Experimental study of hydrothermal aging effects on insulative properties of intumescent coating for steel elements

This paper reports the results of an experimental study of degradation in fire protection performance of two types of intumescent coating after different cycles of accelerated hydrothermal aging tests. Intumescent coating (without top coating) was applied to steel plate to make a test specimen. After subjecting the specimen to the aging test, fire test was carried out to obtain the steel plate temperature. In order to help understand the aging mechanism of intumescent coating, TGA tests, XPS tests and FTIR tests were also conducted on the intumescent coating after the accelerated aging test. In total, tests were performed on 56 intumescent coating protected steel specimens, of which 16 specimens were applied with type-U intumescent coating and the other 40 with type-A intumescent coating. Results of the degradation mechanism study reveal that the hydrophilic components of intumescent coating move to the surface of the coating and can be dissolved by moisture in the air, which can destroy the intended chemical reactions of these components with others and deter formation of the desired effective intumescent char. The consequence of this is reduced expansion of the intumescent coating and increased effective thermal conductivity. Compared to specimens without hydrothermal aging, after 42 cycles of hydrothermal aging (to simulate 20 years of exposure to an assumed exposure environment), the effective thermal conductivity of type-U intumescent coating was 50% higher and that of type-A intumescent coating 100% higher than that of the fresh coating. These increases in effective thermal conductivities resulted in increases in steel temperatures of up to 150 °C and 220 °C higher than the steel temperatures of the specimens without hydrothermal aging for the type-U intumescent coating and type-A intumescent coating specimens, respectively.     

钢结构防火涂料等效热传导系数的确定

针对厚型钢结构防火涂料的热工参数确定问题和膨胀型钢结构防火涂料隔热性能无合适方法评价的现状，提出了根据耐火试验检测测定构件升温过程确定防火涂料等效热传导系数的方法。并分别利用厚型防火涂料和膨胀型防火涂料的检测结果进行试算，取得了较满意的结果。该方法还解决了有膨胀型防火涂料保护层钢构件的温度计算问题，为该类钢构件的抗火计算奠定了基础，并对防火抗火性能试验检测的内容及应提交的结果提出了建议。     

非膨胀型防火涂料等效热传导系数研究

基于防火涂料标准耐火试验方法,对涂覆非膨胀型防火涂料的钢板试件和工字型钢试件进行了耐火试验,用所得的试件升温曲线计算非膨胀型防火涂料的热传导系数随涂层温度变化曲线.提出将涂层温度为400~800℃时的热传导系数平均值作为涂层等效热传导系数,并用以进行被保护钢构件火灾下升温计算,所得钢构件的升温曲线与试验测得的升温曲线符合良好.参数分析表明,等效热传导系数与试件截面形状系数无关,与涂层厚度相关,表明用小尺寸钢板试件耐火试验结果计算所得的等效热传导系数可用于预测其他被保护钢构件在火灾下的升温.对不同涂层厚度热传导系数进行线性拟合,提出以涂层厚度20mm时的等效热传导系数作为非膨胀型防火涂料等效热传导系数特征值.     

碳材料对水性膨胀涂料阻燃抑烟性能的影响

以膨胀石墨（EG）、碳纳米管（CNTs）、富勒烯（C60）、石墨烯（Gr）为填料,研究其在水性膨胀涂料中的阻燃性、热稳定性、抑烟性和耐水性碳材料对水性膨胀涂料防火抑烟性能的影响。用扫描电镜（SEM）、傅立叶变换红外光谱（FTIR）、X 射线衍射（XRD）和粒度分布对碳层进行了表征。结果表明：碳材料可以有效提高水性膨胀涂料的防火性能,受热300 s 时,涂覆防火涂料的板背面温度比无防火涂料的钢板降低了50%,且加入碳材料的防火涂料更能隔热;SP-Gr 的炭层膨胀系数最大,约为未加入碳材料涂料的两倍,且高温加热下加入Gr 的涂料具有最大的炭残余质量;加入碳材料的防火涂料阻烟效果更好,烟密度降低30%以上;加入Gr 的涂料具有最好的耐水性。在水性防火涂料中掺入石墨烯具有最好的性能。     

Effect of temperature on thermal properties of spray applied fire resistive materials

Thermal properties of fire insulation namely thermal conductivity, specific heat, thermal strain and mass loss play a critical role in determining the effectiveness of these materials to improve fire resistance of steel structural members. These properties vary with temperature and are predominantly governed by moisture content and chemical constituents. This paper presents the effect of temperature on thermal properties of different types of spray applied fire resistive materials (SFRM). High temperature property tests were carried out on three types of commercially available SFRM to measure thermal conductivity, specific heat, mass loss and thermal strain in the range of 20–1000 °C. Data from these tests show that temperature has significant influence on thermal conductivity, thermal expansion and mass loss of fire insulation. The measured test data are utilized to develop thermal property relationships for fire insulation in terms of temperature. The proposed relations can be used as input data in thermo-mechanical analysis for evaluating fire resistance of steel structures.     

