feat(steel-detailer-us): bolt-length-from-grip skill (RCSC 2020 §2.7 + Table C-2.2)

20-agents/aeco/engineering/steel-detailer-us/manifest.yaml

@@ -1,5 +1,5 @@
 agent:        steel-detailer-us
-version:      0.2.0
+version:      0.3.0
 sdk-target:   aisc-360-22                 # the code edition these rules are sourced from
 display-name: Steel Detailer — US (AISC)
 
@@ -14,7 +14,7 @@ description: |
   ("no verified source") rather than guessing. Covers bolted + welded connection
   geometry and the governing limit states (edge distance, spacing, hole types,
   weld sizing, block shear), drawing & detailing conventions (AISC 303),
-  materials/sections, and a deterministic lookup command backed by a 66-rule
+  materials/sections, and a deterministic lookup command backed by a 70-rule
   verified JSON database. US/AISC only — never mix with Eurocode (that is the
   separate steel-detailer-uk agent).
 
@@ -93,6 +93,7 @@ skills:
   - bolt-bearing-tearout.md
   - bolt-pretension-and-joint-types.md
   - bolt-washers.md
+  - bolt-length-and-grip.md
   - weld-fillet-sizing.md
   - weld-length-and-pjp.md
   - connecting-elements-block-shear.md

20-agents/aeco/engineering/steel-detailer-us/rules/aisc-360-22.json

@@ -1,8 +1,8 @@
 {
   "agent": "steel-detailer-us",
   "standard": "aisc-360-22",
-  "version": "1.0.0",
-  "last_verified": "2026-06-14",
+  "version": "1.1.0",
+  "last_verified": "2026-06-28",
   "sources": [
     "AISC 360-22 (free — aisc.org/standards)",
     "RCSC 2020 (free — boltcouncil.org)",
@@ -320,6 +320,46 @@
       "source_quote": "The specified minimum pretensions … are based on 70 percent of the tensile strength … rounded to the nearest kip",
       "found": true
     },
+    {
+      "id": "bolt.length.grip",
+      "category": "bolts",
+      "rule": "Grip (basis for bolt-length selection)",
+      "value": "Total thickness of the connected plies the bolt passes through, EXCLUDING washers and direct-tension indicators (DTIs)",
+      "units": "in.",
+      "citation": "RCSC 2020 Glossary (\"Grip\")",
+      "source_quote": "Grip. The total thickness of material a bolt passes through, exclusive of washers or direct-tension indicators.",
+      "found": true
+    },
+    {
+      "id": "bolt.length.engagement",
+      "category": "bolts",
+      "rule": "Bolt length must achieve sufficient thread engagement",
+      "value": "Length chosen so the installed bolt end is at least flush with (or beyond) the outer face of the nut — develops the bolt's strength",
+      "units": "dimensionless",
+      "citation": "RCSC 2020 §2.7; Glossary (\"Sufficient Thread Engagement\")",
+      "source_quote": "The bolt length used shall be such that, when installed, sufficient thread engagement (as defined in the Glossary) is achieved. [Glossary:] … the available bolt threads extending beyond or at least flush with the outer face of the nut; a condition that develops the strength of the bolt.",
+      "found": true
+    },
+    {
+      "id": "bolt.length.select",
+      "category": "bolts",
+      "rule": "Selecting bolt length from grip",
+      "value": "length = grip + add-to-grip value (RCSC Table C-2.2), rounded to nearest ¼ in. (½ in. for lengths over 6 in.)",
+      "units": "in.",
+      "citation": "RCSC 2020 Commentary §2.7, Table C-2.2 (more extensive: Carter 1996, AISC Engineering Journal 2Q)",
+      "source_quote": "To determine the required bolt length, the value shown in Table C-2.2 should be added to the grip … The length determined by the use of Table C-2.2 should be adjusted to the nearest ¼-in. increment (or ½-in. increment for lengths exceeding 6 in.). A more extensive table … is available (Carter, 1996).",
+      "found": true
+    },
+    {
+      "id": "bolt.length.washer.add",
+      "category": "bolts",
+      "rule": "Washer thickness added to grip when selecting bolt length",
+      "value": "+5/32 in. per ASTM F436 flat washer; +5/16 in. per beveled washer (added to grip before length selection)",
+      "units": "in.",
+      "citation": "RCSC 2020 Commentary §2.7, Table C-2.2",
+      "source_quote": "For each ASTM F436 washer that is used, add 5/32 in.; for each beveled washer, add 5/16 in.",
+      "found": true
+    },
     {
       "id": "weld.fillet.min.to.025in",
       "category": "welds",

