钢纤维高强混凝土拉伸应力—应变全曲线的试验研究

作者进行了4组钢纤维高强混凝土试验研究,测试了其基本力学性能,并利用混凝土间接轴向拉伸试验测试方法在普通试验机上测出了各组钢纤维高强混凝土的拉伸应力－应变全过程曲线：在试验的基础上,分析并描述了钢纤维高强混凝土拉伸应力－应变全过程曲线特征,初步分析归纳出了钢纤维高强混凝土受拉本构关系模型,本文介绍了这些研究结果。     

不同初始损伤混凝土动态轴向拉伸试验研究

利用MTS-NEW810动态试验机,通过对30根混凝土棱柱体试件施加应力幅值为1 kN到5 kN、频率为5 Hz、应变速率为10~(-4)/s的5组不同循环荷载,研究不同初始损伤对混凝土棱柱体试件动态轴向拉伸特性的影响。研究结果表明,遭受初始损伤程度越严重,混凝土棱柱体试件动态轴向拉伸破坏断面越整齐,且破坏断面粗骨料被拉断数目越少;随着初始损伤程度的增加,混凝土棱柱体试件逐渐产生有不可恢复变形,随着损伤程度的增加,不可恢复变形的增幅明显增大;初始损伤程度对混凝土棱柱体试件动态拉伸应力应变关系曲线上升段影响较小;混凝土棱柱体试件动态轴向拉伸强度和峰值应变均受初始损伤程度影响不大。     

40m预应力混凝土T梁静载试验与分析

阐述了山东省淄博市某跨铁路立交桥40mT梁的静载试验,介绍了试验成果,并把理论计算数据和试验观测数据进行了对比,得出有益的结论。     

水力冲击内蕴初始裂纹混凝土致裂机理

为研究水力冲击内蕴初始裂纹混凝土破碎机理,采用光滑粒子流体动力学(SPH)方法建立了水力冲击含竖向裂纹混凝土数值模型,并基于图像处理技术,量化表征了混凝土致裂区破碎规律。研究表明:在初始裂纹弱作用区,水锤效应导致液固接触边界出现剪切断裂,贯通后形成近似"碗状"破碎坑;在初始裂纹强作用区,液固接触边界压剪应力和初始裂纹上部应力集中共同作用引发了初始裂纹上尖端裂纹;"水楔+砼楔"效应与初始裂纹下部应力集中导致了初始裂纹下尖端裂纹;水力冲击激发的应力波在自由边界和初始裂纹反射后相互叠加,引发了锥形裂纹;混凝土破碎度沿射流轴向呈非线性阶跃衰减,表明初始裂纹对混凝土破碎演化有明显阻断及强干扰作用。     

预应力混凝土连续箱梁桥的静载力学试验

本文介绍了江苏省兴化市长安大桥静载试验的目的、实施步骤及结果分析,以实施结果阐明主桥具有满足设计要求的强度、刚度和抗裂性,并讨论了设计荷载横向偏载问题,文中结果可供设计部门参考。     

中频三轴向矢量水听器的研究

根据实际工程需要,设计、制作三轴向中频矢量水听器,其声压通道和矢量通道在结构上结合为一体,外形为两端带半球帽的圆柱形结构。矢量水听器体积为Ф44×88（mm）、工作频带为5Hz—8kHz。在驻波管和消声水池中对研制的矢量水听器进行了测试,测试结果表明：矢量通道的声压灵敏度级为-184dB(测量频率1kHz,0dB参考值1V/μPa),具有余弦指向性;声压通道灵敏度级为-198dB(0dB参考值1V/μPa)。研制的矢量水听器具有体积小、通道灵敏度高、使用时悬挂方便等优点,适合构建矢量水听器线阵。     

浅谈预应力混凝土连续箱梁桥静载试验

本文结合预应力混凝土连续箱梁桥静载试验,介绍了检测内容、加载方案以及静载试验评定结果。     

后张法预应力混凝土铁路桥简支箱梁静载试验施工技术

静载弯曲试验是检验简支箱梁结构性能的重要手段,也是检验梁体抗裂性及刚度的常用方法。桥梁是国家实施生产许可证制度的重要铁路工业产品,有着长寿命、高耐久性、不易更换的特殊性,势必要求结构性能100%合格,必须对桥梁产品—箱型简支梁进行静载弯曲试验。本文根据"内力图相似,跨中内力值相等"的荷载布置原则,介绍了客运专线32m全预应力混凝土箱梁采用"五点十载"的静载试验方法。     

结构损伤诊断的轴向振动原理及模态实验

在理论推导梁轴向振动微分方程基础上,提出一种以轴向振动低阶模态振型二阶导数为损伤指标的结构损伤识别方法。在方钢管构件上布置加速度传感器进行轴向振动模态试验,测试时由信号发生器发出正弦波信号,经功率放大器放大后通过电磁激振器对结构进行激励,同时采集各测点的加速度反应信号。在确定结构共振点后,根据共振点处加速度值,编制轴向振动损伤指标的计算程序,分析结果表明该指标对结构损伤的位置和程度均很敏感,既能精确定位损伤,又能标定损伤程度,即在损伤位置将发生相反方向的突变,且突变幅度随损伤程度增大而增大。     

Rate effect of concrete strength under initial static loading

The dynamic strength enhancement of concrete under different initial static loadings is investigated in this paper. The mechanism of the influence of the inertia effect on the dynamic strength of concrete is discussed first by analyzing a single dimension of freedom system, which shows that the inertia effect only influences the dynamic loading part. The dynamic strength of concrete at initial static loading is calculated assuming a single crack model with consideration of free water viscosity using dynamic fracture mechanics. The dynamic stress intensity factor of the crack under linearly increasing loading on the basis of an initial static loading is achieved. The relationship between the dynamic strength increase factor and the static stress level is obtained. The comparison between the results by the model proposed in this paper and those by experiments in some available references indicates a good agreement.     

