边界条件对平板网架结构抗火性能的影响

在正放四角锥网架结构抗火性能研究的基础上,进一步分析了两向正交正放网架、斜放四角锥网架和正放抽空四角锥网架在大空间建筑火灾中的热力耦合反应。基于有限元程序ANSYS建立了网架结构上弦压杆应力比一致的结构分析模型,按温度增量加载的方法,对不同支座布置、温度场及荷载条件下的网架结构全过程反应进行了分析。结果表明,温度场非均匀性是导致网架结构杆件相互约束的主要因素,随着温度场非均匀性系数η的减小,各型网架结构的临界温度呈下降的趋势;在相同的温度场和支座布置条件下,随着荷载比的减小各型网架结构临界温度呈升高趋势;根据不同类型网架的传力特点,释放网架结构在主要传力方向的约束,可以提高网架结构的抗火承载力。上述边界条件对网架结构抗火性能的影响规律,为确定网架结构抗火性能关键参数分析方案提供了理论依据。     

支承刚度对两向正交斜放网架抗火性能的影响

为研究支承刚度对两向正交斜放网架抗火性能的影响,利用非线性有限元分析软件ANSYS,建立两向正交斜放网架火灾高温下的热-结构耦合有限元计算模型,考虑不同荷载比下支承刚度的影响,对该模型在火灾均匀温度场中的全过程反应进行数值模拟计算,得到不同参数条件下两向正交斜放网架结构的临界温度及结构变形的特征.结果表明,采用同种支承刚度的两向正交斜放网架时,荷载比越小,临界温度越高,抗火性能越好;在相同荷载比情况下,两向正交斜放网架的临界温度值随着支座法向支承刚度的逐渐增大而呈现降低的趋势.     

两向正交正放网架抗火性能浅析

本文采用ANSYS非线性有限元软件,建立两向正交正放网架结构在大空间火灾作用下的热力耦合有限元模型,按温度增量加载的方法,考虑支座布置形式、温度场非均匀性等因素对结构抗火性能的影响.对结构在火灾中的全过程反应数值模拟结果表明,结构上弦压杆温度应力增长较快,邻近网架对称轴上弦压杆是网架结构的关键杆件;在实际的网架结构设计过程中需要严格地控制杆件的长细比,尤其是上弦杆件的长细比;支座布置形式对于两向正交正放网架抗火性能影响很大.上述的结论为确定影响正交正放网架抗火性能关键参数提供了参考,并为两向正交正放网架抗火设计提供理论依据.     

火灾均匀温度场中正放四角锥网架结构临界温度研究

随着温度的升高,钢材的力学性能将会发生较大的变化。钢结构在均匀温度场达到承载能力极限状态时的临界温度是钢结构抗火性能的重要特征,而网架结构的临界温度主要受网架的几何特征、荷载比、构件稳定应力的影响。本文通过对不同参数条件下正放四角锥网架结构在均匀温度场中结构反应全过程分析,得到不同参数条件下正放四角锥网架结构的临界温度,为大空间建筑网架结构抗火设计实用方法提供理论依据。     

正放四角锥网架结构的抗火性能分析

基于一正放四角锥网架结构算例,通过对其多火源位置的计算分析表明,杆件通常会在几个时间段内失效,而其余时间段网架则出现暂时的稳定平衡状态,通常都是连续几个荷载步都出现杆件的集体失效,其中以开始阶段的失效最为明显,网架结构的中心部位为抗火的薄弱环节,首批失效的杆件大部分集中在中央上弦.     

网架设计主要问题分析及其应用

网架以其实现跨度大、自重轻,外形现代而越来越广泛地运用于体育场馆、机场、收费站等公共建筑中。 网架结构常用形式有三种: 一、由平桁架系组成的两向正交正放网架、两向正交斜放网架、两向斜交斜放网架、三向网架、单向折线形网架。     

