窗槛墙和防火挑檐阻止火灾竖向蔓延的数值模拟

为了确定窗槛墙和防火挑檐阻止火灾竖向蔓延的效果,运用火灾动力学模拟软件FDS,选择设定办公室及宾馆客房火灾场景,进行了数值模拟研究.研究结果表明:在一定范围内增加窗槛墙的高度将有利于阻止火灾的竖向蔓延,但超出该范围,可能会造成不利影响;防火挑檐比窗槛墙能更有效地阻止火灾的竖向蔓延,且防火挑檐越宽效果越好.     

窗槛墙和挑檐影响火灾烟气蔓延的数值模拟

利用FDS软件,对设有不同外窗结构的3层建筑进行火灾数值模拟,讨论不同高度窗槛墙和不同长度挑檐对火灾烟气经外窗进行竖向蔓延的影响.模拟结果表明,着火后由房间内喷出的烟气会沿建筑物外墙向上蔓延,建筑外墙附近温度迅速升高,增加窗槛墙宽度、挑檐长度均能阻止火灾烟气竖向蔓延.     

超高层建筑窗槛墙对火灾蔓延的影响分析

利用FDS进行数值模拟,选定6种工况对比分析不同窗槛墙高度和设置方式对火灾蔓延的影响。根据模拟结果得到了不同防火分隔方式下,火灾及烟气对着火层上、下层幕墙的影响以及火灾通过建筑外幕墙层间上、下开口的蔓延情况。结果表明,在设定的火灾场景下,仅一定范围内窗槛墙高度和设置方式可有效阻止火灾竖向蔓延,而其他高度或设置方式,可能会造成火灾竖向蔓延。     

窗槛墙设置高度及设置方式优化研究

文章以办公室、客房为研究对象,采用FDS模拟软件对窗槛墙设置高度及设置方式进行数值模拟。模拟结果表明:窗槛墙高度为0.8m时,虽然可以大幅度降低烟气对着火层上层玻璃的影响,但不能满足安全的预期值,需要设置自动喷水灭火系统进行保护;窗槛墙高度设置为1.2m最为合理、经济、安全。在设置方式上,顶板上方设置0.4m、顶板下方设置0.8m的窗槛墙,更有利于阻止火灾的竖向蔓延。     

某酒楼采用窗槛墙替代防火挑檐的可行性探讨

以某酒楼建筑为研究对象,采用FDS数值模拟,对其内部火灾及烟气流动蔓延规律进行研究,主要分析窗槛墙、防火挑檐、风速对烟气运动的影响以及窗户开口处的热辐射通量和温度变化,为该酒楼拟采用一定高度的窗槛墙替代防火挑檐的做法提供数据支持和理论依据.     

窗槛墙和防火挑檐对外墙火灾蔓延影响分析

应用FDS建立建筑外墙开口溢流火灾研究数值模型,采用非稳态t2火模型设计6种工况,对比分析窗槛墙和防火挑檐的阻隔性能,结果表明,窗槛墙高度1、1.2 m时温度分布情况和0.8 m时较类似;随防火挑檐宽度增加,阻隔作用更加明显;窗槛墙和防火挑檐使得除着火层外各层辐射强度均较低。通过小尺寸实验研究防火挑檐对竖向火焰的阻隔性能,结果表明,着火层上方温度随防火挑檐宽度增加而变低,但防火挑檐达到一定宽度后着火层上层卷吸增强,致使温度升高。     

双层玻璃幕墙实体防火试验在北京大兴试验基地进行

2014年12月10日,北京市消防总队与中国建筑科学研究院建筑防火研究所(以下称防火所)在中国建筑科学研究院大兴防火试验基地——北京敬业达新型建筑材料有限公司院内进行了双层玻璃幕墙实体防火试验,以研究双层幕墙内设防火挑檐及窗间墙对阻止火灾跨层蔓延的影响。     

呼吸式玻璃幕墙火灾竖向蔓延阻隔方法对比研究

利用FDS软件模拟,设计了9种工况,对比研究了对呼吸式玻璃幕墙热通道内火灾竖向阻隔的方法,通过模拟计算分析,获得了窗槛墙、防火挑檐、热通道宽度及进出口高度不同时内外幕墙壁面温度分布及着火层上层房间外墙中心温度随时间的变化关系。结果表明,防火挑檐对烟气的阻挡作用较设置窗槛墙明显;热通道在一定范围内增加宽度会降低内幕墙开口处的最高温度;进出风口高度和通风量对内幕墙温度降低影响较小。     

