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。     

模拟局部火灾下受火焰冲击的约束梁性能

钢结构可能会受附近火源的影响而被局部加热。局部火灾所造成的火焰冲击可能会使钢构件暴露于高温之下,从而导致结构失效。对受局部火灾火焰冲击的约束梁的热力学性能进行数值研究。对4个不同尺寸和约束的钢梁进行试验。研究其在火灾发展阶段和稳定阶段的性能。与ISO834火灾标准相比较。研究发现受火焰冲击的钢梁内部的温度分布很不均匀,多是穿过钢梁或在钢梁边沿。在梁的长度方向,火源附近的温度要比远离火源的温度高几百度。由于不同的温度分布,受火焰冲击的约束钢梁的变形模式与受ISO834火灾标准的梁相比明显不同。受局部火灾影响的约束钢的失效温度可能会高于或低于ISO834火灾标准下的约束梁的失效温度。如果潜在的实际火灾为局部火灾,那么根据标准火灾所做的设计可能就不够安全。     

Simulating the behavior of restrained steel beams to flame impingement from localized-fires

Steel structures may be exposed to localized heating by a fire source nearby. Flame impingement from localized fire may lead to high temperatures in the exposed steel members, which may lead to structural failure. This paper numerically investigates the thermal and mechanical behaviors of restrained steel beams exposed to flame impingement from localized fires. Four steel beams with different dimensions and restraints were considered. Both developing and steady burning fires were investigated. The standard ISO834 fire was also used for comparison. The study finds that the temperature distributions within the steel beams subjected to flame impingement are highly non-uniform both across and along the beams. Along the beam length, the temperatures near the fire source may be hundreds of degrees higher than those far from the fire source. Due to different temperature distributions, the deformation mode for restrained steel beam subjected to flame impingement may be significantly different from that of a beam subjected to the standard ISO834 fire. The failure temperatures for restrained steel beams subjected to localized fires may be higher or lower than those for restrained beams subjected to the standard ISO834 fire. Reliance on the standard fire may lead to an unconservative design if the potential real fires are localized fires.     

真实火灾下单层门式刚架抗倒塌性能试验研究

设计完成了一个单层单跨门式刚架厂房的足尺火灾试验,得到了主要构件的温度及位移发展规律,分析了真实火灾下门式刚架厂房结构的受力响应。结果显示：真实火灾下门式刚架的温升曲线与标准升温曲线有较大差别,燃烧室中的上部构件达到较高温度而提前失效,下部构件温度较低;在火灾下,未做防火保护的钢结构很短时间内就会发生垮塌,在火场及构件到达峰值温度前结构已产生较大位移。试验研究发现,受火柱的柱顶出现了热膨胀伸长、轴向压缩、轴向破坏三个阶段,且受顶部热烟气聚集的影响,各柱的柱顶轴向位移均大于柱中位移。试验成果可为门式刚架结构抗火数值模拟研究及结构防火设计提供参考。     

Fire safety assessment of semi-open car parks based on validated CFD simulations

Guidelines for the safe design of semi-open car parks require a minimum amount of open facade in order to ensure an effective removal of heat and smoke during a car fire. In this study the fire safety level of semi-open car parks is assessed by the use of validated computational fluid dynamics (CFD) simulations for seven different variants. The validation of these simulations consisted of two analyses namely a comparison with measured data of a case study and secondly a comparison with the Alpert’s correlations. The dimensions of the seven variants in the assessment are based on a survey of 75 semi-open car parks in the Netherlands, out of which a typical geometry could be determined. The reached fire safety of the car park variants which comply with the guideline NEN2443 are assessed using temperature and sight length criteria for safe deployment of the fire department. Results show that three out of seven studied variants did not meet these criteria, for one variant the safety level was questionable. It is therefore concluded that it is possible to design semi-open car parks which comply with the commonly used Dutch guideline, yet when assessed with criteria for safe deployment of the fire brigade have an insufficient fire safety level.     

