弹性范围内碳纤维混凝土在循环荷载作用下压敏性研究

目的 研究处于三向受压状态下的碳纤维混凝土试件的压敏性,并对比单向受压状态及三向受压状态下试件的压敏性,为试件实际应用到道路测重系统中提供理论依据.方法 分别对处于单向受压状态及三向受压状态下的同一试件施加弹性范围内的循环荷载,观察电阻变化,由此来衡量两种状态下试件的压敏性变化.结果 处于三向受压状态的碳纤维混凝土试件随着荷载的增加,电阻减小,当对试件由加载转化成卸载时,电阻由减小阶段转为增大阶段.结论 碳纤维混凝土试件的电阻变化能正确地反映所施加荷载的变化情况,应用在道路测重系统中具有可行性.     

压实黄土强度和变形各向异性的试验研究

为研究各向异性对压实黄土强度和变形特性的影响,分别对由垂直向和水平向切取的压实黄土试样,进行了不同围压、不同干密度和不同含水率下的真三轴剪切试验.试验结果表明:相同围压、干密度下,垂直向和水平向的应力-应变曲线有明显差异,垂直向试样的轴向应变小于水平试样.轴向应变差异随着干密度和轴向压力的增大而增大,随着含水量和围压的增大而减小;侧向应变差异随着干密度和轴向压力的增大而增大,随着围压的增大而减小.初始变形模量Ei在垂直方向大于水平方向,抗剪强度在垂直方向大于水平方向.     

基于界面效应的碳纤维水泥基复合材料压敏性实验研究

碳纤维水泥基复合材料具有应变-电阻效应。通过碳纤维水泥基复合材料单丝拉伸实验,探究碳纤维水泥基复合材料载荷作用下电阻变化的主要因素。结果表明,在纤维拔出过程中,试样电阻随界面力增大而增大,界面力达到最大值时电阻迅速增大。试样电阻变化规律与界面结构变化一致,弹性变形导致的电阻变化可逆。碳纤维拔出过程中试样电阻的变化主要是由碳纤维—水泥基体界面因素引起的。     

CFRC三向受压状态下力学及电学性能试验

目的 针对三向受压状态下CFRC(碳纤维混凝土)力学量与电学量的关系进行试验研究,为将碳纤维混凝土应用于道路测重提供参考.方法 在变化的竖向荷载作用下,对三向受压碳纤维混凝土试块作单次加载至破坏以及循环加载试验.试验时,将碳纤维混凝土试块与一个电阻串联接入直流回路,记录试块所受荷载与试块两端的电压值,并利用电学中的分压公式,得出随着荷载变化而变化的试块电阻值,进而得到试块所受竖向荷载与其电阻变化率△R/R0之间的关系.结果 处于弹性阶段及弹塑性阶段的碳纤维混凝土试块,在单次加载及循环加载过程中,荷载不断升高时,△R/R0不断减小,而荷载不断减小时,AR/R0不断增大,试块所受竖向荷载与其电阻变化率△R/R0之间具有很好的对应性,说明△R/R0的变化可以反映荷载的变化.结论 处于三向受压状态的碳纤维混凝土具有良好的压敏性,应用于道路测重系统具有可行性.     

双轴受压状态下混凝土动态抗压特性试验研究

由于多轴试验装置的高技术性,混凝土在复杂应力状态下的动力研究相对偏少。为研究双轴受压状态下混凝土的动态抗压特性,采用真三轴静动综合加载试验系统,进行了5种双轴受压状态下混凝土立方体试件的冲击压缩试验,分别从应力-应变曲线特征、强度特性和变形特性等方面分析双轴受压状态对混凝土动力响应的影响规律。结果表明：双轴受压状态下,混凝土承受冲击荷载时呈现典型的脆性破坏,应力-应变曲线初期无明显压实挤密阶段;主轴压比一定时,随单侧压比的增大,混凝土的动态抗压强度呈现出先升高后降低的趋势,峰值应变和平均应变率皆呈现出先减小后增大的趋势;双轴受压对混凝土有加固约束作用,因而提高了其动态抗压强度和抗变形能力,主轴压比：单侧压比为0.4：0.4时作用效果最佳。     

三轴压缩条件下胶结充填体能量耗散特征分析

开展不同灰砂配比、质量分数的充填体三轴压缩试验,研究了不同围压加载阶段充填体的能量耗散与围压、应变以及应力的内在关系.结果表明,在低围压时,充填体的极限抗压强度低;随着围压的增加,充填体的峰值强度随之增大,峰前能耗占总能耗的比重越来越大,说明充填体屈服阶段吸收的能量占总能量的比重提高,围压的增大能够提高充填体的破坏能耗量;充填体的峰前能耗量、峰后能耗量、单位体积变形能以及总能耗与围压呈二次函数曲线关系.当围压一定时,充填体在弹性变形阶段的能量变化与轴向应力、偏应力均呈线性关系,与轴向应变呈指数函数曲线关系;随着轴向载荷增加,能量随轴向应力、偏应力变化的增长速率加大.     

