剪跨比对活性粉末混凝土梁抗剪性能的影响

通过4根活性粉末混凝土(RPC)梁构件的受剪试验,研究活性粉末混凝土在不同剪跨比条件下的破坏形态及剪切延性的影响规律。试验结果表明:高强钢筋RPC梁的剪切延性系数平均值达到0.892。随着剪跨比的增大而增强,但增幅差异较大,其根本原因是剪跨比影响梁的剪力传递方式,剪力传递方式又决定了其剪切延性,当剪跨比适中时,梁构件发生剪压破坏,其延性相对较好。     

活性粉末混凝土梁抗剪承载力预测的相关向量机模型

摘　要: 为了利用活性粉末混凝土梁一些易获取的相关参数较好地预测其抗剪承载力, 提出一种基于相关向量机(RVM) 的抗剪承载力预测模型。通过样本训练建立活性粉末混凝土梁抗剪承载力与混凝土棱柱体抗压强度以及梁剪跨比、 配箍率、 纵筋率等4 个主要影响因素之间的非线性映射关系, 并据此对其他样本的抗剪承载力进行精准预测。在相同样本情况下, 将RVM 模型应用于活性粉末混凝土梁抗剪承载力预测实例与BP 神经网络模型的预测结果进行对比。研究结果表明: RVM 模型预测精度更高、 离散性更小;敏感因子分析进一步探究了4 个影响因素选取的正确性及因素与抗剪承载力之间的相关性, 其中剪跨比敏感因子最高, 在活性粉末混凝土梁抗剪承载力相关研究中应重点分析。     

有腹筋UHPFRC梁抗剪承载力计算

为研究有腹筋UHPFRC梁的抗剪承载力,根据超高性能纤维混凝土梁的剪切破坏机理,结合修正压力场理论,考虑梁上部受压区混凝土和下部受拉区骨料咬合力、箍筋及裂缝间钢纤维共同承受剪力,推导了有腹筋超高性能纤维混凝土梁的抗剪承载力计算公式.与9根超高性能纤维混凝土梁的剪切试验结果进行对比,用推导公式计算的抗剪承载力与试验结果吻合较好,且变异系数较小,可用于有腹筋超高性能纤维混凝土梁的抗剪分析和设计.     

钢纤维高强混凝土箍筋梁抗剪性能试验

为了提高高强混凝土的韧性和抗剪能力,在高强钢筋混凝土梁中掺入钢纤维.对20根(ffcu=52.4~84.7)钢纤维高强混凝土箍筋梁(fρ=0.5%~1.5%)和2根高强混凝土箍筋梁对比试件进行了试验.试验的主要变化参数为钢纤维体积掺率、钢纤维种类、配箍率和混凝土强度.试验结果表明钢纤维能够显著地改善梁的抗剪性能.基于试验结果,分析了钢纤维、箍筋、混凝土的强度和剪跨比对梁的斜截面抗裂和抗剪承载力的影响.在考虑钢纤维影响的基础上,提出了与普通钢筋混凝土梁斜截面计算公式相协调的钢纤维混凝土梁的斜截面开裂和极限承载力计算的经验公式.     

高强钢筋活性粉末混凝土简支梁受剪性能试验研究

利用稳定可靠的试验系统,通过改变试验梁的剪跨比、配箍率、纵筋率和钢筋等级等因素,对6根不同高强钢筋活性粉末混凝土简支梁进行试验。根据试验结果,分析了不同因素对试验梁其破坏形态、剪切延性和受剪承载力的影响。结果表明:HRB500级等高强钢筋与活性粉末混凝土具有良好的协同抗剪工作性能,较好的抗剪承载力和剪切延性;对于剪跨比(1<λ≤3)一定的梁,适当配置箍筋可以提高承载能力,改善受剪延性;配箍率、纵筋配筋率和剪跨比等参数对试验梁的抗剪承载力和剪切延性影响显著。     

高强无腹筋梁抗剪承载力分析

收集了国内外134个集中荷载下高强无腹筋简支梁的抗剪试验数据,将实测承载力与中国国标GB50010-2010和美国的ACI318-08的预测结果进行了对比,结果表明:2国标准对于计算高强无腹筋梁安全度不够。GB50010-2010预测大剪跨比、有效截面高度偏大,纵筋率偏小的高强钢筋混凝土构件,可靠度偏低。     

基于修正压力场理论的超高性能钢纤维混凝土柱抗剪承载力

为了分析超高性能钢纤维混凝土柱抗剪性能,基于修正压力场理论提出了柱子抗剪承载力计算模型.该模型通过柱端部截面中心正应变来考虑轴力和弯矩对抗剪承载力的影响,通过关键参数混凝土主压应变与主压应力间的角度和平均正应变来反映剪跨比、轴力以及配箍率对柱抗剪承载力的影响.结果表明:对剪跨比为1:5-2:0的柱子,该模型剪力计算值与试验值吻合良好.     

