Shear design of reinforced concrete beams, slabs and walls

The paper presents the background to the shear design provisions for reinforced concrete beams and slabs used in the Australian practice. Correlation of design equations with experimental results are given. The design provisions are illustrated by examples. The importance of shear strength in the design of structural walls is discussed. A new expression to calculate the shear strength of walls is presented.     

钢筋混凝土楼板火灾反应数值计算模型

基于退化壳原理,考虑火灾下板壳截面的不均匀温度场分布而引入分层模型,同时在每分层上考虑材料在不同温度下的热力弹塑性本构关系,建立了火灾下钢筋混凝土板壳结构的有限元数值计算模型。另外,通过全拉格朗日方法考虑了大位移的几何非线性影响。最后通过一钢筋混凝土板在高温下的试验进行了验证,并分析了配筋率和保护层厚度的影响。结果表明:提出的火灾下钢筋混凝土壳单元数值计算模型的计算结果与试验结果吻合较好,可以用来分析火灾下钢筋混凝土框架结构楼板的反应。     

Evaluating the fire endurance of concrete slabs reinforced with FRP bars: Considerations for a holistic approach

In recent years, there has been increased interest in the use of fibre reinforced polymers (FRP) bars as flexural and shear reinforcement in concrete slabs and beams. When used in building applications, provision of appropriate fire endurance in structural members is a major safety requirement that must be considered. This paper presents an overview of experimental and numerical studies carried out on FRP-reinforced concrete slabs under standard fire conditions. The factors that are likely to influence the fire performance of FRP-reinforced concrete slabs are presented and discussed, and the development of initial design guidance for evaluating of the fire resistance of concrete slabs reinforced with FRP bars is outlined. Examples are presented for illustrating the application of existing design charts for evaluating the fire endurance of concrete slabs reinforced with FRP bars. Suggestions for further research are presented.     

粘贴钢板加固钢筋混凝土梁的分离式有限元模型

提出了外粘钢板加固受弯钢筋混凝土梁的非线性有限元模型。该模型中采用了一种特殊的、具有剥离破坏功能的界面单元来模拟混凝土梁和外粘钢板之间的粘结层,这种剥离破坏主要发生在粘贴钢板端部区域和弯曲、剪切裂缝附近。影响这种剥离破坏的主要因素有两个:一是粘贴钢板的端部与加固梁支座距离;二是粘贴钢板的厚度。传统的梁理论不能描述这种加固梁破坏模式,采用有限元方法能全方位地描述这种加固梁的各种性状和破坏模式。数值计算结果与粘贴不同厚度钢板加固梁的试验结果相吻合。     

A calculation method of cracking moment for the high strength concrete beams under pure torsion

In this study, a method is given to calculate cracking moments of high strength reinforced concrete beams under the effect of pure torsion. To determine the method, both elastic and plastic theories were used. In this method, dimensions of beam cross-section were considered besides stirrup and longitudinal reinforcements. Two plain high strength concrete (without reinforcement) and eight high strength reinforced concrete beams which have two different cross-sections (150 × 250 mm and 150 × 300 mm) were produced to examine the validity of the proposed method. The predictions of the proposed approach for the calculation of the cracking moment of beams under pure torsion were compared with the experimental and the analytical results of previous studies. From these comparisons it is concluded that the predictions of the proposed equations for the cracking moment of plain and reinforced high strength concrete beams under pure torsion are closer to the experimental data compared to the analytical results of previous theories.     

Ductility of FRP plated flexural members

The design of reinforced concrete (RC) flexural members such as beams, slabs and columns is intrinsically based on the inherent ductility of the member. In reinforced concrete beams and slabs, ductility is generally achieved by using ‘under-reinforced’ sections and generally governed by the neutral axis depth parameter k_u which requires ultimate failure by concrete crushing at a specified strain ε_c. As the plates of fibre reinforced polymer (FRP) plated RC beams can fracture or debond before the concrete crushes at ε_c, the k_u approach is not directly applicable. Hence, new fundamental approaches and a deeper understanding of ductility are required which are the subjects of this paper.     

Design equations for reinforced concrete members strengthened in shear with external FRP reinforcement formulated in an evolutionary multi-objective framework

Methods for predicting the shear capacity of FRP shear strengthened RC beams assume the traditional approach of superimposing the contribution of the FRP reinforcing to the contributions from the reinforcing steel and the concrete. These methods become the basis for most guides for the design of externally bonded FRP systems for strengthening concrete structures. The variations among them come from the way they account for the effect of basic shear design parameters on shear capacity. This paper presents a simple method for defining improved equations to calculate the shear capacity of reinforced concrete beams externally shear strengthened with FRP. For the first time, the equations are obtained in a multiobjective optimization framework solved by using genetic algorithms, resulting from considering simultaneously the experimental results of beams with and without FRP external reinforcement. The performance of the new proposed equations is compared to the predictions with some of the current shear design guidelines for strengthening concrete structures using FRPs. The proposed procedure is also reformulated as a constrained optimization problem to provide more conservative shear predictions.     