FRP-混凝土-钢管组合方柱偏心受压性能研究

通过9根方柱的偏心受压试验,重点研究偏心距、FRP层数对FRP-混凝土-钢管组合方柱性能的影响.结果表明:随着偏心距的增大,试件的极限承载力下降.相同偏心距下,随着轴向FRP布层数的增加,试件极限承载力有所增大.偏心距对试件的极限承载力、侧向挠度和组合柱受压侧轴向应变的影响显著.轴向FRP布层数对试件的侧向挠度和组合柱受拉侧轴向应变的影响较小.     

CFRP筋及其加筋混凝土梁感知性能试验与分析

对14个CFRP筋试件进行受拉试验,试验采集(carbon fiber reinforced polymer)CFRP筋的应力、应变和电阻值,基于压阻效应CFRP筋电阻随拉应变增加而增加.当CFRP筋破坏时其电阻变化率为31%-64%,直径4 mm和6 mm的CFRP筋应变敏感系数分别是30.5和38.6,是普通电阻应变片灵敏系数的13.80倍和17.47倍.CFRP筋电阻变化主要是由于电阻率变化引起的,碳纤维的弹性变形引起的电阻变化很小.对6根CFRP加筋混凝土梁进行三分点静力加载试验,试验记录了梁中CFRP筋电阻随梁跨中变形增加的变化曲线.当混凝土梁破坏时CFRP筋电阻变化率为2.54%-6.87%.试验研究表明CFRP筋既可用作混凝土结构的受力筋,又可用作传感器进行结构健康监测.     

不同初始状态软黏土在主应力轴耦合旋转下的孔压及3维变形规律

土体在受波浪、地震以及交通荷载等荷载作用时,其相应的应力状态较为复杂,以致于偏应力和主应力轴方位角同时变化的情况普遍存在于实际工程中,目前关于这种应力条件下原状软黏土的物理力学特性的研究尚处于起步阶段。主应力轴耦合旋转即是指在主应力轴方向旋转的同时,偏应力不断增大,而平均主应力、中主应力系数均保持不变。本文为了研究主应力轴耦合旋转时原状软黏土的变形和孔压特性,基于空心圆柱扭剪系统（HCA）对原状软黏土进行了一系列不同初始状态的扭剪试验,探讨了不同固结倾角、中主应力系数在主应力轴耦合旋转条件下对原状软黏土的变形、孔压等特性的影响。结果表明：不同初始固结状态对软黏土的变形特性有明显的影响;主应力轴耦合旋转过程中软黏土试样在b = 0和b = 0.5时的轴向变形以受压为主,在 b = 1时试样的轴向变形在主要表现为受拉状态;不同固结倾角下,主应力轴耦合旋转下试样的轴向、环向和剪切变形趋势均有明显的不同,径向应变值差别不大,在b = 0.5时试样的径向应变值接近0;不同初始固结倾角条件下试样的孔压峰值对应的大主应力方位角也不同,孔压累积与应变开展并不一一对应;应力和应变的变化与偏应力和主应力方位角的增加不同步,即存在明显的非共轴现象。     

一字型钢管束混凝土剪力墙轴压力学性能有限元分析

为研究一字型钢管束混凝土剪力墙的轴压力学性能,采用有限元分析软件建立了９个一字形钢管束混凝土剪力墙模型,研究了钢管束管壁厚度分别为３、６和９ｍｍ时,Ｃ３０、Ｃ４０和Ｃ５０混凝土对此类剪力墙轴压性能的影响,得到了剪力墙的破坏模式、荷载位移曲线及控制点的应力应变关系。结果表明：钢管约束作用下,核心混凝土处于三向受压状态,混凝土的抗压强度明显提高;混凝土强度等级相同时,增加钢管束管壁的厚度,剪力墙轴向受压承载力的提升幅度呈先增加后减小的趋势;剪力墙混凝土强度等级为Ｃ３０、Ｃ４０和Ｃ５０时,钢管束管壁厚度从３ｍｍ到６ｍｍ,其轴向受压承载力增加最为明显;９个模型的核心混凝土紧箍系数均≥１,混凝土呈现出明显的塑性材料性能。     

