diff --git a/PROGRESS.md b/PROGRESS.md
index 600df4c..3e75ac0 100644
--- a/PROGRESS.md
+++ b/PROGRESS.md
@@ -12,6 +12,11 @@
 ## 타임라인
 
 ### 2026-04-15 (계속)
+- code — Sprint 35: IFC 뷰어 통합 + Pset_BeamCommon.
+  - `cimery-viewer` 에 `cimery-ifc` 의존성 추가. `project_file::scene_params_to_ifc()` 변환 함수 (SceneParams → BridgeExportParams 전 필드 매핑).
+  - 프로젝트 섹션에 "📤 IFC4X3 익스포트" 버튼. `projects/bridge.ifc` 로 저장, 현재 파라미터(경간 수·교각 형식·skew·헌치·단면 등) 그대로 반영.
+  - `write_pset_beam_common()` 추가: Reference(이름) + Span(mm) + LoadBearing + IsExternal 4 속성, `IFCRELDEFINESBYPROPERTIES` 로 거더 각 beam 에 연결.
+  - `IfcSectionKind` public re-export. 테스트 17개 통과.
 - code — Sprint 34: IFC4X3 Add2 익스포터 Phase 2. 정확도·커버리지 확장.
   - PSC-I 실제 14점 단면 `IFCARBITRARYCLOSEDPROFILEDEF` + `IFCPOLYLINE` 구현 (도심 중심화 Y 평행이동). `IfcSectionKind` enum 으로 단면 종류 분기.
   - Skew 회전 `write_local_placement_skewed()`: `IFCAXIS2PLACEMENT3D` RefDirection 을 Y축 회전 X축으로 설정. 교대·피어·받침·신축이음에 적용. 거더·데크는 직선 유지.
diff --git a/cimery/crates/ifc/src/bridge_export.rs b/cimery/crates/ifc/src/bridge_export.rs
index 2fbdbfe..75c2587 100644
--- a/cimery/crates/ifc/src/bridge_export.rs
+++ b/cimery/crates/ifc/src/bridge_export.rs
@@ -154,16 +154,19 @@ pub fn export_bridge(p: &BridgeExportParams) -> String {
             let profile = write_girder_profile(&mut w, p.section_kind, p.girder_height);
             let shape = write_extrude_shape(&mut w, geom_ctx, profile, span_mm);
             let beam = w.alloc();
+            let girder_label = format!("Girder S{}-G{}", s + 1, i + 1);
             w.emit(
                 beam,
                 &format!(
                     "IFCBEAM({},$,{},$,$,{},{},$,.BEAM.)",
                     lit(&new_ifc_guid()),
-                    lit(&format!("Girder S{}-G{}", s + 1, i + 1)),
+                    lit(&girder_label),
                     placement,
                     shape,
                 ),
             );
+            // Pset_BeamCommon (Sprint 35).
+            write_pset_beam_common(&mut w, beam, &girder_label, span_mm);
             elements.push(beam);
         }
     }
@@ -438,6 +441,46 @@ fn write_girder_profile(
     }
 }
 
+/// Pset_BeamCommon 생성 + `IfcRelDefinesByProperties` 로 beam 에 연결 (Sprint 35 Phase 3a).
+///
+/// # 속성
+/// - `Reference`: 거더 식별자 (프로젝트별 시퀀스)
+/// - `Span`: 경간 길이 [mm] — IfcLengthMeasure
+/// - `LoadBearing`: `.T.` (true)
+/// - `IsExternal`: `.F.`
+fn write_pset_beam_common(
+    w: &mut IfcWriter,
+    beam: Ref,
+    reference: &str,
+    span_mm: f64,
+) {
+    let p_ref = w.write(&format!(
+        "IFCPROPERTYSINGLEVALUE('Reference',$,IFCIDENTIFIER({}),$)",
+        lit(reference),
+    ));
+    let p_span = w.write(&format!(
+        "IFCPROPERTYSINGLEVALUE('Span',$,IFCLENGTHMEASURE({}),$)",
+        real(span_mm),
+    ));
+    let p_lb = w.write(
+        "IFCPROPERTYSINGLEVALUE('LoadBearing',$,IFCBOOLEAN(.T.),$)",
+    );
+    let p_ext = w.write(
+        "IFCPROPERTYSINGLEVALUE('IsExternal',$,IFCBOOLEAN(.F.),$)",
+    );
+    let pset = w.write(&format!(
+        "IFCPROPERTYSET({},$,'Pset_BeamCommon',$,{})",
+        lit(&new_ifc_guid()),
+        ref_list(&[p_ref, p_span, p_lb, p_ext]),
+    ));
+    w.write(&format!(
+        "IFCRELDEFINESBYPROPERTIES({},$,$,$,({}),{})",
+        lit(&new_ifc_guid()),
+        beam,
+        pset,
+    ));
+}
+
 /// Skew 회전 + 평행이동 LocalPlacement — 지점부 요소(교대·피어·받침·joint)에 적용.
 /// skew_rad 는 Y축 중심 회전, pivot_z 기준 반지름 오프셋은 placement origin 에 반영.
 fn write_local_placement_skewed(
@@ -568,6 +611,16 @@ mod tests {
         assert_ne!(zero, skewed);
     }
 