Effect of fluoride corrosion on the bonding strength of Ti-porcelain under static loads

The effect of fluoride corrosion on the bonding strength of Ti-porcelain under different static loads was investigated. The adhesion between the titanium and porcelain was evaluated by three-point flexure test. After being immersed in artificial saliva with pH 2.7 under 0 N, 1 N and 2 N static loads, respectively, no decrease of the bonding strength of Ti-porcelain occurred. However, the decrease of bonding strength was about 30%, 37%, and 46% after being immersed in artificial saliva with pH 2.7/F⁻ 100 ppm under 0 N, 1 N and 2 N static loads, respectively. The failure of the titanium-porcelain predominantly occurred at the titanium-oxide interface. Immersion in the artificial saliva did not affect the fracture mode of the titanium-porcelain system. The corrosion of the Ti-porcelain interface resulted in the reduction of bonding strength. The static loads enhanced the F⁻ corrosion on the Ti-porcelain interface.     

Experimental investigation on uniaxial tensile strength of hybrid fibre concrete

In an experimental study on fracture properties of hybrid fibre concrete, specimens with varying fibre content (mixtures of short and long fibres) were loaded in uniaxial tension. Dog-bone shaped specimens of four different sizes in a size range of 1:8 were tested. Focus of the study was the determination of the size effect on nominal strength and fracture processes. A vacuum impregnation technique was used to investigate the fracture process. Experiments showed that multiple cracks, which formed before the peak, localised into one major crack beyond peak. Multiple cracking could be obtained by increasing the amount of thin short fibres whereas the large fibres can enhance the bridging of localised macrocracks. With decreasing strength, the size effect on the strength appears to increase. It is observed that the size effect on nominal tensile strength decreases with increasing material ductility. Preliminary analysis of the results showed that the observed size effect can be considered as a combination of statistical and structural size effects.     

Tension stiffening in textile-reinforced concrete under high speed tensile loads

Damage mechanism in glass textile-reinforced concrete (TRC) with and without the addition of Alkali resistant short glass fibers under high speed tensile loading was investigated. The high strain rates ranging from 25 to 100 s⁻¹ were achieved using a high speed servo-hydraulic testing machine. Image analysis by means of digital image correlation (DIC) method was used to obtain the evolution of crack width which was subsequently correlated with stress response. The non-uniform strain distribution was characterized as three distinct response zones of localization, shear lag, and uniform strain and quantitatively measured in each zone. Mechanism corresponding to the basic aspects of tension stiffening modeling were identified by computing the average stress in the matrix phase between two cracks. The width of crack localization zone as well as crack spacing were also obtained using DIC as indications of bonding properties. A finite difference method simulating tension stiffening behavior was employed to predict crack spacing and stress–strain responses of TRC systems. Improvements in bond properties and mitigation of cracking with the addition of short fibers were verified using multiple methods.     

An experimental study on the tensile strength of steel fiber reinforced concrete

This paper deals with steel fiber reinforced concrete mechanical static behaviour and with its classification with respect to fibers content and mix-design variations. A number of experimental tests were conducted to investigate uniaxial compressive strength and tensile strength. Different mixtures were prepared varying both mix-design and fiber length. Fibers content in volume was of 1% and 2%. Mechanical characterization was performed by means of uniaxial compression tests with the aim of deriving the ultimate compressive strength of fiber concrete. Four-point bending tests on notched specimens were carried out to derive the first crack strength and the ductility indexes. The tensile strength of steel fiber reinforced concrete (SFRC) was obtained both from an experimental procedure and by using an analytical modelling. The experimental tests showed the different behaviour of SFRC with respect of the different fiber content and length. Based on the experimental results, an analytical model, reported in literature and used for the theoretical determination of direct tensile strength, was applied with the aim of making a comparison with experimental results. The comparison showed good overall agreement.     

Microcracking of concrete under compression and its influence on tensile strength

A new parameter representing damage of concrete due to compressive stresses is investigated. Very important tensile strength losses are obtained after compressive loading over 40% of the compressive strength. Microcracking of concrete takes place under such load leading to tensile strength losses depending also on time under load, water content and type of aggregate. Under maximum compressive load a tensile strength reduction of about 50% is obtained.     

钢纤维混凝土动态抗拉强度的实验研究

基于线弹性和一维应力波假定,采用Φ75mmSHPB对钢纤维体积率Vf分别为0、0.75%和1.50%的三种混凝土材料进行了一维杆层裂实验,考虑了应力波在混凝土材料内传播时的波形弥散效应和应力幅值衰减,通过计算应变片记录的应力信号确定了材料的动态抗拉强度。结果表明,钢纤维混凝土的动态抗拉强度受应变率和钢纤维体积率的影响,本文为测试脆性材料的动态抗拉强度提供了一种有效方法。基于微观扫描技术,对钢纤维增强机理进行了分析。