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...     

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.     

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.     

Thermal bowing on steel columns embedded on walls under fire conditions

The contact of steel columns with building walls is responsible for huge thermal gradients within its cross-section during fire. Current regulatory codes for fire design of steel members provide a formulation to assess the load-bearing capacity of these members assuming uniform temperature through the cross-section; however, this is not what happens in the major part of the cases in real structures where the columns are embedded on walls. The walls on one hand will provide a temperature reduction on the columns, which is somehow favourable in terms of its fire resistance, on the other hand the differential heating on the columns cross-section may lead to unfavourable stresses (bending moments) responsible for instability (thermal bowing). Considering that the structural behaviour of columns is strongly dependent of the second order effects this is an important phenomenon which may lead to a significant reduction on its fire resistance. This paper presents the results of a numerical study to assess the influence of the differential heating on the fire design of steel columns. New interaction axial force–bending moment diagrams for non-uniformly heated H steel columns are proposed.     

Capacity reduction and fire load factors for LRFD of steel columns exposed to fire

Capacity reduction and fire load factors corresponding to the load and resistance factor design (LRFD) format are developed for steel columns exposed to fire. A sample deterministic framework to determine fire and steel temperatures and the capacity of steel columns is adopted for this analysis to structure the methodology. A specific number of parameters that affect the structural response, including the fire load, ratio of floor area to the total area of the fire compartment, opening factor, thermal absorptivity of compartment boundaries, thickness, density and thermal conductivity of insulation, dead load, and live load are taken as random variables. Mechanical and sectional properties of steel (e.g., yield strength, cross-sectional area, etc.), are also considered to be random variables. The effect of active fire protection systems (e.g., sprinklers, smoke and heat detectors, fire brigade, etc.), in reducing the probability of occurrence of a severe fire is included. Given the choice of framework and based on detailed reliability analyses, it is shown that the capacity reduction and fire load factors should vary depending on the presence of active fire protection systems in a building.     

火灾下钢结构楼板的薄膜作用

通过对真实火灾中的足尺火灾试验和观察显示，合组合楼板和承载钢梁的建筑物的结构承载力比现行杭大设计方法的建议值高出许多。因此规范中规定所有承载钢梁都要添加被动防火保护是不必要的。现行设计方法和实际结构性能之间产生这种差异是由于设计方法中忽略了楼板的薄膜作用。本根据国外有关资料给出了几种简单计算方法，允许在钢结构杭大设计中考虑楼板的薄膜作用。从而可以更精确地评估火灾下建筑物的真实承载能力，在给定的耐火时间内能减少相当数量钢梁的防火保护。     

建筑外墙外保温材料防火安全的选型设计探讨

近年来,我国因建筑外墙外保温材料防火安全问题而导致特大火灾事故频发,尤其是上海胶州路教师公寓火灾、沈阳皇朝万鑫大厦火灾和北京央视大楼火灾,造成重大人员伤亡和财产损失,使得建筑外墙外保温材料防火安全成为人们关注的焦点。该文针对目前建筑外墙外保温材料选型设计中不注重防火安全的实际问题,分析了各种建筑外墙外保温材料防火性能,探讨其不同的使用局限性和优缺点,为建筑外墙外保温材料的选型设计提供参考。     

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.     

A group-AHP decision analysis for the selection of applied fire protection to steel structures

Decisions related to selecting the most suitable fire protection for steel structures subject to fully developed fires are critical to addressing design and construction uncertainties. Fire design stakeholders are faced with the challenge of managing their divergent opinions to make design decisions given the many options or engineered solutions available to meet performance objectives. This paper demonstrates the viability of a group-Analytic Hierarchy Process (AHP) as a multi-criteria decision analysis (MCDA) technique for managing fire design stakeholder opinions on economic, safety, environmental and societal considerations toward selecting suitable fire protection for steel structures. Based on 22 structural fire design decision criteria gathered from literature and expert opinion, 36 New Zealand stakeholders from 12 fire design stakeholder categories have been interviewed to elicit ratings from their relative comparisons of the structural fire design decision criteria. The Geometric Mean Method-Analytic Hierarchy Process (GMM-AHP) is used to assess four applied fire protection options or alternatively to use unprotected steel. The results show the seamless aggregation of multiple stakeholder desires, the importance levels of different stakeholder opinions and the systematic approach in ranking the proposed fire protection options. The ranking shows that given a general selection of passive fire protection by stakeholders having equal weights, there is a stronger preference for the concrete encasement of steel.     

