feat(rebar): 상면 주철근(C1–C6) 이음 무시/반영, 위치 기둥 중심/단부

- 기본 '이음 무시' (사양 결정). '반영'이면 정척(12000) 초과 철근을 l_s 겹침 2조각으로 나눔
- 위치: 기둥 중심 = 전체의 절반, 단부 = 정척 안에서 가장 끝 쪽 (짧은 조각 = 전체 + l_s − 12000, 긴 조각 = 12000)
- 철근표 조각 목록과 비고, 3D 두 조각(l_s 겹침)에 반영
- STANDARD_BAR를 common.ts로 옮겨 순환 import 방지

Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com>

src/core/rebar/common.ts

@@ -117,6 +117,9 @@ export function developmentLength(db: number, fy: number, fck: number, lambda =
   return (0.6 * db * fy) / (lambda * Math.sqrt(fck));
 }
 
+/** 정척 L_bar (mm) from 확대기초철근.md §1.2. Bars longer than this need a splice. */
+export const STANDARD_BAR = 12000;
+
 /** Lap splice length l_s = 1.3·l_d (spec §4 공통 설계 규약). */
 export function spliceLength(db: number, fy: number, fck: number, lambda = MATERIAL_DEFAULTS.lambda): number {
   return 1.3 * developmentLength(db, fy, fck, lambda);

src/core/rebar/coping-main.ts

@@ -1,5 +1,5 @@
-import { DEFAULT_MATERIAL, fyOf, hookLength, Material, NOMINAL_DIAMETER, spliceLength } from './common';
-import { type CopingRebarSettings, DEFAULT_COPING_REBAR } from './coping-settings';
+import { DEFAULT_MATERIAL, fyOf, hookLength, Material, NOMINAL_DIAMETER, spliceLength, STANDARD_BAR } from './common';
+import { type CopingRebarSettings, DEFAULT_COPING_REBAR, type TopSpliceAt } from './coping-settings';
 
 /**
  * C1–C8 상·하면 주철근 (plan C3 continued). Source: RAG/코핑철근.md §5, 2026-10-22 최종 정리.
@@ -71,6 +71,19 @@ export function topBarLength(L: number, k: number): number {
   return path + 2 * MAIN.hook;
 }
 
+/**
+ * Top bar C1–C6 when its 이음 is applied (승인 2026-10-26). Only a bar longer than the standard length is split (2 pieces, l_s lap).
+ * splitFromLeft is measured from the bar's left end (mm). 기둥 중심: the centre. 단부: the split closest to the end that keeps
+ * both pieces within the standard length, so the short piece is total + l_s − standard and the long piece is the standard length.
+ */
+export function topSplicePieces(L: number, k: number, at: TopSpliceAt, m: Material = DEFAULT_MATERIAL): { pieces: [number, number]; splitFromLeft: number; lap: number } | null {
+  const total = topBarLength(L, k);
+  if (total <= STANDARD_BAR) return null;
+  const lap = spliceLength(NOMINAL_DIAMETER.H29, fyOf(m, 'H29'), m.fck);
+  const splitFromLeft = at === 'center' ? total / 2 : total + lap / 2 - STANDARD_BAR;
+  return { pieces: [splitFromLeft + lap / 2, total - splitFromLeft + lap / 2], splitFromLeft, lap };
+}
+
 /**
  * Bottom bar C7·C8 (spliced at the column centre, 하면 겹침이음). Each piece:
  * path/2 + l_s/2 + l_h, with path = 2·slope + Level and l_s = 1.3·l_d for H29 (nominal 28.6, with the material inputs).

src/core/rebar/coping-settings.ts

@@ -60,6 +60,18 @@ export const COPING_REBAR_RANGES: Record<keyof CopingRebarSettings, [number, num
   c14LowerSpacing: [1500, 2500],
 };
 