面漆对湿热环境下膨胀型防火涂层隔热性能的影响

通过105个试件的湿热老化试验和隔热性能试验,研究了2种面漆对膨胀型钢结构防火涂层耐湿热老化性能和隔热性能的影响.结果表明：在经过84次湿热老化循环后,无面漆试件等效导热常数比未老化试件增大131%,涂有2层E型和A型面漆试件的等效导热常数分别比未老化试件增大42%和21%,面漆降低了湿热环境对膨胀型钢结构防火涂层导热系数的影响,涂层隔热性能提高;面漆抑制了涂层膨胀,膨胀层隔热性能降低;当老化时间较短时,面漆对涂层膨胀的抑制作用大于其对涂层耐老化性能的提高,总体上降低了涂层的隔热性能;随着老化时间的延长,面漆的正向作用逐渐显现;膨胀型钢结构防火涂层的隔热性能随面漆厚度的增加而增大.     

不同火灾下膨胀型钢结构防火涂层的隔热性能

基于36个试件在标准火与大空间火下的隔热性能测试,计算膨胀型钢结构防火涂层的等效导热系数,研究升温条件对防火涂层隔热性能的影响规律及机理.结果表明,防火涂层是否反应完整取决于火场的最高温度,升温速率影响膨胀-固化阶段防火涂层的发泡程度;升温历史不同,防火涂层的膨胀倍率和炭化层泡孔结构不同,最终表现为防火涂层隔热性能的差异.防火涂层在标准火下的隔热性能优于大空间火下的隔热性能,两者的等效导热系数代表值λr最大差异为65%.升温速率越快,火场最高温度越高,防火涂层的等效导热系数值越低,隔热性能越好,因此,用标准火下防火涂层隔热性能的检测结果来指导大空间火下防火涂层的设计是不安全的.大空间火下防火涂层等效导热系数随升温条件变化的程度还要受涂层厚度的影响,随涂层厚度增加,不同工况下的防火涂层等效导热系数差异程度减小.     

自然火灾下隔热钢杆耐温上限的简化计算方法

分析钢结构的耐火性能时,应考虑自然火灾下关键杆件的钢材耐温上限。自然火灾很复杂,需要先进的分析模拟技术,以获得自然火灾下钢杆的温度分布。要完成这种设计,需要建立较准确的简化计算方法。故建立了计算自然火灾下绝缘钢杆耐温上限的简化方法。采用时间当量关联自然火灾和标准火灾,并采用简化的二次方程式计算温度上限。数值和试验结果对比表明,这种方法能给出300～600°C范围内的较满意的耐温上限结果。这种方法需要手算,在实际操作中比较容易和方便。     

钢结构膨胀型防火涂料研究综述

钢结构建筑在我国应用广泛,然而钢结构的耐火性差的缺点也使得钢结构防火涂料的研究备受重视。总结了防火涂料种类划分、防火机理以及五种膨胀型防火涂料改良优化方法,并且给出相应参考。     

建筑钢结构膨胀型耐火涂料的性能研究

研究不同膨胀型阻燃剂配方在火灾下对钢材性能的 影响。以硅灰(SF)为粘结剂,蛋壳(CES)为填料,合成了水基膨胀 涂料。采用热重分析(TGA)、扫描电镜(SEM)、小型煤气喷灯试 验和加热炉试验研究了粘结剂和填料对涂料性能和耐火性能的影 响。TGA 结果表明,在 SEM 图像中单独添加 SF 或与 CES 复 合均能提高涂料的残余重量和热稳定性,同时改善了涂料的表面 结构。SF、CES 与阻燃添加剂的组合防火性能最佳,具有最高的 热稳定性、最大膨胀度和最致密的表面结构,且在火灾暴露过程中 具有足够的附着性。     

A Simple Method to Predict Temperatures in Steel Joints with Partial Intumescent Coating Fire Protection

Based on temperatures measured in steel joints with different extents of fire protection, this paper proposes a simple method to calculate temperatures in steel joints with partial intumescent coating fire protection. The method combines the simple temperature calculation methods in EN 1993-1-2 (Committee of European Normalisation CEN, Eurocode 3: design of steel structures—part 1-2: general rules—structural fire design, 2005) for unprotected and protected steel structures through the introduction of an exposure factor, which is the ratio of the unprotected surface area of the joint region to the total surface area of the joint area. Using the measured temperatures for fully protected steel joints, this paper first extracts the effective thermal conductivity of the intumescent coating used in the fire tests. Afterwards, this paper presents validation results based on fire test results on joints with partial fire protection. Finally, this paper presents methods to calculate the exposure factor for different types of partially fire protected steel joints.     