预应力活性粉末混凝土梁斜截面抗裂性能试验

为研究预应力技术对ＲＰＣ梁斜截面抗裂性能的影响,对３根预应力ＲＰＣ工字梁及１根非预应力ＲＰＣ工字梁进行单点加载下的斜截面抗裂性能试验。分析了预应力度及剪跨比对预应力ＲＰＣ梁斜截面开裂裂缝形态、主斜裂缝倾角及宽度、主斜裂缝投影长度的影响,探讨了预应力度及剪跨比等因素对预应力ＲＰＣ梁斜截面开裂荷载的影响规律,并建立了预应力ＲＰＣ梁斜截面抗裂强度计算公式。研究表明：预应力的施加可以有效提升ＲＰＣ梁的斜截面开裂荷载,但这种有利作用会随剪跨比的增加而降低;预应力可改变ＲＰＣ工字梁的初始斜裂缝形态、减小主斜裂缝的倾角,但其对主斜裂缝投影长及主斜裂缝最终宽度影响不大。     

活性粉末混凝土受弯构件中钢筋粘结性能

为了研究活性粉末混凝土构件中钢筋的粘结特性,采用梁式试验方法分析了各因素对粘结性能的影响,建立了粘结应力-滑移本构模型,并与普通C40混凝土进行对比.研究表明:活性粉末混凝土试件与C40混凝土试件的粘结应力-滑移曲线整体规律相同,活性粉末混凝土的抗压强度及粘结强度都远大于普通混凝土,其中极限粘结强度τu约为C40混凝土的3倍,其对应的滑移值su约为C10混凝土的2倍,相对粘结强度τu/(fcu)i约为C10混凝土的1.6倍;根据试验曲线及试件破坏过程对活性粉末混凝土与钢筋之间的粘结机理进行分析,并根据试验数据统计回归出多因素影响下锚固特征值的经验公式,建立了四折线的粘结应力-滑移本构模型.     

高强钢筋RPC梁受弯构件正截面承载力试验研究

对6根高强钢筋RPC(Reactive Powder Concrete)简支梁进行了静力三分点加载试验,分析了不同纵筋配筋率、纵筋等级、纵筋直径和受压钢筋直径不同时对梁的受力性能影响,得到结论为:平截面假定对于高强钢筋RPC梁同样适用;配筋率是高强钢筋RPC梁承载力的主要影响因素;参照普通钢筋混凝土梁正截面承载力计算模型,导出了高强钢筋RPC受弯构件正截面承载力计算公式;高强钢筋RPC梁的界限相对受压区高度为0.62。     

高强箍筋高强混凝土梁抗剪试验研究

普通配筋的高强混凝土构件抗剪性能较差,脆性性质明显.配置高强箍筋能改善高强混凝土梁的抗剪性能,减小脆性性质.通过6根配有高强箍筋的简支梁试验,研究高强箍筋高强混凝土梁的抗剪性能,以及各种因素对构件抗剪性能的影响.试验中使用极限强度为800N/mm2和1 100N/mm2的箍筋,结果证实合理配置高强箍筋能有效改善构件的抗剪性能.     

Mesomechanism of steel fiber reinforcement and toughening of reactive powder concrete

Reactive powder concrete (RPC) is a novel cement-based composite material with ultra-high strength. Embedding a certain amount of short steel fibers in the matrix can improve the RPC's toughness and overcome the disadvantage of high brittleness. In this paper, a number of direct uniaxial tension tests have been carried out with '8-shape' RPC200 specimens. The bond-slip process, mesoscopic structural variation and mechanical characteristics of a fiber pullout of the matrix have been investigated using the real-time SEM loading system and CCD observation techniques. The influence of the volume of embedded short steel fibers in matrix on the mesoscopic morphology of attachments on the surface of a pulled individual fiber, the initial cracking force, the ultimate pullout force, interfacial bond strength and the pullout rupture energy have been analyzed. A general formulation relating these quantities to the volume of fibers in matrix has been proposed. The components comprising the interfacial bond strength have been outlined. In addition, the contribution that fibers make to enhance and toughen the reactive powder concrete has been discussed. It is shown that there exists an optimal threshold of fiber volume ρv, opt =1.5% at which the bond performance of a fiber pullout of RPC behaves best.     

活性粉末混凝土强度影响因素研究

研究养护时间和钢纤维掺量对活性粉末混凝土抗折、抗压强度的影响,探索低成本、超高强高性能活性粉末混凝土的配制技术,旨在促进活性粉末混凝土的推广应用.     