Sensitivity Study on Using Different Formulae for Calculating the Temperature of Insulated Steel Members in Natural Fires

The applicability of using different formulae for calculating the temperature of insulated steel members exposed to natural fires which include heating and cooling phases has been investigated. The widely referenced ‘Swedish’ fire curves and measured temperature time curves in real fire tests are adopted to represent different natural fire environments. Parameters including insulation thickness, section factor, and protection material are considered in sensitivity studies. The steel temperatures predicted by different formulae are compared with the numerical results predicted by FEM. Comparatively, the formula given by Chinese Code CECS200 gives best prediction of steel temperatures. Studies also show that the approach adopted by Eurocode 3 for avoiding the negative steel temperature increment at the early heating phase in standard fire should not be used for calculation in natural fires. The formula given by CECS200 is recommended as the most satisfactory formula for the temperature calculation of insulated steel members in natural fires.     

On safety systems for underground car parks

Safety systems including ventilation systems and fire protection systems for an underground car park to be constructed in Hong Kong, are discussed and their design illustrated. The thermal environment at the occupied zone was assessed by using computational fluid dynamics (CFD). The predicted air speed was used to calculate the mean age of the air and the percentage of people dissatisfied with the air quality. The probable fire environment was studied by using a fire zone model. Designs for smoke control and the thermal sensitivity of the sprinkler heads were evaluated. Based on the investigations, designs on the fire protection and ventilation systems are recommended for providing a healthy and safety environment in this underground car park. A field survey of 27 enclosed car parks was carried out, and correlation equations fitted from this paper were used to assess the fire safety aspects of those car parks.     

火灾下钢框架结构非线性反应分析与试验研究

采用不平衡力法 ,进行火灾下钢框架结构非线性反应分析。该方法可模拟结构的实际升温过程 ,考虑材料非线性和几何非线性的影响 ,并可考虑截面温度的非均匀分布并介绍了最近完成的三榀钢框架抗火试验情况。通过试验进行分析 ,验证了方法的有效性和可靠性。     

火灾作用下钢-混凝土组合楼板的性能分析

对液体和热机械模型间的单向耦合过程进行数值研究,从而评估火灾条件下复合钢-混凝土结构的性能。分析的第一阶段包括使用三维的计算流体力学(CFD)来完成对火灾动力学的评估。火灾作用下构件的温度变化是分析的第二阶段,计算火灾的时间,获得计算流体力学的热通量,且材料的热性能随温度而变。最后,根据有限元方法(Vulcan方案)和欧洲规范1.2对钢板和混凝土包括应力-应变-温度关系的结构性能进行评估。所完成的三维有限元模型的结构模型涉及到对柱、梁和板局部和整体失效模式的识别。在非线性力学分析中对如膜和悬链效应这样的二阶效应进行解释说明。使用所提出的计算流体力学的有限元模型分析一个实际案例。分析结果验证了耦合三维流体热力学模型可成为目前防火设计分析的一部分,介绍了一种更实际和经济的防火设计方法。     

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。     

Numerical studies on atrium smoke movement and control with validation by field tests

Many computer fire models were developed in the literature with the rapid advancement of information technology. With the possibility of implementing engineering performance-based fire codes, fire models are used frequently in hazard assessment. Among the different approaches, fire field models using the technique of computational fluid dynamics (CFD) are widely used. The approach takes the advantage of predicting the fire environment in a ‘microscopic’ picture. Air flow pattern, pressure and temperature contours can be predicted. However, it is not easy to validate the CFD predicted results. Most of the field models are only validated by some experiments not specially designed for such purpose. There are very few studies on comparison with field measurements in actual sites. Whether those models are suitable for use are queried, leading to challenges. In this paper, the CFD tool fire dynamics simulator developed at the National Institute of Standards and Technology in USA will be applied to study atrium fires. Smoke layer interface height and air temperatures inside the atrium are simulated. The experimental data on atrium hot smoke tests carried out recently was used. CFD results predicted can be validated by comparing with the experimental results.     

Thermal Analysis of Hollow Steel Columns Exposed to Localised Fires

In fires in large compartments like enclosed car parks, airport terminals and industrial halls, the uniform distribution of gas temperature of post-flashover stages are unlikely to occur; in these cases, the thermal actions of a localised fire must be taken into account. In order to design steel structures for a localised fire, very detailed data concerning the development of temperatures in steel is required. EN 1991-1-2 presents a simplified model for calculating the temperatures in ceiling slabs and in the beams that may support such slabs; however, no simplified calculation model for the heat transfer in vertical elements, such as columns, is yet available. There is a need for more experimental data on real scale structures exposed to localised fires. A research project on the evaluation of temperatures in steel columns exposed to localised fires was carried out at the University of Coimbra. Full-scale natural fire tests were used to test columns, instead of conducting the usual furnace tests. This paper presents and discusses the results of the experimental tests on unprotected hollow steel columns exposed to localised fires, each of them simulating a distinct fire scenario according to different fire loads, positions and ventilation conditions. During the fire tests, real measurements showed flame heights and burning times different to those preliminarily estimated: flame heights had been conservatively predicted; while, the duration of the burning had been significantly underestimated.     