FRP筋混凝土T形和矩形截面梁抗弯承载力计算方法

为建立纤维增强复合材料(fiber-reinforced polymer,FRP)筋混凝土T形和矩形截面梁抗弯承载力简化计算方法,根据平衡破坏状态下的截面分析,定义了等效FRP配筋率ρ_ef和相应的平衡配筋率ρ_{ef, b}。在此基础上,基于257根FRP筋混凝土梁试验结果的统计分析,改进了受拉破坏和受压破坏皆可能发生的过渡区范围(ρ_{ef, b} <ρ_ef≤1.5ρ_{ef, b})。编制了受拉破坏控制截面的非线性分析程序,考虑多个设计参数的影响,开展了25 344个截面的参数分析。通过对参数分析结果的多元回归分析,推导了受拉破坏控制截面的抗弯承载力简化计算公式。此外,基于截面内力平衡和协调条件,推导了受压破坏控制截面的抗弯承载力计算公式。以国内外257根梁抗弯承载力试验结果,验证了所提方法的适用性。     

钢筋混凝土框架抗连续倒塌的压拱机制分析模型

钢筋混凝土框架结构依靠梁板组成的楼盖系统来抵抗连续倒塌,其在小变形下的连续倒塌抗力由梁板内的压拱机制提供。现有压拱机制的宏观理论分析模型参数过多且不能考虑楼板的影响,因此难以在工程设计中进行应用。该文基于楼盖系统微观受力机理的分析,建立了压拱机制下梁板子结构系统的连续倒塌抗力分析模型。和现有模型相比,该文计算模型的参数大幅减少、公式显著简化,且能够考虑楼板和梁抵抗连续倒塌的共同作用。通过与国内外47个梁试件和6个梁板子结构试件的试验结果进行对比,发现该文计算模型在计算梁试件时计算精度和现有模型精度相同,而在计算梁板共同作用下的连续倒塌抗力时精度提高显著,能够为混凝土框架结构的抗连续倒塌工程设计提供参考。     

Structural response of hyperstatic concrete beams reinforced with GFRP bars: Effect of increasing concrete confinement

The design of concrete structures reinforced with glass fibre reinforced polymer (GFRP) bars is influenced by their reduced stiffness and brittleness. In hyperstatic structures, the methodology used in force analysis depends on the ductility of the structural systems, which in this case, being essentially provided by the concrete, can be potentially increased by confining concrete in critical zones. This paper presents experimental and numerical investigations about the flexural behaviour of continuous beams reinforced with GFRP bars, namely of their service and failure responses, and the effect of increasing concrete confinement in critical cross-sections. A calculation procedure to quantify the confinement effect in beams due to the reduction of the spacing between shear stirrups is first presented. The experimental investigations comprised a comparative study in which two-span concrete beams reinforced with either GFRP or steel bars were tested in bending. In the former, the effect of reducing the shear stirrups spacing was analyzed together with the under- and over-reinforcement at the central support and midspan cross-sections, respectively. The development of a crack hinge in the continuity support zone highlighted the better performance of beams under-reinforced on the top layer with GFRP bars compared to “equivalent” beams reinforced with steel, namely at the resistance level. In addition, the confinement at critical zones increased significantly the strength and ductility. The numerical investigations included the development of non-linear finite element models for all beams tested - numerical results are in good agreement with test data and seem to confirm the confinement effect observed in the experiments.     

预应力型钢超高强混凝土梁受剪承载力试验研究

基于12榀预应力型钢超高强混凝土简支梁和2榀预应力型钢普通强度混凝土简支梁的受剪试验,揭示了影响试验梁受剪性能的主要因素,探讨了剪跨比、箍筋间距、腹板厚度、混凝土强度和预应力度对试验梁的破坏形态、荷载-挠度曲线、斜截面开裂荷载和受剪承载力的影响规律。试验结果表明:预应力型钢超高强混凝土梁具有更好的受剪承载力和剪切延性,以及更大的刚度;基于试验结果建立了预应力型钢超高强混凝土梁的受剪承载力建议计算公式,计算结果与试验结果吻合较好,表明了该文提出的计算公式具有较高的精度。研究成果将为预应力型钢超高强混凝土梁的设计计算和工程应用提供理论依据。     