高温后RPC立方体抗压强度退化规律研究

为摸清活性粉末混凝土(RPC)的高温爆裂情况及高温后立方体抗压强度的退化规律,对300个70.7 mm×70.7 mm×70.7 mm的RPC立方体试件和120个40 mm×40 mm×160 mm的RPC棱柱体试件进行高温试验与高温后抗压试验,考察纤维种类、纤维掺量、温度、尺寸效应等因素对RPC立方体抗压强度及受压破坏特征的影响。结果表明：单掺钢纤维体积率为2%或单掺聚丙烯纤维体积率为0.3%时可以有效防止RPC发生爆裂;钢纤维可以有效提高RPC高温后立方体抗压强度并改善其受压破坏特征,聚丙烯纤维对抗压强度有不利影响． 高温后RPC立方体抗压强度随经历温度的升高呈先增大后减小的变化规律,通过回归分析,建立了RPC立方体抗压强度随温度变化的计算公式．     

Size effect on compressive strength of reactive powder concrete

In this paper the coefficient and law of the size effect of RPC were studied through experiments and theoretical analysis. The size-effect coefficients for the compressive strength of RPC are deduced through experiments. They indicate that RPC without fiber behaves quite the same as normal or high strength concrete. The size effect on compressive strength is more prominent in RPC containing fiber. Bazant's size effect formula of compressive strength applies to RPC. A formula is given to predict the compressive strength of cubic RPC specimens 100 mm on a side where the fiber dosage ranges from 0-2%.     

Toughness and characterization of reactive powder concrete with ultra-high strength

A number of three-point bending and fracture tests of 200 MPa-level reactive powder concrete (RPC) with the various fiber contents have been conducted to probe the nature and characteristics of toughness of RPC200. The contribution of the embedded fibers to improving the crack-resistant capacity, energy absorption capacity and toughness with various deformation mechanisms has been analyzed. Taking account of that the first-crack deformation, peak-load deformation and their improvement varied with the fiber contents and that the deformation mechanism affected differently the performance at the first crack and the peak load, we took the peak-load deformation of plain RPC200 as the reference deformation to measure the toughness of fibered RPC200. Two toughness indices T _2(n−1)(n) and FT _2(n−1)(n) have been formulated based on P-δ responses and P-CMOD responses. The indices quantify the toughness of RPC200 with the various deformation mechanisms relative to perfectly elastoplastic materials by setting the toughness level 2(n−1) as the initial reference. It is shown that the toughness index T _2(n−1)(n) reflects the function of fibers to improve the toughness of RPC with the deformation throughout specimens, but overestimates the contribution to enhancing the toughness in post-peak periods. It underestimates, on other hands, the contribution to improving the toughness in the period from the first crack to the peak load. In contrast, the toughness index FT _2(n−1)(n) properly presents the capability that fibers absorb energy and constrain crack propagation in the matrix when the deformation is concentrated on the open crack. The proposed index unveils the contribution of fibers to toughening RPC200 both in the period from the first-crack to the peak load and in the period of post peak. This characterization method not only reveals the nature of toughness but also levels the toughness of RPC200. It could provide a way to establish an objective toughness characterization for RPC200 and facilitate its applications. Supported by the New Century Excellent Talents Program (Grant No. NCET-05-0215), the Natural Science and Engineering Research Council of Canada (Grant No. PGS D2 2006), the Laboratory Innovation Plan of Beijing Science and Education Committee (Grant No. JD102900671) and the National Basic Research Project of China (“973” Project) (Grant No. 2002CB412705)     

锈蚀钢筋混凝土梁的抗剪承载力分析模型

锈蚀钢筋混凝土梁的传统抗剪承载力模型大多属于经验模型,考虑的影响因素不全面且缺乏严密的理论推导,导致计算精度有限。基于修正压力场理论,建立了可以综合考虑钢筋锈蚀对临界斜裂缝倾角、梁有效抗剪截面积、配筋率、配箍率等关键因素影响的锈蚀钢筋混凝土梁的抗剪承载力模型,通过与85组试验数据和现有模型的对比分析,验证了模型的适用性和计算精度。结果表明,该模型具有严密的理论基础,考虑的影响因素全面,计算精度较高、离散性较小。     

Durability and micro-structure of reactive powder concrete

Durability of traditional reactive powder concrete (RPC) with rich cement and high volume of fly-ash reactive powder concrete (FRPC) were studied. The X-diffraction and scanning electron microscope (SEM) measurement was imployed to analyze the microstructure. The results show that both types of RPC have higher compressive strength, less volume shrinkage ratio and better carbonation-, chloride-, freezing-resistances than the conventional concrete. The results of X-diffraction indicate that they basically have C-S-H as the main composition without Ca(OH)₂ crystal and ettringite. SEM results show that hydration products of FRPC is mainly III-C-S-H which is piled up closely like densely arranged stone body and it has very compacted structure, in addition, Ca/Si ratio of C-S-H gel is lower than 1.5.