diff --git a/src/core/project.ts b/src/core/project.ts
index 450413e..610e702 100644
--- a/src/core/project.ts
+++ b/src/core/project.ts
@@ -68,7 +68,7 @@ export function parseProject(text: string): ProjectFile {
   if (!Array.isArray(obj.piers)) throw new Error('piers 목록이 없습니다.');
   if (obj.fckByMember !== undefined) {
     for (const [member, value] of Object.entries(obj.fckByMember)) {
-      if (!['column', 'coping', 'footing'].includes(member) || typeof value !== 'number' || !(value > 0)) {
+      if (!['column', 'coping', 'footing', 'abutFooting'].includes(member) || typeof value !== 'number' || !(value > 0)) {
         throw new Error(`부재별 fck 값이 맞지 않습니다 (${member}: ${String(value)}).`);
       }
     }
diff --git a/src/core/rebar/common.ts b/src/core/rebar/common.ts
index c0e25df..48e4576 100644
--- a/src/core/rebar/common.ts
+++ b/src/core/rebar/common.ts
@@ -84,15 +84,15 @@ export function materialFrom(raw: unknown): Material {
 }
 
 /** Members that can take their own fck on ② (부재 카드). Other members always use the 공통 fck. */
-export type FckMember = 'column' | 'coping' | 'footing';
+export type FckMember = 'column' | 'coping' | 'footing' | 'abutFooting';
 /** The members of {@link FckMember}, for the ② cards. */
-export const FCK_MEMBERS: readonly FckMember[] = ['column', 'coping', 'footing'];
+export const FCK_MEMBERS: readonly FckMember[] = ['column', 'coping', 'footing', 'abutFooting'];
 
 /** Per-member fck (MPa). A member without an entry uses the ③ 공통 설정 fck. */
 export type FckByMember = Partial<Record<FckMember, number>>;
 
-/** 교각도 기준 부재별 기본 fck (MPa). 되돌리기는 이 값으로 돌아가고, 이 값과 다르면 주황색으로 표시합니다. */
-export const IMPORTED_FCK: Record<FckMember, number> = { column: 40, coping: 40, footing: 27 };
+/** 교각도 · 교대도 기준 부재별 기본 fck (MPa). 되돌리기는 이 값으로 돌아가고, 이 값과 다르면 주황색으로 표시합니다. 교대 저판 27 (spec_abut §6, 2026-11-03). */
+export const IMPORTED_FCK: Record<FckMember, number> = { column: 40, coping: 40, footing: 27, abutFooting: 27 };
 
 /** True when the member's fck is set and differs from its imported default. An unset member is not changed. */
 export function fckChanged(byMember: FckByMember, member: FckMember): boolean {
diff --git a/src/main.ts b/src/main.ts
index c300711..fe8d2c2 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -109,7 +109,7 @@ import { choose, defaultSummary, isSelectable, SHAPE_GROUPS, UNDEFINED_REASON, t
 import { parseProject, SCHEMA_VERSION, serializeProject, type ProjectFile, type ProjectInfo } from './core/project';
 import { clearBackup, readBackup, writeBackup, type Backup } from './view/backup';
 import type { Issue, PierInput, PierType, StrataRow } from './core/types';
-import { buildPierScene, setRebarView, viewPosition, type PartName, type PierScene, type ViewKind } from './view/scene';
+import { buildPierScene, setRebarView, setRebarViewOn, viewPosition, type PartName, type PierScene, type ViewKind } from './view/scene';
 import { buildAllPiers, type AllPiers } from './view/all-piers';
 import { buildTerrainMapGroup, disposeTerrainMapGroup, setTerrainMapMode } from './view/terrain-map';
 
