火灾下楼板的薄膜作用的建模分析

通过观察试验现象以及真实建筑中火灾引起的破坏,可以发现薄膜作用在提高楼板抗火承载力方面起着很重要的作用。通过考虑火灾下楼板的薄膜作用机理,建立了一个显式的理论模型。基于火灾下楼板中力和弯矩的平衡关系,得到了火灾条件下考虑薄膜作用效应的楼板极限承载力的计算公式。通过和试验结果以及不同的理论仿真结果的对比,验证了该文提出的火灾下考虑薄膜作用理论的有效性。     

火灾下钢结构建筑楼板的薄膜效应模型验证及实用方法

通过已有试验结果对火灾下考虑薄膜效应的楼板极限承载力计算方法进行了验证,证明了提出的计算方法的可靠性。根据楼板的薄膜效应分析模型,分析了温度、楼板长短边比例、配筋分布和挠度等参数对楼板极限承载力的影响。分析表明,楼板挠度越大,楼板的长跨比越小,长跨与短跨配筋率的比值越小,楼板在火灾下产生的薄膜效应就越明显,对楼板火灾下的极限承载力提高就越大。根据考虑薄膜效应计算楼板极限承载力的理论方法,提出了对无防火保护的楼板(包括次梁)进行抗火设计验算的简化实用方法,在满足1.5h耐火时间楼板不坍塌的条件下,可减小楼板及次梁的防火成本。本方法可供工程设计人员在进行楼盖的抗火设计时参考。     

组合楼板受火薄膜效应试验研究

为了验证火灾作用下压型钢板组合楼板的受拉薄膜效应,观察楼板破坏现象,了解受火后组合楼板的温度场、位移及钢筋和混凝土的应变状态,本文进行了4个足尺压型钢板组合楼板受火性能试验。在试验过程中,对试验炉温、楼板温度、钢筋温度、钢筋应变、混凝土应变及楼板中心挠度进行了测量,对试验现象进行了解释。通过试验中采集的温度、位移以及应变等数据,对试验结果进行分析,证实了火灾作用下楼板受拉薄膜效应的存在及其在高温下维持楼板承载力的作用。根据试验分析结果得出,由于楼板的薄膜效应的产生,可不对压型钢板组合楼板及板区内的次梁进行防火保护。     

基于楼板薄膜效应的钢框架抗连续倒塌研究

组合楼板作为钢框架结构的主要构件,在支撑柱失效情况下能产生很大的挠度,进而产生薄膜效应影响结构的抗连续倒塌性能。通过研究楼板挠曲悬链线阶段组合楼板薄膜效应对多层钢框架抗连续倒塌性能的影响,分析组合楼板在连续倒塌过程中的受力,提出考虑楼板薄膜效应的结构承载力计算方法。通过有限元分析软件进行框架连续倒塌分析,验证计算方法的准确性,探讨楼板对塑性铰发展、结构极限承载力、失效点位移的影响。研究表明:组合楼板能显著提高结构的抗连续倒塌性能。     

机动法评定既有结构楼板承载力的简化方法

为解决既有建筑使用过程中局部区域使用功能改变后,楼板承载力需要进行评定的问题,论文提出了一种楼板承载力评定的简化方法。楼板几何条件、强度及钢筋配置可现场检测,截面的抵抗弯矩可以计算得出,利用塑性铰线理论的机动法评定楼板承载力,评定过程中不再使用楼板设计中求解内力的传统方法,而是在单位转角下,根据抵抗能与外力做功的比较进行评定。同时还提供了考虑薄膜效应提高承载力的量化计算方法。     

压型钢板-混凝土组合楼板抗火性能非线性分析

压型钢板-混凝土组合楼板是目前广泛运用的一种新型结构构件,但由于缺乏对组合楼板抗火性能的研究,现有设计方法并没有充分发挥材料的性能。本文在建立室内火灾传热模型基础上,在空间上运用有限单元法和在时间上运用有限差分的混合解法,编制计算程序解算出火灾下组合楼板在不同时刻的温度场,进而利用钢筋混凝土非线性有限单元法,对多种工况下组合楼板的抗火性能进行了分析,为组合楼板的抗火设计及研究提供了一定的基础。     

