diff --git a/src/core/changes.ts b/src/core/changes.ts
index b4ca707..ce00698 100644
--- a/src/core/changes.ts
+++ b/src/core/changes.ts
@@ -23,7 +23,7 @@ export const EDITABLE_FIELDS = [
 ] as const;
 
 /** Inputs tracked for overrides and pending changes: the numeric cards plus 열별 본수 (an array, compared by value). */
-export const TRACKED_KEYS = [...EDITABLE_FIELDS.map((f) => f.key), 'pileRows', 'groundPosition', 'groundWaterOn', 'groundWaterEl', 'floodLevelEl', 'scourDepthM', 'highWaterEl', 'lowWaterEl', 'strataRows', 'bearingType', 'bearingLayout', 'blockRebar', 'copingRebar'] as const;
+export const TRACKED_KEYS = [...EDITABLE_FIELDS.map((f) => f.key), 'pileRows', 'groundPosition', 'groundWaterOn', 'groundWaterEl', 'floodLevelEl', 'scourDepthM', 'highWaterEl', 'lowWaterEl', 'strataRows', 'bearingType', 'bearingLayout', 'blockRebar', 'copingRebar', 'topSplice'] as const;
 
 export type EditableKey = (typeof TRACKED_KEYS)[number];
 
@@ -55,6 +55,7 @@ export const FIELD_LABELS: Record<EditableKey, string> = {
   bearingLayout: '받침 배치',
   blockRebar: '받침블럭 철근 설정',
   copingRebar: '코핑 배근 입력',
+  topSplice: '상면 주철근 이음',
   strataRows: '지층 행',
 };
 
diff --git a/src/core/geometry.ts b/src/core/geometry.ts
index 7866d17..1198c2e 100644
--- a/src/core/geometry.ts
+++ b/src/core/geometry.ts
@@ -1,7 +1,7 @@
 import { buildAxis, copingSpan, fromAxis, kinkArc, nearKink, toAxis } from './axis';
 import { buildIntegratedBlocks, type IntegratedBlock } from './integrated-block';
 import { type BlockRebarSettings, DEFAULT_BLOCK_REBAR } from './rebar/bearing-block';
-import { type CopingRebarSettings, DEFAULT_COPING_REBAR } from './rebar/coping-settings';
+import { type CopingRebarSettings, DEFAULT_COPING_REBAR, DEFAULT_TOP_SPLICE, type TopSpliceSettings } from './rebar/coping-settings';
 import { layoutText, resolveRowCounts, rowLayout, type PileGeometry } from './piles';
 import type { PierInput, Row } from './types';
 import { type CopingGeom, P1_COPING_GEOM } from './coping-geom';
@@ -179,6 +179,8 @@ export interface PierModel {
   blockRebar: BlockRebarSettings;
   /** 코핑 배근 입력 used by the coping rebar (승인 2026-10-26). */
   copingRebar: CopingRebarSettings;
+  /** 상면 주철근 이음 used by the coping rebar (승인 2026-10-26). */
+  topSplice: TopSpliceSettings;
   columns: ColumnModel[];
   footings: FootingModel[];
   blindings: BlindingModel[];
@@ -468,6 +470,7 @@ export function buildPier(input: PierInput): PierModel {
     integratedBlocks: buildIntegratedBlocks(blocks, input.bearingLayout === '일체'),
     blockRebar: { ...DEFAULT_BLOCK_REBAR, ...input.blockRebar },
     copingRebar: { ...DEFAULT_COPING_REBAR, ...input.copingRebar },
+    topSplice: { ...DEFAULT_TOP_SPLICE, ...input.topSplice },
     columns,
     footings,
     blindings,
diff --git a/src/core/rebar/common.ts b/src/core/rebar/common.ts
index b9a0f31..20bfa42 100644
--- a/src/core/rebar/common.ts
+++ b/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);
diff --git a/src/core/rebar/coping-main.ts b/src/core/rebar/coping-main.ts
index 37baa5f..9227be3 100644
--- a/src/core/rebar/coping-main.ts
+++ b/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).
diff --git a/src/core/rebar/coping-settings.ts b/src/core/rebar/coping-settings.ts
index 7f2f529..b416927 100644
--- a/src/core/rebar/coping-settings.ts
+++ b/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;
diff --git a/src/core/rebar/summary.ts b/src/core/rebar/summary.ts
index a3ab2d5..d1d38ec 100644
--- a/src/core/rebar/summary.ts
+++ b/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' });
diff --git a/src/core/types.ts b/src/core/types.ts
index 410684d..d4e13c6 100644
--- a/src/core/types.ts
+++ b/src/core/types.ts
@@ -1,4 +1,4 @@
-import type { CopingRebarSettings } from './rebar/coping-settings';
+import type { CopingRebarSettings, TopSpliceSettings } from './rebar/coping-settings';
 