@@ -631,6 +631,7 @@ function setupScene(): void {
           const member = group.getObjectByName(name);
           if (member) member.visible = on;
         }
+        setRebarViewOn(group, state.stage === 'rebar');
         abutGroups.push(group);
         abutGroupByName.set(rec.name, group);
         world.add(group);
@@ -1486,6 +1487,18 @@ function fillAbutFootingExtras(
   auto('길이 (자동)', `${L.toFixed(3)} m`, '교좌면 길이 (skew)');
   auto('말뚝 길이', `${Math.round(rec.pileLengthMm)} mm`, '① 기본 정보에서 수정');
   auto('선단 EL (자동)', built.members.pileBottomEl === undefined ? '—' : `${built.members.pileBottomEl.toFixed(3)} m`, '= 기초 하단 − 말뚝 길이');
+  // 교대 저판 fck: 교각 기초 fck와 따로 둔다 (사용자 결정 2026-11-04). 비우면 기본값으로 돌아간다.
+  const fckId = idOf('fck');
+  const fckLab = el('label', 'fck (MPa)');
+  fckLab.htmlFor = fckId;
+  const fckIn = el('input');
+  fckIn.id = fckId;
+  fckIn.type = 'number';
+  fckIn.step = 'any';
+  fckIn.value = String(state.fckByMember.abutFooting ?? state.material.fck);
+  if (fckChanged(state.fckByMember, 'abutFooting')) fckIn.classList.add('changed-input');
+  fckIn.addEventListener('change', () => setMemberFck('abutFooting', fckIn.value));
+  box.append(fckLab, fckIn, el('span', `기본 ${IMPORTED_FCK.abutFooting} · 교각 기초와 별도 · 배근에만 반영`, 'muted small'));
   // 열 위치 (배면부터): "650 · 2000 · 1300 · 650". The last one (전면 연단) follows from the 폭.
   const id = idOf('pile-rows');
   const lab = el('label', '열 위치 · 배면부터 (mm)');
@@ -2549,6 +2562,7 @@ function setStage(stage: Stage): void {
   // Entering or leaving ② changes which objects are drawn (visibility.ts), so the scene is rebuilt then.
   if ((allPiers !== null) !== multiSceneOn() || stage === 'plan' || previous === 'plan') setupScene();
   if (state.scene) setRebarView(state.scene, stage === 'rebar');
+  for (const g of abutGroups) setRebarViewOn(g, stage === 'rebar');
   $<HTMLElement>('view-shape').hidden = stage !== 'shape';
   $<HTMLElement>('view-plan').hidden = stage !== 'plan';
   $<HTMLElement>('view-rebar').hidden = stage !== 'rebar';
@@ -3083,7 +3097,7 @@ function abutFootingBuilt(rec: AbutRecord): { geom: AbutFootingGeom; result: Abu
     const model = buildAbut(toAbutInput(rec));
     const members = buildMembers(model, { bottomEl: rec.foundationBottomEl, pileLengthMm: rec.pileLengthMm }, rec.shape);
     const geom = abutFootingGeom(model.length, members.shape, skewAngle(rec.skewDeg));
-    const result = abutFootingRebar(geom, rec.rebar?.footing, materialFor(state.material, state.fckByMember, 'footing'), rec.name);
+    const result = abutFootingRebar(geom, rec.rebar?.footing, materialFor(state.material, state.fckByMember, 'abutFooting'), rec.name);
     return { geom, result, skewK: abutSkewK(model) };
   } catch {
     return null;
@@ -3273,7 +3287,7 @@ function fillAbutFootingRebarCard(box: HTMLDivElement, rec: AbutRecord, built: {
     grid2.append(cell);
   }
   // 자동 값.
-  const fck = materialFor(state.material, state.fckByMember, 'footing').fck;
+  const fck = materialFor(state.material, state.fckByMember, 'abutFooting').fck;
   const fy = (size: string) => fyOf(state.material, size);
   const auto = (label: string, value: string) => {
     const cell = el('div', undefined, 'abut-rebar-auto');
diff --git a/src/view/scene.ts b/src/view/scene.ts
index f468267..c94ba0f 100644
--- a/src/view/scene.ts
+++ b/src/view/scene.ts
@@ -208,17 +208,21 @@ const REBAR_VIEW_ALPHA = 0.5;
 
 /** Turns the ③ rebar view on or off. Off restores each part's own opacity. Depth writes stop while on, so bars behind a member stay visible. */
 export function setRebarView(scene: PierScene, on: boolean): void {
-  for (const group of Object.values(scene.parts)) {
-    group.traverse((o) => {
-      if (!(o instanceof THREE.Mesh)) return;
-      const mat = o.material as THREE.MeshStandardMaterial;
-      const base = mat.userData.baseOpacity as number;
-      mat.opacity = on ? REBAR_VIEW_ALPHA : base;
-      mat.transparent = on || base < 1;
-      mat.depthWrite = !on;
-      mat.needsUpdate = true;
-    });
-  }
+  for (const group of Object.values(scene.parts)) setRebarViewOn(group, on);
+}
+
+/** {@link setRebarView} for any group (교대 3D). A material without a recorded base opacity takes its current one as the base. */
+export function setRebarViewOn(root: THREE.Object3D, on: boolean): void {
+  root.traverse((o) => {
+    if (!(o instanceof THREE.Mesh)) return;
+    const mat = o.material as THREE.MeshStandardMaterial;
+    mat.userData.baseOpacity ??= mat.opacity;
+    const base = mat.userData.baseOpacity as number;
+    mat.opacity = on ? REBAR_VIEW_ALPHA : base;
+    mat.transparent = on || base < 1;
+    mat.depthWrite = !on && base >= 1;
+    mat.needsUpdate = true;
+  });
 }
 