Tests of continuous concrete slabs reinforced with carbon fibre reinforced polymer bars

Although several research studies have been conducted on simply supported concrete elements reinforced with fibre reinforced polymer (FRP) bars, there is little reported work on the behaviour of continuous elements. This paper reports the testing of four continuously supported concrete slabs reinforced with carbon fibre reinforced polymer (CFRP) bars. Different arrangements of CFRP reinforcement at mid-span and over the middle support were considered. Two simply supported concrete slabs reinforced with under and over CFRP reinforcement and a continuous concrete slab reinforced with steel bars were also tested for comparison purposes. All continuous CFRP reinforced concrete slabs exhibited a combined shear–flexure failure mode. It was also shown that increasing the bottom mid-span CFRP reinforcement of continuous slabs is more effective than the top over middle support CFRP reinforcement in improving the load capacity and reducing mid-span deflections. The ACI 440.1R–06 formulas overestimated the experimental moment at failure but better predicted the load capacity of continuous CFRP reinforced concrete slabs tested. The ACI 440.1R–06, ISIS–M03–07 and CSA S806-06 design code equations reasonably predicted the deflections of the CFRP continuously supported slabs having under reinforcement at the bottom layer but underestimated deflections of continuous slabs with over-reinforcement at the bottom layer.     

两种组合钢框架火灾变形性能的试验研究

利用自行研制的火灾加温试验炉及相关测试装置,对2种不同连接方式共4榀组合钢框架在不同的火灾工况下的火灾变形性能进行了试验研究,火灾工况包括:梁、板、柱同时受火而节点不受火和梁、板受火而柱、节点不受火2种。试验中量测了炉温,H型钢梁、柱及钢筋混凝土楼板中的温度分布,结果表明:裸钢的温度相差很小,而埋入混凝土中的钢的升温曲线与裸钢的有较大差异;混凝土的升温曲线则与钢的升温曲线差别较大,加温初期不久由于混凝土凝结水等的原因致使温升曲线存在有一平缓阶段,且随着距受火面距离增大混凝土的温升曲线有明显的滞后现象,当炉温和裸钢的温度开始下降时,混凝土的温度却仍在升高。该文对框架的变形和组合梁变形进行了分析,经比对2种连接方式组合钢框架的火灾行为后,给出了工程应用建议。     

钢筋混凝土柱偏心受压力学性能的细观数值研究

钢筋混凝土构件的宏观力学性能由其组分-钢筋和混凝土两部分的力学性能决定。结合混凝土细观结构形式,认为混凝土是由骨料颗粒、砂浆基质及界面过渡区组成的复合材料,假定钢筋与混凝土之间完好粘结,基于钢筋混凝土柱偏心受压试验,建立了钢筋混凝土柱偏心受压加载下力学特性及破坏行为研究的细观尺度力学分析模型。通过对混凝土方形和矩形试件进行受压力学特性模拟,采用反演法确定了界面的力学参数,进而模拟了钢筋混凝土柱偏心受压加载下的宏观力学性能。结果表明,相比于宏观尺度模型,细观数值分析模型能够充分体现材料的非均质性,能够较好的模拟试件的宏观力学性能,并且能够细致的描述裂缝发展及试件破坏过程,与试验结果吻合良好。该文建立的细观尺度分析模型与方法,为钢筋混凝土构件层次宏观力学非线性及其尺寸效应研究提供了理论支持。     

Strengthening and repair of concrete foundation beams with carbon fiber composite materials

For several years Carbon Fiber Reinforced Polymer (CFRP) have been gradually replacing steel plates in the reinforcement of concrete structures that are damaged or need increased resistance. It has long been established that the addition of CFRP laminates to structures such as beams and slabs, increases their bending and shearing strength considerably. However, the behaviour of foundation beams with these reinforcements is not clear. The essential issue in the analysis of reinforced structures with composite materials is to understand the individual behaviour of each material and its interaction with the remaining ones. In this paper, bending and shearing strength of concrete foundation beams with CFRP reinforcement are analyzed through the study of their load capacity variation and beam deflections. Different height/span beam relations are considered. The numerical modeling is performed by the Finite Elements Method with the Abaqus program. Non-linear models are used for concrete and soil, and a linear elastic model is adopted for composites materials.     