+    #[test]
+    fn pset_beam_common_attached_to_girders() {
+        let ifc = export_bridge(&BridgeExportParams::default());
+        assert!(ifc.contains("IFCPROPERTYSET"), "no Pset emitted");
+        assert!(ifc.contains("'Pset_BeamCommon'"), "Pset name missing");
+        assert!(ifc.contains("IFCRELDEFINESBYPROPERTIES"), "Pset not attached");
+        assert!(ifc.contains("LoadBearing"));
+        assert!(ifc.contains("Span"));
+    }
+
     #[test]
     fn haunch_moves_deck_up() {
         // haunch 0 vs 200 → deck slab 중심 Y 위치가 다름. ifc text diff 로 확인.
diff --git a/cimery/crates/ifc/src/lib.rs b/cimery/crates/ifc/src/lib.rs
index 7fb73a6..e18e04e 100644
--- a/cimery/crates/ifc/src/lib.rs
+++ b/cimery/crates/ifc/src/lib.rs
@@ -27,5 +27,5 @@ pub mod writer;
 pub mod guid;
 pub mod bridge_export;
 
-pub use bridge_export::{BridgeExportParams, export_bridge};
+pub use bridge_export::{BridgeExportParams, IfcSectionKind, export_bridge};
 pub use writer::IfcWriter;
diff --git a/cimery/crates/viewer/Cargo.toml b/cimery/crates/viewer/Cargo.toml
index 8f97013..9a95d87 100644
--- a/cimery/crates/viewer/Cargo.toml
+++ b/cimery/crates/viewer/Cargo.toml
@@ -19,6 +19,7 @@ path = "src/main.rs"
 
 [dependencies]
 cimery-kernel = { workspace = true }
+cimery-ifc    = { workspace = true }
 log           = { workspace = true }
 env_logger    = { workspace = true }
 wgpu          = "22"
diff --git a/cimery/crates/viewer/src/lib.rs b/cimery/crates/viewer/src/lib.rs
index 779976f..854b0ea 100644
--- a/cimery/crates/viewer/src/lib.rs
+++ b/cimery/crates/viewer/src/lib.rs
@@ -764,6 +764,18 @@ impl RenderState {
                                     }
                                 }
                             });
+                            // Sprint 35: IFC4X3 Add2 익스포트 (현재 파라미터 기준).
+                            if ui.button("📤 IFC4X3 익스포트").clicked() {
+                                let params = project_file::scene_params_to_ifc(&p, "bridge");
+                                let ifc = cimery_ifc::export_bridge(&params);
+                                let path = project_file::default_ifc_path("bridge");
+                                match std::fs::write(&path, &ifc) {
+                                    Ok(_) => log::info!(
+                                        "IFC exported: {:?} ({} bytes)", path, ifc.len()
+                                    ),
+                                    Err(e) => log::error!("IFC export failed: {e}"),
+                                }
+                            }
                         });
 
                     ui.separator();
diff --git a/cimery/crates/viewer/src/project_file.rs b/cimery/crates/viewer/src/project_file.rs
index 5f61b0d..a5986d7 100644
--- a/cimery/crates/viewer/src/project_file.rs
+++ b/cimery/crates/viewer/src/project_file.rs
@@ -131,3 +131,37 @@ pub fn default_save_path(name: &str) -> std::path::PathBuf {
     p.push(format!("{}.cimery.json", name));
     p
 }
+
+/// IFC 파일 기본 저장 경로.
+pub fn default_ifc_path(name: &str) -> std::path::PathBuf {
+    let mut p = std::path::PathBuf::from("projects");
+    std::fs::create_dir_all(&p).ok();
+    p.push(format!("{}.ifc", name));
+    p
+}
+
+/// SceneParams → cimery-ifc::BridgeExportParams 변환.
+///
+/// viewer 의 SceneParams 에 있는 모든 파라미터를 IFC 익스포터 입력으로 매핑.
+/// 선형(alignment)·camber 는 IFC Phase 3 로드맵(미반영).
+pub fn scene_params_to_ifc(p: &SceneParams, name: &str) -> cimery_ifc::BridgeExportParams {
+    use cimery_ifc::{BridgeExportParams, IfcSectionKind};
+    BridgeExportParams {
+        name:           name.to_owned(),
+        span_m:         p.span_m,
+        span_count:     p.span_count,
+        girder_count:   p.girder_count,
+        girder_spacing: p.girder_spacing as f64,
+        girder_height:  p.girder_height as f64,
+        slab_thickness: p.slab_thickness as f64,
+        bearing_height: 60.0,
+        section_kind:   match p.section_type {
+            GirderSectionType::PscI     => IfcSectionKind::PscI,
+            GirderSectionType::SteelBox => IfcSectionKind::SteelBox,
+        },
+        skew_deg:       p.skew_deg as f64,
+        haunch_depth:   p.haunch_depth as f64,
+        show_parapets:  true,
+        show_joints:    p.show_expansion_joints,
+    }
+}