Capacities of headed stud shear connectors in composite steel beams with precast hollowcore slabs

In steel-concrete composite beams, the longitudinal shear force is transferred across the steel flange/concrete slab interface by the mechanical action of the shear connectors. The ability of the shear connectors to transfer these longitudinal shear forces depends on their strength, and also on the resistance of the concrete slab against longitudinal cracking induced by the high concentration of shear force. Most of the research in composite construction has concentrated on the more traditional reinforced concrete and metal deck construction, and little information is given on shear capacity of the headed studs in precast hollowcore slabs. In this paper, a standard push test procedure for use with composite beams with precast hollowcore slabs is proposed. Seven exploratory push tests were carried out on headed studs in solid RC slabs to validate the testing procedures, and the results showed that the new test is compatible with the results specified in the codes of practice for solid RC slabs. Once a standard procedure is established, 72 full-scale push tests on headed studs in hollowcore slabs were performed to determine the capacities of the headed stud connectors in precast hollowcore slabs and the results of the experimental study are analysed and findings on the effect of all the parameters on connectors’ strength and ductility are presented. Newly proposed design equations for calculating the shear connectors’ capacity for this form of composite construction are also be given.     

Modelling of unbonded post-tensioned concrete slabs under fire conditions

This paper investigates the structural behaviour of unbonded post-tensioned one-way spanning concrete slabs in fire conditions. The slabs were simply supported and reinforced with 15.7 mm nominal diameter seven-wire mono-strand tendons. A nonlinear finite element model for the analysis of post-tensioned unbonded concrete slabs at elevated temperatures was developed. The mechanical and thermal material nonlinearities of the concrete, prestressing tendon and anchorages have been carefully inserted into the model. The interface between the tendon and surrounding concrete was also modelled, allowing the tendon to retain its profile shape during the deformation of the slab. The temperature distribution throughout the slab, time–deflection behaviour, time–longitudinal expansion, time–stress behaviour in the tendon, and the failure modes were predicted by the model and verified against test data. The study has shown that the coefficients of thermal expansion currently used in the European Code for calcareous and siliceous concrete can lead to inaccurate predictions of the structural behaviour. A parametric study was conducted to investigate the effects on the global structural behaviour due to the change in the aggregate type, load ratio and boundary conditions. It was shown that by varying the boundary conditions the fire resistance was greatly affected. Although changing the aggregate type and load ratio affected the time-displacement response, the fire resistance defined by failure of the slab was not affected due to the splitting mode of failure above the tendon locations not being affected by these parameters. Comparison with the codes shows that the UK code BS8110 is generally unconservative, whereas the Eurocode EN1992-1-2 provides reasonable design rules.     

预应力混凝土空心板桥加固设计

针对某空心板桥部分截面极限承载力不满足规范要求,需予以补强、加固的情况,提出了因地制宜的改造加固方案,并详细介绍了粘贴钢板加固的计算方法,以期指导该桥加固工作。     

预应力混凝土在超长大面积地下室底板中的应用研究

预应力混凝土从本质上改善了钢筋混凝土构件的性能,相对于普通混凝土,预应力混凝土技术在地下室底板中的应用有其自身的特点,作者就预应力技术在超长大面积地下室底板工程中的应用进行了探讨.     

两跨无粘结预应力混凝土连续板抗火性能试验与分析

完成了9块两跨无粘结预应力混凝土连续单向板抗火试验。通过布置于试验板内的热电偶,获得了试验板截面的温度场分布。通过布置于无粘结筋锚固端的力传感器和试验板上的位移传感器,获得了试验板中无粘结筋应力和试验板新增变形在火灾下的变化过程。通过布置于各试验板边支座上的压力传感器,获得了两跨连续板支座反力在火灾下的变化过程。受火过程中试验板背火面经历了水分溢出、水蒸气形成和发展、溢出水干涸及水蒸气消失的过程。基于不同试件不同时刻的无粘结钢丝应力实测值、边支座反力实测值、跨中新增变形实测值,拟合出了考虑各关键参数影响的火灾下两跨连续板中无粘结钢丝应力计算公式、边支座反力计算公式和跨中新增变形计算公式。针对在抗火试验中有4块试验板板顶负弯矩的钢筋截断处出现了贯穿裂缝的现象,提出了火灾下两跨连续板中支座两侧负弯矩钢筋的截断建议。     

The tensile membrane action of unrestrained composite slabs simulated under fire conditions

Following a major fire test programme on a full-scale, steel-framed building it was found that the composite flooring system, comprising lightweight concrete, anti-crack mesh reinforcement and steel deck, had a greater inherent fire resistance than suggested by current codified design methods. It was felt that this was due to tensile membrane action occurring in the slab at large displacements. This led to an independent test being conducted at the Building Research Establishment where a 9.5 m×6.5 m composite slab, with nominal horizontal restraint to its edges, was tested to failure. To simulate the behaviour of the slab in fire, the steel deck was removed, leaving the concrete and anti-crack reinforcement, before load was applied. Tensile membrane action was shown to occur, with the failure load being approximately double that calculated using the classic yield line theory.     

