A Simplified Approach for Predicting Temperature Profile in Steel Members With Locally Damaged Fire Protection

Steel structures in building are to be provided with external insulation to delay temperature rise and associated strength degradation when exposed to fire. However, due to delicateness and fragility of some insulation systems, damage might occur in these insulation systems during their service life, and such damage can lead to rapid rise in steel temperature and result in lower fire resistance of structural members. Currently, there are no simple calculation methods for quantifying the effect of insulation loss on steel temperature. In this paper, a simple approach is proposed for tracing the temperature profile in steel members with partial loss of fire protection. The method is developed based on modifying the existing one-dimensional finite difference solutions of the heat transfer equation. The validity of the proposed method is established by comparing the predictions from the proposed method against temperatures obtained from finite element heat transfer model that is created using ANSYS. The comparisons indicate that the proposed method is capable of predicting temperature in steel members with partially damaged insulation to a good degree of accuracy over a wide range of situations. Further, the simplicity of the proposed method makes it attractive for use in fire resistance assessment in steel structures.     

基于场模型的大空间建筑火灾钢构件升温的简化计算方法

高大空间建筑火灾中，热量主要通过热烟气的辐射传热和对流传热方式，向无防火保护层的钢构件表面或钢构件的防火保护层传递，防火保护层再以热传导方式向钢构件表面传递。假定钢构件截面温度均匀分布，将高大空间建筑火灾中的实用空气升温曲线作为构件升温边界条件，对集总热容法建立的热平衡方程求解，得出钢构件在火灾下的温度一时间曲线。为便于工程应用，在钢构件升温影响参数分析的基础上，通过曲线拟舍得出实用的钢构件升温计算公式，为研究大空间钢结构建筑在火灾下的结构全过程反应，提供钢构件升温条件。     

Optimum insulation for rectangular basements

The general solution of soil temperature variation is developed for a rectangular basement with a known heat flux distribution along the walls and the floor. The Interzone Temperature Profile Estimation (or ITPE) technique is applied to determine the steady-state variation of temperature within the ground. A water table at constant temperature is assumed to exist at a given depth below the soil surface. As an application of the general solution, the optimum thermal insulation distribution is determined for various basement configurations. A parametric analysis is conducted to determine the effect of basement depth and amount of heat flux required on the optimum insulation distribution along the surfaces of a rectangular basement.     

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.     

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...     

Sensitivity study of time delay coefficient of heat transfer formulations for insulated steel members exposed to fire

Heat transfer analysis for an insulated steel member exposed to fire conditions, in general, involves solving a 2D transient conduction equation with well-posed conditions. For design purpose, the current Eurocode 3 provisions adopt a closed-form solution from the SP approach which employs a simplified 1D characteristic heat transfer model. A virtual “time delay” has been incorporated in the analytical solution based on the assumption that the heat capacitance of insulation material is small compared to that of steel section. A sensitivity study is presented in this paper to assess the validity of the time delay coefficient. Results of the study indicate that for insulation with large heat capacitance, the time delay estimation in the SP approach yields significant discrepancy compared against exact solution. An exact formulation of time delay is recommended, which gives accurate results for insulation material with either small or large heat capacitance.     

内嵌管式辐射地板传热简化模型研究

本文建立了考虑绝热层向下传热的内嵌管式辐射地板传热的简化计算模型,并获取了其解析解。同时对该地板辐射传热进行了数值模拟,计算结果可作为评价解析解准确性的参考标准。计算结果表明,不考虑绝热层向下传热的地板表面温度及热流解析解结果与数值模拟结果有很大的差异;考虑绝热层向下传热的地板表面温度及热流解析解结果与数值模拟结果比较吻合,温度平均误差为0.22℃,热流平均相对误差为3.2%。     

Ventilation as a means of air-conditioning power saving in reinforced concrete telephone-exchange buildings-analysis and directions for design

The paper presents a computer-aided analysis of the combined use of ventilation and structural heat capacity and insulation as a means of saving air-conditioning power in digital telephone exchanges. It is shown that such savings can be effected by increasing air change with outdoor cool air at night, and when feasible, also in daytime, through the air change unit, in a conventional air-conditioning cycle. The total thermal time constant (TTTC) method of calculation used enables the evaluation of daily or seasonal heat-flow balance for a given indoor temperature, considering the tendency of the heat capacity of the building and of envelope components to flatten the fluctuations of this temperature.     

Determination of specific heat capacity by transient plane source

A standard TPS measurement gives the thermal conductivity and thermal diffusivity of an isotropic material which in turn gives the heat capacity. The thermal properties of an anisotropic material can be measured if the heat capacity is known. A method for heat capacity measurement exists, where the TPS sensor is attached to a sample container which is surrounded by insulation. However, it's based on an assumption of negligible heat losses which leads to uncertainties in the results. From that position, this work aims to model the heat losses from the specific heat measurements with TPS. A new set-up is introduced, where the sensor with the container hangs freely in a steel tube to get more predictable heat losses. The results show that the measurements can be modelled as a network of lumps connected by conductances approximated as constant. Thereby, the conductances out from the system can be solved from a reference measurement and used as input for a model of a measurement with a sample. The model seems to underestimate the heat capacity, which might be a consequence of temperature dependent effects on the conductances from convection. The tube in the set-up could be evacuated to minimize those losses.     