压力水-岩耦合作用下砂岩断口微观破坏机理

为了研究流固耦合作用下岩石的损伤劣化机理,以砂岩岩样为研究对象,采用流固耦合力学实验系统开展轴压水压耦合作用下单轴压缩、三轴压缩及三轴蠕变实验,借助扫描电子显微镜对岩样破裂断口的微观结构特征进行分析。结果表明:单轴饱水岩样破裂断口表面比干燥岩样出现更多的裂纹核,且断口形貌以沿晶断裂为主,穿晶断裂为辅;随着水压增大,三轴压缩岩样破裂断口表面裂纹核逐渐变少,剪切平行裂纹逐渐增多,岩样的宏观破坏形式从以张拉破坏为主逐渐向以剪切破坏为主转变;与三轴压缩岩样断口相比,三轴蠕变岩样破裂断口表面平整度和光滑度较差,晶体间联结更加紧密,剪切裂纹密度和深度增加。     

圆钢管轻骨料混凝土轴压短柱的力学性能分析

分析现有钢管轻骨料混凝土轴压短柱力学性能实验结果,提出轻骨料混凝土轴对称三轴受压轴向应力-应变关系,应用连续介质力学,确立圆钢管轻骨料混凝土同心圆柱体共同受压时的计算模型,建立了圆钢管轻骨料混凝土组合弹性模量理论计算公式和组合应力-应变关系的理论表达式,编制相应计算程序.结果表明,核心混凝土由于受钢管约束,其纵向应力有较大提高,延性得到显著改善,钢管在为轻骨料混凝土提供径向约束的同时,其纵向应力大幅降低;钢管对轻骨料混凝土的约束效果要低于对普通混凝土的约束效果.通过大量参数分析,得到钢管轻骨料混凝土轴压短柱极限承载力计算公式和组合应力-应变关系全曲线,计算与实验结果吻合良好.     

早龄期混凝土力学性能试验及其单轴本构模型

为了研究早龄期混凝土的立方体抗压强度、轴心抗压强度、劈裂抗拉强度、静力受压弹性模量以及单轴受压应力应变曲线的规律,进行了系统的加载试验和试验数据分析.总结了早龄期阶段力学指标随龄期的变化规律以及与立方体抗压强度之间的换算关系,通过拟合相关参数,提出了分段式的受压应力应变全曲线拟合公式,拟合结果与试验数据吻合较好.试验结果表明,早龄期C40混凝土的强度和弹性模量随着龄期非线性增长,7 d是增长变化的分界时点;随着龄期的增长,峰值应变减少,脆性变大;早龄期C40混凝土的单轴受压应力应变曲线与充分养护龄期混凝土形状相似.     

Behavior of concrete and concrete-filled circular steel tubular stub columns at constant high temperatures

Based on reanalyzing test results of uniaxial compressive behavior of concrete at constant high temperatures in China, with the compressive cube strength of concrete from 20 to 80 MPa, unified formulas for uniaxial compressive strength, elastic modulus, strain at peak uniaxial compression and mathematical expression for unaxial compressive stress-strain relations for the concrete at constant high temperatures were studied. Furthermore, the axial stress-axial strain relations between laterally confined concrete under axial compression and multiaxial stress-strain relations for steel at constant high temperatures were studied. Finally, based on continuum mechanics, the mechanics model for concentric cylinders of circular steel tube with concrete core of entire section loaded at constant high temperatures was established. Applying elasto-plastic analysis method, a FORTRAN program was developed, and the concrete-filled circular steel tubular （CFST） stub colunms at constant high temperatures were analyzed. The analysis results are in agreement with the experiment ones from references.     

核电用双钢板-混凝土单元轴心受压组合效应

为了研究核电用双钢板-混凝土（SCS）结构在轴压荷载作用下钢与混凝土的组合效应,从材料泊松效应的角度出发,分析双钢板-混凝土单元中钢板与混凝土的应力重分布规律,总结钢混组合效应下的2类应力状态和混凝土受侧向约束的特点,采用轴压试验进行论证. 研究表明：钢板与混凝土的应力重分布规律取决于2种材料泊松比的相对变化,对于单轴受压的SCS单元,在达到承载力极限状态时,钢板处于平面压-拉应力状态,混凝土处于三向受压应力状态并存在“约束强化效应”.     

Compression sensibility of magnetic-concentrated fly ash mortar under uniaxial loading

The electrical conductivity, compression sensibility, workability and cost are factors that affect the application of conductive smart materials in civil structures. Consequently, the resistance and compression sensibility of magnetic-concentrated fly ash (MCFA) mortar were investigated using two electrode method, and the difference of compression sensibility between MCFA mortar and carbon fiber reinforced cement (CFRC) under uniaxial loading was studied. Factors affecting the compression sensibility of MCFA mortar, such as MCFA content, loading rate and stress cycles, were analyzed. Results show that fly ash with high content of Fe3O4 can be used to prepare conductive mortar since Fe3O4 is a kind of nonstoichiometric oxide and usually acts as semiconductor. MCFA mortar exhibits the same electrical conductivity to that of CFRC when the content of MCFA is more than 40% by weight of sample. The compression sensibility of mortar is improved with the increase of MCFA content and loading rate. The compression sensibility of MCFA mortar is reversible with the circling of loading. Results show that the application of MCFA in concrete not only provides excellent performances of electrical-functionality and workability, but also reduces the cost of conductive concrete.     

