-axis, §H2 unsymmetric, §H3.1/3.2 HSS torsion, §H3.3 non-HSS torsion limit).

from apeSteel import (
    compute_combined_strength_H1_1,
    compute_combined_strength_H1_2,
    compute_combined_strength_H1_3,
    compute_combined_strength_H2,
    compute_combined_strength_H3_2,
    compute_Cb_amplification_factor_H1_2,
    compute_Pey_H1_2,
    compute_torsional_strength_rect_HSS_H3_1,
    compute_torsional_strength_round_HSS_H3_1,
    compute_nonHSS_torsion_limit_H3_3,
    ensure_h1_3_applicable,
)

Pr/Mrx/Mry passed to §H1 are the required second-order strengths — already amplified by the Direct Analysis Method. No Appendix-8 B1/B2 machinery happens inside apeSteel (see design note 09).

---

8. Seismic and joint checks

BeamColumnConnection aggregates a (beam, column) pair of Elements and exposes joint-level seismic checks. Build it via either:

joint = beam_element.connected_to(column_element)
# or
from apeSteel import BeamColumnConnection
joint = BeamColumnConnection(beam=beam_element, column=column_element)

Free-function checks (use directly or via the joint):

Function	AISC clause
check_column_flange_tension_341(...)	341 §E3.6e — column-flange tension at moment connection
check_panel_zone_shear_341(...)	360 §J10.6 (capacity-amplified by Ry,col)
recommend_doubler_plate_thickness_341(...)	shop-practical doubler sizing
check_continuity_plates_required_358(...)	358 stiffener need + minimum dims

Out of scope for now (the architecture accommodates them — they're roadmap items): D2-2 tension rupture / §J4 block shear, composite members (I), connections (J/K), AISC 358 prequalified moment connections beyond the continuity-plate slice, system-level 341 checks.

---

9. Serviceability

Closed-form elastic deflection helpers (no LTB / second-order — pure elastic beam theory):

from apeSteel import (
    compute_deflection_simply_supported_udl,
    compute_deflection_simply_supported_point_load_midspan,
    compute_deflection_simply_supported_point_load_arbitrary,
    compute_deflection_cantilever_udl_and_tip_load,
    recommend_camber_from_dead_load_deflection,
)

Each returns a typed report carrying the deflection limit denominator defaults (DEFAULT_LIVE_LOAD_DEFLECTION_LIMIT_DENOMINATOR, DEFAULT_TOTAL_LOAD_DEFLECTION_LIMIT_DENOMINATOR — i.e. L/360, L/240).

---

10. Materials

Pre-built grades carrying AISC 341 Table A3.1 Ry / Rt:

Name	Spec	Notes
A36	ASTM A36	structural carbon
A992	ASTM A992	wide-flange default for new US construction
A572_Gr50	ASTM A572 Gr 50	plates, channels
S275, S355, S460	EN 10025	European grades for IPE/HE pairings

SteelMaterial is a frozen dataclass — build your own:

from apeSteel import SteelMaterial
custom = SteelMaterial(
    name="Custom",
    yield_stress_Fy = 420 * u.MPa,
    tensile_stress_Fu = 540 * u.MPa,
    elastic_modulus_E = 200e3 * u.MPa,
    shear_modulus_G   = 77.2e3 * u.MPa,
    density_rho       = 7.85e-9,        # tonne/mm³
    expected_yield_ratio_Ry = 1.1,
    expected_tensile_ratio_Rt = 1.1,
)

---

11. Architecture (one-screen summary)

apeSteel.checks   ← BeamCheck facade (orchestrates only, no math)
   ▲
apeSteel.flexure, .shear, .compression, .combined, .seismic, .serviceability, .classification
   ▲      (each returns a typed Report)
apeSteel.sections (.geometry → .properties → .catalog)
   ▲
apeSteel.core (.units → .materials → .result_types)

Each layer depends only on the layers strictly below; tests enforce this by inspecting imports. Polymorphism happens at the SectionProperties boundary — downstream calculators talk only to that frozen dataclass, never to a concrete shape class. No SteelSection ABC.

---

12. Citation discipline

Every Report carries cited_clauses: tuple[AISCClauseReference, ...]. An AISCClauseReference is (specification, section, equation, page) and pretty-prints itself:

report.cited_clauses[0].short()
# → "AISC 360-22 §F2.2 Eq. F2-5"

If you add new calculators, every equation you touch must be cited. Tests enforce this.