泡沫玻璃外墙外保温系统温度场的数值模拟

计算数据来源于泡沫玻璃外墙外保温系统墙体大型耐候性试验,结合COMSOL软件分别对泡沫玻璃外墙外保温系统耐候性试验的高温—淋水循环和加热—冷冻循环进行了数值模拟,以在耐候性试验机箱体内的环境实时温度作为试验墙体的温度条件,墙体内外表面考虑对流换热边界条件,忽略热辐射的影响,并且忽略层间热阻.对泡沫玻璃外保温系统的主要功能层沿厚度方向和同一层平面不同位置的温度场进行比较,模拟结果表明泡沫玻璃外保温系统具有良好的保温作用,窗户等周围部位是外保温墙体的薄弱位置,温度场和温度应力变化较大,易产生裂缝,在实际工程中应给予重视.     

Rational design methodology for fire exposed load bearing structures

The state-of-art of reliability studies in the area of fire-exposed structures or structural members is illustrated, taking examples from published papers concerning load-bearing building structures of steel, reinforced concrete, and wood. In parallel, trends are described in the present development of rational structural fire design methods, principally adapted to modern loading and safety philosophy for the non-fire state. Statistically derived results are presented for fire-exposed, insulated steel structures in office buildings, giving the breakdown of the total variance in maximum steel temperature and load-bearing capacity into component variances as a function of the insulation characteristics. The safety index and probability of failure are compared numerically for different fire design procedures. The data presented are examples of the information which is required as input in a qualified systems analysis of fire exposed load-bearing structures.     

考虑衬砌和隔热层的寒区隧道温度场解析解

将隧道非齐次的瞬态传热分解为周期函数边界下的瞬态传热和恒温边界下的稳态传热,利用分离变量与Laplace变换相结合的方法,求解有保温隔热层的寒区隧道瞬态温度场的显式解析解。根据能量守恒,建立隧道洞内气体的气–固耦合传热模型,并获得洞内气体年平均温度和温度振幅的显式解析解。衬砌温度影响因素分析表明,随着隧道埋深和年平均气温的增加,二衬内、外两侧的温度呈线性增加,当年平均气温低于0℃,季冻区隧道埋深小于80m时,5cm厚隔热层很难单独满足防寒需求,应与主动供暖措施联合;随着隔热层厚度的增加,二衬的温度呈增长趋势,但增长速率却逐渐减小;当隔热层厚度超过5cm时,通过增加隔热层厚度来提高衬砌温度要考虑其经济性。依据隧址区的气候及地形条件,采用工程类比和解析解相结合的方法分段计算隔热层厚度。与实测值对比结果表明,理论解满足工程精度要求。     

Heat mitigation in geosynthetic composite liners exposed to elevated temperatures

The hydrothermal behaviour of single and double composite liners subjected to elevated temperatures is examined. Particular interest is given to the effect of the presence of wrinkles in the geomembrane (GMB) as well as defects, and the existence of a gap between the primary and the secondary liners caused by the presence of a leak detection system. Heat flow resulting from elevated temperature was found to be mainly influenced by the size of the air-filled gaps present within the composite lining systems. The larger the air-filled gap size, the lower was the heat flow through a barrier system. The presence of a leak detection layer (i.e., large air-filled gap) and GMB layers were found to be the primary factors to reduce heat flow substantially through the lining systems. Therefore, the presence of a leak detection layer combined with a secondary GMB can improve the overall thermal insulation capacity of a double liner system, minimise heat flow through the secondary liner and offer the possibility of protecting the GCL (if present) and the subgrade from possible heat induced drying/desiccation. A leak in the geomembrane can minimise the gain in thermal insulation. However, this effect can be reduced if the liquid is regularly pumped out.     

钢结构工程中的“冷桥”及其处理方法

随着钢结构项目的普及 ,针对寒冷地区和一些特殊行业 ,如何防治“冷桥”现象对建筑物的正常使用、节能及保温有十分重要的意义。从一些常见的钢结构节点设计、施工过程出发 ,总结了以往的节点处理经验 ,着重介绍了如何处理及防止节点出现“冷桥”现象的几种方法     

喷涂保温材料-原竹骨架组合墙体抗震性能研究

喷涂保温材料-原竹骨架组合墙体是在原竹骨架外喷涂轻质保温材料制成。通过对喷涂保温材料-原竹骨架组合墙体试件进行低周反复加载试验,分析了试件的受力过程和破坏形态,研究了试件的滞回曲线、骨架曲线、承载能力、抗侧刚度及延性等抗震性能,并通过有限元分析比较了组合墙体和原竹骨架的抗侧承载能力,最后将试验结果与已有喷涂保温材料-冷弯薄壁型钢组合墙体的试验数据进行了对比分析。结果表明：喷涂保温材料-原竹骨架组合墙体具有较高的受剪承载力、抗侧刚度以及良好的抗震性能;组合墙体的抗侧承载能力为原竹骨架的2.9倍;与喷涂保温材料-冷弯薄壁型钢组合墙体相比,喷涂保温材料-原竹骨架组合墙体受剪承载力和抗侧刚度略有降低,但该组合墙体同样具有一定的推广价值。     