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.     

Analysis of experimental hydrocarbon localised fires with and without engulfed steel members

Localised fires can represent an important hazard to structural safety of buildings where a fully generalised fire cannot develop or when it is at its early stage. Plume correlations given in the codes are valid for undisturbed plume and it is not known whether the presence of a structural element engulfed into the localised fire can affect the validity of such correlations. In structural design, this may lead to highly conservative assumptions or, even, to possible misuses of the correlations. In order to provide insight into this issue, a comprehensive experimental programme aimed at providing data on hydrocarbon localised fires with and without engulfed vertical steel members was performed. In detail, a series of 22 tests of circular hydrocarbon pool fires in well-ventilated conditions of diameters ranging from 0.6 m to 2.2 m were performed with diesel and heptane. The particular aspect of these tests is that they were performed by means of a system that controlled the fuel flow and thus the rate of heat release (RHR) of the fire. The flame length and the temperatures of the fire plume measured experimentally were compared with existing plume correlations, data in the literature and the Eurocode correlations. The results show that: the presence of the column contributed to “straighten” the flame; although pool fires with same diameters were characterised by the same RHR, the flame length was different depending on the fuel type; experimental gas temperatures were lower than the temperature correlation given in the Eurocodes. In sum, the correlations included in the Eurocodes provided reasonable predictions in terms of flame length and of fire plume temperature rise around a steel vertical element located along the centreline of the localised fire.     

Modelling of heat and carbon monoxide emitted from moving cars in an underground car park

Three computational fluid dynamics (CFD)-based numerical models—the average-diffused model, the random-stationary and the random-average model-are proposed and developed to simulate the distribution of temperature and carbon monoxide concentration in an underground car park. The average-diffused model provides information on the effectiveness of ventilation system to remove the heat and dilute carbon monoxide contaminant in a well-mixed scenario. The random models are able to account for the movement of cars and the accumulating effect of heat and carbon monoxide contamination. By assuming that heat and CO emitted from cars are highly mixed, the random-average model shows reasonable result as compared with that of random-stationary model. The distribution of velocity, temperature and CO of the three models are compared and discussed. The study explored the possibility of assisting in the design of the ventilation system for an underground car park using the CFD technique.     

大空间火灾下铝合金构件温升计算方法

性能化抗火设计过程中,火灾下结构构件的温升计算方法对设计结果具有重大影响。为研究大空间火灾下铝合金构件的温升计算方法及火焰辐射对构件温升的影响,对2种常见的铝合金构件截面试件进行了火灾温升试验。试验结果表明,由于火焰辐射的作用,构件温度与周围空气温度较为接近。基于铝合金构件的导热微分方程,提出了一般室内火灾和大空间火灾下铝合金构件的温升计算方法,并与试验结果进行了对比分析。结果表明：计算大空间火灾下铝合金构件温升时,忽略火焰辐射的作用会导致结果偏于不安全;所提出的基于点火源假定的火焰辐射热量计算方法较欧洲规范中的计算方法更为简单准确。此外,火焰辐射下烟气黑度值对构件温升的计算具有较大影响,并根据试验结果拟合了烟气黑度的实用计算式,计算结果与试验拟合结果吻合良好。     