+/** 상면 주철근(C1–C6) 이음 (승인 2026-10-26): ignore = 이음 무시 (사양 기본), apply = 정척 초과 시 2조각 겹침. */
+export type TopSpliceMode = 'ignore' | 'apply';
+/** 이음 위치: center = 기둥 중심, end = 단부 (정척 안에서 가장 끝 쪽). */
+export type TopSpliceAt = 'center' | 'end';
+
+export interface TopSpliceSettings {
+  mode: TopSpliceMode;
+  at: TopSpliceAt;
+}
+
+export const DEFAULT_TOP_SPLICE: TopSpliceSettings = { mode: 'ignore', at: 'center' };
+
 export interface CopingSettingsIssue {
   code: 'CP01' | 'CP02';
   key: keyof CopingRebarSettings;

src/core/rebar/summary.ts

@@ -1,12 +1,12 @@
 import type { PierModel } from '../geometry';
 import { barLength, bearingBlockRebar, DEFAULT_BLOCK_REBAR, totals } from './bearing-block';
 import { DEFAULT_COPING_REBAR } from './coping-settings';
-import { bottomPiece, topBarLength, widthLayout } from './coping-main';
+import { bottomPiece, topBarLength, widthLayout, topSplicePieces } from './coping-main';
 import { shearBars, shearBarsMulti, copingSideBars, SIDE_HOOK_LEG, c14Bars, c14Length, stairBars, stepDevLength, undersideAt, shearULength, capLength, PIECES_PER_POSITION } from './coping';
 import { sideRowLevels } from '../coping-geom';
 import { columnRebar, columnInputFor } from './column';
 import { bottomBars, crossBars, sideBars, assemblyBars, shearB9 } from './footing';
-import { DEFAULT_MATERIAL, FckByMember, fyOf, isAssumedMaterial, Material, materialFor, splitPieces } from './common';
+import { DEFAULT_MATERIAL, FckByMember, fyOf, isAssumedMaterial, Material, materialFor, splitPieces, STANDARD_BAR } from './common';
 
 /** 근거 badge (spec §6.1): where the value comes from. */
 export type Basis = 'input' | 'default' | 'calc' | 'assumed';
@@ -89,8 +89,7 @@ const FALLBACK: Pick<RebarRow, 'spacing' | 'actual' | 'position' | 'direction' |
   spacing: '—', actual: '—', position: '—', direction: '—', shape: '—', basis: 'calc',
 };
 
-/** 정척 L_bar (mm) from 확대기초철근.md §1.2. Bars longer than this need a splice. */
-export const STANDARD_BAR = 12000;
+export { STANDARD_BAR };
 
 /**
  * 철근표 for one pier (③ screen v1): bearing blocks, coping, column, footing. Built from the generated model.
@@ -195,8 +194,14 @@ export function rebarSummary(
     warnings.push({ code: 'CP04', message: `주철근 개수 ${width.count}(n+3)은 홀수라 cycle-1·cycle-2를 나눌 수 없습니다 (기본간격 ${width.spacing}, 끝단 여유 ${model.copingRebar.mainEndGap}). 기본간격을 확인하세요.`, target: 'coping' });
   }
   // C1–C3 and C4–C6 are the same three top rows (row 1, 2, 3), one set per cycle.
+  const AT_LABEL = { center: '기둥 중심', end: '단부' } as const;
   for (const [name, k] of [['C1', 1], ['C2', 2], ['C3', 3], ['C4', 1], ['C5', 2], ['C6', 3]] as const) {
-    rows.push({ member: 'coping', name, size: 'H29', count: perRow, length: topBarLength(L, k), note: '상면, 이음 무시' });
+    const sp = model.topSplice.mode === 'apply' ? topSplicePieces(L, k, model.topSplice.at, mCoping) : null;
+    if (sp) {
+      rows.push({ member: 'coping', name, size: 'H29', count: perRow, length: null, pieces: [{ length: sp.pieces[0], count: perRow }, { length: sp.pieces[1], count: perRow }], note: `상면, 2조각 겹침이음 (${AT_LABEL[model.topSplice.at]}, l_s ${Math.round(sp.lap)})` });
+    } else {
+      rows.push({ member: 'coping', name, size: 'H29', count: perRow, length: topBarLength(L, k), note: '상면, 이음 무시' });
+    }
   }
   const bottom = bottomPiece(mCoping);
   rows.push({ member: 'coping', name: 'C7', size: 'H29', count: perRow, length: bottom.piece, note: '하면, 2조각 겹침이음' });