火灾下门式钢刚架倒塌预警可靠度研究

为了解决实际火灾救援中火灾场景、荷载水平等不确定因素对倒塌预警准确性的影响，基于可靠度理论提出了预测受火建筑倒塌剩余时间的方法。采用经试验验证的三维有限元模型对火灾下门式钢刚架结构倒塌进行仿真模拟，基于火灾下门式钢刚架结构四种倒塌模式和三级倒塌预警指标，研究升温工况、柱脚刚性、荷载比等因素对倒塌剩余时间预测的不定性影响，通过蒙特卡罗抽样，研究考虑各种影响的火灾下门式钢刚架倒塌预警指标概率统计参数。结果表明：倒塌剩余时间比仅与可靠度和倒塌模式有关，不受火灾现场的各种不确定性因素影响，可以在火灾发生前通过理论分析提前计算得到；火灾中采用可靠度60%～80%对应的倒塌剩余时间比可以快速合理地预测受火刚架的剩余倒塌时间。     

火灾下门式钢刚架倒塌试验与雷达位移测试系统有效性研究

近年来火灾下钢结构倒塌造成消防官兵伤亡的事故频繁发生,亟需开展建筑火灾倒塌预警研究。现有研究已表明：可以通过测量门式钢刚架柱顶和屋脊处的微变形来预测火灾下结构的倒塌,但由于高温和热烟气的存在,火灾下位移的实时测量问题尚需研究。该文通过试验方法研究雷达在实际火场位移测量中的可行性,首先设计一个缩尺单跨门式钢刚架的火灾试验,得到结构的升温特点和位移变化规律;采用雷达位移测试系统对门式钢刚架火灾试验的关键点位移进行了测量,并与传统拉线位移测试系统的测量结果进行对比,验证雷达位移测试系统用于火灾条件下的结构位移实时测量的有效性与准确性;采用有限元软件ABAQUS模拟火灾下刚架的倒塌过程,数值模拟发现：考虑了次要构件约束作用的三维结构分析模型,可以较准确地模拟火灾下门式钢刚架的倒塌过程。     

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。     

单跨门式钢刚架结构抗火设计实用方法

采用有限元数值分析方法,对门式钢刚架在多参数影响下的抗火性能进行了研究。基于经典结构力学,建立非均匀温度场中单跨门式钢刚架结构的内力方程,以此判断高温下,结构最不利截面几何位置。研究表明,在大空间建筑火灾中,主要是梁跨中截面和梁端截面影响门式钢刚架结构抗火承载力;根据数值分析结果,建立不同温度场非均匀性、荷载比、高跨比和楔率参数条件下门式钢刚架结构临界温度的大数据库,并拟合得到各参数影响下结构的临界温度经验公式,在临界温度法框架下,建议了单跨门式钢刚架结构抗火设计实用方法,为基于计算的门式钢刚架结构在大空间建筑火灾下的抗火性能评估提供了参考。     

局部区域火灾下门式钢刚架三维结构分析的模拟方法

采用有限元方法对局部区域火灾下门式钢刚架三维整体结构的响应进行了数值模拟分析,得到刚架在温度-结构耦合响应下的变形及其规律,以及区域内构件破坏对整体结构的影响,为局部火灾下大跨度钢结构分析提供有效方法,并对该类结构的实用防火设计提出了建议.     

建筑结构火灾下倒塌监测及预警技术

对我国近年来建筑结构在火灾中发生倒塌的部分典型案例及长时间火灾下未倒塌的案例进行了总结,介绍了倒塌监测及预警的流程及关键技术,总结了近年来国内外针对建筑结构火灾下的倒塌进行监测及预警的相关研究情况。分析表明,利用结构变形、温度、振动等特征参数进行倒塌监测及预警的相关研究较多,但仍处于理论研究阶段,距离实际应用仍存在很大距离;面向消防救援实战需求,便捷、易用、精准、有效的系统和多方法联用的倒塌监测及预警方法是值得关注的研究方向。     

高温下门式刚架结构的有限元计算分析

首先对高温下门式刚架结构的极限状态进行详细的阐述,然后建立火灾下高温门式刚架的有限元计算的理论模型,编制相关的有限元程序,对其高温下的变形进行相关的有限元计算分析,并与试验结果进行比较,验证了计算结果的正确性,为火灾高温下门式刚架的设计计算提供相关的指导理论依据。     

标准火灾作用下钢管混凝土短柱落锤动态冲击试验研究

采用落锤冲击实验机进行ISO-834标准火灾作用下钢管混凝土短柱抗冲击性能试验研究,考察受火时间、冲击速度、冲击能量和含钢率对其抗冲击性能的影响。试验量测钢管表面温度、冲击力与压缩变形时程曲线。试验结果表明,受火时间、冲击速度、冲击能量和含钢率均对高温下钢管混凝土的动态力学性能有影响;受火时间对冲击极限承载力和残余变形的影响最为显著,其余参数对冲击承载力影响不大,而试件的残余变形随着受火时间和冲击能量的增大而增大,随着含钢率的增大而减小。常温和火灾下钢管混凝土在冲击荷载作用下产生显著的压缩变形,遭受不同程度的破坏,但仍能够保持很好的截面完整性,说明钢管混凝土在火灾(高温)下具有良好的抗冲击能力,适用于有火灾(高温)抗冲击、抗倒塌设计需求的结构。     