 export type PierType = 'T형' | '2주형' | '3주형';
 export type FoundationType = '말뚝기초' | '직접기초' | '현장타설말뚝';
@@ -78,6 +78,8 @@ export interface PierInput {
   bearingLayout?: '분리' | '일체';
   /** 코핑 배근 입력 (승인 2026-10-26): the 12 numbers of ③ 코핑 배근. Absent = the 코핑철근.md defaults. */
   copingRebar?: Partial<CopingRebarSettings>;
+  /** 상면 주철근(C1–C6) 이음 (승인 2026-10-26). Absent = 이음 무시, 기둥 중심. */
+  topSplice?: Partial<TopSpliceSettings>;
   strataRows?: StrataRow[];
 }
 
diff --git a/src/main.ts b/src/main.ts
index 5210972..8847b53 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -27,7 +27,7 @@ import { blockRebarPlanSvg } from './view/block-rebar-plan-svg';
 import { copingEndStation, copingFrontSvg, copingSectionSvg } from './view/coping-rebar-svg';
 import { BLOCK_REBAR_RANGES } from './core/rebar/block-check';
 import { DEFAULT_BLOCK_REBAR, type BlockRebarSettings } from './core/rebar/bearing-block';
-import { COPING_REBAR_RANGES, copingSettingsIssues, type CopingRebarSettings, DEFAULT_COPING_REBAR } from './core/rebar/coping-settings';
+import { COPING_REBAR_RANGES, copingSettingsIssues, type CopingRebarSettings, DEFAULT_COPING_REBAR, DEFAULT_TOP_SPLICE, type TopSpliceSettings } from './core/rebar/coping-settings';
 import { groundSectionSvg } from './view/ground-svg';
 import { parseBearingElevationTable, parseSolplateTable, readDxfTexts } from './core/dxf-table';
 import { columnDiameterIssues } from './core/column-check';
@@ -1091,13 +1091,26 @@ const COPING_REBAR_FIELDS: { key: keyof CopingRebarSettings; label: string }[] =
 ];
 
 /** 적용: the values go to the draft and the model is rebuilt only when every check passes (CP01·CP02). */
-function applyCopingRebar(name: string, next: CopingRebarSettings): void {
+function applyCopingRebar(name: string, next: CopingRebarSettings, splice: TopSpliceSettings): void {
   const p = state.piers.find((q) => q.input.name === name);
   if (!p) return;
-  p.draft = { ...p.draft, copingRebar: next };
+  p.draft = { ...p.draft, copingRebar: next, topSplice: splice };
   regenerateOne(name);
 }
 
