钢筋增强高延性ECC/混凝土组合梁的受弯性能(英文)

采用高延性纤维增强水泥基材料部分代替钢筋混凝土梁受拉区的混凝土得到 ECC/RC 组合梁构件,可以有效提高梁的延性及抗裂性能. 基于平截面假定和材料本构模型,分析组合梁构件在受力过程中各个阶段的截面应力应变状态,得到各阶段承载力的计算方法. 根据混凝土结构设计规范,提出了 ECC/RC 组合梁极限承载力的简化计算方法,并给出了组合梁构件的弯矩-曲率关系,得到组合梁延性的简便计算方法.最后,采用一个组合梁的试验结果对理论公式进行验征. 结果表明: 计算结果和试验结果吻合得较好,证明所提出的组合梁各阶段受弯承载力计算方法是正确的,具有一定的理论意义和参考价值.     

箱形型钢混凝土梁的试验研究

以7根1:3模型梁为研究对象,试验研究箱形型钢混凝土(SRC)梁的性能.试验结果表明,箱形SRC梁的抗弯强度随纵筋配筋率和型钢翼缘板厚度的增大而提高,剪切强度随型钢腹板的厚度增大而提高.箱形型钢内浇注混凝土不但可避免型钢屈曲破坏而且还可提高梁的极限荷载.型钢和混凝土间的连接需要改善以加强混凝土和型钢的共同工作作用.给出了箱形SRC组合梁的抗弯承载力和抗剪承载力计算公式,计算结果和试验结果吻合良好.箱形SRC组合梁是一种延性构件,适用于工程实践应用.     

Flexural rigidity evolvement laws of reinforced concrete beams strengthened with carbon fiber laminates

Extensive research has shown that externally bonded carbon fiber reinforced polymer (CFRP) laminates are particularly suitable for improving the fatigue behavior of reinforced concrete (RC) beams. This paper presents the research on flexural rigidity evolvement laws by testing 14 simple-supported RC beams strengthened with carbon fiber laminates (CFL) under cyclic load, and 2 under monotone load as a reference. The cyclic load tests revealed the peak load applied onto the surface of a supported RC beam strengthened with CFL is linear to the logarithm of its fatigue life, and the flexural rigidity evolvement undergoes three distinct phases: a rapid decrease from the start to about 5% of the fatigue life; an even development from 5% to about 99% of the fatigue life; and a succedent rapid decrease to failure. When the ratio of fatigue cycles to the fatigue life is within 0.05 to 0.99, the flexural rigidity varies linearly with the ratio. The peak load does not affect the flexural rigidity evolvement if it is not high enough to make the main reinforcements yield. The dependences of the flexural rigidity of specimens formed in the same group upon their fatigue cycles normalized by fatigue life are almost coincident. This implies the flexural rigidity may be a material parameter independent of the stress level. These relationships of flexural rigidity to fatigue cycles, and fatigue life may be able to provide some hints for fatigue design and fatigue life evaluation of RC member strengthened with CFL; nevertheless the findings still need verifying by more experiments.     

Shear strengthening of pre-damaged reinforced concrete beams with carbon fiber reinforced polymer sheet strips

This paper presents the results of an experimental investigation on the response of pre-damaged reinforced concrete (RC) beam strengthened in shear using applied-epoxy unidirectional carbon fiber reinforced polymer (CFRP) sheet. The reasearch included four test rectangular simply supported RC beams in shear capacity. One is the control beam, two RC beams are damaged to a predetermined degree from ultimate shear capacity of the control beam, and the last beam is left without pre-damaged and then strengthened with using externally bonded carbon fiber reinforced polymer to upgrade their shear capacity. We focused on the damage degree to beams during strengthening, therefore, only the beams with side- bonded CFRPs strips and horizontal anchored strips were used. The results show the feasibility of using CFRPs to restore or increase the load-carrying capacity in the shear of damaged RC beams. The failure mode of all the CFRP-strengthened beams is debonding of CFRP vertical strips. Two prediction available models in ACI-440 and fib European code were compared with the experimental results.     

