diff --git a/src/core/bearing-pair.ts b/src/core/bearing-pair.ts
new file mode 100644
index 0000000..fc692f6
--- /dev/null
+++ b/src/core/bearing-pair.ts
@@ -0,0 +1,115 @@
+/**
+ * 거더 짝 받침 · 종단경사 S · 솔플레이트 열 두께 (결정 2026-11-06, RAG/받침방위각_솔플레이트검토.md §3, Q-SH1·4·8·9).
+ * Pure. Not wired into the model yet: the height rule (Q-SH7, 블럭 상면 = z − (T − T_ref)) conflicts with the 2026-11-03
+ * C안 already in use (받침높이 H 고정, h3 = H − T, src/core/solplate-rule.ts), so only the parts both rules need live here.
+ *
+ * Frame: (E, N) in m as in the model (x = E, y = N). Azimuth: the model's 진북 방위각 (deg, clockwise from north), i.e. the
+ * workbook CAD angle θ_CAD converted by 90 − θ_CAD. A girder at azimuth θ runs along (sin θ, cos θ).
+ */
+
+export interface PairBearing {
+  no: number;
+  x: number;
+  y: number;
+  /** z (EL m). Q-SH5: both ends on the 받침블럭 상면 basis; the pier z definition is still spec Q16. */
+  z: number;
+  azimuthDeg: number;
+}
+
+export interface PairStructure {
+  name: string;
+  bearings: PairBearing[];
+}
+
+/** Q-SH1 tolerances and the Q-SH4 azimuth check. */
+export const PAIR_AZIMUTH_TOL_DEG = 0.1;
+export const PAIR_OFFSET_TOL_M = 0.1;
+export const AZIMUTH_CHECK_SEC = 10;
+
+export type PairWarning = 'WS01' | 'WS04';
+
+export interface BearingPair {
+  /** The bearing on structure k and its partner on structure k + 1 (structure order A1, P1 … Pn, A2). */
+  from: { structure: string; no: number };
+  to: { structure: string; no: number };
+  /** Horizontal distance (m), distance off the girder line of `from` (m), azimuth difference |θ_to − θ_from| (deg). */
+  distanceM: number;
+  offsetM: number;
+  azimuthDiffDeg: number;
+  /** Direction from → to as an azimuth (deg), and its difference from each input azimuth (arc seconds). */
+  directionDeg: number;
+  fromCheckSec: number;
+  toCheckSec: number;
+  /** S = (z_to − z_from) / distance × 100 (%), sign along the structure order (− = lower towards the later structure). */
+  slopePct: number;
+  /** The structure on the higher end: the 오르막 쪽 where T1 sits for both bearings. */
+  uphill: string;
+  warnings: PairWarning[];
+}
+
+const DEG = Math.PI / 180;
+const angleDiffDeg = (a: number, b: number) => Math.abs(((a - b + 540) % 360) - 180);
+
+/**
+ * Girder pairs between neighbouring structures (Q-SH1, Q-SH4). For each bearing b on structure k the candidates on k + 1 lie
+ * ahead along b's azimuth, within 0.1° of its azimuth and 0.1 m of its girder line; the closest to the line is the pair
+ * (WS04 when there were two or more). WS01 when either input azimuth is more than 10″ from the pair direction.