火灾下大跨度弦支穹顶结构的性能分析

基于实用大空间火灾空气升温经验公式及预应力钢结构材料高温力学模型,采用考虑时间积分效应的非线性有限元数值分析法,建立了用于大跨度弦支穹顶结构抗火性能分析的数值模型。通过对大跨度弦支穹顶结构的抗火分析,研究结构的温度场分布、位移和应力特征以及支座约束条件对结构抗火的影响。分析结果表明:在火灾作用下,大跨度弦支穹顶结构具有较好的抗火性能,结构的抗火薄弱区域位于上层网壳的中心区域;火灾下引起弦支穹顶结构产生较大变形的主要原因是环向约束作用、材料升温膨胀以及结构刚度的降低。     

高层建筑结构在水平荷载作用下楼板应力分析与设计

楼板作为主要水平构件,不仅需要承受和传递荷载,而且需要协调各抗侧力构件之间的变形。高层建筑结构楼板设计时,目前只考虑竖向荷载引起的面外弯矩,而忽视了水平荷载作用下产生的楼板面外弯矩和面内内力的影响,对高层建筑楼板面内应力分析与设计进行了探讨,介绍了常用计算程序中分析应力的方法,给出了楼板承载力验算方法。通过工程案例说明了方法的应用。     

简支组合楼板的火灾试验研究

本文对3块压型钢板-混凝土简支组合楼板进行了恒载条件下的火灾试验研究。对组合楼板的抗火性能与火灾行为进行了研究,考虑了组合楼板的跨度与抗剪连接件对简支组合楼板耐火极限的影响。试验结果表明:简支组合楼板的抗火性能较差,3块板的耐火极限均在30min左右;板的跨度对耐火极限的影响很大,而抗剪件的影响相对较小。     

局部火灾下基于网架热力效应解耦方法的杆件约束刚度求解

局部火灾下,网架结构整体升温呈非均匀状态,由于各杆件轴向的温度膨胀变形不同,导致了杆件间的轴向约束效应,这种轴向约束使网架结构杆件受火屈曲后仍具有一定的承载力.定量确定网架结构杆件间的相互约束是正确评价杆件抗火承载力的重要条件.分别将上、下弦杆层连续化,参考拟夹层板法,基于力平衡方程和位移协调方程,分别得到非均匀温度场中考虑温度膨胀效应和静力荷载效应的网架上、下弦杆层的面内位移及竖向挠度解析解.同时采用数值分析方法,分别得到非均匀温度场中,在温度、杆件间相互约束和静力荷载耦合作用下的网架上、下弦杆层面内及竖向位移数值解以及杆件间相互约束效应产生的附加温度内力.上述位移解析解与数值解之差值即为网架各杆件在约束效应下所产生的轴向变形,该轴向变形量与附加温度内力之比,即为杆件的轴向约束刚度.这种轴向约束刚度计算方法有效地将杆件由于温度膨胀受到约束产生的轴向变形量从耦合效应中剥离出来,从而较准确地得出升温历程中杆件间的瞬态约束刚度.     

A New Method to Analyze the Membrane Action of Composite Floor Slabs in Fire Condition

During 1995 and 1996, a total of six localized fire tests were conducted on a full-scale, eight-storey, steel framed building at Building Research Establishment Laboratory at Cardington. The test results show that the fire performance of steel-concrete composite floor is better than that obtained from traditional design method, and the load capacity of composite floor slab in fire condition is usually higher than the predicted capacity without considering membrane action. In the past decade, researchers have done a series of analyses in this area, such as Bailey, Usmani, and Li. In this paper, a new method to calculate the load capacity of simply supported composite floor slabs with considering the membrane action is presented. The slab is divided into five parts at the limit state of load capacity, including a center-elliptic part and four rigid parts around. The deflection of the slab, the force of rebars in high temperature, and the force distribution between four rigid parts are reasonably assumed. According to force and moment equilibrium requirements on the slab, a series of equations are obtained to calculate the ultimate load capacity of floor slabs in fire condition. The effectiveness of this new method is validated through comparison with results from experiments and different theoretical simulations. The comparison shows that this new method is more reasonable in predicting the deflection and ultimate load capacity of floor slabs in fire condition than previous methods.     