门式钢刚架局部火灾下三维整体结构性能的响应分析

建立了单跨门式钢刚架整体结构的模型。基于大空间局部火灾下的升温曲线,采用有限元方法对结构进行了数值模拟,分别得到了整体结构在不同防火保护方式下的变形云图以及檩条和斜梁构件的挠度随时间变化的曲线。最后对该类结构的实用抗火设计提出建议。     

基于实际火灾场景的钢框架结构倒塌机制分析

采用ABAQUS建立无楼板的多层钢框架模型,采用顺序热-固耦合法,综合考虑实际火灾场景下局部火源位置、火源功率变化、非均匀分布温度场及火灾作用下梁柱失效进行分析,研究了在梁柱的受火形式和失效柱位置两种因素影响下钢框架结构的初始破坏机理与倒塌机制。结果表明：钢框架结构的连续倒塌始于受火柱的屈曲失效,与之相连的梁由于失去竖向支撑挠度增大并产生拉力,使内力重分布柱产生侧移,进而在火灾的持续作用下结构位移不断发展,破坏向周围扩散,最终导致结构发生连续性倒塌;当底层失效柱为角柱和边柱时,结构发生倾覆式连续性倒塌;当底层失效柱主要分布在结构对称轴上时,结构发生下沉式连续性倒塌,该类型倒塌发生较为突然。     

门式钢刚架结构实用抗火临界温度计算方法

本文应用Ansys程序,针对门式钢刚架结构,变化各种参数,进行了多个不同算例的结构整体抗火临界温度的计算。在对算例结果进行参数分析的基础上,忽略次要参数,考虑主要参数,得出了适用于跨度小于52m,高度小于10m,截面高度小于900mm的任意门式钢刚架结构整体抗火临界温度的简化计算表格,可方便地用于该类结构的抗火设计。     

Robustness assessment of planar steel frames caused by failure of a side column under localized fire

Progressive collapse of a building structure under fire is a disaster that may cause heavy casualties and serious economic loss. However, there is a lack of codified method to assess fire‐induced progressive collapse of building structures. A global–local analysis method (GLAM) has recently been proposed by the authors and their colleagues to assess progressive collapse of steel buildings under localized fire, and its application on fire scenarios that causes one inner column to fail has been verified. This paper extends the application of GLAM to fire scenarios that causes a side column to fail in a planar steel frame. The predictions of the GLAM were validated against the results obtained from nonlinear dynamic analysis of the whole frame model. Besides, effects of location of the heated column at different storeys and load level of the frame were also studied. The results show that GLAM gives the same collapse predictions to the case studies with detailed nonlinear dynamic analysis. The differences between the critical load obtained from GLAM and that provided by the nonlinear dynamic analysis is within 7%. Therefore, GLAM has good applicability on robustness assessment of planar steel frames caused by failure of a side column under localized fire.     

Influence of Semi‐Rigid Connections and Local Joint Damage on Progressive Collapse of Steel Frameworks

Abstract: Semi‐rigidly connected steel frames are more vulnerable than rigidly connected frames to resist progressive collapse due to abnormal loading events. This article extends the threat‐independent method for progressive‐failure analysis of rigid frames to analysis accounting for semi‐rigid connections. The influence of joint damage caused by disengagement of member(s) is also considered in the analysis, and the degree of damage is modeled by a health index. A compound element model is employed to include the contributions of nonlinear behavior of beam‐to‐column connections, connection and member‐end damage, member inelasticity, member shear deformation, and geometrical nonlinearity to structural response. Four beam collapse modes are illustrated for the progressive collapse analysis associated with debris loading generated when disengaged structural components fall onto lower parts of the structure. The impact effect is taken into account for the quasi‐static nonlinear analysis by utilizing an impact amplification factor according to GSA and DoD guidelines. Any progressive collapse occurring thereafter involves a series of collapse events associated with topological changes of the frame. The analysis procedure is illustrated for the progressive collapse behavior of two planar steel frames. The results demonstrate that the proposed method is potentially an effective tool for the progressive collapse analysis of semi‐rigid steel frames under abnormal loading events.     