+ */
+export function girderPairs(structures: PairStructure[]): BearingPair[] {
+  const pairs: BearingPair[] = [];
+  for (let k = 0; k + 1 < structures.length; k++) {
+    const here = structures[k], next = structures[k + 1];
+    for (const b of here.bearings) {
+      const u = { e: Math.sin(b.azimuthDeg * DEG), n: Math.cos(b.azimuthDeg * DEG) };
+      const candidates = next.bearings.map((c) => {
+        const d = { e: c.x - b.x, n: c.y - b.y };
+        return { c, along: d.e * u.e + d.n * u.n, offset: Math.abs(d.e * u.n - d.n * u.e), dAz: angleDiffDeg(c.azimuthDeg, b.azimuthDeg), d };
+      }).filter((t) => t.along > 0 && t.dAz <= PAIR_AZIMUTH_TOL_DEG && t.offset <= PAIR_OFFSET_TOL_M)
+        .sort((p, q) => p.offset - q.offset);
+      if (!candidates.length) continue;
+      const best = candidates[0];
+      const distanceM = Math.hypot(best.d.e, best.d.n);
+      const directionDeg = (Math.atan2(best.d.e, best.d.n) / DEG + 360) % 360;
+      const fromCheckSec = angleDiffDeg(directionDeg, b.azimuthDeg) * 3600;
+      const toCheckSec = angleDiffDeg(directionDeg, best.c.azimuthDeg) * 3600;
+      const slopePct = ((best.c.z - b.z) / distanceM) * 100;
+      const warnings: PairWarning[] = [];
+      if (fromCheckSec > AZIMUTH_CHECK_SEC || toCheckSec > AZIMUTH_CHECK_SEC) warnings.push('WS01');
+      if (candidates.length > 1) warnings.push('WS04');
+      pairs.push({
+        from: { structure: here.name, no: b.no }, to: { structure: next.name, no: best.c.no },
+        distanceM, offsetM: best.offset, azimuthDiffDeg: best.dAz, directionDeg, fromCheckSec, toCheckSec,
+        slopePct, uphill: best.c.z > b.z ? next.name : here.name, warnings,
+      });
+    }
+  }
+  return pairs;
+}
+
+/** The pair a bearing belongs to, on either end; undefined when it has none (then WS03 with a fallback S, not done here). */
+export function pairOf(pairs: BearingPair[], structure: string, no: number): BearingPair | undefined {
+  return pairs.find((p) => (p.from.structure === structure && p.from.no === no) || (p.to.structure === structure && p.to.no === no));
+}
+
+/** Smallest allowed thin-end thickness T_min (mm, Q-SH3). */
+export const SOLE_T_MIN_MM = 22;
+
+/** Thickness one bearing needs: T_req = T_min + L·|S|/2 (L mm, S %). */
+export function soleRequiredT(lengthMm: number, slopePct: number, tMinMm: number = SOLE_T_MIN_MM): number {
+  return tMinMm + (lengthMm * Math.abs(slopePct)) / 200;
+}
+
+/**
+ * Row thickness and end thicknesses (Q-SH8·9): T_row = max(T_min, ⌈max T_req⌉) over the row; per bearing
+ * T1 = round(T_row + L·|S|/2) on the 오르막 쪽 and T2 = round(T_row − L·|S|/2) (≥ T_min by construction).
+ */
+export function soleRowThickness(items: { lengthMm: number; slopePct: number }[], tMinMm: number = SOLE_T_MIN_MM) {
+  const T = Math.max(tMinMm, Math.ceil(Math.max(...items.map((i) => soleRequiredT(i.lengthMm, i.slopePct, tMinMm))) - 1e-9));
+  return {
+    T,
+    ends: items.map((i) => {
+      const half = (i.lengthMm * Math.abs(i.slopePct)) / 200;
+      return { T1: Math.round(T + half), T2: Math.round(T - half) };
+    }),
+  };
+}
diff --git a/tests/bearing-pair.test.ts b/tests/bearing-pair.test.ts
new file mode 100644
index 0000000..c400b0c
--- /dev/null
+++ b/tests/bearing-pair.test.ts
@@ -0,0 +1,71 @@
+import { readFileSync } from 'node:fs';
+import { fileURLToPath } from 'node:url';
+import * as XLSX from 'xlsx';
+import { describe, expect, it } from 'vitest';
+import { parseAbutments } from '../src/core/abut/parse';
+import { girderPairs, pairOf, type PairStructure, soleRowThickness } from '../src/core/bearing-pair';
+import { loadP1 } from './helpers';
+
+// RAG/받침방위각_솔플레이트검토.md §2 · §6 (Q-SH1·4·8·9). A1 from the RAG workbook's Abut sheet, P1 from the same input.