Bearing capacity of composite columns reinforced by concrete filled steel tube

In this study, nine simplified short composite columns consisting of core CFST (concrete filled steel tube) of different diameters and outer reinforced concrete were constructed to study their compressive performance under axial or eccentric compression. The failure mode is characterized by the crush of the outer concrete. The bearing capacity increases at first and then decreases with further increase of the position coefficient. It can be concluded that position coefficient is an important structural parameter that has considerable influences on the ultimate bearing capacity of the composite columns. The outer concrete, steel tubes and longitudinal reinforcement are found to work in a cooperative manner under axial or eccentric compression when the position coefficient is about 0.5. An improved bearing capacity algorithm that takes the position coefficient into account has been proposed based on the experimental and simulation results and current technical specification in China. It has been proven to be precise and safe.     

钢纤维增强混凝土抗裂性能试验研究

通过试验研究剪切型钢纤维对混凝土的塑性开裂、干燥收缩及混凝土力学性能的影响.试验结果表明,钢纤维对改善混凝土开裂有明显效果,并且还探讨了钢纤维的抗裂、增强机理.     

内嵌碳纤维板条抗剪加固混凝土梁性能研究

通过9根表层嵌入碳纤维增强塑料板条抗剪加固的钢筋混凝土梁和4根对比梁的静载试验,分析了构件的破坏形态、斜截面纤维应变分布特征及加固后极限承载力的影响因素。研究结果表明：嵌入式加固与外贴加固相比,可以明显地提高钢筋混凝土梁的抗剪承载力,并改变构件的变形性能。最后,在国内外研究资料的基础上,提出了加固后混凝土梁的受剪承载力计算公式,并对计算值与试验值进行了比较,结果吻合较好。     

Seismic behavior of steel reinforced ultra high strength concrete column and reinforced concrete beam connection

To investigate the seismic behavior of connections composed of steel reinforced ultra high strength concrete （SRUHSC） column and reinforced concrete （RC） beam, six interior strong-column-weak-beam connection specimens were tested subjected to reversal cyclic load. Effects of applied axial load ratio and volumetric stirrup ratio on ductility, energy dissipation capacity, strength degradation and rigidity degradation were discussed. It was found that all connection specimens failed in bending in a ductile manner with a beam plastic hinge. The ductility and energy dissipation capacity increased with the decrease of applied axial load ratio or increase of volumetric stirrup ratio. The displacement ductility coefficient and equivalent damping coefficient lay between those of steel reinforced ordinary concrete connection and those of reinforced concrete connection. The applied axial load ratio and volumetric stirrup ratio had less influence on the strength degradation and more influence on the stiffness degradation. The stiffness degraded sharply with the decrease of volumetric stirrup ratio or increase of applied axial load ratio. The experimental results indicate that SRUHSC column and RC beam connection exhibited better seismic performance and can provide reference for engineering application.     

Effect of corrosion on bond behavior and bending strength of reinforced concrete beams

There is growing concern for corrosion damage in reinforced concrete structures with several decades’ service. Pullout tests and beam tests were carried out to study the effect of reinforcement corrosion on the bond behavior and bending strength of reinforced concrete beams. The bond strength of plain bars and concrete initially increases with increasing corrosion, then declines. The turning point depends on the cracking of the concrete cover. The bond strength of deformed bars and concrete increases with corrosion up to a certain amount, but with progressive increase in corrosion, the bond strength decreases, and the cracking of the concrete cover seems to have no effect on the bond strength. On the basis of test data, the bond strength coefficient recommended here, which, together with the bond strength of uncorroded steel bars and concrete, can be used to easily calculate the bond strength of corroded steel bars and concrete. The bond strength coefficient proposed in this paper can be used to study the bond stress-slip relationship of corroded steel bars and concrete. The bending strength of corroded reinforced concrete beams declines with increasing reinforcement corrosion. Decreased bending strength of corroded RC beam is due to reduction in steel bar cross section, reduction of yield strength of steel bar, and reduction of bond capacity between steel bar and concrete. Project supported by Cao Guanbiao Key Technology Development Founding of Zhejiang University and Construction Ministry of China.     

