Japanese specifications for railing design have introduced two new improvements in functions for railings since 2004. The first is to require a landscape-friendly appearance and the other is to take account of flow in the road user's view from bridges. The concern with these functions has led to changes in design with requirements for more slender forms of railing beams and posts. Current Japanese specifications for railing design are concerned only with straight railings. Some researchers and engineers suspect that curved railings are more dangerous. The purpose of this research is accordingly to contribute to the development of two new types of curved bridge steel railings satisfying the new functional requirements and also to verify the above suspicion. A full-scale test is the ideal methodology for this study but this test involves a considerable cost and effort. Thus a combination between partial experimental tests for the new types of posts and numerical analyses is relied on here to study the performance of the new-type steel curved bridge railings. The procedures followed are : (1) to study performances of new posts experimentally under static and collision conditions ; (2) to develop numerical analyses to study performances of straight railings ; and (3) to apply these analyses to instances of new-type posts in curved railings in order to obtain a comparison with straight ones. The LS-DYNA 3D is engine software used for the numerical analysis. Based on the results of the study, a design recommendation is proposed for new-type curved steel railings.
This paper describes a fundamental study conducted for establishing a technique of low-temperature autoclave curing, with the focus placed on the water cement ratio and silica fume content. The experimental results showed that silica fume-added specimens cured at 150°C had similar compressive strength to those cured at 180°C. The low-temperature autoclave curing was made possible by the addition of silica fume which increased the gel porosity and reduced the total porosity through accelerated pozzolanic reaction. In addition, the gel porosity did not show significant change against the autoclave curing temperature in the presence of silica fume. This was considered to be the key factor in the mechanism of low-temperature autoclave curing. It was also demonstrated in this study that the presence of tobermolite was not an essential requirement for the high strength development in which C-S-H played a predominant role.
The purpose of this study is to evaluate the fatigue strength of headed studs using an improved welding ferrule under rotating shear force. In the fatigue tests, to prevent up-lift of the specimen, vertical force was introduced in proportion to the rotating shear force. From the fatigue test results, two kinds of failure modes were observed. One of those is a failure of the headed stud accompanying with concrete crushing around its weld collar. Another is a failure of the bottom steel plate due to initiation of a fatigue crack from the weld toe. The fatigue life of the headed studs tested in this study showed some scatter in the same manner as the fatigue life of concrete. Hence, the treatment of probability is needed to evaluate the S-N curve for the conventional and durable headed studs. In this study, the test results indicated that probability distributions of the fatigue life conform to logarithmic normal distribution and 3-parameter Weibull distribution. Finally, the logarithmic normal distribution was applied to determine the average fatigue life of the conventional and durable headed studs tested and the S-N curves for both headed studs were obtained. Then, the average fatigue life of the durable headed studs increased in three times when compared to that of the conventional headed studs.
The multiaxial fiber sheet is one of the continuous fiber sheets, and it has features to arrange the continuous fiber in parallel with angling variously. The purpose of this study is to clear the mechanical properties of the multiaxial carbon fiber sheet. Secondly, as the basic study on reinforcement for concrete member with this sheet, compressive test using cylinder specimen are performed. As a result, 1) the mechanical properties of this sheet can be controlled by designed of knitting conditions, 2) the compressive strengthening is evaluated from the mechanical properties of the sheet.
A self-crack-healing behavior of SiNx/SiCy nano-laminated thin film under high temperature environment was investigated. The films were fabricated on silicon substrate by an ion beam assisted deposition. The thickness of the SiNx/SiCy nano-laminated film was 1μm and four layered film was deposited. To compare with the crack healing behavior of laminated film, SiNx and SiCy monolayer films were also fabricated. After the deposition, the pre-cracked samples were heated using an electric furnace in an air atmosphere at the temperature of 600°C to 1200°C. In the case of SiNx and SiCy monolayer films, the crack was poorly healed after heating at the temperature lower than 800°C. This was because the size of a crack opening increased after heating due to the release of residual stress. On the other hand, slight crack healing occurred for 24h at the temperature of 600°C. It was confirmed that Auger electron count for oxygen atom was high along the healed crack, indicating that the crack healing was achieved by oxidation reaction on crack plane. Crack healing improved with an increase in the heating temperature and time. Moreover, the crack healing finished for 72 and 24h at 600 and 800°C, respectively. From these results, we concluded that SiNx/SiCy nano-laminated film has a superior self-crack-healing ability. However, the heating over 1200°C caused oxidation of film overall and disappeared the laminate structure. From these results, it is suggested that an upper limitation of heating temperature exists for self-crack-healing of SiNx/SiCy nano-laminated thin film.
The strength evaluation of glass short fiber reinforced phenolic resin (G/P) made by transfer forming was studied in this paper. In order to investigate the strength of G/P in comparison with various volume fiber content Vf (=0%, 20%, 50%), three kinds of basic strength test (3-point bending, 4-point bending, and tensile test) at room temperature were carried out. The Weibull statistic theory was applied to evaluating size effect of each specimen. The strength distribution was consistent with the Weibull chart, and obtained Weibull coefficients, m, were ranged from 5.8 to 17.6. The effective volume, Veff, and Weibull coefficients m0 were estimated based on effective volume theory. Relationships between strength, σf, and effective volume, Veff, shows good agreement with the equation of the effective volume theory onto the double logarithmic chart. To verify the efficiency of the effective volume theory, open hole specimen (OH specimen) of G/P were subjected to tensile test. Veff of OH specimens was calculated by integrating the stress distribution, which obtained by finite element analysis, with the volume. And then, the distribution of fracture probabilities was predicted by Weibull statistical theory. As a result of tensile test for OH specimens, it was concluded that the prediction method by effective volume theory based on Weibull statistical theory was applicable to strength evaluation of G/P.
Creep damage assessment methods considering the effect of stress multiaxiality are discussed in order to evaluate creep crack initiation from stress concentrating fields such as notch roots. Creep tests using notched specimens were performed and damaging features around the notch root were investigated. Micro damages such as small creep cracks were mainly observed around several hundred micro-meters below the surface. Inelastic analyses taking primary creep into account were also performed. The area of high stress multiaxiality obtained from the analyses coincides with the area where micro damages were observed. Creep damage evaluation methods are also discussed. The strain based method was in good agreement with experimental results. Stress multiaxiality should be considered in evaluation of creep damage in stress concentrating fields.