 export type ViewKind = 'iso' | 'front' | 'side' | 'top';
diff --git a/tests/abut-scene.test.ts b/tests/abut-scene.test.ts
index 8fff2b3..0924a4f 100644
--- a/tests/abut-scene.test.ts
+++ b/tests/abut-scene.test.ts
@@ -8,6 +8,7 @@ import { parseAbutments, toAbutInput } from '../src/core/abut/parse';
 import { buildMembers } from '../src/core/abut/members';
 import { buildWings } from '../src/core/abut/wings';
 import { abutPlacement, buildAbutGroup, cameraForBox, covers } from '../src/view/abut-scene';
+import { setRebarViewOn } from '../src/view/scene';
 import type { TerrainGrid } from '../src/core/ground-model';
 
 const RAG = fileURLToPath(new URL('../../../RAG/운곡교P1입력.xlsx', import.meta.url));
@@ -132,3 +133,37 @@ describe('교대 선택 시 카메라', () => {
     expect(cam.position.distanceTo(cam.target)).toBeGreaterThan(12);
   });
 });
+
+describe('③ 배근 보기 반투명 (교각과 같음, 2026-11-04)', () => {
+  const g = buildAbutGroup(model, members, wings, undefined, GROUND_EL);
+  const mats = () => {
+    const out: THREE.MeshStandardMaterial[] = [];
+    g.traverse((o) => {
+      if (o instanceof THREE.Mesh) out.push(o.material as THREE.MeshStandardMaterial);
+    });
+    return out;
+  };
+  const ground = () => (g.getObjectByName('ground') as THREE.Group).children[0] as THREE.Mesh;
+
+  it('turns every member and the ground to half opacity with depth writes off', () => {
+    setRebarViewOn(g, true);
+    for (const m of mats()) {
+      expect(m.opacity).toBe(0.5);
+      expect(m.transparent).toBe(true);
+      expect(m.depthWrite).toBe(false);
+    }
+  });
+
+  it('restores each part: members opaque, the ground at 0.35 without depth writes', () => {
+    setRebarViewOn(g, false);
+    const groundMat = ground().material as THREE.MeshStandardMaterial;
+    for (const m of mats()) {
+      if (m === groundMat) continue;
+      expect(m.opacity).toBe(1);
+      expect(m.transparent).toBe(false);
+      expect(m.depthWrite).toBe(true);
+    }
+    expect(groundMat.opacity).toBe(0.35);
+    expect(groundMat.depthWrite).toBe(false);
+  });
+});
diff --git a/tests/member-fck.test.ts b/tests/member-fck.test.ts
index c71cbf0..35108bc 100644
--- a/tests/member-fck.test.ts
+++ b/tests/member-fck.test.ts
@@ -1,15 +1,15 @@
 import { describe, expect, it } from 'vitest';
-import { fckChanged, IMPORTED_FCK } from '../src/core/rebar/common';
+import { DEFAULT_MATERIAL, fckChanged, IMPORTED_FCK, materialFor } from '../src/core/rebar/common';
 
-describe('IMPORTED_FCK (교각도 기준 부재별 기본 fck)', () => {
-  it('is 40 for 기둥·코핑 and 27 for 확대기초', () => {
-    expect(IMPORTED_FCK).toEqual({ column: 40, coping: 40, footing: 27 });
+describe('IMPORTED_FCK (교각도 · 교대도 기준 부재별 기본 fck)', () => {
+  it('is 40 for 기둥·코핑, 27 for 확대기초 and 27 for 교대 저판', () => {
+    expect(IMPORTED_FCK).toEqual({ column: 40, coping: 40, footing: 27, abutFooting: 27 });
   });
 });
 
 describe('fckChanged (기본과 다르면 주황색)', () => {
   it('is false at the imported default', () => {
-    expect(fckChanged({ column: 40, coping: 40, footing: 27 }, 'coping')).toBe(false);
+    expect(fckChanged({ column: 40, coping: 40, footing: 27, abutFooting: 27 }, 'coping')).toBe(false);
   });
 
   it('is true when the member differs from its imported default', () => {
@@ -21,3 +21,15 @@ describe('fckChanged (기본과 다르면 주황색)', () => {
     expect(fckChanged({}, 'column')).toBe(false);
   });
 });
+
+describe('교대 저판 fck (교각 기초와 별도, 2026-11-04)', () => {
+  it('follows abutFooting, not the pier footing', () => {
+    const byMember = { footing: 30, abutFooting: 35 };
+    expect(materialFor(DEFAULT_MATERIAL, byMember, 'abutFooting').fck).toBe(35);
+    expect(materialFor(DEFAULT_MATERIAL, byMember, 'footing').fck).toBe(30);
+  });
+
+  it('falls back to the 공통 fck when unset (old project files)', () => {
+    expect(materialFor({ ...DEFAULT_MATERIAL, fck: 24 }, { footing: 30 }, 'abutFooting').fck).toBe(24);
+  });
+});