+const RAG = fileURLToPath(new URL('../../../RAG/운곡교P1입력.xlsx', import.meta.url));
+const a1 = parseAbutments(XLSX.read(readFileSync(RAG), { type: 'buffer' })).abutments[0];
+const A1: PairStructure = { name: 'A1', bearings: a1.bearings.map((b) => ({ no: b.no, x: b.pos.e, y: b.pos.n, z: b.z, azimuthDeg: b.azimuthDeg! })) };
+const p1 = loadP1();
+const P1: PairStructure = { name: 'P1', bearings: p1.bearings.map((b) => ({ no: b.no, x: b.x, y: b.y, z: b.z, azimuthDeg: b.azimuthDeg })) };
+
+describe('거더 짝 받침 · 종단경사 S (Q-SH1·4·5)', () => {
+  const pairs = girderPairs([A1, P1]);
+
+  it('pairs A1 ①–⑤ with P1 ①–⑤ on the girder line (offset 0.000 m, azimuth difference ≤ 0.1″)', () => {
+    expect(pairs.map((p) => [p.from.no, p.to.no])).toEqual([[1, 1], [2, 2], [3, 3], [4, 4], [5, 5]]);
+    for (const p of pairs) {
+      expect(p.offsetM).toBeLessThan(0.0005);
+      expect(p.fromCheckSec).toBeLessThanOrEqual(0.5);
+      expect(p.distanceM).toBeCloseTo(48.791, 3);
+      expect(p.warnings).toEqual([]);
+    }
+  });
+
+  it('S = −1.908 / −1.906 / −1.904 / −1.904 / −1.902 % (상세도 −1.910 … −1.901, ≤ 0.002 %), A1 is the 오르막 쪽', () => {
+    expect(pairs.map((p) => p.slopePct.toFixed(3))).toEqual(['-1.908', '-1.906', '-1.904', '-1.904', '-1.902']);
+    const drawing = [-1.910, -1.907, -1.905, -1.903, -1.901];
+    pairs.forEach((p, i) => expect(Math.abs(p.slopePct - drawing[i])).toBeLessThanOrEqual(0.0025));
+    expect(pairs.every((p) => p.uphill === 'A1')).toBe(true);
+  });
+
+  it('P1 back row ⑥–⑩ (next span, P2 not in the workbook) has no pair', () => {
+    for (const no of [6, 7, 8, 9, 10]) expect(pairOf(pairs, 'P1', no)).toBeUndefined();
+    expect(pairOf(pairs, 'P1', 3)!.from).toEqual({ structure: 'A1', no: 3 });
+  });
+
+  it('WS01: P1 ③ azimuth typed as 75°59′ (CAD) is kept but flagged', () => {
+    const typo: PairStructure = { ...P1, bearings: P1.bearings.map((b) => (b.no === 3 ? { ...b, azimuthDeg: 90 - (75 + 59 / 60) } : b)) };
+    const p = girderPairs([A1, typo]).find((q) => q.to.no === 3)!;
+    expect(p.warnings).toContain('WS01');
+    expect(p.toCheckSec).toBeGreaterThan(10);
+    expect(girderPairs([A1, typo]).filter((q) => q.to.no !== 3).every((q) => !q.warnings.includes('WS01'))).toBe(true);
+  });
+
+  it('WS04: two candidates within tolerance → the closest to the girder line is used', () => {
+    const b1 = P1.bearings[0];
+    const extra = { ...b1, no: 99, x: b1.x + 0.05 * Math.cos(b1.azimuthDeg * Math.PI / 180), y: b1.y - 0.05 * Math.sin(b1.azimuthDeg * Math.PI / 180) };
+    const p = girderPairs([A1, { ...P1, bearings: [...P1.bearings, extra] }]).find((q) => q.from.no === 1)!;
+    expect(p.warnings).toContain('WS04');
+    expect(p.to.no).toBe(1);
+  });
+});
+
+describe('솔플레이트 열 두께 (Q-SH3·8·9, L 800)', () => {
+  it('S 1.908 % → T 30, T1 38 / T2 22 (P1 상세도)', () => {
+    expect(soleRowThickness([{ lengthMm: 800, slopePct: -1.908 }])).toEqual({ T: 30, ends: [{ T1: 38, T2: 22 }] });
+  });
+  it('S 3 % → T 34, T1 46 / T2 22; S 0 → T 22', () => {
+    expect(soleRowThickness([{ lengthMm: 800, slopePct: 3 }])).toEqual({ T: 34, ends: [{ T1: 46, T2: 22 }] });
+    expect(soleRowThickness([{ lengthMm: 800, slopePct: 0 }]).T).toBe(22);
+  });
+  it('one T per row: the largest requirement wins, the flatter bearing gets a thicker T2', () => {
+    const row = soleRowThickness([{ lengthMm: 800, slopePct: 3 }, { lengthMm: 800, slopePct: 1 }]);
+    expect(row.T).toBe(34);
+    expect(row.ends[1]).toEqual({ T1: 38, T2: 30 });
+  });
+});