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。     

Non-linear structural modelling of a fire test subject to high restraint

The computer code VULCAN has been developed for the three-dimensional structural analysis of composite and steel-framed buildings in fire. In this paper, the main features of the program are outlined, with particular emphasis on the most recent development to the layered procedure for modelling of concrete floor slabs. This development has introduced geometric non-linearity into the modelling of slabs, whose layer structure already allowed temperature distributions and change of material properties through the thickness, as well as modelling the effect of the ribs at the bottom of composite decking slabs. The capabilities of the model are firstly tested at ambient temperature for a uniformly loaded ribbed reinforced concrete slab with simply supported edges, and this is followed by a very detailed modelling of the Cardington restrained beam fire test. In both cases the development of membrane action is demonstrated and the structural behaviour is compared with the geometrically linear case. A number of studies are carried out to demonstrate the influence of the major floor slab details on the behaviour of the structure in fire conditions. These studies provide evidence that when exposed steel temperatures are less than 400°C the concrete slab has little influence, other than to play a part in generating thermal curvature to composite beams. For temperatures higher than about 500°C the effect of the slab progressively becomes much greater, and it is very important to model concrete slabs correctly. The influence of membrane action cannot be ignored, particularly when the fire compartment is subject to high restraint because it is surrounded by cool, stiff structure. At very high temperatures the floor slab becomes the main load-bearing element and the floor loads above the fire compartment are carried by the membrane forces developed in the slab, with tension being carried mainly by the steel anti-cracking mesh or reinforcing bars. However, the effect of the very high in-plane restraint to thermal expansion in the particular Cardington test considered is to enhance the peripheral zone of compressive membrane force and to reduce the extent of the central area of tensile force compared with more usual cases.     

The effects of protected beams and their connections on the fire resistance of composite buildings

According to full-scale fire tests, it is noticed that tensile membrane action within the concrete floor slabs plays an important role in affecting the fire resistance of composite buildings. It is well known that the development of tensile membrane actions relies on the vertical support along the edges of the slab panel. However, there is at present a lack of research into the influence of vertical supports on the tensile membrane actions of the floor slabs. In this paper, the performances of a generic three dimensional 45 m×45 m composite floor subjected to ISO834 Fire and Natural Fire are investigated. Different vertical support conditions and three steel meshes are applied in order to assess the impact of vertical supports on tensile membrane action of floor slabs. Unlike other existing large scale modelling which assumes the connections behave as pinned or rigid for simplicity, two robust 2-node connection element models developed by the authors are used to model the behaviour of end-plate and partial end-plate connections of composite structures under fire conditions. The impact of connections on the 3D behaviour of composite floor is taken into consideration. The load-transfer mechanisms of composite floor when connections fail due to axial tension, vertical shear and bending are investigated. Based on the results obtained, some design recommendations are proposed to enhance the fire resistance of composite buildings.     