建筑结构用再生混凝土水平受力构件研究进展

建筑结构水平构件混凝土用量较大,且对混凝土力学性能要求相对不高,更适合再生混凝土的结构化应用。本文总结分析了国内外学者及笔者所在课题组近年来在再生混凝土材料性能、钢-再生混凝土黏结性能以及钢筋再生混凝土板、梁和钢-再生混凝土组合板、组合梁等水平受力构件力学性能方面的研究成果。结果表明:研究学者针对再生混凝土的材料性能进行了三十余年的试验研究与机理分析,积累了充足的试验数据,并提出了相对可靠的预测模型,为其在建筑结构中的应用奠定了基础;通过对钢筋再生混凝土板与梁的受弯、受剪以及长期性能的试验研究与理论分析,提出了成套的钢筋再生混凝土水平受力构件设计方法,现已纳入了再生混凝土结构技术规程;近十年来,研究学者对钢-再生混凝土组合板与组合梁的受弯、受剪以及长期性能进行了试验研究与有限元分析,发现再生混凝土在组合结构中的应用是可行的,但相关研究尚待深入。未来仍需对再生混凝土水平受力构件设计方法的可靠度进行系统研究,并拓展再生混凝土水平受力构件的疲劳性能、耐久性能及抗火性能等研究。     

Investigation of structural behaviours of laterally restrained GFRP reinforced concrete slabs

The corrosion of reinforcement in concrete bridge deck has been the cause of major deterioration and of high costs in repair and maintenance. Glass fibre reinforced polymer (GFRP) reinforcement is a more durable alternative to steel reinforcement and has higher strength to weight ratio. Due to the low value of elasticity and brittle behaviour of GFRP, the service behaviour of GFRP reinforced concrete structure is critical. However, laterally restrained slabs, such as those in bridge deck slabs, exhibit arching action or compressive membrane action (CMA) which has a beneficial influence on the service behaviour such as the deflection. This paper presents the results of experimental tests and numerical analysis of laterally restrained GFRP reinforced concrete slabs with varying some structural variables. The analysis results are discussed and conclusions on the compressive membrane action in GFRP reinforced concrete slabs are presented.     

Fire behaviour of FRP-strengthened reinforced concrete structural elements: A state-of-the-art review

The last two decades have seen increasing applications of fibre reinforced polymer (FRP) materials in civil engineering structures due to their many advantages over traditional strengthening and reinforcing materials. Among the most common applications is bonding or wrapping FRP products (strips or sheets) to the exterior of reinforced concrete (RC) members to increase their strength or deformability. However, widespread application of FRP strengthening systems in buildings, where structural fire ratings are required, is hindered due to unknowns surrounding the reduction in their mechanical and bond properties at elevated temperatures. This paper presents a state-of-the-art review on the fire performance of FRP-strengthened RC structural elements. The review addresses first the mechanical behaviour at high temperature of the constituent materials of FRPs and how their bond to concrete is affected when heated. The paper then discusses available experimental and numerical studies on the fire behaviour of FRP-strengthened RC beams, slabs, and columns. Available design guidance is also discussed. Finally, recommendations for future research are given.     

负弯矩作用下考虑滑移效应的组合梁承载力分析

钢梁与混凝土之间的滑移效应对组合梁在弹性阶段的性能有很大影响。基于组合梁在负弯矩作用下的滑移微分方程,求出了连续组合梁负弯矩区的滑移及滑移应变解。根据滑移应变解,分析了组合梁在负弯矩作用下的截面应变分布,建立了考虑滑移效应的组合梁弹性承载力计算方法。计算表明,滑移效应导致组合梁截面曲率增大和钢筋应变滞后,在一定程度上减小了构件的弹性抗弯承载力,需要在设计和使用中予以重视。     

爆炸作用下高强钢绞线网片-聚合物砂浆加固钢筋混凝土板的数值模拟

为了探究高强钢绞线-聚合物砂浆加固技术对钢筋混凝土板的抗爆性能的影响,应用有限元分析软件ANSYS/LS-DYNA对其进行了在爆炸荷载作用下的数值模拟。在验证有限元模型合理性的基础上,对比分析了爆炸荷载作用下砂浆层厚度、砂浆强度和钢绞线直径等不同加固参数对钢筋混凝土板的破坏形态与板底位移的影响。结果表明:采用高强钢绞线-聚合物砂浆加固后钢筋混凝土板的抗爆性能显著提高;在砂浆加固层厚度、砂浆强度、钢绞线直径3种加固影响参数中,砂浆加固层厚度对钢筋混凝土板的加固效果影响显著,而砂浆强度和钢绞线直径对板的加固效果不明显。如果运用该技术提高钢筋混凝土板的抗爆性能,优先考虑增大加固层厚度。