A simplified approach for predicting temperatures in insulated RC members exposed to standard fire

Fire resistance of concrete structural members can be enhanced through the application of external fire insulation on the surfaces of concrete member. For evaluating fire resistance of such insulated RC members, temperatures in concrete and steel reinforcement are to be known. This paper develops a simplified approach for predicting cross-sectional temperatures in an insulated RC structural member exposed to standard fire. The approach is derived by replacing the insulation layer into an equivalent concrete thickness layer and then undertaking statistical regression analysis on temperature data of modified concrete section. The effect of critical parameters, including geometry of concrete member and insulation, thermal properties of concrete and fire insulation, and duration of fire exposure is accounted for in temperature equations. The validity of the approach is established by comparing predictions from the proposed equation with data generated from fire tests and finite element analysis. These comparisons show the proposed equation gives reasonable prediction of temperatures, within a range of ±10%, in insulated concrete members. The applicability of the proposed approach in design situations is illustrated though a numerical example. The simplicity of the proposed method makes it attractive for use in design situations and for incorporation in design manuals.     

Variation of Intumescent Coatings Revealing Different Modes of Action for Good Protection Performance

Thermal insulation and mechanical resistance play a crucial role for the performance of an intumescent coating. Both properties depend strongly on the morphology and morphological development of the foamed residue. Small amounts (4 wt%) of fiberglass, clay and a copper salt, respectively, are incorporated into an intumescent coating to study their influence on the morphology and performance of the residues. The bench scale fire tests were performed on 75 × 75 × 2 mm³ coated steel plates according to the standard time–temperature curve in the Standard Time Temperature Muffle Furnace⁺ (STT Mufu⁺). It provided information about foaming dynamics (expansion rates) and thermal insulation. Adding the copper salt halved the expansion height, whereas the clay and fiberglass change the height of the residue only moderately. The time to reach 500°C was improved by 31% for clay and 15% for the other two fillers. Nondestructive micro computed tomography is used to assess the inner structure of the residues. A transition of the residue from a black, carbonaceous foam with closed cells into an inorganic, residual open cell sponge occurs at high temperatures. This transition is due to a loss of carbon; the change in microstructure is analyzed by scanning electron microscopy. Additional mechanical tests are performed and interpreted with respect to the results of the morphology analysis. Adding clay or copper salt improved the mechanical resistance tested by a factor 4. The additives significantly influence the thickness and foaming dynamics as well as the inner structure of the residues, whereas their influence on insulation performance is moderate. In conclusion, different modes of action are observed to achieve similar insulation performance during the fire test.     

预测火灾下钢构件温度的简单方法

为评价钢结构构件的抗火性能,需要了解构件横截面的温度。给出了一种预测火灾下有外保护层的钢构件截面温度的简单方法。利用标准火灾条件下的简化假设得到该方法,并推广到设计火灾情况。该方法适用于有保护层和没有保护层的型钢构件。将预测温度与ANSYS有限元分析结果进行比较,验证了该方法的有效性。此外,该方法的预测结果也与"最佳拟合"法的预测温度进行了比较。与试验结果、有限元计算结果和"最佳拟合"法预测结果的比较表明,所提出的简化方法能够较好地预测各种火灾下型钢构件的热梯度和温度历史。该方法简单明了,适合设计时使用。     

钢结构围护-防火一体化材料耐火性能试验研究

根据钢结构防火保护材料的相关技术要求,通过对常见的钢结构围护材料进行评价,筛选了包括水泥基材料中的无机轻集料砂浆、胶粉聚苯颗粒、蒸压轻质加气混凝土(autoclaved lightweight concrete,ALC),保温浆料中的石膏基保温浆料、微孔硅酸钙浆料,以及保温板材中的发泡陶瓷保温板和岩棉板在内的3类可以兼...     

