Numerical Analysis of Fire Behavior of Concrete Filled Box Columns

關鍵詞：混凝土填充箱型柱、火害行為、數值分析 本研究製作兩支實尺寸混凝土填充箱型柱（Concrete Filled Box Column，或簡稱 CFBC）試體，以比較其內部配置鋼筋對耐火時效的影響。試體 SP-A 箱型柱內部僅填充混凝土，試體 SP-B 內則配置縱向竹節鋼筋並填充混凝土，混凝土強度皆為 420 kgf/cm2。試體斷面尺寸為 500 mm × 500 mm，其長度為 4350 mm。試體外部係採用四片鋼板組銲而成，鋼材屬 SN 490B 等級，其厚度為 22 mm。試體兩端設有加勁鋼板，以傳遞設定載重，並避免影響其熱負載能力。此外，於柱試體受 熱段四個不同高度斷面各埋設 9 個 K 型熱電偶，以測析其表面至內部核心的溫度分布。柱試體係於高溫實驗爐中進行定載升溫之火害試驗，即先對其施加 0.47 倍設計斷面極限強度的載重，再依 CNS 12514 標準升溫曲線加熱至設定的實驗終止條件。另方面，亦使用 ANSYS 軟體建構數值分析模式，以預測高溫下柱試體表面至內部核心的溫度分布情形，並與試驗值作一比較。 研究結果顯示，試體 SP-A 火害升溫試驗進行至第 52 分鐘時，柱試體軸向變形量已超過容許值，已達到規範所定義之破壞基準。據此，試體 SP-A 之防火時效為 51 分鐘。試體 SP-B 火害升溫試驗進行至第 112 分鐘時其軸向變形量已超過容許值，其防火時效為 111 分鐘。試體無法再承載軸向荷重而達破壞，其破壞模式均為柱身鋼板局部挫屈與內部混凝土碎裂。因此，在 0.47 倍設計斷面極限強度的載重作用下，配置縱向竹節鋼筋對 CFBC 耐火時效的影響相當顯著。此外，依據Eurocode 4 所提供的力學性質，可在 ANSYS 所建構之數值分析模式中合理預測試 體之軸向變型曲線，而於各時間歷程的橫截面溫度分布則須做修正。Keywords : Concrete Filled Box Columns, Fire Behavior, Numerical Analysis. This study manufactured two full-scale concrete filled box column (CFBC)specimens to consider the impact of reinforcement arrangement on the fire resistance period of CFBC. Specimen SP-A filled with concrete internal only, and the specimen SP-B configured vertical deformed bar and filled with concrete, the strengths of concrete were all 420 kgf / cm2.The tested columns' cross sections were 500 mm × 500 mm with 4350 mm length and were filled with plain concrete. All of the steel sections of the specimens were fabricated from steel plate of 22 mm wall thickness. These plates were joined by longitudinal fillet welds at the vertices. Each of the CFBC had end plates welded to them in order to transfer the load, and end stiffeners were also introduced to ensure that end conditions did not affect the failure resistance of thermal load. Besides,the temperature from the specimen's surface to the inner central core was measured with type K thermocouples located at different depths in four sections of the column. The columns were subjected to a constant compressive load, during the whole test, located on the head of the piston of a jack. The applied load corresponded to 47% of the design value of buckling resistance of the column at room temperature. Thermal load was applied on the columns in form of CNS 12514 time-temperature curve in a natural gas-fired large-scale laboratory furnace until the set experiment termination condition was reached. On the other hand, a numerical model was established for predicting temperature distribution at surface and inner portions of the CFBC at elevated temperatures by ANSYS, and thus making a comparison with the experimental values. The result shows that, after the first 52 minutes of temperature-raising experiment, the axial deformation of the specimen SP-A has exceeded the allowable value, which means it has reached the destruction standard which has been defined. Thus, the fire-resistance period of specimen SP-A is 51 minutes. In the other hand, after 112 minutes of temperature-raising experiment, the axial deformation of the specimen SP-B has exceeded the allowable value, which means the fire-resistance period of specimen SP-B is 111 minutes. The failure models that specimen can no longer carry axial load and destructed are mostly because the following reasons, partial buckling of the coated steel and the crack of concrete inside. Therefore, under the conditions of 0.47 times the strength design, the configuration of vertical slab-steel reinforcement significantly influences the fire-resistance period of specimen SP-A. In addition, according to the mechanical properties provided by Eurocode 4, we can reasonably predicted the axial deformation curve of the specimen form the numerical analysis mode of ANSYS. Nevertheless, the cross-sectional temperature distributions of each time period still need to be fixed.摘要 .................................................... i ABSTRACT ............................................... ii 目次 ................................................... iv 表目次 ............................................... viii 圖目次 ................................................. ix 照片目次 ............................................. xiii 第一章緒論 ............................................... 1 1.1. 研究緣起與背景 ...................................... 1 1.2. 研究目的 ............................................ 2 1.3. 