火災時におけるコンクリート内部温度の予測手法
概略外形寸法が300・400・500 mmの角形と円形の無耐火被覆CFT柱6体を対象に、ISO 834に基づく3時間の加熱試験を行って内部温度を精度よく測定し、その温度解析を通して熱定数を検討した。その結果、コンクリートの熱伝導率をEC4の0.8倍、比熱をEC4の1.2倍とし、鋼材の熱定数をEC4とすることにより、内部温度解析値と実測値が良く一致し、無耐火被覆CFT柱の内部温度の実用的な予測を可能にした。さらに同様の温度解析によって、強度が異なる無耐火被覆CFT柱や T形合成梁、およびRABT加熱を受けるAFRコンクリート平板の内部温度も実用的に予測できることを確認した。
Calculating Temperatures in Concrete Elements Exposed to Fire
Six concrete-filled steel tube column specimens without fire protection measures were subjected to fire test for three hours using the fire temperature-time curve prescribed in ISO 834. The specimens were circular sections with diameters of 300, 400 and 500 mm, and rectangular sections with side lengths of 300, 400 and 500 mm. During fire test, the temperatures inside the specimens were accurately measured. The test results were used to investigate thermal properties and were applied to numerical simulation of temperatures. The calculated temperatures agreed well with the measured temperatures when the Eurocode 4's recommended values for thermal conductivity and specific heat of concrete were multiplied by 0.8 and 1.2, respectively. These corrected thermal properties for concrete were validated by a numerical simulation of the temperatures in building elements exposed to an ISO 834 test fire. The building elements used in this test consisted of unprotected steel tube columns filled with concrete of various strengths, and T-shaped composite girders. The method also proved valid for calculating temperatures in tunnel fires, as shown by numerical simulations using reinforced concrete segments made with AFR (Advanced Fire Resistant) concrete in a RABT fire.
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