预应力混凝土结构抗火研究进展

总结了近年来预应力混凝土结构抗火研究进展,包括预应力筋高温力学性能、预应力混凝土梁板抗火试验、足尺预应力混凝土梁板抗火性能、活性粉末混凝土高温力学性能、高温下混凝土的爆裂规律、CFRP布加固混凝土梁板抗火性能、预应力混凝土梁板以及用耐高温无机胶粘贴CFRP布加固的混凝土梁板抗火设计方法等,分析了预应力混凝土结构和CFRP布加固混凝土结构抗火研究中尚存在的一些问题。分析表明：大尺度预应力混凝土梁的抗火性能优于小尺度梁,用耐高温无机胶替代环氧类有机胶粘贴CFRP布加固混凝土梁板并以此提高结构的抗火性能是可行的,大尺度预应力构件及预应力整体结构的抗火性能及其抗火设计方法等是今后一段时间预应力混凝土结构抗火研究领域值得关注的课题。     

Performance of insulated FRP-strengthened concrete flexural members under fire conditions

This paper presents the results of fire resistance tests on carbon fiber-reinforced polymer (CFRP) strengthened concrete flexural members, i.e., T-beams and slabs. The strengthened members were protected with fire insulation and tested under the combined effects of thermal and structural loading. The variables considered in the tests include the applied load level, extent of strengthening, and thickness of the fire insulation applied to the beams and slabs. Furthermore, a previously developed numerical model was validated against the data generated from the fire tests; subsequently, it was utilized to undertake a case study. Results from fire tests and numerical studies indicate that owing to the protection provided by the fire insulation, the insulated CFRP-strengthened beams and slabs can withstand four and three hours of standard fire exposure, respectively, under service load conditions. The insulation layer impedes the temperature rise in the member; therefore, the CFRP–concrete composite action remains active for a longer duration and the steel reinforcement temperature remains below 400°C, which in turn enhances the capacity of the beams and slabs.     

Analysis on shear capacity of prestressed concrete spatial connections

Based on experimental results of prestressed concrete spatial connections, nonlinear finite element models were established to analyze the shear capacity of spatial connections and parametric studies were performed using ANSYS. It is found that the shear capacity of spatial connection is influenced by joint hoop, beam prestress, column compressive load, and direction of resultant shear force. The parametric studies also indicate that the shear capacity of spatial connection under biaxial cyclic loading is lower than that of corresponding connections under plane loading. A design formula for calculating the shear capacity of spatial connections is proposed based on the parametric studies and verified by the available test results.     

无粘结预应力混凝土连续板火灾行为的试验分析

对9块无粘结预应力混凝土连续板进行了受火性能的试验研究。通过对这些试验的综合分析，给出了出现裂缝的主要种类、成因及由此造成的破坏形式。根据裂缝的发展趋势和板的破坏形式说明了内力重分布的规律，并与由支反力推算得的弯矩变化规律相互验证。从火灾初期弯矩变化规律图可以发现，在受火的前5min，结构内己产生剧烈的内力重分布，火灾初期结构的内力重分布主要是由热膨胀应变引起的。根据板的破坏形式和预应力筋被拉断等现象提出了保证连续构件必要的耐火极限的防护措施。     

预应力混凝土管桩与承台结合部抗剪承载力的试验研究

在地震作用下,预应力混凝土管桩桩顶受到水平剪力作用,而空心管桩的抗剪承载力通常比较弱。常在管桩上部埋入钢筋,浇筑一段混凝土与承台相连,以改善其抗剪性能。在试验的基础上对预应力管桩的抗剪承载力进行了研究,并对填芯混凝土在抗剪承载力中的作用进行了探讨。研究表明,填芯混凝土提高了管桩抗剪承载力,改善了管桩脆性性能。为管桩抗剪承载力计算提供了试验基础及理论依据。     

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。     

预应力混凝土空心叠合板结构性能试验研究

通过对4块170 mm厚预应力混凝土空心叠合板进行结构性能试验,得出该类构件结构性能的相关结论,并对该类构件结构性能的影响因素进行了分析,对预应力混凝土空心板作底板的装配整体式叠合楼盖的工程应用提出了相关建议。     