研究方法 ............................................ 3 1.4. 研究內容 ............................................ 3 第二章國內外規範與文獻回顧 ................................ 5 2.1. 火害工程研究 ........................................ 5 2.2. 國內外耐火試驗規範 .................................. 8 2.2.1. ISO 834 與 CNS 12514 規範 ........................ 8 2.2.2. BS 476 規範 ...................................... 9 2.2.3. UL 263 規範 ...................................... 9 2.3. 鋼骨鋼筋混凝土構造設計規範 ........................... 9 2.4. 混凝土材料之熱學性質及溫度對其影響 .................. 10 2.4.1. 混凝土密度與溫度之關係 ............................ 10 2.4.2. 混凝土熱膨脹係數與溫度之關係 .......................11 2.4.3. 混凝土熱傳導係數與溫度之關係 .......................11 2.4.4. 溫度對混凝土熱容量之影響 .......................... 12 2.5. 火害對混凝土之影響 ................................. 13 2.5.1. 高溫對混凝土微結構之影響 .......................... 13 2.5.2. 高溫下混凝土之剝落或爆裂行為 ...................... 14 2.5.3. 高溫下混凝土之強度衰減 ............................ 16 2.5.4. 混凝土應力-應變曲線與溫度之關係 ................... 17 2.5.5. 混凝土彈性模數與溫度之關係 ........................ 17 2.5.6. 混凝土強度與溫度之關係 ............................ 17 2.5.7. 鋼筋性質隨溫度之變化關係 .......................... 18 2.6.火害混凝土之力學性質評估 ............................. 18 2.7. 鋼骨鋼筋混凝土柱於高溫下之行為 ...................... 20 2.7.1. 鋼骨鋼筋混凝土柱之高溫潛變挫屈行為 ................ 20 2.7.2. 混凝土填充型鋼骨柱於高溫下之行為 .................. 20 2.8. 火害下構件行為之數值分析 ............................ 24 2.8.1. 場模式火災模擬軟體比較 ............................ 24 2.8.2. 火害下構件行為之數值分析成果 ...................... 25 第三章試驗過程與結果分析 ................................. 42 3.1. 試驗規劃及設置 ..................................... 42 3.1.1. 試驗規劃 ......................................... 42 3.1.2. 試體規劃 ......................................... 42 3.1.3. 試體製作 ......................................... 43 3.1.4. 量測儀器設置 ..................................... 43 3.1.5. 試驗設置 ......................................... 44 3.1.6. 試驗步驟 ......................................... 45 3.1.6.1. 試驗開始前 ..................................... 45 3.1.6.2. 試驗過程中 ..................................... 46 3.1.6.3. 量測與觀察 ..................................... 46 3.2. 試驗終止條件及性能基準與判定 ........................ 46 3.3. 混凝土填充箱型柱試體強度計算 ........................ 47 3.4. 試體之混凝土抗壓強度試驗結果 ........................ 49 3.5. 試體 SP-A 之試驗結果 ............................... 49 3.6. 試體 SP-B 之試驗結果 ............................... 50 第四章數值分析結果與討論 ................................. 84 4.1. 數值模擬分析設定 ................................... 84 4.1.1. 模擬試體描述 ..................................... 84 4.1.2. ANSYS 分析步驟 ................................... 84 4.1.2.1. 建立模型 ....................................... 84 4.1.2.2. 載入求解 ....................................... 85 4.1.2.3. 後處理 ........................................ 85 4.1.3. ANSYS 有限元素法分析 ............................. 85 4.1.3.1. 基本假設 ....................................... 85 4.1.3.2. 設定模擬試體 ................................... 85 4.1.3.3. ANSYS 參數設定 ................................. 85 4.2. 材料性質定義 ....................................... 87 4.2.1. 鋼材之材料性質 ................................... 87 4.2.1.1. 密度 .......................................... 87 4.2.1.2. 熱導率 ........................................ 87 4.2.1.3. 比熱容 ........................................ 88 4.2.1.4. 彈性模數 ...................................... 88 4.2.1.5. 熱膨脹係數 ..................................... 88 4.2.2. 混凝土之材料性質 ................................. 88 4.2.2.1. 密度 .......................................... 88 4.2.2.2. 熱導率 ........................................ 89 4.2.2.3. 比熱容 ........................................ 89 4.2.2.4. 彈性模數 ...................................... 90 4.2.2.5. 熱膨脹係數 .................................... 90 4.3. 試體 SP-A 數值模擬結果 ............................. 90 4.3.1. 軸向變形 ......................................... 90 4.3.2. 鋼板表面溫度變化 ................................. 91 4.3.3. 混凝土溫度變化 ................................... 91 4.4. 試體 SP-B 數值模擬結果 ............................. 91 4.4.1. 軸向變形 ......................................... 91 4.4.2. 鋼板表面溫度變化 ................................. 92 4.4.3. 混凝土溫度變化 ................................... 92 4.5. 數值模擬結果比較 ................................... 93 第五章結論與建議 ........................................114 5.1. 結論 ..............................................114 5.2. 建議 ..............................................115 參考書目 ................................................11