Assess the Fire Resistance of Intumescent Coatings by Equivalent Constant Thermal Resistance

Intumescent coatings are now the dominant passive fire protection materials used for steel construction. Intumescent coatings will react at high temperatures and the thermal properties of intumescent coatings can not be measured directly by the current standard test methods which are originally designed for the traditional inert fireproofing materials. This paper proposed a simple procedure to assess the fire resistance of intumescent coatings by using the concept of equivalent constant thermal resistance. The procedure is based on the approximate formula for predicting the limiting temperatures of protected steel members subjected to the standard fire. Test data from investigations on both small-scale samples and full-scale steel members are used to calculate the equivalent constant thermal resistance. Using the equivalent constant thermal resistance of intumescent coatings, the calculated steel temperatures agree well with the test data in the range of the limiting temperatures from 400°C to 600°C. The procedure needs no complex computation and is recommended for practical usage. The equivalent constant thermal resistance could be used to quantify the insulation capacity of intumescent coatings.     

Evaluation of duct opening protection in two-hour fire walls and partitions

There is a continuing debate among fire protection specialists on the value and role of fire dampers in preventing fire spread via HVAC duct systems. It has been recognized that fire dampers are not required under all circumstances. For example, NFPA 90A,Standard for the Installation of Air Conditioning and Ventilation Systems, does not require the installation of fire dampers in ducts penetrating one-hour fire-rated walls and partitions. Additionally, there are circumstances where the closure of dampers may affect critical environmental air systems. In these situations, the value of fire dampers must be determined in terms of an overall risk assessment. It has been suggested that the role of fire dampers be considered in terms of the total building fire protection system, but a quantitative approach for such an assessment has been previously unavailable. In particular, there has been no data related to the performance of a duct system when subjected to a standard two-hour fire exposure. Gewain et al. have described an equivalency approach and full-scale fire test data for the protection of duct openings in two-hour fire-resistant walls and partitions. The objective of this paper is to review and summarize the equivalency rationale and test data and describe engineering methods available to apply an equivalency approach more generally. The approach was developed for situations where horizontal steel ventilation ducts penetrate fire-rated walls and partitions. The approach does not address smoke dampers or ducts containing combustible materials.     

钢屋盖结构防火的性能化消防工程分析

因为建筑学上和构造上的原因,越来越多的建筑设计采用了钢结构。为了保证建筑结构构件的完整性,建筑规范提出了结构耐火性能的要求。但是,已规定的要求没有促进具有良好经济效益的设计,并且假定遵照规范是达到安全等级的唯一途径。本论文提出采用以性能设计为基础的消防工程理论方法来证明火灾中钢构件的性能。消防工程准则已发展至符合规范的要求,并能保证结构在火灾中的安全性能。本文采用一个游泳/跳水馆作为例子来讨论对钢屋顶结构进行耐火保护。本例的研究表明,游泳/跳水馆的钢屋顶结构可以不用耐火涂料,并且不会降低整个建筑的防火安全等级。     

钢结构柱与墙体围护-防火一体化可行性初步探究

对目前钢结构建筑常用的围护墙体材料的高温稳定性、热工特性、变形适应性等性能进行调研、分析,初步筛选出有一定防火性能的围护材料和构造形式后,以蒸压轻质加气混凝土(ALC)板、石膏岩棉组合墙体、砌体为例,利用有限元软件ABAQUS进行传热分析的数值计算,得到火灾下受围护体系包裹的H形钢柱的温度分布情况。并对墙体的厚度、热工性能和构造形式等进行相关的参数分析,结合规范评估将围护构件兼作钢结构防火保护的可行性。结果表明,当采用合适的厚度和构造方式时,3种围护构造均能达到钢结构防火保护的要求,这也初步验证了围护墙体与钢结构柱防火一体化的可行性,为围护与防火一体化技术的设计及构造提供了参考。     

Optimising design decision-making for steel structures in fire using a hybrid analysis technique