北京亚运会新建体育场馆屋盖结构

高度或}用钢量场馆名称结构形式平面及尺寸(m)施工安装方法厚度(m)}(kg/m’)北京大学生体育馆两向正交斜放网架{方形64又64挑6m4 .2地面拼装整体吊装地坛体育馆三向网架正六边形,边长603 .75满堂脚手高空散装光彩体育馆星形四角锥网架矩形46.8又67.63 .5分段吊装滑移就位海淀体育馆正放四角锥网架矩形48又524 .0三段吊装滑移就分位月坛体育馆斜放四角锥网架八角形57只663。8地面拼装整体吊装悬挑4.2~4.5m北京国际网球中心 网球馆斜放四角锥网架矩形60只603~4 .5分段吊装积累滑移悬挑3m国家奥林匹克体育 中心田径场看台正放四角锥网架扇形2 .…     

乌鲁木齐国际机场101机库提升网架桅杆的基础承重设计

1工程概况乌鲁木齐地窝堡国际机场改扩建工程包括网机架、门厅桁架,检修走道,墙架柱及屋面檩条等制作安装、涂装。钢结构屋盖由两种不同的结构形式组合,大厅桁架以焊接H型钢,热轧角钢、钢管、槽钢、钢板为附杆件。网架为焊接空心球节点,三层斜放抽空四角锥平板结构。轴线投影尺     

深海工程浮式网架结构单元的静力分析

将浮式网架结构应用于深海工程可为人类开发深海提供所需要的空间。选取正放四角锥网架为结构单元,利用Morison方程计算波浪力、海流力,通过函数关系找出作用于结构自身荷载的最大值,平均施加到水面以下球节点上,并施加重力、浮力、上部荷载,模拟结构在海洋环境荷载作用下的力学响应,用百年一遇的海况进行校核,得出该网架结构单元相对承载力较高、安全可靠的结论。由于承载力出现较大的富余,为进一步优化结构,可通过网架结构布局上的改进来实现,包括整体上采用抽空四角锥网架等杆件较为简单的网架体系,局部抽除某些内力较小的杆件,或者将抽掉的杆件替换成与钢结构有较好融合且适应海洋环境的其他材料,使得浮式网架结构更经济安全地应用于实际工程。     

轴向约束杆件高温屈曲后强度对网架结构高温极限承载力的影响

局部火灾下,网架结构升温具有明显的非均匀性,结构中温度高的杆件热膨胀受到温度较低杆件的约束,使得网架结构的部分杆件具有显著的约束杆件高温力学特征。基于局部火灾下网架结构力学反应全过程数值追踪技术,考察结构升温非均匀性、结构荷载比、火源位置和结构跨度影响因素下,网架结构杆件高温屈曲后强度对整体结构抗火极限承载力的贡献。研究表明:当结构温度分布非均匀系数η在0.2≤η<0.6区间取值,且结构荷载比R在0.2～0.7范围内,杆件高温屈曲后强度对网架结构高温极限承载力有较大贡献;随着火源位置从网架几何中心偏移,杆件高温屈曲后强度对结构抗火极限承载力的贡献增大;随着网架跨度的增加,当结构荷载比R≤0.5时,杆件高温屈曲后强度对结构抗火极限承载力的贡献逐渐增大,当荷载比R>0.5时,杆件高温屈曲后强度对结构抗火极限承载力的贡献先逐渐减小然后转变为逐渐增大。上述研究结论可为建立网架结构第2阶段失效准则提供理论依据。     

Application of fire-resistant steel to beam-to-column moment connections at elevated temperatures

This paper presents a new method of using fire-resistant steel to improve the fire-resistance of beam-to-column moment connections in steel structures. Two full-scale beam-to-column moment connection specimens were tested at elevated temperatures according to the standard ISO-834 fire to verify the feasibility of the proposed method. In addition, a detailed 3-D finite element model was developed to simulate the structural behavior of the column-tree moment connection specimens in fire. The fire test results show that the proposed method can effectively extend the fire endurance time, reduce structural deformation, and raise the critical temperature to failure for the beam-to-column moment connections. The numerical results obtained from the 3-D finite element analyses for the two specimens successfully simulated the fire test results.     

A simple method for combining fire and structural models and its application to fire safety evaluation

To consider the actual fire characteristics in the fire response analysis of building structures and to simplify the complex relationship between the fire analysis model and the structural finite element analysis model, a spatio-temporal model of the fire temperature and heat flux boundary for heat conduction analysis is developed. The proposed model adopts a two-way orthogonal polynomial approach for fitting the discrete data from the fire simulation and obtains continuous spatial polynomial equations. It is shown to be accurate for capturing the distributions of temperature and heat flux that are required for a heat conduction analysis and a thermal mechanical coupling analysis. Finally, the model is implemented through user-subroutines UTEMP and DFLUX in ABAQUS, and it is applied to a new archive in Beijing. The results show that this method may be used to combine fire simulation and structural analysis for the safety evaluation of structures under fire.     