大尺寸大开间页岩陶粒混凝土双向叠合板足尺试验研究

针对目前装配式建筑中常用的钢筋混凝土叠合楼板自重较大、工厂标准化生产的预制底板规格尺寸较小的问题,提出了一种由两块预制普通混凝土大板通过一条整体式接缝拼装,并后浇轻质页岩陶粒混凝土而成的大开间叠合楼板,页岩陶粒混凝土后浇层可有效减小楼板自重,提高楼板的保温、隔热和隔声性能。通过进行叠合板足尺试件的堆载试验,研究其在竖向荷载作用下的承载力、变形特征、破坏形态及整体式接缝的传力性能。结果表明,该大开间叠合板试件在正常使用极限状态下的跨中挠度和裂缝宽度均满足相关规范要求,且表现出明显的双向板裂缝分布特征,所采用的整体式接缝具有良好的传力性能,可以作为结构楼板使用。此外,有限元模型所选取的材料本构模型和接触面设定较为合理,计算结果与试验结果吻合良好,可用于轻质混凝土叠合楼板受力性能及影响参数分析。     

预应力叠合板抗火性能试验研究

为了解预应力叠合板在火灾中及火灾后的受力性能,制作了12块不同叠合层厚度的预应力叠合板,通过受火试验及受火后的静载试验,研究叠合板在高温和荷载耦合作用下的受力性能以及不同受火时间下受火后的受力机制和剩余承载力。结果表明：预应力叠合板在高温和荷载耦合作用下,叠合面将会产生水平裂缝,燃烧时间越长,这种现象越明显,甚至出现预制层与叠合层脱离;钢筋桁架对预应力叠合板的抗火性能具有重要作用,保证了叠合层与预制层脱离后板仍具有一定的整体工作性能;预应力叠合板在高温和荷载耦合作用下,将会产生顺筋裂缝,发生黏结破坏;受火后预应力叠合板再施加荷载,预制层与叠合层将会完全分离脱开,板的受力机制发生变化,由受弯构件转化为桁架结构;对于受火时间不超过60min、保护层厚度为20mm的预应力叠合板,其剩余承载力仍能达到未受火叠合板的80%以上;对于保护层厚度为20mm、预制层厚度为40mm、叠合层厚度不小于70mm的叠合板,其耐火极限可达2h以上。     

Fire performance assessment of HPLWC hollow core slabs through full-scale furnace testing

High-Performance Light-Weight Concrete (HPLWC) is used for many structural applications when superior strength and low self-weight of the structural components are required. Among these applications there are thin floor structures, like hollow core slabs, that require characteristics of lightness, relatively high resistance and superior durability. Although the fire performance of normal strength concrete hollow core slabs has been extensively studied, the behavior of HPLWC hollow core slabs has not been suitably investigated.The paper reports the results of two full-scale furnace tests on HPLWC hollow core slabs. Each of them involved one panel with an applied load and one without load. The evolution of temperature inside the slabs was measured along with the load bearing capacity under fire conditions. During the first test severe spalling occurred in the loaded slab while during the second one, performed on slabs cured for some months under dry conditions, spalling did not occur. Finite elements simulations were also carried out in order to support the interpretation of the experimental results. Experimental and numerical investigations gave insight into the fire performance of HPLWC hollow core slabs and highlighted the influence of dry curing conditions in reducing the spalling and increasing the fire resistance.     

基于楼板双向受拉模型的钢框架结构连续倒塌分析

组合楼板作为钢框架结构的主要构件,对结构的抗连续倒塌能力产生较大影响,但现有的结构抗连续倒塌研究大多没有考虑楼板的影响。基于组合楼板的双向受拉模型,分析组合楼板在钢框架结构连续倒塌过程中的受力,提出考虑楼板拉结力作用的失效点竖向承载力简便计算方法。基于简化模型,通过有限元分析软件进行框架连续倒塌分析,验证计算方法的准确性,探讨楼板对塑性铰机制、极限承载力、失效点动态反应的振幅和周期的影响。研究表明,楼板能有效地提高结构抗连续倒塌性能。     

某高层住宅楼大跨度楼板加固处理

通过加固工程实例介绍了大跨度楼板板面有墙荷载,楼板承载力不足时,采用板面浇筑混凝土叠合层,板底粘贴碳纤维布的加固方法。对该大跨度楼板进行加固处理后,后期使用荷载作用下的挠度进行了计算,找出加固时需要进行顶升处理的楼板,针对现场情况提出了一种简单、易行的顶升处理方法。