20-agents/aeco/engineering/steel-detailer-us/skills/bolt-length-and-grip.md

@@ -0,0 +1,57 @@
+---
+name: steel-detailer-us-bolt-length-and-grip
+description: Use for US high-strength bolt LENGTH selection — how long a bolt must be for a given grip (the clamped plies), the grip definition, the "sufficient thread engagement" requirement that sets length, adding washer thickness to grip, and where the add-to-grip length table lives. RCSC 2020 §2.7, Glossary, and Commentary Table C-2.2.
+---
+
+# Bolt length & grip (RCSC)
+
+A high-strength bolt must be **long enough to develop its strength** — i.e. long enough that, when
+installed, it achieves **sufficient thread engagement** with the nut. Length is selected from the **grip**.
+
+- **Grip** = the **total thickness of the connected plies** the bolt passes through, **excluding washers
+  and direct-tension indicators (DTIs).** (`grip` is the clamped structural material only.)
+- **The length requirement is normative (RCSC §2.7):** the bolt length used **shall** be such that, when
+  installed, **sufficient thread engagement** is achieved. *"Sufficient thread engagement"* = the end of
+  the bolt (excluding a spline-end's spline) is **at least flush with — or extends beyond — the outer face
+  of the nut**; the condition that develops the bolt's strength (Glossary). Too short → the threads do not
+  fully engage the nut; the joint cannot develop the bolt.
+- **How length is selected (method):** required length = **grip + the add-to-grip value from RCSC
+  Table C-2.2**, then **rounded to the nearest ¼ in. (½ in. for lengths over 6 in.)**. The tabulated
+  add-to-grip values already provide for manufacturing tolerances and sufficient thread engagement.
+- **Washers add to the grip *for length selection*** (even though washers are not part of the grip
+  itself): add **5/32 in. per ASTM F436 flat washer** and **5/16 in. per beveled washer** to the grip
+  before selecting the length.
+- **Where the add-to-grip table lives:** the per-diameter add-to-grip values are in **RCSC 2020
+  Table C-2.2** (free, in the RCSC Commentary). RCSC itself points to a *more extensive* selection table —
+  **Carter (1996)**, *"Specifying Bolt Length for High-Strength Bolts,"* AISC *Engineering Journal*,
+  2nd Qtr. 1996 (free, and RCSC's own cited reference). The AISC *Steel Construction Manual* has
+  historically tabulated the same selection (paid — reference only, never reproduced).
+
+This agent gives the **rule + grip concept**, not the tabulated length values — read Table C-2.2 in the
+free RCSC PDF (or Carter, 1996) for the per-diameter add-to-grip numbers.
+
+> **Rule** → length develops the bolt only with sufficient thread engagement. **Condition** → every
+> high-strength bolt; length = grip (+ washer thicknesses) + Table C-2.2 allowance, rounded. **Source** ↓.
+
+## Source
+
+- **Normative requirement — RCSC 2020 §2.7 ("Geometry of Bolting Components and Assemblies").**
+  *"The bolt length used shall be such that, when installed, sufficient thread engagement (as defined in
+  the Glossary) is achieved."*
+- **Grip — RCSC 2020 Glossary.** *"Grip. The total thickness of material a bolt passes through, exclusive
+  of washers or direct-tension indicators."*
+- **Sufficient Thread Engagement — RCSC 2020 Glossary.** *"Having the end of the bolt, not including the
+  spline of a spline-end bolt, or the available bolt threads extending beyond or at least flush with the
+  outer face of the nut; a condition that develops the strength of the bolt."*
+- **Selection method — RCSC 2020 Commentary to §2.7, Table C-2.2.** *"To determine the required bolt
+  length, the value shown in Table C-2.2 should be added to the grip (i.e., the total thickness of all
+  connected material, exclusive of washers). For each ASTM F436 washer that is used, add 5/32 in.; for
+  each beveled washer, add 5/16 in. … The length determined by the use of Table C-2.2 should be adjusted
+  to the nearest ¼-in. increment (or ½-in. increment for lengths exceeding 6 in.). A more extensive table
+  for bolt length selection based upon these rules is available (Carter, 1996 …)."*
+- RCSC's *"more extensive table … (Carter, 1996)"* is **Carter, C.J., *"Specifying Bolt Length for
+  High-Strength Bolts,"* AISC *Engineering Journal*, Vol. 33, No. 2 (2nd Qtr. 1996)** — the free,
+  canonical bolt-length-selection reference. (The AISC *Steel Construction Manual* also tabulates this
+  selection — paid; reference only, never reproduced. Edition numbering varies, so it is not cited to a
+  specific table number here.)
+- Verified against the genuine RCSC 2020 PDF. Verify free at boltcouncil.org.