+/** A row of toggle buttons (aria-pressed), as on the 배치 chips of ②. */
+function toggleRow<T extends string>(options: [T, string][], current: T, onPick: (v: T) => void): HTMLDivElement {
+  const row = el('div', undefined, 'opts');
+  for (const [v, label] of options) {
+    const b = el('button', label, 'btn small');
+    b.type = 'button';
+    b.setAttribute('aria-pressed', String(v === current));
+    b.addEventListener('click', () => onPick(v));
+    row.appendChild(b);
+  }
+  return row;
+}
+
 function renderCopingSettings(box: HTMLDivElement, pier: Pier): void {
   if (!pier.model) return;
   const wrap = el('div', undefined, 'bearing-ref');
@@ -1135,6 +1148,23 @@ function renderCopingSettings(box: HTMLDivElement, pier: Pier): void {
     grid.appendChild(row);
   }
   wrap.appendChild(grid);
+  // 상면 주철근(C1–C6) 이음 (승인 2026-10-26): 무시 (사양 기본) / 반영, and the 위치 when 반영.
+  let splice: TopSpliceSettings = { ...DEFAULT_TOP_SPLICE, ...pier.draft.topSplice };
+  const spliceBox = el('div', undefined, 'bearing-ref');
+  const drawSplice = (): void => {
+    spliceBox.replaceChildren(el('p', '상면 주철근(C1–C6) 이음', 'muted small'), toggleRow([['ignore', '이음 무시'], ['apply', '반영']] as const, splice.mode, (v) => {
+      splice = { ...splice, mode: v };
+      drawSplice();
+    }));
+    if (splice.mode === 'apply') {
+      spliceBox.appendChild(toggleRow([['center', '기둥 중심'], ['end', '단부']] as const, splice.at, (v) => {
+        splice = { ...splice, at: v };
+        drawSplice();
+      }));
+    }
+  };
+  drawSplice();
+  wrap.appendChild(spliceBox);
   const msg = el('p', undefined, 'muted small');
   const apply = el('button', '적용', 'btn small');
   apply.type = 'button';
@@ -1147,7 +1177,7 @@ function renderCopingSettings(box: HTMLDivElement, pier: Pier): void {
       setError('코핑 배근 입력을 확인하세요. 값은 반영되지 않았습니다.');
       return;
     }
-    applyCopingRebar(pier.input.name, next);
+    applyCopingRebar(pier.input.name, next, splice);
   });
   wrap.append(msg, apply);
   box.appendChild(wrap);
diff --git a/src/view/rebar3d.ts b/src/view/rebar3d.ts
index 46ca8e8..a627585 100644
--- a/src/view/rebar3d.ts
+++ b/src/view/rebar3d.ts
@@ -1,7 +1,7 @@
 import * as THREE from 'three';
 import type { PierModel } from '../core/geometry';
 import { assemblyEndOffset, assemblyJs, b10Levels, b9Bars, FOOTING_DEFAULTS, gridPositions, grid, layers, legLength, legOffsets, sideDepth } from '../core/rebar/footing';
-import { bottomPiece, MAIN, widthLayout } from '../core/rebar/coping-main';
+import { bottomPiece, MAIN, topSplicePieces, widthLayout } from '../core/rebar/coping-main';
 import { C14_INSET, c14Bars, CAP, COPING_REBAR, SHEAR_LOOP_STEP, shearBars, shearBarsMulti, shearUHeight, copingSideBars, SIDE_HOOK_LEG, stairBars, undersideAt } from '../core/rebar/coping';
 import { sideRowLevels } from '../core/coping-geom';
 import { columnRebar, columnInputFor, COLUMN_P1 } from '../core/rebar/column';
@@ -152,8 +152,17 @@ export function buildRebar3D(m: PierModel, common: Material = DEFAULT_MATERIAL,
     for (let k = 1; k <= 3; k++) {
       const z = topEl - 0.127 - (k - 1) * (m.copingRebar.mainLayerGap / 1000);
       const xk = cover + ((k - 1) * MAIN.layHorizontal) / 1000;
+      // 상면 이음 (승인 2026-10-26): when applied and longer than the standard, the bar is two pieces overlapping by l_s at the split.
+      const sp = m.topSplice.mode === 'apply' ? topSplicePieces(L * 1000, k, m.topSplice.at, mCoping) : null;
+      const splitX = sp ? xk + (sp.splitFromLeft - MAIN.hook) / 1000 : 0;
+      const half = sp ? sp.lap / 2000 : 0;
       xs.forEach((n, j) => {
         const name = `C${k + (j % 2 === 1 ? 0 : 3)}`;
+        if (sp) {
+          addPath(name, 0, [[xk, z - hookTop, n], [xk, z, n], [splitX + half, z, n]], NOMINAL_DIAMETER.H29, COLOR.coping);
+          addPath(name, 0, [[splitX - half, z, n], [L - xk, z, n], [L - xk, z - hookTop, n]], NOMINAL_DIAMETER.H29, COLOR.coping);
+          return;
+        }
         const pts: [number, number, number][] = [
           [xk, z - hookTop, n],
           [xk, z, n],
diff --git a/tests/rebar-coping-main.test.ts b/tests/rebar-coping-main.test.ts
index f0d743a..850e6a1 100644
--- a/tests/rebar-coping-main.test.ts
+++ b/tests/rebar-coping-main.test.ts
@@ -1,6 +1,6 @@
 import { describe, expect, it } from 'vitest';
 import { developmentLength, hookLength, NOMINAL_DIAMETER, spliceLength } from '../src/core/rebar/common';
-import { bottomPiece, topBarLength, topRowEl, widthLayout } from '../src/core/rebar/coping-main';
+import { bottomPiece, topBarLength, topRowEl, topSplicePieces, widthLayout } from '../src/core/rebar/coping-main';
 import { buildPier } from '../src/core/geometry';
 import { rebarSummary } from '../src/core/rebar/summary';
 import { DEFAULT_COPING_REBAR } from '../src/core/rebar/coping-settings';
@@ -54,6 +54,42 @@ describe('C1–C8 상·하면 주철근 (코핑철근.md §5, plan C3)', () => {
     expect([s1.spacing, s1.actual, s1.basis]).toEqual(['130', '130', 'input']);
   });
 