室外风下防火挑檐对外立面火蔓延的影响分析

通过1/2缩尺寸实验和FDS研究无风状态下防火挑檐对建筑外立面竖向火溢流蔓延的阻隔性能,实验结果与模拟结果吻合良好,验证了所建立模型的正确性。并应用FDS研究了室外风对防火挑檐竖向阻隔性能的影响。结果表明,在无风状态下,当防火挑檐的伸出长度为0.6m时,有效的阻隔开口溢出火羽流竖向蔓延;在室外风下,当室外风速为3m/s,风向为水平右侧吹风,窗槛墙高度为0.4m时,0.6m伸出长度的防火挑檐可继续有效阻隔火溢流的竖向蔓延。     

外墙窗户面积及位置对建筑外立面火蔓延的影响

搭建20层的全尺寸办公建筑三维模型,通过设置不同窗户面积、窗户位置研究外窗对建筑外立面竖向火蔓延的影响。研究发现窗户面积较大时,火灾竖向蔓延速率更快,室内温度升高更快,采用大的窗墙比更容易加快火灾在建筑外立面的竖向蔓延。在竖直位置上,随着窗户上移,各楼层的引燃时间均增加。     

Vertical separation of windows using spandrel walls and horizontal projections

Actual fires and full-scale tests demonstrate the hazard of the leap frog spread of fire from a window to the one above. A spandrel wall or a horizontal projection (such as a canopy or a balcony), installed above an exposing window, protects storeys above from flames issuing from the opening. The described tests show that a horizontal projection is very effective; however, for a spandrel wall to be equally effective, an impractical height of spandrel is required.     

Upper bound limit analysis of meso-mechanical spandrel models for the pushover analysis of 2D masonry frames

In this paper, a numerical model for the pushover analysis of in-plane loaded unreinforced masonry walls is presented. For the analysis of the walls, which consist of vertical piers connected by horizontal masonry spandrels, an equivalent frame model is adopted. The analysis approach consists of two steps: In Step I, ultimate bending moment-shear force strength domains of the masonry spandrels are derived by means of a heterogeneous upper bound FE limit analysis and the results are stored in a database. Assessing the capacity of the spandrels correctly is crucial for the ultimate resistance of masonry walls that are loaded in-plane. Heterogeneous limit analysis is particularly suitable for computing the failure load of unreinforced masonry members since it permits a distinct modelling of bricks and mortar joints. Appropriate static and kinematic boundary conditions are imposed to account for the complex interaction of internal forces and deformed shapes of the spandrel beams at failure. In Step II, a frame model of the masonry wall is assembled. In this frame model the spandrels are modelled as elastic Timoshenko beams. At each analysis step it is checked that the internal forces of these coupling beams are smaller than the failure loads stored in the database created in Step I. If the capacity is exceeded, flexural hinges are introduced at both ends of the coupling beam. The resistance of the element is set to zero when a limit chord rotation is exceeded. The piers are modelled in a similar manner. The shear force and bending moment capacity of the piers are, however, simply estimated according to the Italian Design Code. Pushover analysis results compare favourably with computationally expensive 2D nonlinear heterogeneous FE analyses, but also confirm that the ultimate lateral resistance of masonry walls is very sensitive to the assumed spandrel strength if an equivalent frame model is used.     

多层砌体结构窗下墙破坏模式试验研究

为验证多层砌体结构开洞墙体窗下墙破坏模式震害现象,设计缩尺比例为1:3的三层三跨砌体结构开洞墙体试件,对其进行拟静力低周往复加载试验。分析多层砌体墙体窗下墙破坏模式的破坏特征,研究整体墙及各层墙体的滞回特性、骨架曲线、刚度退化规律、耗能特性、延性与变形特征等抗震性能。试验结果表明：发生窗下墙破坏模式的开洞墙体破坏过程分为裂缝出现、变形发展与强度退化三个阶段;窗下墙作为第一道抗震防线可提前参与整体结构耗能、降低墙体刚度退化速率、增加整体墙的延性和变形能力,其破坏模式相对窗间墙破坏模式更为合理。研究结果揭示了发生窗下墙破坏模式墙体的抗震性能与变形特征,为实现砌体结构合理破坏机制提供依据。     

The contribution of flames under ceilings to fire spread in compartments

An experimental investigation has been made of flames spreading beneath both combustible and non-combustible ceilings. Experiments were performed in a model representing the ceiling of a corridor with a fire at one end: a gas burner was used to represent the fire, this was replaced by wooden cribs in experiments to be described in later part of this report.

