以社會住宅案例探討結構減碳設計策略

Abstract

本研究以我國三個公共工程社會住宅新建案例（TA14、NT17、TY17）為主要研究對象，旨在比較內政部建築研究所「低蘊含碳建築評估系統」（LEBR）主結構標準計算法與本研究之「設計估算碳排計算法」（參考公共工程經費電腦估價系統 PCCES 原則）所計算的地上層主結構蘊含碳排放量。研究過程中，蒐集各案例之結構設計參數、材料用量及強度規格，並探討新版設計規範下建築設計變因（如平面形狀、周長面積比、長寬比、出挑係數、跨距變化）對碳排放的影響。主要發現如下： 1.評估方法結果之差異與限制： 新建案例（新版規範，2023年）： 針對依新版規範（2023年混凝土結構設計規範）設計的三個新建案例，本研究設計估算碳排計算法的結果普遍顯著高於 LEBR 基準值，呈現「增碳」現象 [3, 7, 96 (表 4.6)]。此現象反映 LEBR 簡化公式未能充分反映因新版規範提升混凝土強度及箍筋配置所致的實際材料用量變動。 低碳混凝土效益評估： LEBR 公式法將低碳混凝土減碳效益固定為 5%-6%，而本研究設計估算法則顯示其在新建案例中可實現約 11%至 24% 的減碳效益 [106 (表 4.13), 108 (表 4.16), 111 (表 4.19)]。這凸顯了 LEBR 簡化公式在反映實際材料優化精確減碳幅度上的局限性。 2 樓層碳排趨勢： 本研究的三個新建案例均顯示，底層承載最大荷重導致碳排最高；樓層越高，結構愈輕，碳排則愈低。此趨勢與既有研究相符 [138, 5.1.3.a]。 3. 幾何設計變因之評估困境： 由於樣本數量（三個案例）有限，且各案例涵蓋不同混凝土強度級配、相異地質與施工限制，導致存在大量不可控變因。因此，針對平面形狀（周長面積比、長寬比）及平面出挑係數與碳排放量之間的關係，未能形成清晰的線性或規律性趨勢，也無法直接推導新的經驗公式 [179, 5.1.3.b]。 4. 實務減碳策略： 透過案例分析與結構技師訪談，本研究歸納出四項具體且經實務驗證有效的結構減碳策略 [138, 5.1.3.c]： 強度分層配置：依樓層調整混凝土強度，例如底層使用 5,000–10,000 psi 高強度混凝土，上層維持 4,000 psi，以縮減柱、梁斷面 [125, 138 (5.1.3.c)]。 構件尺寸精實：優化梁柱斷面，配合統一模矩，避免因施工便利性而留有過大裕度 [126, 138 (5.1.3.c)]。 結構系統優化：在中高層建築中加入剪力牆或斜撐以轉移彎矩，減少梁筋與梁高；或在多棟相連大樓設置伸縮縫分棟 [124, 128, 138 (5.1.3.c)]。 鋼筋配筋上限管制：控制柱筋配比在 3% 以內、梁筋在 2% 以內，並利用 SD490W 等高強度鋼筋替代 SD420，可將同一截面鋼量降低 10%～15% [126, 138 (5.1.3.c)]。 本研究建議： 1.雙軌管控評估： 建議設計初期可採用 LEBR 進行快速減碳率評估，但需理解其為簡化公式，不宜作為單一案件實際減碳成果的絕對依據 [179, 5.1.1]；細部設計階段應同步搭配設計估算碳排計算法精算碳排量，以獲取更精確的實際碳排數據並進行雙軌管控 [179, 5.1.1]。 2.更新 LEBR 公式： 建議更新 LEBR 公式，納入多規格混凝土碳排係數並加強對新版規範中鋼筋配置影響的修正 [184, 5.2.3]。 3.制定動態蘊含碳基準值： 借鏡丹麥動態修訂機制 [139, 5.2.2]，建議由內政部、公共工程會及建研所共同主導，定期以 PCCES 真實工程數據與本研究計算法輸出為樣本，建立並動態更新我國蘊含碳基準值 [139, 5.2.2]。 4.開發通用評估工具： 建議整合 BIM 技術與 PCCES 資料庫，開發通用的建築結構減碳評估工具，以提升公共工程碳排放管控效率與精準度，共同推動臺灣邁向 2050 淨零碳排目標 [185, 5.2.4]。

