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。     

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。     

防火板保护钢柱四面受火时截面温度计算方法

研究了采用防火板保护钢柱四面受火时的截面温度计算方法,分别考虑了防火板与钢柱无间隙及防火板与钢柱有间隙两种情况。由于采用防火板保护时,钢构件与防火保护层内表面之间主要通过热辐射进行热量传递,与现行欧洲规范(EC 3)公式假定构件防火保护层之间通过热传导进行热量传递不同。现行EC 3规范公式能较为准确地计算热传导系数较小的防火涂料保护时构件升温,但不能准确计算火灾下热传导系数较大的防火薄型板保护钢柱的温度。通过在现行规范公式中增加空气的热阻一项,以考虑热辐射传热方式对构件截面升温的影响。分别采用有限元方法和建议公式,对防火薄型板保护,不同保护层厚度和不同截面系数钢柱截面升温规律进行分析,结果表明修正公式的计算结果与有限元结果吻合良好。     

轻质防火保护层铝合金构件升温计算简化

由于铝合金材料的密度和比热容与钢材相比差别较大,在ISO 834标准升温条件下,铝合金构件的升温过程与钢构件存在明显差异.为了得到有轻质保护层铝合金构件的升温计算简化公式,采用增量法计算了ISO 834标准升温下的轻质保护层铝合金构件升温曲线,并对数据进行非线性拟合分析,得到了有轻质保护层铝合金构件升温计算简化公式,进...     

火灾下钢结构构件的升温

本文将分无保护层、有保护层和截面温度非均匀分布三种情况介绍钢结构构件在火灾下温度分布的计算方法,较系统地介绍了国内外所采用的分析方法及欧洲和英国标准所采用的计算方法.     

火灾中受保护钢构件的温度数值计算

利用传热学原理，考虑保护层表面热阻和保护层厚度内温度的非线性变化，建立受保护钢构件在火灾条件下瞬态导热微分方程，并计算其截面温度。     

钢结构构件热响应的研究现状

钢材在高温下强度和刚度都将迅速降低，介绍了国内外关于钢结构构件在火灾中热响应的试验和计算机数值模拟的研究成果，并着重介绍了在无保护层、有保护层和截面温度非均匀分布三种情况下构件的热响应分析计算方法，提出了火灾中钢结构构件抗火设计今后需要研究的问题。     

火灾导致世贸中心塔楼坍塌的一种解释

本文基于建筑通风因素对世贸中心塔楼钢桁架构件在火灾中的温度做了计算。用 CIB相关性研究火灾。传热分析考虑了钢材和耐火保护材料的各种性质。本文提出了一种基于桁架杆件杨氏模量降低而发生压缩弯曲的结构破坏模式 ,计算所得两塔楼楼层估计破坏或开始塌陷的时间分别为 :北楼(WTC1) 10 5± 2 0 min,南楼 (WTC2 ) 5 1± 9min,与飞机撞击后两楼实际坍塌时间 10 4 min和 5 6 min相当吻合。看来 ,耐火保护层的厚度及其在两楼中分别为 38.1mm和 19.1mm的差别对两塔楼的坍塌有着根本性的影响。     

防火涂料局部破损对钢构件在火灾下的温度分布影响

采用有限元方法分析由于防火涂料局部破损而造成的火灾下钢构件内的三维热传导问题,给出构件内温度的分布规律.之前先用该有限元模型分析防火涂料完整的钢构件内的二维热传导问题,并将有限元结果与利用傅立叶导热定律建立的传热方程的差分结果进行对比,从而验证了有限元方法进行温度分析的可行性及可靠性.     

考虑火焰辐射的钢构件升温计算方法对比研究

目前《建筑钢结构防火技术规范》中对火灾下钢构件升温的计算忽略了火焰辐射的影响,可能导致大空间火灾中钢构件温度计算值偏低.本文介绍了三种考虑火焰辐射的钢构件升温历程计算方法,对既往大空间火灾试验进行数值模拟与计算,验证了三种方法的准确性,并针对不同的火灾场景与构件位置进行了对比计算分析.分析结果表明在本文的火灾场景下考虑...     

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.     

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.     

Prediction to nonlinear behavior of steel frames subjected to fire

A new approach is presented for analysis of nonlinear behavior of steel frames subjected to fire. The material and geometrical nonlinearity as well as the non-uniform profile of temperature across section of frame members are taken into account. Thermal forces induced by temperature variation are also considered. The elasto-plastic stiffness equation of elements is established by using the generalized Clough model. The analysis of strutures subjected to fire is converted to analysis of structures subjected to unbalanced forces induced by temperature increment. Then a procedure to calculate the nonlinear response and ultimate load of steel frames exposed to fire is proposed.

For verifying the validity of the approach proposed, tests on two large-scale models of single-story two-bay steel frames are conducted in gas furnace to simulate fire. The temperature elevation and deformation response of the models due to fire are measured. Good agreements between the results measured and calculated are demonstrated on the behavior of the models exposed to fire.     

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。     

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.     

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.     

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.     

基于ANSYS分析有防火保护的碳纤维加固混凝土构件的温度场

在确定碳纤维加固混凝土构件防火方法的基础上,利用有限元分析软件ANSYS对火灾下有防火保护的碳纤维加固混凝土构件的温度场进行分析,并获得构件截面温度分布的规律。结果表明:碳纤维加固构件的温度场计算结果与试验结果符合较好,为进一步研究火灾下有防火保护的碳纤维加固混凝土构件的力学性能和耐火极限创造了条件。     

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...