Mechanical property and permeability of raw coal containing methane under unloading confining pressure

Based on domestic-developed triaxial servo-controlled seepage equipment for thermal–hydrological–mechanical coupling of coal containing methane, an experimental study was carried out to investigate mechanical property and gas permeability of raw coal, under the situation of conventional triaxial compression and unloading confining pressure tests in different gas pressure conditions. Triaxial unloading confining pressure process was reducing confining pressure while increasing axial pressure. The research results show that, compared with the peak intensity of conventional triaxial loading, the ultimate strength of coal samples of triaxial unloading confining pressure was lower, deformation under loading was far less than unloading, dilation caused by unloading was more obvious than loading. The change trend of volumetric strain would embody change of gas permeability of coal, the permeability first reduced along with volumetric strain increase, and then raised with volume strain decrease, furthermore, the change trends of permeability of coal before and after destruction were different in the stage of decreasing volume strain due to the effect of gas pressure. When gas pressure was greater, the effective confining pressure was smaller, and the radial deformation produced by unloading was greater. When the unloading failed confining pressure difference was smaller, coal would be easier to get unstable failure.     

轴心受压核心高强素混凝土短柱试验分析

为考察核心高强混凝土柱的受力性能,进行了16根轴心受压核心高强混凝土短柱的试验研究,.单轴受压时核心高强混凝土的峰值压应变高于外围普通混凝土的峰值压应变,由加载到破坏的过程中,外围普通混凝土先达到峰值压应变,核心高强混凝土后达到峰值压应变.所考察柱的轴心受压正截面承载力由核心高强混凝土和外围普通混凝土共同提供,但核心高强混凝土和外围普通混凝土所提供的抗力需分别乘以考虑两部分混凝土峰值压应变不同的抗力调整系数n1和n 2.基于16个试件的试验结果和189根核心高强混凝土柱的数值计算结果,拟合得到了核心高强混凝土抗力调整系数n1和外围普通混凝土抗力调整系数n 2的表达式.按照建议公式所得轴心受压承载力计算值与试件的抗力试验值吻合良好.     

Experimental investigation of rigid confinement effects of radial strain on dynamic mechanical properties and failure modes of concrete

In this study, to confirm the effect of confining pressure on dynamic mechanical behavior and failure modes of concrete, a split Hopkinson pressure bar dynamic loading device was utilized to perform dynamic compressive experiments under confined and unconfined conditions. The confining pressure was achieved by applying a lateral metal sleeve on the testing specimen which was loaded in the axial direction. The experimental results prove that dynamic peak axial stress, dynamic peak lateral stress,and peak axial strain of concrete are strongly sensitive to the strain rate under confined conditions.Moreover, the failure patterns are significantly affected by the stress-loading rate and confining pressure.Concrete shows stronger strain rate effects under an unconfined condition than that under a confined condition. More cracks are created in concrete subjected to uniaxial dynamic compression at a higher strain rate, which can be explained by a thermal-activated mechanism. By contrast, crack generation is prevented by confinement. Fitting formulas of the dynamic peak stress and dynamic peak axial strain are established by considering strain rate effects(50–250 s~(-1)) as well as the dynamic confining increase factor(DIFc).     

硫酸盐腐蚀后混凝土单轴受压本构关系

为了研究硫酸盐侵蚀环境下混凝土力学性能的变化,对受硫酸盐腐蚀的普通混凝土进行单轴受压实验.通过实验室加速腐蚀的实验方法,测定不同腐蚀时期的混凝土的应力应变全曲线,研究受腐蚀混凝土应力-应变曲线上的几个特征值(峰值应力及应变、弹性模量、割线模量、拐点应力及应变、收敛点应力及应变)随腐蚀程度变化的规律,对腐蚀后混凝土的应力应变全曲线进行拟合.结果表明:随腐蚀的进行,混凝土峰值应力、弹性模量先增加后减小,而峰值应变是先稍微有所减小,而后急剧增大;该实验条件下获得了受腐蚀后混凝土应力应变曲线上各特征值与峰值应力fc′的关系式,建立了曲线上升段参数αa的数学表达式.可以以受腐蚀混凝土的强度为基本参数,分别求解受腐蚀混凝土峰值应变、弹性模量,上升段曲线拟合参数、拐点应力以及收敛点应力.从而得到受腐蚀混凝土一系列的力学参数和本构关系.