This study analyzes three new social housing projects in Taiwan (TA14, NT17, TY17) to compare above-ground main structure embodied carbon emissions using the Ministry of the Interior's LEBR system and this study's Design Estimation Carbon Emission Calculation Method (based on PCCES principles). The research also explored the impact of design variables under new codes. Key findings include: 1.Assessment Method Discrepancies: For new cases designed under the 2023 concrete structure code, the Design Estimation method yielded significantly higher emissions than LEBR baseline values, showing a "carbon increase" phenomenon [3, 7, 96 (Table 4.6), 249]. This highlights LEBR's limitation in reflecting actual material changes due to enhanced concrete strength and stricter rebar configurations. Furthermore, while LEBR fixed low-carbon concrete benefits at 5-6%, Design Estimation demonstrated 11% to 24% carbon reduction [106 (Table 4.13), 108 (Table 4.16), 111 (Table 4.19), 249], indicating LEBR's simplified formula underestimates actual material optimization impacts. 2.Floor Carbon Emission Trends: All three new cases consistently showed highest carbon emissions on the lowest floors due to maximum load bearing, with emissions decreasing on higher floors [138, 5.1.3.a, 249]. 3.Geometric Design Variables Challenges: Due to limited sample size and numerous uncontrolled variables, this study could not establish clear linear trends or derive new empirical formulas for the relationship between plan configuration (perimeter-to-area ratio, aspect ratio) or cantilever coefficient and carbon emissions [179, 5.1.3.b, 249]. 4. Practical Carbon Reduction Strategies: Based on case analysis and structural engineer interviews, four effective strategies were identified [138, 5.1.3.c, 249]: Strength Stratified Configuration: Adjusting concrete strength by floor (e.g., 5,000–10,000 psi for lower, 4,000 psi for upper) to reduce column/beam sections [125, 138 (5.1.3.c), 249]. Component Size Optimization: Optimizing beam and column sections using standardized modular systems, avoiding excessive allowances for construction ease [126, 138 (5.1.3.c), 249]. Structural System Optimization: Incorporating shear walls or braces in mid-to-high rise buildings to transfer bending moments, reducing beam rebar/height; or using expansion joints in connected complexes [124, 128, 138 (5.1.3.c), 249]. Rebar Ratio Cap Control: Limiting column rebar to within 3% and beam rebar to within 2%, or substituting SD420 with high-strength SD490W rebar, can reduce steel quantity by 10%–15% [126, 138 (5.1.3.c), 249]. This study recommends: 1. Dual-Track Management: Use LEBR for early rapid assessment, but complement with Design Estimation for precise quantification during detailed design [179, 5.1.1, 249]. 2. Updating LEBR Formula: Update LEBR to include multi-grade concrete carbon coefficients and better reflect rebar configuration impacts under new codes [184, 5.2.3, 249]. 3. Dynamic Embodied Carbon Benchmarks: Based on Denmark's model [139, 5.2.2, 249], Taiwan's Ministry of the Interior, PCC, and ABRI should jointly establish and dynamically update national embodied carbon benchmarks using PCCES data and this study's method [139, 5.2.2, 249]. 4. General Assessment Tool Development: Integrate BIM technology with PCCES databases to develop a universal tool for building structure carbon reduction assessment, improving efficiency and accuracy in public works and supporting Taiwan's 2050 net-zero goal [185, 5.2.4, 249].