Resistance and thermal insulation of a composite FRP–steel beam

For an optimal design of roof-elements for long spans one has to consider both load-carrying capacity and heat conductivity. In this paper three different alternative web configurations for joining web to flange in a roof-element are investigated. A composite web in combination with fibre reinforced plastics (FRP) is proposed as a solution to achieve an optimised performance. The connection is designed as a mechanical pin-type fastener with a general purpose polyester matrix FRP. Full-scale beam tests and small-scale properties test were carried out. Where connection failure took place, the derived connection capacity load matches fairly. A predicted span length of a roof element is in the order of 8–10 m in a design situation should be possible using the FRP–steel web. The load-carrying and thermal insulation performance of FRP–steel, expanded metal and slotted steel beams are compared by finite element analysis.     

航站楼使用阶段钢结构温度取值研究

为了准确确定大跨度钢结构在使用阶段的温度作用和方便钢结构温度变化模拟分析,对厦门高崎机场T4航站楼屋盖钢结构夏季的温度进行了全面测试,提出太阳辐射与室外气象温度的日变化计算模型。根据气象条件、室内分层温度控制方法以及屋面构造做法,通过CFD模拟技术研究高大空间温度场沿高度方向的变化规律,并在天窗部位考虑了太阳辐射的影响。结果表明:金属屋面具有良好的保温隔热性能,室内与室外钢结构的最高温度均与最高气温非常接近,钢结构昼夜温差主要受室外气温变化的影响;受到太阳辐射的影响,天窗部位钢结构的温度明显高于最高气温;CFD模拟计算得到高大空间空气温度沿竖向分布的结果与实测值的变化趋势相一致,顶部热滞留区的温度明显高于等温空调区,计算温度与实测温度相对误差为5%~10%;通过实测与模拟分析,可以较为合理地确定在使用阶段大跨度钢结构的温度,该方法可供类似大型公共建筑设计时参考。     

非膨胀型防火涂料保护钢板的温度场分析

为明确非膨胀型防火涂料的隔热性能,采用有限元方法分析了标准升温曲线火灾作用下,非膨胀型防火涂料保护钢板的温度场。开展了非膨胀型防火涂料保护钢板的温度场试验。采用试验验证的有限元模型,对非膨胀型防火涂料的主要热工参数进行分析。研究结果表明：建立的有限元模型可以较好地模拟非膨胀型防火涂料保护钢板的温度场变化;导热系数是影响非膨胀型防火涂料隔热性能最重要的热工参数;密度和比热容对于非膨胀型防火涂料的隔热性能的影响有限。     

多跨连续压型钢板承载力的近似计算

提出了一个估算多跨连续压型钢板极限承载力的近似方法,即拟简单塑性铰方法。该方法考虑了连续压型钢板中的弯矩重分布,能够较为准确地估算多跨连续压型钢板的承载力。与已有文献中的试验相比,该方法估算的承载力是偏于安全的。由该法还得到了估算这种压型钢板在均布荷载下的承载力的显式,便于实际应用。     

火灾作用下锚具对预应力钢棒锚固性能退化规律研究

为研究火灾作用下锚具对预应力（PC）钢棒锚固性能退化规律,完成65组由JXM型锚具、混凝土块、抗拉强度标准值为970 MPa的φ7高强PC钢棒及反力架组成的预应力锚固系统高温性能试验,其中29组为裸露锚具高温瞬态试验,18组为裸露锚具高温稳态试验,18组为带防火保护的锚具高温瞬态试验。研究PC钢棒应力水平（0.2~0.7）、温度（20~800℃）、防火保护措施（灌浆料封锚、涂抹防火涂料、灌浆料封锚后再涂抹防火涂料）和升温速率（10.0、26.7℃/min）对锚固性能的影响。裸露锚具高温瞬态试验结果表明：高温下锚固系统破坏模式为PC钢棒在锚具中发生滑移;PC钢棒的应力水平越高、温度越高、升温速率越大,锚固系统破坏时间越短。高温稳态试验结果表明：温度低于400℃时,锚固系统破坏模式为PC钢棒被拉断,温度高于400℃时,破坏模式为PC钢棒从锚具中滑移;高温后锚具不能再使用。带防火保护的高温瞬态试验结果表明：锚固系统破坏模式为PC钢棒从锚具中滑移,防火保护不改变锚固系统的破坏模式;与无防火保护措施相比,三种保护措施下锚固系统破坏时间均提高100%以上;若将GB 14907-2002《钢结构防火涂料》关于钢结构防火涂料厚度的要求直接应用于预应力锚具防火,将偏于不安全。