Recent advances in fire–structure analysis

One of the recommendations of the National Construction Safety Team (NCST) for the Federal Building and Fire Safety Investigation of the World Trade Center Disaster [NIST NCSTAR 1 Final report on the collapse of the World Trade Center Towers. NCST for the Federal Building and Fire Safety Investigation of the World Trade Center Disaster, National Institute of Standards and Technology, Gaithersburg, MD, September 2005] is to enhance the capability of available computational software to predict the effects of fires in buildings, for use in the design of fire protection systems and the analysis of building response to fires. Following this recommendation, this paper presents two new interfaces in fire–thermal–structural analysis. The first interface uses adiabatic surface temperatures to provide an efficient way of transferring thermal results from a fire simulation to a thermal analysis. It assigns these temperatures to surface elements of structural members based on proximity and directionality. The second interface allows the transfer of temperature results from a thermal analysis modeled with solid elements to a structural analysis modeled with beams and shells. The interface also allows the reverse, namely the geometric updating of the thermal model with deflections and strains obtained from the structural analysis. This last step is particularly useful in intense fires of long duration, where significant deflections and strains could cause damage to insulation and displace the structure to a different thermal regime. The procedures can be used for a variety of fire simulation, thermal, and structural analysis software.     

An effective thermal property framework for softwood in parametric design fires: Comparison of the Eurocode 5 parametric charring approach and advanced calculation models

Timber, like other structural materials such as concrete and steel, has its own Eurocode (Eurocode 5 part 1.2) for the structural fire design of buildings. However unlike other fire parts of the Eurocodes it is not widely adopted due to its inherent limitations. With the exception of a single Annex, the timber Eurocode (EN 1995-1-2) is only applicable to standard fire exposure. Annex A gives guidance on the charring rates of initially un-protected timber members in parametric fires, however in the UK the use of the Annex is prohibited by the national Annex to the code.The concrete and steel industries have undoubtedly benefited from performance based design whereby the structural fire design strategy is centred on a design fire (typically a parametric fire), which is more credible than the standard fire curve. Such an approach has resulted in more flexible, innovative buildings which have been designed based upon fundamental structural mechanics at elevated temperature, using advanced numerical models. At present however the same principals cannot be applied to the advanced fire design of timber buildings due to current limitations in the timber Eurocode. Where advanced calculation procedures are considered by the code (Annex B), much like many of the methods contained therein, the procedures are only applicable to standard fire exposure.The scope of applicability of the code stems from a fundamental problem regarding a lack of understanding of the heat transfer characteristics of timber in natural fires. The thermo-physical properties contained in the code are ‘effective’ properties. This essentially means that they are calibrated against test results to account for a lack of understanding regarding mass transfer, cracking and ablation both within the timber and char layer. Such calibrations have only been performed on timber members exposed to standard furnace conditions.To attempt to overcome this barrier and extend the scope of thermo-physical properties in the code a study has been undertaken to establish how the conductivity properties of the char layer influence the depth of char in parametric fires. Through calibration of an effective conductivity of the char layer against the parametric charring method contained in Annex A of EN 1995-1-2, it has been possible to establish a relationship between ‘heating rate’ and the effective conductivity of the char layer, in the heating phase of parametric fires. The modified conductivity model is shown to be applicable to a range of densities and moisture contents of timber and also variations in heating rate and fire load density. The latter is a direct result of the method used in the adaptation of the properties. The modified model is objectively critiqued and proposed further work is discussed in detail. The applicability of the modified model in the cooling phase of fires is also discussed.     

耐火钢梁的抗火性能参数分析与抗火设计

介绍了耐火钢的高温性能参数及火灾下耐火钢构件的升温计算 ,利用ANSYS有限元分析软件所建立的火灾升温条件下耐火钢梁的非线性有限元分析模型 ,进行了大量的参数分析 ,研究各种参数的变化对耐火钢梁抗火临界温度的影响 ,进而提出耐火钢梁抗火设计的简便方法。最后通过算例验证了方法的可靠性。     

Experimental investigation of the behaviour of fin plate connections in fire

Accidental fires and full-scale structural tests have indicated that steel connections can be subjected to large deformations and fracture in fire. This is not currently considered in fire engineering design approaches because the connections are assumed to heat up more slowly than the structural frame members and therefore retain a greater proportion of their strength. A project at the Universities of Sheffield and Manchester has investigated the robustness of common types of steel connections when subjected to fire. In the test programme the connections were subjected to combinations of shear force and tying force, and loaded to large deformation and fracture. This paper reports on the test results on fin plate connections. The test results indicate that bolts are vulnerable to shear fracture and that failure is usually controlled by bolt shear rather than by plate bearing. Fin plate connection resistance reduces rapidly with increase of temperature.The test results are compared to values suggested by the current United Kingdom design guidance and Eurocode 3 Part 1.8. A previously developed component-based model is also used to simulate the test results.