钢管混凝土组合平面框架结构热—结构耦合分析

采用数值模拟方法,利用有限元软件ANSYS计算分析了无保护层的3层3跨钢管混凝土柱—钢梁平面框架在局部受火条件下的抗火性能,运用顺序耦合方法对结构进行了热—结构耦合分析,得到了结构的耐火极限、临界温度及破坏形态。     

A holistic numerical approach to simulating the thermal and mechanical behaviour of a tunnel lining subject to fire

Conventional heat transfer analysis for the prediction of fire-induced damage in a tunnel is performed without consideration of the spalling and dehydration of concrete, meaning that the fire-induced damage of concrete may be underestimated. This study proposes a new model that is able to simulate structural loss during a fire by eliminating the elements exceeding a pre-determined critical temperature in a finite element analysis. The important parameters for the application of the proposed element elimination model include the critical temperature chosen as the element elimination criterion and the changes of the combined heat transfer coefficients, which are dependent on element size and the time–temperature history during a fire, respectively. These parameters are derived from a series of parametric studies based on real fire experiments using a high-temperature furnace. In order to verify the applicability of thermo-mechanical coupling analysis using the proposed model, the fire-induced damage of an unreinforced concrete tunnel lining was estimated with a focus on the spalling depth, temperature distribution, and equivalent stress in the remaining part of the concrete lining under RABT and RWS fire scenarios.     

Performance-based analysis of large steel truss roof structure in fire

Due to the fast developments of large-space multi-functional architectures, large-span steel structures have been widely used in recent years. Therefore, the fire-resistance design of this kind of structures has attracted more attentions. Since traditional ISO834 standard fire curve is not suitable for large space structures, performance-based fire resistance design method is required. This paper presents the comprehensive case studies on the fire performance of a large space exhibition centre in Shanxi province, China under real fire scenarios including heating and cooling phases. The non-uniform fire temperature fields of the large space exhibition centre for the designed fire scenarios have been generated by using Fire Dynamic Simulator (FDS). A finite element (FE) model has been developed using FE software ANSYS for modelling the structural behaviour of the exhibition centre under different fire scenarios. Based on the results generated in this research some recommendations for the fire resistance design of large space steel truss structures have been proposed.     

钢管桁架抗火试验及有限元分析

进行了2个足尺钢管桁架的抗火试验,建立了桁架的有限元模型,经比较,有限元与试验结果吻合良好。火灾试验和有限元分析结果表明:火灾作用下平面圆钢管桁架的破坏主要是由于腹杆管壁局部屈服引起的;并且随着荷载比的增加,平面圆钢管桁架的耐火极限温度逐渐降低。     

Macroscopic FE model for tracing the fire response of reinforced concrete structures

A macroscopic finite element model for tracing the fire response of reinforced concrete (RC) structural members is presented. The model accounts for critical factors that are to be considered for performance-based fire resistance assessment of RC structural members. Fire induced spalling, various strain components, high temperature material properties, restraint effects, different fire scenarios and failure criteria are incorporated in the model. The validity of the numerical model is established by comparing the predictions from the computer program with results from full-scale fire resistance tests. Case studies are conducted to demonstrate the use of the computer program for tracing the response of RC members under standard and design fire exposures. Through the results of the case studies, it is shown that the fire scenario has a significant effect on the fire resistance of RC columns and beams. It is also shown that macroscopic finite element models are capable of predicting the fire response of RC structural members with an adequate accuracy for practical applications.     

高大空间火灾空气升温条件下整体网架抗火性能分析

为了研究网架在高大空间火灾空气升温条件下的抗火性能,结合某正放四角锥网架,采用有限元方法对网架在高大空间温度场下的抗火性能进行模拟分析。火源中心分别选择了3种不同位置对结构进行温度场划分和抗火分析。确定网架结构的耐火极限准则,得到不同工况下结构的极限抗火时间;研究不同工况下结构的内力、位移等响应变化过程及分布规律;同时对比分析各工况下网架结构抗火性能的差异。