Key Engineering Materials Vols. 385-387

Abstract: In order to study the damage evolution law for layered fiber reinforced concrete subjected to flexural fatigue, the flexural fatigue tests were carried out on both layered steel fiber reinforced concrete(LSFRC) and layered hybrid fiber reinforced concrete(LHFRC) beams of which the type of steel fiber was uniform on the same concrete mix. At the same time the flexural fatigue tests with original concrete(OC) were carried out. Based on the experiments, both flexural fatigue life and damage characteristic of LSFRC LHFRC and OC were compared and analyzed. The results indicated that the fatigue life of LHFRC was a little larger than that of LSFRC under the stress level, which was more than an order of magnitude of OC. And the fatigue distortion of LSFRC, LHFRC and OC were similar. They all followed three-phase law. However, the proportion of every phase was different, which proved that layered steel fibers and polypropylene fibers could effectively restrain the degradation of concrete.

Abstract: When the RC structure degraded in sea environment, chloride ion is one of the most important factors of degradation. Therefore, the purpose of this analytical study is measuring diffusion coefficient of patching repair material and the structure which repaired with patching repair material by RCPT. Also with this experimental result, Finite Element Method (FEM) is used for determining service year of building and concentration of chloride ion in the structure material. As the result of RCPT, diffusion coefficient of patching repair material is 0.44×10-8cm2/sec, which is 18.7% of concrete (3.18×10-8cm2/sec). Meanwhile, as the result of FEM, patching repair material is effective for prevent chloride ion. When service year of normal concrete structure is 16years, on the other hand, the structure recovered 10mm of patching repair material will take 49 years to its service year. Furthermore, the result derived from equation given from JSCE predicts service year of the structure is little bit less than FEM.

Abstract: Concrete is a type of porous materials and is physically and chemically damaged due to exposure to various environments from the placing to the service life. These reactions affect the corrosion of steel bars applied in concrete and that decreases the durability life and strength of such steel bars. Thus, it is very important to insert rust inhibitors into steel bars in the case of a deterioration element that exceeds the critical amount of corrosion in the location of steel bars. However, it is very difficult to guarantee corrosion resistance at the location of steel bars using conventional technology that applies corrosion inhibitors only on the surface of concrete. This study attempts to develop a method that penetrates corrosion inhibitors up to the location of steel bars and investigate the penetration depth of corrosion inhibitors by verifying moisture migration in concrete under an applied pressure.

Abstract: This paper demonstrates the jig set for the crash test and the crash test results of the tension bolts with respect to an applied pre-tension. The tension and shear bolts are adopted at Light Collision Safety Devices as a mechanical fuse when tension bolts reach designed failure load. The kinetic energy due to the crash is absorbed by secondary energy absorbing devices after the fracture of tension bolts. One tension bolt was designed to be failed at the load of 375 kN. The jig set was designed to convert a compressive loading to a tensile loading and installed at the high speed crash tester. The strain gauges were attached at the parallel section of the tension bolts to measure the level of the pre-tension acting on the tension bolts. Crash tests were performed with a barrier whose mass was 250 kg and initial speed of the barrier was 9.5 m/sec. The result includes the load response of the tension bolts during both the crash tests and finite element analysis.

Abstract: Ceramic matrix composites (CMCs) have evolved as potential candidate materials for high-temperature structural applications due to lightweight, high-temperature strength and excellent corrosion and wear resistance. In this investigation, damage evolution and heat generation of CMCs during monotonic loadings were investigated using different types of nondestructive evaluation (NDE) techniques, such as acoustic emission (AE) and infrared (IR) thermography and microstructural characterization. IR camera was used for in-situ monitoring of temperature evolution, and the temperature changes during testing were measured. A significant temperature increase has been observed at the time of failure. Microstructural characterizations using scanning electron microscopy (SEM) were performed to investigate fracture behavior of CMC samples. In this investigation, the NDE technique and SEM characterization were employed to analyze damage evolution and progress of ceramic matrix composites during monotonic loading.

Abstract: This study aimed to model the long-term creep curves above 105 hours by implementing a nonlinear least square fitting (NLSF) of the Kachanov-Rabotnov (K-R) model. For this purpose, the short-term creep curves obtained from a series of creep tests at 950oC were used. In the NLSF of their full creep curves, the K-R model represented a poor match to the experimental curves, but the modified K-R one revealed a good agreement to them. The Monkman-Grant (M-G) strain represented the behavior of a stress dependency, but the 􀁏 parameter was constant with a stress independency. The 􀁏 value in the modified K-R model was 2.78. Long-term creep curves above 105 hours from short-term creep data were modeled by the modified K-R model.

Abstract: Silica fume constitutes an element of extreme importance in improving the strength and fluidity of UHPC. The adopted amount of silica fume generally is generally exceeding 25% of cement in weight but the influence of this amount on the properties of UHPC is still remaining as a domain to be investigated. Accordingly, this paper investigates the effects of the amount of silica fume on the mechanical characteristics of the fluidity, compressive strength, elastic modulus and flexural strength and on the micro structure of UHPC by means of SEM and MIP. Results revealed that adequate amount of silica fume is improving the fluidity and strength. MIP tests demonstrated that such improvement is brought by the increase of hydrates due to the pozzolan reaction and the effective densification inside concrete due to the filler. It seemed also that similar mechanical characteristics can be obtained for a volumetric ratio to cement ranging between 10 and 25%.

Abstract: An isochronous stress-strain curve (ISSC) needs to be generated for a creep design application for high-temperature materials. To generate the ISSC for type 316LN stainless steel (SS), a series of creep data, which was obtained from creep tests with different stress levels at 600oC, was used. Creep curves were modeled by means of a nonlinear least square fitting (NLSF) of the Garofalo model. In the fitting of the creep curve, a secondary creep region was separated into first and second phases, and its fitting range was suitable to use for the first phase. The Garofalo model revealed a good agreement with the experimental creep data, and its parameters, P1, P2 and P3 revealed a good linear relationship as a function of a stress. The ISSCs for type 316LN SS at 600oC were successfully generated up to 300,000 hours.

Abstract: Post-tensioned (PT) flat plate frames are commonly used to support gravity load in connections in high seismic regions. But test results of many studies indicated that PT flat plate connections were possessed of later-resisting capacity for lateral load though this capacity is not enough to be used by itself in high seismic regions. So this study evaluated the cyclic behavior of PT flat plate connections and developed an analytical model for predicting nonlinear behavior of those to estimate the seismic performance of PT flat plate frames accurately. For this purpose, the test results of static pushover test and shaking table test of 2 story PT flat plate frame were used to evaluate the characters of failure mode for PT flat plate connections and to compare with analysis results. The test results indicated two failure modes which are classified the shear failure mode or the moment failure mode as for shear strength of PT connections to resist lateral loads acted on the specimens. So the analytical model was designed to consider these failure modes of PT connections and the results of comparing with test results predict the nonlinear behavior of PT connections.