圓形斷面木樑燃燒試驗之炭化特性

Abstract

本研究主要是利用國產造林木中小徑木台灣杉、柳杉與杉木，其中將台灣杉、柳杉與杉木製成圓形斷面木樑，徑級分別為20 cm、25 cm與30 cm三種，以CNS 12514標準進行60 min與30 min之樑構件燃燒試驗。杉木則另以披麻捉灰再製成披麻捉灰處理材，徑級為20 cm、25 cm與30 cm，進行30 min之燃燒試驗；及利用孔廟替換下來的杉木古蹟腐朽材，徑級20 cm，進行30 min之燃燒試驗以探討其耐火特性。 研究結果顯示健全材方面底部平均炭化速率為台灣杉(0.80 mm/min)＞柳杉(0.79 mm/min)＞杉木(0.74 mm/min)；台灣杉與杉木之炭化速率會隨密度增加而下降，但柳杉的趨勢不一樣。斷面尺寸方面，徑級越大燃燒速率越大，即炭化速率均會隨原木之徑級增大而略為增加。一般來說節的密度會較大，而密度為影響炭化深度的主要原因，本研究結果指出節的炭化深度明顯小於健全材平均炭化深度。 杉木各處理材方面的平均炭化速率為古蹟腐朽材(1.31 mm/min)＞披麻捉灰材(0.83 mm/min)＞健全材(0.74 mm/min)；古蹟腐朽材的炭化速率較高，主要原因為其表面已經不同程度的嚴重腐朽，故炭化速率較快。腐朽炭化速率結果側部在1.13-4.18mm/min，為健全材的2-7倍；底部在0.87-2.14mm/min，為健全材的1-3倍。只有底部的腐朽炭化速率會隨腐朽率增加而增大，側部並不明顯。 此外再以四次式來推估其斷面輪廓炭化形狀，求得健全材之斷面形狀輪廓推估圖，可得知其燃燒時間為30 min時斷面形狀接近圓形，燃燒時間60 min時斷面型狀近似水滴型；且底部炭化深度較上部嚴重。杉木健全材與杉木披麻捉灰材的斷面輪廓模擬圖中，杉木披麻捉灰材的炭化較健全材嚴重，且斷面形狀都近似圓形，而模擬輪廓在兩側均較不符合，頂部與底部較適合此模型。杉木古蹟腐朽材燃燒時間為30 min之斷面輪廓模擬圖極不適合，故四次式模型仍需進一步修正。

The purpose of this study was to investigate the fire performance of beam with circular cross section from Taiwania, Japanese cedar and China fir. First of all, three different diameters, 20 cm, 25 cm, and 30 cm of three species, were tested under 30 min and 60 min by CNS 12514. Further, China fir logs were treated with a traditional method called “Pi-Ma-Jou-Huei” which applied linen with paste of pig blood-mortar on member surface then painted with color drawing for avoiding biological and physical decaying, and also made into three different diameters 20 cm, 25 cm, and 30 cm, and were tested under 30 min by CNS 12514. Finally six decay logs of China fir which tore down from Confucian Temple, Taipei, in 2002. Their diameter was 20 cm and were tested under 30 min by CNS 12514. The results indicated that the charring rate of sound logs at bottom position showed a decreasing order in Taiwania (0.80 mm/min) ＞ Japanese cedar (0.79 mm/min) ＞ China fir(0.74 mm/min). The charring rate of Taiwania logs and China fir logs increased with diameter increasing. Generally, the density was the main reason to effect on the charring rate, and the results show that the charring depth of knots was obviously smaller than that of sound logs. The charring rate of China fir logs with different treatments at the bottom position showed a decreasing order in Decay logs (1.31 mm/min) ＞ Pi-Ma-Jou-Huei logs (0.83 mm/min) ＞ Sound logs (0.74 mm/min). The charring rate of decay logs was the largest because there were seriously decayed on the surface. The charring rate of decay part at the bottom increased with decay proportion increasing, but the trend was not significant at side position. The charring rate of decay part at side position was 1.13-4.18 mm/min, about 2-7 times of sound logs while it at the bottom position was 0.87-2.14 mm/min, about 1-3 times of sound logs. In addition, a quartic-equation was derived to profile charring cross section. The sound logs’ profile was still like circular form when it tested under 30 min, and it like a droplet form when it tested under 60 min. The charring depth was the largest at the bottom position than it at any other position. The profiles of sound logs and Pi-Ma-Jou-Huei logs of China fir were also like circular form also, however, the charring depth of Pi-Ma-Jou-Huei logs was larger than that of sound logs. The profile was not match the cross section of decay log, so the quartic equation needs to be modified in order.