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隧道火灾与环境因素作用下气凝胶复合SCC抗火性能及其连续梁的可靠性
论文作者:童鞋论文网  论文来源:www.txlunwenw.com  发布时间:2019/9/11 8:25:25  

摘要:随着隧道及地下空间修建技术的快速发展,自密实混凝土(Self-compactingConcrete,SCC)因其自流平、无振捣等环境友好特点而广泛应用于隧道衬砌结构,但由于SCC的高强度与致密性及湿度与温度等环境因素的影响,在隧道火灾下极易发生爆炸剥落,对人员和结构安全构成威胁。利用气凝胶材料超绝热性能对SCC表面进行涂层处理以消除高温剥落或延长安全撤离时间,对隧道结构火灾下的结构安全和人员逃生具有重要的科研和社会价值,目前国内外相关研究缺乏。

采用商用SiO2气凝胶制备涂层砂浆,以温度与湿度为环境因素变量,采用Eurocodes HC隧道火灾升温曲线,试验对比研究了有涂层与无涂层的SCC试件的抗火性能。测试了隧道火灾下SCC爆裂剥落持续时间、爆裂剥落初始温度、爆裂剥落次数等剥落特征参数,结合火灾高温后SCC的外观形貌及残余强度,探讨了气凝胶砂浆对SCC爆裂剥落的改善效应。基于热传导理论,运用ABAQUS有限元模拟软件对气凝胶复合混凝土连续梁构件进行了温度场分析。采用一次二阶矩法探讨了火灾高温作用下有无气凝胶砂浆涂层混凝土梁构件的可靠性。具体研究内容如下:

(1)在体积掺量为80 %条件下,以商用SiO2气凝胶为骨料制备了气凝胶涂层砂浆。实测28 d抗压强度、抗折强度、干密度和导热系数分别为1.5 MPa、0.8 MPa、668kg/m3和0.185 W/ (m K),这些结果证实了气凝胶砂浆具有作为隧道防火涂层的潜力。

(2)以温度(最高温度为1080 ℃)与湿度(0 %、25 %、50 %、75 %和100 %共5个湿含量)为环境因素变量,采用Eurocodes HC隧道火灾升温曲线,对比研究了有涂层(厚度6 mm)与无涂层的SCC试件在模拟隧道火灾下的爆裂剥落行为。研究发现,随着湿含量的增加,SCC发生爆裂剥落的时间越早,初始爆裂温度越低,无气凝胶砂浆涂层的SCC试件爆裂剥落损伤愈严重;湿含量为75 %的SCC试件爆裂剥落持续时间最长且爆裂次数最多。隧道火灾后SCC试件的外观形貌及SEM图分析表明,无气凝胶砂浆涂层的SCC试件湿含量越高,爆裂剥落几率越大,内部结构越松散;气凝胶涂层有效抑制了SCC试件的爆裂剥落,提高了其抗火性能。

(3)基于耐火试验结果并参照相关文献中混凝土热工参数的研究成果,运用ABAQUS有限元模拟软件对气凝胶复合混凝土连续梁构件抗火性能进行了模拟。结果表明,隧道火灾下梁截面的高温区逐渐由受火面的径向方向往混凝土内部发展,在60~90 min范围内模拟火灾温度场便传导至混凝土15 cm深度范围且随着高温区的继续发展,整个混凝土连续梁梁构件截面的温度场发展趋势发生了改变;混凝土表面温度上升速率最大,在50 min内温度便接近于600 ℃,在50~150min内,升温速率逐渐降低,最终在180 min达到1080 ℃。然而,在未涂覆气凝胶砂浆涂层的混凝土表面,30 min便达到了1080 ℃。通过有无气凝胶砂浆涂层的混凝土内部温度的对照,充分显示了气凝胶砂浆抗高温的优越性。