The flames rising vertically from the fire in effect drew air up into the horizontal layer of flames and gases beneath the ceiling. Depending on the rate of flow of fuel gas (or rate of burning of the cribs) this air could be sufficient for complete combusion of the fuel gases and the flame length was then apparently determined by mixing processes within the layer. When this air was not sufficient, the remaining air for combustion was entrained vertically into the horizontal layer from the cool air beneath and the flames became much longer.

Correlations of lengths of horizontal flames beneath non-combustible ceilings have been derived and related to the much shorter lengths of vertical flames. Relationships have been derived from the experimental data from which it is possible to estimate the radiation downwards from a hot non-combustible ceiling and the gases beneath it to the floor with a view to estimating the contribution to fire spread on the floor. A heat balance of the ceiling gases was satisfactory, so confirming the validity of the calculations. Horizontal flames radiate more of the heat produced at a level sufficient to assist fire spread than do vertical ones.

A combustible ceiling lining results in longer flames, an increase in the distance over which heat radiated downwards at an intensity sufficient to promote fire spread and a faster rate of increase of radiation than a non-combustible one with similar thermal constants.

The aspect of performance which best related to the results of BS 476 tests was the rate of increase of radiation downwards in the early part of the experiments. The radiation downwards was apparently partly determined by extraneous factors such as the detachment of the board from its holding nails and whether the decomposition products were emitted as jets.

The rate of spread of fire along a narrow strip of wood on the floor beneath a burning ceiling lining has been calculated and the results related to the index of performance on the Fire Propagation Test.     

商业建筑广告牌火灾蔓延数值模拟

采用FDS对重庆沙坪坝区"11·3"火灾进行模拟,通过在广告牌上方布置宽度为0.5 m的不燃隔板,分析对比有、无隔板情况下火灾的竖直和水平蔓延情况。结果显示,当存在广告牌的每层都设置不燃隔板时,可以有效延缓火灾在竖直方向的蔓延,并且在相当长的时间内,建筑外的玻璃窗不会破碎,有效阻止了室外火向室内火的转变。     

双层幕墙性能化消防设计初探

提出了双层幕墙所带来的消防安全问题。采用计算流体力学(CFD)方法对火焰和烟气在双幕墙结构中的传播进行了模拟分析，模拟分析针对两种工况，一种是上、下楼层设有窗槛墙的工况；另一种是在通风夹层内上、下楼层之间设置防火挑檐的工况。通过对模拟结果的分析，提出了有关双层幕墙消防安全措施的建议。     

城市综合体灭火救援技战术的特点及应用

当前大型城市综合体建筑普遍存在消防隐患多、大空间立体燃烧的问题,这不仅加剧了城市建筑火灾风险,也增加了火灾发生时人员逃生疏散工作和被困人员救援工作的难度,再加上此类建筑排烟散热性能较差,这导致火灾损失更加严重。为了降低大型城市综合体火灾损失,文章将从如何开展大型城市综合体火灾扑救工作出发,深入研究火灾扑救战术。     

着火列车制动进站过程烟气扩散特性模拟

为探究火灾列车制动驶向地下车站进行救援时的烟气扩散特性，采用理论分析和数值模拟的方法研究在不同控制烟气措施下，火灾列车减速至停止过程中烟气在车站轨行区及站台层的扩散规律，以及车站防灾通风系统受到的影响。结果表明：火灾列车制动进站时受移动火源与活塞风两大特性影响，烟气在上下游表现出明显的不均匀、不对称分布规律；屏蔽门虽能有效阻止烟气蔓延至站台层，但同时会增大轨行区活塞风速，增加烟气蔓延速度，不利于安全疏散；受活塞风影响，轨行区排烟效率下降了14%，轨行区各排烟阀火灾中下游排烟效率更高。     

机场塔台无高位消防水箱之增强措施探讨

机场塔台顶层指挥明室因空管工艺需求,屋顶采用轻钢结构,受结构承载力和限高的要求,塔台无法设置高位消防水箱。通过火灾场景、烟气流动模拟和人员安全疏散分析,提出消防强化措施,主要包括采用稳高压消防系统、两路供水、两路供电、采用快速响应喷头、优化管材选择、采用物联网消防设备和配置空气呼吸机等。模拟结果显示,在发生火灾区域的自动灭火系统和排烟系统有效的情况下,清晰高度处的人员可用疏散时间较长,该消防方案能达到防止火灾大规模蔓延和保障建筑内人员安全的消防设计安全目标。