T形配钢型钢混凝土偏压构件力学性能研究

建立了T形配钢型钢混凝土偏压构件力学性能分析的有限元模型,计算结果得到以往实验结果的验证。在此基础上,分析了不同阶段材料应力状态和各参数对偏压构件力学性能的影响。结果表明:T形配钢型钢混凝土构件在不同加载角下的性能有所不同,加载角为180°时极限承载力大于其他角度情况;混凝土抗压强度、型钢含钢率、配筋率、荷载偏心率、长细比对构件荷载-变形曲线的影响较大,随着混凝土强度、型钢含钢率、配筋率的增加,极限承载力和刚度增加;随着荷载偏心率的增加,极限承载力和刚度下降;随着构件长细比的增加,构件承载力总体呈现线性下降趋势,刚度下降明显。     

外包钢-混凝土组合梁正截面极限抗弯承载力的试验研究

基于外包钢混凝土组合梁的试验研究和塑性理论,按照钢梁和混凝土塑性中和轴相对位置的不同,分别推导了完全剪切连接和部分剪切连接的外包钢混凝土组合梁的正截面极限抗弯承载力的计算公式,并对外包钢混凝土组合梁进行了非线性有限元分析,分析中重点考虑了材料非线性和接触非线性.8根完全剪切连接和3根部分剪切连接试件的正截面极限抗弯承载力的计算结果及有限元分析结果与试验结果吻合良好.     

碳纤维布加固钢筋砼吊车梁抗弯疲劳性能试验

为研究碳纤维布(CFRP)对加固后钢筋混凝土梁的抗弯疲劳性能的影响,进行了3根CFRP加固梁及1根对比梁的抗弯疲劳试验.研究了碳纤维布加固方式、构件使用荷载等参数对碳纤维布加固损伤钢筋混凝土吊车梁的抗弯疲劳性能影响.试验研究表明:采用碳纤维布加固后,构件裂缝的宽度减小50.2%~66%,发展速度也得到控制,钢筋应力减小24.1%~28.2%,构件的刚度提高14.9%~16.1%.依据试验结果,从现有规范中关于构件刚度计算方法出发,进行了CFRP加固钢筋混凝土吊车梁的疲劳刚度计算分析,该计算方法可用于吊车梁加固工程设计.最后给出了CFRP加固梁的疲劳设计的合理化建议.     

Numerical simulation on dynamic bending strength of three-graded concrete beam based on meso-mechanics

To study the bending strength of mass concrete under dynamic loading, the pure bending zone of three-graded concrete beam is considered as a three-phase composite composed of matrix, aggregate and interface between them on meso-level. Dynamic constitutive model considering strain-rate strengthening effect and damage softening effect is adopted to describe the cocrete and meso-element's damage. The failure mechanisms of beam under impact loading, triagle wave load, dynamic load coupling with initial static loading were simulated by using displacement-controlled FEM. Furthermore, stress-strain curve of the specimens and their dynamic bending strength were obtained. The results obtained from numerical simulation agreed well with experimental data.     

碳纤维布与钢构套复合加固锈蚀钢筋混凝土柱抗震性能研究(英文)

为改善锈蚀钢筋混凝土柱的抗震性能, 利用碳纤维布与角钢对锈蚀柱进行复合抗震加固. 试验共对12根试件进行了低周反复加载试验, 研究参量包括钢筋锈蚀程度、轴向荷载、碳纤维布层数和角钢用量. 试验结果表明, 利用碳纤维布和角钢复合加固锈蚀柱可以显著改善锈蚀柱的承载能力、延性和耗能能力. 复合加固后, 加固柱的强度和延性与锈蚀柱相比, 可分别提高0.9倍和1倍以上. 基于试验结果, 提出了计算加固构件屈服荷载、最大荷载和位移延性系数的简化公式, 计算结果与试验结果极为吻合.     