---

13. Project conventions in one paragraph

Python ≥ 3.11. pyright runs in strict mode with zero errors; the package is Any-free and uses no implicit Optional. Every result type is @dataclass(frozen=True, slots=True). ruff + ruff format gate CI, plus pytest with coverage ≥ 90 %. The 1 300+ regression tests (-m regression) are snapshots of apeSteel's own output and catch drift, not formula errors; numerical correctness of Chapter F is anchored independently by tests/golden/test_chapterF_independent.py, which re-derives every Mn from AISC 360-22 with no apeSteel.flexure import.

When adding code: keep the layering, keep the citations, write the free function first and the Element wrapper second, keep names verbose with the AISC symbol suffix, and never print inside the engine.

---

14. Cross-references

• AISC code theory, worked examples, derivations — aisc-steel-design skill. This skill assumes the spec is already understood; if the user asks "why §F4-2 has that form" or "what's the basis for c in §F2-8b", reach for aisc-steel-design.
• FEM modelling that feeds demands into apeSteel checks — apegmsh-helper. Typical handoff: apeGmsh produces nodal/element results, the user pulls (Pr, Mrx, Mry, V) and passes them into Element.combined_strength_H1(...).
• OpenSees post-processing — mpco-recorder / stko-to-python for pulling MPCO data, then back to this skill for the code check.

---

15. Worktree gotcha

When testing from a .claude/worktrees/<branch>/ tree on this machine, set PYTHONPATH=<worktree>\src before running tests, otherwise import apeSteel resolves to the install on main and silently runs the wrong code. (Recorded in user memory as worktree-pythonpath-gating.)

---

16. Web-tapered members — partial (DG 25, axial only so far)

The prismatic core (Element, every SectionGeometry) is constant (bf, tf, h, tw) and does not handle tapers — the Chapter E orchestrator still raises NotImplementedError on a variable-section route. Web-tapered doubly-symmetric I-members are instead handled by a separate subpackage, apeSteel.tapered, built on the DG 25 γ (elastic- buckling-ratio) stress-format method.

Not re-exported at top level. Import from the subpackage: from apeSteel.tapered import TaperedMember, TaperedISection, ….

Status (design note 11 / _DG25_citation_reference.md): T-0 geometry

• demand and T-1 axial (§5.3) are complete; flexure (T-2) and shear + combined (T-3) are NOT yet built. So: web-tapered DS I-member compression is supported today; tapered flexure/shear/combined are still roadmap — tell users exactly that, don't claim tapers are wholly unsupported (that was true in v1, not now).

Shipped apeSteel.tapered surface (all in its __all__):

• TaperedISection / StationSection — variable-section geometry, sampled station-by-station; each station is polymorphic at the SectionProperties boundary so the prismatic classify_flexural_compactness_B4_1b is reused per station unchanged.
• BucklingProvider / ClosedFormProvider — the member-buckling provider supplying γ (DG 25 App. A.1 closed-form estimator, no solver). The seam is designed to also ingest an eigenvalue λ from apeGmsh/OpenSees.
• compute_compression_tapered — the stress-format §E7 engine; wraps the prismatic curves in stress (first-yield) format fed by γ.
• TaperedMember — the member-level facade (the taper analogue of Element; strength depends on a member eigenvalue, not just local geometry, so it is a member-level object, not a SectionGeometry).
• TaperedCompressionReport / CompressionStationResult — the frozen, AISC/DG-25-cited Reports; the AISCClauseReference contract carries over verbatim with DG 25 clause refs added to the citation source.

The design method (for explaining it): AISC 360 has no tapered chapter; the reference is AISC Design Guide 25, Frame Design Using Web-Tapered Members. For the full γ-based methodology — equation numbers, pages, the stress-format mapping onto §E7/§F4/F5 — read the aisc-steel-design skill's references/dg25_tapered_members.md. One- paragraph version: reuse the prismatic strength curves in stress (first- yield) format, fed by a member buckling ratio γ = (elastic buckling load)/(required strength) from an eigenvalue analysis; Cb scales Fe.LTB (not Mn); classify B4 and check the unity ratio station-by-station along the length.

Still to come (T-2 / T-3), following the same seams: tapered flexure reuses the §F4/F5 engines in stress format fed by γ (Cb scales Fe.LTB, not Mn); shear (§G2) and combined (§H1) close out the member check. They land as more stress-format wrappers + TaperedMember methods, with the frozen-Report + DG 25 AISCClauseReference contract unchanged. Until then, calling for tapered flexure/shear/combined has no engine — route the user to prismatic per-station estimates or say it's pending.