Flush Endplate Connections in Fire: Time-Dependent Behavior of Tension Bolts

Steel connections play a crucial role in maintaining the integrity and stability of steel building frames especially when exposed to fire temperatures. The behavior of flush endplate connections in fire is shown to be governed by tension bolt failure as bolts lose their strength and stiffness more rapidly at higher temperatures. As a result, the ability to predict the development of stresses in tension bolts of flush endplate connections at different stages of fire is of special importance. One of the factors influencing bolt stresses in fire is the thermal creep or time-dependent inelastic response of steel to elevated temperatures. Therefore, time- and temperature-dependent behavior of tension bolts of flush endplate connections in fire is the focus of this study. Stress-time histories in tension bolts are obtained by explicit consideration of thermal creep of steel in FE models of flush endplate connections at elevated temperatures. To better understand the effect of thermal creep on tension bolt behavior, the correlation between time-dependent rotational deformation of flush endplate connections and bolt stresses is also investigated. Further, the isochronous representation is utilized to study the rotational deformation and the tension bolt stresses under various applied moments ranging from 50% to 95% of the moment capacity and fire temperatures ranging from 450°C to 600°C with 25°C increment. Through such representation, it is indicated that the connection behavior is not only dependent on bolt strength degradation and applied moment, but also affected by the time duration of applied moments and temperatures. Also, with the inclusion of thermal creep of steel, the connection experiences higher rotation and excessive endplate deformation with stress relaxation leading to top tension bolt failure at earlier stages of fire. More specifically, for time exposure greater than or equal to 60 min, the failure temperature of the connection decreases from 600°C to around 550°C. Therefore, neglecting thermal creep of structural steel may result in an unsafe prediction of the overall response of flush endplate connections in fire.     

The relationship between temperature behaviors and section factors of fire spray protection coated composite beams exposed to standard fire

Concrete-steel composite beams, when they are exposed to high temperatures, it increases the quantity of heat inside the composite beams that restrain temperature rise caused by concretes. As a result, composite beams appear to have better fire resistance efficiency than regular steel beams due to the integrated structure between materials. In the case of composite beams, the temperature rise of steel exposed externally is directly related to the shape of sections and the degree of exposure. In this study, fireproof spray coat, approved as fire resistant construction for composite beams and regular steel beams, are coated in the same thickness and exposed to standard fire conditions. Then, the relationship between temperature history of steel and section factors of composite beams, derived from the fire resistance test result, is compared and analyzed. As a result, we came to a conclusion that the steel temperature measurement results and section factors per material are closely related, and it suggests that a standard approval of fire resistant construction can be widely used, instead of getting approval for each member, if relatively better performance can be predicted by distinct condition of fire resistance efficiency of members.     

Experimental Testing and Analytical Prediction of the Behaviour of Timber Bolted Connections Subjected to Fire

The ultimate strength of bolted and dowelled connections in timber members at ambient temperatures have been assessed using Johansen’s yield equations in Europe and USA. More recently, several researchers have begun to investigate the strength of bolted and dowelled connections at elevated temperatures. Research has been carried out at the University of Canterbury to investigate the application of Johansen’s yield equations to the prediction of the failure strength of bolted connections in fire conditions. A series of single bolted connections using steel side plates was heated at constant temperature for several hours, then loaded to failure and used to determine the embedment strength of the wood over a range of temperatures from ambient to 300°C. The temperature-dependent embedment strengths are employed in Johansen’s equations for connections using a central steel plate as well as connections using steel and wood side members. Comparisons are also being made with the results of several similar connections tested in fire conditions and show considerable promise for predicting failure of such joints. A proposal for implementation of an easy-to-use approach for the prediction of the fire resistance of bolted joints is discussed in the paper, based on an extension of the Johansen’s yield equations to fire conditions, including a model for the variation of the embedment strength with temperature.     

掺入CES膨胀型阻燃涂料的试验研究

研究蛋壳（CES）废料作为环保生物填料的膨胀型阻燃涂料的性能。将聚磷酸铵II、季戊四醇和三聚氰胺与阻燃填料和丙烯酸树脂黏合剂混合,制成膨胀型阻燃涂料,进行火焰表面扩散试验、火焰蔓延试验、热重分析试验、粘结强度试验等测试涂料的防火性能。结果表明,试件B、C、D、E在火焰下暴露时均未显示出火焰表面扩散。在涂料B、E中添加质量分数为5.0％、2.5％的蛋壳生物填料,由于炭化而改善了防火性能。试件D、E的总火焰传播指数分别为4.5、5.0,显示出优良的阻燃性能。防火涂料具有良好的耐水性、热稳定性和粘结强度,具有良好的防火性能。