钢管混凝土、型钢混凝土、钢筋混凝土平面框架耐火性能对比分析

对常温下承载能力和刚度接近的钢管混凝土柱—钢梁平面框架、型钢混凝土平面框架、钢筋混凝土平面框架火灾下的破坏形态和耐火极限进行了对比分析。研究表明,三种框架的破坏形态存在明显差别,钢管混凝土框架出现了钢梁破坏,其他两种框架出现了受火柱破坏,型钢混凝土框架耐火性能最好。     

Collapse analysis of regular and irregular tall steel moment frames under fire loading

This study is carried out to evaluate the progressive collapse of steel buildings under fire event. To this end, a 15‐story steel structure with moment‐resisting system and composite floors is considered. The effects of various parameters such as beam section size, gravity load ratio, vertical irregularity of resisting system, and location of fire compartments on collapse modes are investigated numerically. Different temperature‐time curves are defined across the composite floors according to the Eurocode 4. It is found that local collapse of the frames at the ground floor fire is triggered by the buckling of the interior heated columns at approximately 540°C. The redistributed loads by floors delay the global collapse at least 45 min. Increasing gravity loads accelerates the global collapse of the frames significantly. The heated columns of the middle floor buckle at higher temperature compared to the ground floor heated columns and no global collapse occur due to this scenario. In general, the potential of collapse of the regular and irregular frame due to fire in the edge bay is higher compared to the fire in the middle bay. It is also found that the local and global collapse of regular frames occur earlier than irregular frames.     

Thermal and structural response of two-storey two-bay composite steel frames under furnace loading

The collapse of the World Trade Center Towers and other recent fires in tall buildings has motivated this study to understand the performance of structural frames under fire loading. Three two-storey, two-bay composite steel frames were constructed and subjected to dead loads by applying weight blocks, and to thermal load by placing the frame in a furnace. The furnace was specially designed to allow for controlled heating of the structural elements that formed the four compartments of the test frame. This paper describes the experimental results of furnace test conducted on the three full-scale composite frames. The three tests differed from each other in the number and location of compartments that were heated by the furnace. For each test, the structural elements were subjected to a heating-up phase followed by a cooling-down phase. The furnace temperatures and the steel and concrete temperatures recorded during the test are presented. The thermally induced horizontal displacements of the columns and vertical deflections of the composite beams are discussed. Observations on local buckling of the steel beam, cracking of the concrete slab and failure of the beam-to-column connections are tabulated. Experimental results of the three tests are compared with each other by studying the complete deformation process of the test frames over time. Results indicate that the deformation process of the test frames was highly dependent on the number and location of compartments that were subjected to thermal loading.     

门式钢刚架结构实用抗火设计方法

利用针对变截面钢刚架结构抗火设计的有限元专用分析程序 ,通过研究各种参数变化对门式钢刚架结构的抗火临界温度的影响 ,推导出门式钢刚架结构实用抗火设计方法。通过算例介绍了方法的使用 ,并验证了方法的可靠性     

Seismic performance of Y‐type eccentrically braced frames combined with high‐strength steel based on performance‐based seismic design

In the Y‐type eccentrically braced frame structures, the links as fuses are generally located outside the beams; the links can be easily repairable or replaceable after earthquake without obvious damage in the slab and beam. The non‐dissipative member (beams, braces, and columns) in the Y‐type eccentrically braced frames are overestimated designed to ensure adequate plastic deformation of links with dissipating sufficient energy. However, the traditionally code design not only wastes steel but also limits the application of eccentrically braced frames. In this paper, Y‐type eccentrically braced steel frames with high‐strength steel is proposed; links and braces are fabricated with Q345 steel (the nominal yield stress is 345 MPa); the beams and columns are fabricated with high‐strength steel. The usage of high‐strength steel effectively decreases the cross sections of structural members as well as reduces the construction cost. The performance‐based seismic design of eccentrically braced frames was proposed to achieve the ideal failure mode and the same objective. Based on this method, four groups Y‐type eccentrically braced frames of 5‐story, 10‐story, 15‐story, and 20‐story models with ideal failure modes were designed, and each group includes Y‐type eccentrically braced frames with ordinary steel and Y‐type eccentrically braced frames with high‐strength steel. Nonlinear pushover and nonlinear dynamic analyses were performed on all prototypes, and the near‐fault and far‐fault ground motions are considered. The bearing capacity, lateral stiffness, story drift, link rotations, and failure modes were compared. The results indicated that Y‐type eccentrically braced frames with high‐strength steel have a similar bearing capacity to ordinary steel; however, the lateral stiffness of Y‐type eccentrically braced frames with high‐strength steel is smaller. Similar failure modes and story drift distribution of the prototype structures designed using the performance‐based seismic design method are performed under rare earthquake conditions.     

高温下钢筋混凝土受力性能的试验研究

本文介绍钢筋混凝土材料及其构件和结构在高温(火灾)下受力性能的试验研究概况.给出的主要研究成果和重要现象有标准的火灾升温-时间曲线;构件截面上的温度分布;高温下混凝土和钢材(筋)的强度和变形性能的劣化规律;混凝土的温度-应力耦合本构关系;受弯构件、轴心和偏心受压构件在四面受火和三面受火情况的主要性能,包括破坏特征、极限承载力和耐火极限、变形、荷载-温度途径的影响以及各种影响因素的分析等;连续梁和框架等超静定结构的高温性能,包括破坏特征和机构、塑性铰的特点、内力重分布过程以及极限承载力和耐火极限等.