+  it('상면 이음 (승인 2026-10-26): 기둥 중심 → total/2 + l_s/2 each; 단부 → total + l_s − 12000 and 12000', () => {
+    const center = topSplicePieces(12000, 1, 'center')!;
+    expect(center.lap).toBeGreaterThan(1700);
+    expect(center.pieces[0]).toBeCloseTo(12744 / 2 + center.lap / 2, 3);
+    expect(center.pieces[1]).toBeCloseTo(center.pieces[0], 3);
+    expect(center.pieces[0] + center.pieces[1]).toBeCloseTo(12744 + center.lap, 3);
+
+    const end = topSplicePieces(12000, 1, 'end')!;
+    expect(end.pieces[0]).toBeCloseTo(12744 + end.lap - 12000, 3);
+    expect(end.pieces[1]).toBeCloseTo(12000, 3);
+  });
+
+  it('상면 이음: a bar within the standard length is not split', () => {
+    expect(topSplicePieces(10000, 1, 'center')).toBeNull();
+  });
+
+  it('철근표: 이음 무시 → 단일 길이 12744 · 반영(기둥 중심) → 2조각, 각 조각 개수 = 행 개수', () => {
+    const ignore = rebarSummary(buildPier(loadP1())).rows.find((r) => r.name === 'C1')!;
+    expect(ignore.length).toBeCloseTo(12744, 0);
+    expect(ignore.pieces).toBeUndefined();
+
+    const applied = rebarSummary(buildPier({ ...loadP1(), topSplice: { mode: 'apply', at: 'center' } })).rows;
+    const c1 = applied.find((r) => r.name === 'C1')!;
+    const lap = topSplicePieces(12000, 1, 'center')!.lap;
+    expect(c1.length).toBeNull();
+    expect(c1.pieces).toHaveLength(2);
+    expect(c1.pieces![0].count).toBe(c1.count);
+    expect(c1.pieces![0].length).toBeCloseTo(12744 / 2 + lap / 2, 3);
+    expect(c1.pieces![1].length).toBeCloseTo(12744 / 2 + lap / 2, 3);
+    expect(c1.note).toContain('기둥 중심');
+
+    const end = rebarSummary(buildPier({ ...loadP1(), topSplice: { mode: 'apply', at: 'end' } })).rows.find((r) => r.name === 'C1')!;
+    expect(end.pieces![1].length).toBeCloseTo(12000, 3);
+    expect(end.note).toContain('단부');
+  });
+
   it('CP04: the default P1 has an even count (no warning); 기본간격 120 gives an odd count and a CP04 warning', () => {
     const base = rebarSummary(buildPier(loadP1())).warnings.filter((w) => w.code === 'CP04');
     expect(base).toEqual([]);