Quarterly Report of RTRI Vol. 55(2014) No. 4

Concrete filled steel tube (CFT) members have been applied to the columns of rigid frame structures. However, the failure mode, the bending capacity and deformation performance of CFT members with small shear-span ratio are not clear because there have been few studies on them. In this study, cyclic loading tests were conducted on short-column CFT members with constant vertical loads. As a result, it was confirmed that they show a flexural failure mode, but the existing design method overestimates their bending capacity. Therefore, a new evaluation method was proposed for their bending capacity and deformation performance.

A number of calculation equations for the design shear capacity of steel reinforced concrete (SRC) members with simple support are given in the Design Standards for Railway Structures and Commentary (Steel-Concrete Hybrid Structures). However, there are some equations that are applicable to a certain member because the scope of application for these equations is unclear. In addition, support conditions for transverse beams on railway viaducts are different from simple supports because both transverse beam ends are fixed. In this study, the scope of application for existing equations was clarified, and an equation to calculate the shear capacity of SRC beams under antisymmetric moment distribution was proposed.

The new installation of Continuous Welded Rail (CWR) on existing steel bridges is often restricted because of their limited steel bearing capacity of longitudinal axial forces exerted by CWR loads. On the other hand, the capacity is mainly based on design calculation which has not been verified actually. In this research, the actual behavior and performance of CWR load and the bearing capacity were evaluated by field measurements and laboratory experiments with a view to promoting CWR installation on existing steel bridges.

Two types of short sleeper were manufactured, both using fiber-reinforced geopolymers instead of ordinary Portland cement. One type of short sleeper was produced with reduced use of steel rods which provide tensile reinforcement, and the other without any steel rods. Plug pull-out tests and flexural tests on the two types of short sleeper showed that model, containing 1.5 vol% steel fibers without any steel rods, met the performance requirements of short sleepers. And the other type of sleepers, containing 1.5 vol% polyvinyl alcohol (PVA) fibers, 2.0 vol% polypropylene (PP) fibers, and 1.0 vol% aramid (AR) fibers with reduced use of steel rods, met the performance requirements of short sleepers.

The use of high-strength flame-resistant magnesium alloy appears to be a promising route to reduce the weight of car body shells. Since research and development of flame-resistant magnesium alloy has just started, basic data and processing technologies still need to be investigated. This paper presents the results of investigations on its test processing, evaluation of its mechanical properties and workability. The trial manufacturing of hollow extruded materials and welding processes using this alloy are also briefly described.

A long-life gear oil for electric railway trains was developed to reduce the workload and cost of gear unit maintenance. A semi-synthetic base oil, a mixture of polyalphaolefin (PAO) and highly purified mineral oil, was used in the developed gear oil in order to improve high temperature oxidation stability. The composition of additives was also modified to enhance oxidation stability. In an accelerated oxidation test (Indiana stirring oxidation test at 135 ℃/96 hours), the developed gear oil demonstrated sufficient oxidation stability to enable an electric train to run 1,200,000 km without an oil change. Reliability at low temperatures was also shown to be better compared with existing gear oils, because the viscosity at low temperatures and the pour-point was reduced by virtue of the semi-synthetic base oil.

When a high speed train enters a tunnel, a micro-pressure wave radiates out from its exit portal. The micro-pressure wave can cause wayside environmental problems. Topography around the tunnel exit portal affects the peak value of the micro-pressure wave. In this paper, model experiments using a train model launcher were performed for investigating the effects of topography around the tunnel portal on the micro-pressure wave. Four types of topographic models, infinite flat ground, excavation on one side, excavation on both sides and elevated bridge, were used to measure the spatial distribution of the peak values of the micro-pressure waves. Furthermore, a modification of a prediction model for the peak value of the micro-pressure wave radiation was made on the basis of the experimental results.

Areas on each side of overbridges in embankment sections form border zones between the embankment and the girder, where ballast support rigidity varies, and track subsidence tends to occur. Investigations were thus conducted into the influence that ballast support rigidity variation and track subsidence can have on dynamic forces and the characteristics of ground vibration propagation, by means of a parameter study using dynamic analysis models. The effect was also evaluated of countermeasures for ground vibrations generated around the girder.

In order to investigate the running effects on aerodynamic characteristics of a railway vehicle under strong cross winds, the author performed Large-Eddy Simulation of flow around a simple running train model. To simulate the cross winds which affect a running train, the author used an inflow turbulence generation technique based on an unsteady flow simulation method in the frame of a train moving coordinate system. In the case where the train speeds are 10m/s, 5.8m/s, 1.8m/s and 0m/s and the wind speed is 10m/s in the direction perpendicular to the train running direction, the pressure coefficient distribution on the surface of the running train was obtained by numerical simulation and compared with that from experimental studies. The detailed flow fields around the running train were also presented. Based on the comparison between the running train simulation and stationary train simulation with the same relative wind angles to the train, the running effects on aerodynamic characteristics in the case of the simple train model were discussed.