Steel structures can be protected against the effects of fully-developed fires by the use of sprayed on materials, board systems and intumescent paints, etc. or by using sufficiently large unprotected elements. This paper presents how optimum decisions for the protection of steel structures in fires can be achieved in a performance-based design environment, given conflicting structural fire design decision criteria and multidisciplinary fire design stakeholder views. In particular, a novel hybrid analysis approach is proposed for combining stakeholder views on the different fire protection options and the numerical outcomes of structural fire analysis. As for the stakeholder views, reference is made to benefits and costs criteria priorities for assessing competing options resulting from a previous study from the same authors. The fire protection structural performance is numerically and probabilistically assessed according to a parametric study. The proposed approach is exemplified by making reference to a limit state structural fire design of single steel elements. A synthesis and ranking technique is then applied to integrate the qualitative results obtained in terms of benefits and costs priority scores; and the quantitative measures of failure probabilities and costs for the different fire protection options. The results show that the ranking technique accounts for multidimensionality in synthesising the structural fire design decision problem. The results also show that intumescent paints and board systems are the most cost-effective options in different stakeholder influence scenarios, given a general selection of steel structural fire protection. The hybrid technique is proposed to support an optimal and cost-effective structural fire design decision-making for buildings in a performance-based design environment.     

圆钢管及钢管混凝土柱的抗火设计

分别对圆钢管、钢管混凝土、中空夹层钢管混凝土柱进行了抗火设计,并对结果进行比较分析。结果表明,在较高荷载比下柱的耐火极限不能满足实际要求,必须进行防火保护。在相同条件下,耐火极限从大到小排序为:圆钢管混凝土、中空夹层钢管混凝土、钢管柱。在一级耐火等级下,钢管混凝土柱和中空夹层钢管混凝土柱需要厚涂型钢结构防火涂料的厚度可比钢管柱分别少55%和18%以上。随着荷载比的减小或截面尺寸的增加,柱的耐火极限提高,需要的保护层厚度减小。对于钢管混凝土柱,若采用水泥砂浆保护层,其厚度是防火涂料的3倍及以上。     

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。     

Modelling of axial restraints for limiting temperature calculation of steel members in fire

At ambient temperature, design actions calculated for a beam under lateral loading may remain unchanged irrespective of whether axial restraints at the beam’s ends are present or not. However, at elevated temperatures, axial restraints may induce significantly different design actions from those calculated at ambient temperature, mainly due to thermal restraining reactions. As a result, the limiting temperature may be reduced. In this paper, a method is presented for limiting temperature calculation of steel beams in fire in multi-storey buildings. The method takes into account the fact that the axial force generated in a steel beam in fire by axial restraints may increase to such a magnitude that the strength criterion, in terms of axial-bending interaction, may be breached. In addition, it has been recognised that the degree of axial restraints provided at the ends of a steel beam varies, depending on the axial restraint stiffness provided by neighbouring members. A simple technique to model the axial restraints provided to a steel beam by neighbouring members and the procedure for its limiting temperature calculation in a multi-bay situation in a building will be presented. The approach caters for different end conditions of the columns below and above the beam under consideration. Catenary action due to large deflection effect for beams in fire will also be discussed.     

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.     

Determination of fire resistance ratings for glulam connectors within US high rise timber buildings

Multi-storey mass timber buildings constructed with cross laminated timber and glulam are being developed globally. Where engineered timber such as glulam is utilized, the column to beam connections need to be constructed with a fire resistance rating equal to that of the connecting members. The preferred glulam connectors are either a concealed steel plate with bolts and dowels; or a concealed proprietary screw-in sleeve type connector. The fire resistance of connectors for glulam members is an unresolved design issue, as there is no clear methodology to assess their capacity under fire, when the timber is exposed and not clad behind fire protective plasterboard. There is limited fire test data on concealed connectors under shear forces, which is the normal loading condition within a constructed building. Fire test data is also limited on full-size specimens. Correlations developed to date to calculate concealed connector fire resistance have only limited application.A methodology for the design of glulam beam to column connections has been developed based on an extensive literature review, examining the key issues for connection failure. It has been determined that char rate for the timber at the connection needs to be increased above the normally accepted design values, due to the influence of the steel connectors. Secondly, the reduction in timber strength behind the char layer needs to be accounted for, by including a greater depth of reduced strength and stiffness timber, such that the connection can effectively transfer the applied forces through the timber to the steel connector. The methodology detailed within this paper provides a simple approach to evaluate the timber cover to the concealed steel connector, where the timber strength and stiffness are effective.