(4)建立了高温环境下SCC连续梁构件的可靠性模型,总结了隧道结构的抗力分布和载荷分布,总结了隧道火灾高温环境作用下SCC连续梁构件可靠度的影响因素及其极限承载力模型和功能函数,采用一次二阶矩法计算了相应的可靠度指标。通过有和没有气凝胶砂浆涂层的SCC连续梁可靠度指标计算结果对照分析,证实了气凝胶砂浆涂层可大幅提高SCC连续梁的抗火性能。

With the rapid development of tunnel andunderground space construction technology, self-compacting concrete (SCC) waswidely used in tunnel lining structures for its environment-friendly featuressuch as self-leveling and non-vibration. However, due to the high strength andcompactness of SCC and the influence of environmental humidity and temperature,SCC was prone to explosion and spalling in tunnel fire, which poses a threat tothe safety of personnel and structure. Utilizing the adiabatic properties ofaerogel materials to coat the surface of SCC to eliminate high temperaturespalling or prolong the safe evacuation time, it has important scientific andsocial value for structural safety and personnel escape under fire in tunnelstructure. At present, there is a lack of relevant research at home and abroad.

The commercial SiO2 aerogel was used toprepare the coating mortar. The temperature and humidity were used asenvironmental variables. The fire resistance curve of the Eurocodes HC tunnelfire was used to test the fire resistance of the coated and uncoated SCCspecimens. The SCC bursting duration, bursting initial temperature and burstingfrequency and other spalling characteristic parameters under tunnel fire weretested. Combined with the appearance appearance and residual strength of SCCunder high fire temperature, the improvement effect of aerogel mortar on SCCspalling was discussed. Based on the heat conduction theory, the ABAQUS finiteelement simulation software was used to analyze the temperature field ofaerogel composite concrete continuous beam members. The reliability of theaerogel mortar-coated concrete beam members under high temperature fire wasinvestigated by using a second-order moment method. The specific researchcontents are as follows:

(1) Aerogel mortar was prepared withmodified commercial SiO2 aerogel as fine aggregate under the condition of 80%volume content. The measured compressive strength and flexural strength of 28d, dry density and thermal conductivity were 1.5 MPa, 0.8 MPa, 668 kg/m3 and0.185 W/ (m K), respectively. These results confirmed that aerogel mortar haspotential as a fire-retardant coating for tunnels.

(2) The spalling behavior of SCC specimenswith and without coatings under simulated tunnel fire was studied by usingEurocodes HC tunnel fire heating curve with temperature (maximum temperature is1080 ℃) and humidity (0 %, 25 %, 50 %, 75 % and 100 % moisture content) asenvironmental variables. It was found that with the increase of moisturecontent, the earlier the burst and spalling time of SCC, the lower the initialburst temperature. The more serious the burst and exfoliation damage of SCCspecimens without aerogel mortar coating, the longer the burst spalling and themost frequent burst of SCC specimens with moisture content of 75%. Theappearance and SEM diagram of the SCC specimen after the tunnel fire showedthat the higher the moisture content of the SCC specimen, the greater theprobability of explosive peeling and the looser the internal structure. Theaerogel coating effectively inhibited the burst and spalling of the SCCspecimen and improved its fire resistance.

(3) Based on the results of the fire testand referring to the research results of concrete thermal parameters in therelevant documents, the fire resistance of aerogel composite concretecontinuous beams is simulated by using ABAQUS finite element simulationsoftware. The results show that the high temperature zone of the beam section undertunnel fire gradually develops from the radial direction of the fire surface tothe interior of the concrete. The simulated fire temperature field in the rangeof 60-90 minutes is transmitted to the depth of 15 cm of the concrete. With thecontinuous development of the high temperature zone, the development trend ofthe temperature field of the whole section of the concrete continuous beam haschanged.Within 50 minutes.

关键词:混凝土;隧道;火灾;温度场分析;可靠性

concrete; tunnel; fire; temperature fieldanalysis; reliability

上一篇:耕作型湿地生物-生态耦合净化村落污水实验研究     下一篇:聚酰亚胺基复合光催化剂的制备及用于降解水中有机染料性能研究
 
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