预应力混凝土管桩在某工程中的应用研究

针对预应力混凝土管桩的性能特点,结合工程实例,对其竖向及水平向承载力的影响因素进行了分析,并根据其影响因素,对预应力混凝土管桩的设计、施工提出了合理化建议。     

预应力混凝土设计中的几个问题

在设计预应力混凝土结构时常常遇到一些问题。这些问题大都缘于现行规范没有给出明确的规定,本文从抗裂验算问题、预应力结构抗震设计问题、整体预应力结构设计等三个方面论述了作者的观点。希望有关规范,规程及标准修订时予以解决。     

Experimental study on shear behavior of prestressed reactive powder concrete I-girders

As a new generation of concrete, RPC(Reactive Powder Concrete) has attracted great research attention for its ultra-high strength and high durability. In the present paper, experimental results from tests on eight prestressed RPC I-section girders failing in shear are reported herein. The beams with RPC of 120 MPa in compression were designed to assess the ability to carry shear stress in thin webbed prestressed beams with stirrups. The test variables were the level of prestressing, shear span-depth ratio (a/d) and stirrup ratio. Shear deformation, shear capacity and crack pattern were experimentally investigated in detail. With regard to the shear resistance of the test beams, the predictions from three standards (AFGC, JSCE and SIA) on the design of UHPC structures were compared with the experimental result suggesting that the experimental strength is almost always higher than predicted. RPC, as a new concrete, was different from normal concrete and fiber reinforced concrete. Further study should be needed to develop an analytical method and computation model for shear strength of RPC beams.     

预应力混凝土叠合双向板叠合后的刚度分析

对预应力混凝土叠合双向板的抗弯刚度进行了分析研究,提出了预应力混凝土叠合双向板叠合后的刚度理论计算公式,为进一步研究预应力混凝土叠合双向板叠合后的刚度提供了理论依据。     

无粘结预应力混凝土框架火灾下的温度反应分析

火灾中影响无粘结预应力结构反应的因素较多，其中结构在火灾时对温度的反应是研究结构抗火性能的重要方面。本文通过模拟真实火灾环境，对4榀无粘结预应力混凝土框架进行了火灾试验，测出了在火环境下结构的温度场分布情况，并用计算机模拟温度场，从而为结构理论分析提供了温度数据。     

火灾作用下锚具对预应力钢棒锚固性能退化规律研究

为研究火灾作用下锚具对预应力（PC）钢棒锚固性能退化规律,完成65组由JXM型锚具、混凝土块、抗拉强度标准值为970 MPa的φ7高强PC钢棒及反力架组成的预应力锚固系统高温性能试验,其中29组为裸露锚具高温瞬态试验,18组为裸露锚具高温稳态试验,18组为带防火保护的锚具高温瞬态试验。研究PC钢棒应力水平（0.2~0.7）、温度（20~800℃）、防火保护措施（灌浆料封锚、涂抹防火涂料、灌浆料封锚后再涂抹防火涂料）和升温速率（10.0、26.7℃/min）对锚固性能的影响。裸露锚具高温瞬态试验结果表明：高温下锚固系统破坏模式为PC钢棒在锚具中发生滑移;PC钢棒的应力水平越高、温度越高、升温速率越大,锚固系统破坏时间越短。高温稳态试验结果表明：温度低于400℃时,锚固系统破坏模式为PC钢棒被拉断,温度高于400℃时,破坏模式为PC钢棒从锚具中滑移;高温后锚具不能再使用。带防火保护的高温瞬态试验结果表明：锚固系统破坏模式为PC钢棒从锚具中滑移,防火保护不改变锚固系统的破坏模式;与无防火保护措施相比,三种保护措施下锚固系统破坏时间均提高100%以上;若将GB 14907-2002《钢结构防火涂料》关于钢结构防火涂料厚度的要求直接应用于预应力锚具防火,将偏于不安全。     

预应力混凝土简支板抗火性能试验与分析

完成了9块无粘结和1块有粘结预应力混凝土单向简支板的抗火试验。各试验板内的热电偶在火灾下的实测结果表明,温度由迎火面至背火面逐渐递减,由迎火面至背火面的温度变化梯度随离迎火面距离的增大而减小。布置于无粘结预应力筋锚固端的力传感器和试验板上的位移传感器的测试结果表明,受火初期试验板挠曲变形增长较快,无粘结预应力筋应力呈增长趋势;受火一段时间之后试验板变形增长速度有所减缓,无粘结预应力筋应力呈减小趋势,且这种趋势一直延续到停火后一段时间;停火一段时间之后,试验板有变形恢复趋势,无粘结预应力筋应力水平又有所恢复。在受火过程中试验板背火面经历了水分溢出、水蒸气形成和发展、溢出水干涸及水蒸气消失的过程。在试验炉两侧壁的观察孔观测到有6块试验板发生了爆裂,爆裂发生在预应力度较高、荷载作用水平较低的试验板的邻近支座区域。基于试验结果,试算确定了对流换热系数、辐射换热相当发射率系数、混凝土导热系数和比热的取值,应用ANSYS