Behavior of slender steel concrete composite columns in eccentric loading

Ten slender steel reinforced cencrete (SRC) composite columns are tested under eccentric loading conditions.Effects of concrete strength, slenderness of columns and eccentricity of the axial load are studied. The load-carrying capacity is reduced with increased slenderness ratio and eccentricity. Concrete strength has no obvious influence on eccentrically loaded columns. Then, a nonlinear numerical method of pin-ended slender columns is also presented. This method is applicable for determining the material failure load or buckling failure load of a slender steel reinforced concrete composite column. In this method both material and geometric nonlinearities are taken into account. The results of numerical analysis accord well with the test results. The test results are also compared with the results predicted by ACI318-05 and the China Specifications.     

碳纤维布加固法在建筑工程中的应用

钢筋混凝土结构中,由于钢筋的锈蚀而使钢筋混凝土结构的耐久性大大降低.针对沿海建筑加固工程的设计、施工过程,对锈蚀钢筋混凝土构件的受弯破坏形态,提出了碳纤维布加固锈蚀钢筋混凝土结构的实用设计与施工方法.     

Shear capacity of reinforced concrete columns strengthened with CFRP sheet

INTRODUCTION There is increased need in recent years for strengthening or rehabilitation of existing reinforced concrete structures adversely affected by overloading, construction material deterioration, seismic loads, structural deformation, etc. An effective method for increasing the shear capacity of reinforced concrete columns is the use of externally bonded carbon fiber reinforced plastic (CFRP) systems (ACI, 2002). FRP systems were first applied to reinforced concrete col-umns i…     

Theoretical study on constitutive relationship of fiber reinforced polymer confined concrete

We proposed a bilinearity constitutive curve model of fiber reinforced polymer （FRP） confined concrete which includes a parabola in the first stage and a straight line in the second stage. The FRP-confined concrete has powerful confinement status and weak confinement status leading to different equations of parabola. We analyzed the impacts of factors such as confinement ratio and restrain stiffness on confined concrete compressive strength, ultimate strain and other control parameters through finite element analysis. The results show that the confinement ratio determines the confinement status, and the increase of the confinement ratio has a limited capacity to increase the compressive strength, The deformation of confined concrete is influenced by restrain stiffness. The stronger the restrain stiffness is, the less the lateral deformation is and the greater ultimate axial strain will be. The consideration of equivalent section coefficient kse is needed in the non-circular section confined concrete. We analyzed the results and proposed boundary values of strong and weak confinement styles, a peak/inflection point stress and strain model, and a compressive strength and ultimate strain model.     

基于状态方程法的钢筋混凝土梁桥随机地震反应概率分析

钢筋混凝土梁桥在地震作用下结构可简化为一多自由度体系，基于状态方程法的一般原理，推导了钢筋混凝土梁桥的自由振动解和强迫振动解，并对结构在平稳白噪声激励下进行了随机地震反应分析。     

利用高延性水泥基材料抑制钢/混凝土连接区域的断裂破坏(英文)

为了避免混凝土的脆性断裂破坏,在钢/混凝土连接区域中用高延性水泥基材料(ECC)代替了普通混凝土. 采用剪力键/ECC 的抗剪试验、二维锚固螺栓/ECC 拔出试验和有限元模拟研究了 ECC 材料的延性对于连接区域破坏模式、结构性能的影响. 实验结果表明: 通过微观力学原理设计的 ECC 具有 300 倍于普通混凝土的拉伸延性,从而使钢/混凝土连接区中混凝土断裂破坏模式由脆性转变为延性. 混凝土材料的高延性使结构承载能力和变形性能获得改善,这也同时为有限元模拟结果所验证. 通过改变混凝土材料延性而提高结构性能的理念也可在其他类似的钢/混凝土组合结构中得到应用.