The authors propose sheet-pile foundation as a new viable foundation structure. The construction costs of this type of foundation are lower than those for pile foundation, and it can be used more widely than shallow foundation. In this research, a series of laboratory static loading tests and full-scale field tests were carried out to evaluate the fundamental characteristics of sheet-pile foundation. The tests showed that its horizontal resistance is larger than that of shallow foundation, and that it exhibits excellent performance against seismic forces.
We performed an anecdotal survey and simulation analysis to clarify the deformation behavior of existing tunnels resulting from adjacent construction of embankments or cuttings. Case studies showed relationships between the deformation modulus of the ground, the geometrical shape of the adjacent construction and their influence on existing tunnels. We confirmed the validity of these relationships through parametric analysis of existing tunnels. Based on the results, we proposed adequate guidelines that are more applicable to construction adjacent to existing tunnels in consideration of the ground stiffness and the geometrical shape of the embankment or cutting.
It is well known that the non-stationary nature of earthquake motion is intensely controlled by the phase spectrum. However, it has not yet been verified how the stochastic characteristics of phase spectrum of such motion affects the response of structures. We therefore modeled the stochastic characteristics of the phase spectrum, and derived a theoretical solution for mean and R.M.S. response time histories for an SDOF system excited by a non-stationary input ground motion controlled by these stochastic phase characteristics. We also derived a methodology to estimate the peak response value using the concept of a complex envelope function.
When trains pass through stations at high speeds, large variations in air pressure occur. As the structural members that make up station facilities are susceptible to these repeated variations, it can be assumed that the likelihood of member deterioration is high. Since future train speed increases will result in larger air pressure variations, it is essential to make efforts to ensure the structural safety of stations. To this end, we developed calculation equations for air pressure variations based on the results of field measurements and model tests, and also proposed prediction methods for response deformation and an evaluation method for the fatigue strength of members exposed to air pressure variations.
Public awareness of global warming and recycling has created a demand to respect environmental conservation and reduce the environmental burden posed by railways. To this end, it is necessary to extend the replacement frequency of the contact wire in the overhead contact line system and apply a copper alloy to improve its recycling efficiency. We therefore selected a new type of equipment (known as PHC simple catenary equipment) through research into the overhead contact line system, performance calculations from simulation, and running tests at our institute. In the final stage of development, we installed the PHC simple catenary equipment on a commercial line to confirm its performance.
In order to adopt rigid conductor lines in tunnels of small sections, it is necessary to install a transition structure just outside the tunnel to allow a smooth pantograph shift between the catenary-type contact line and the rigid conductor line. However, the present transition structure is complicated, has inferior current collection characteristics that impair train acceleration, and involves high construction costs for the extensive support equipment required. In order to solve these problems, we have developed a new structure that demonstrates satisfactory performance for trains operating at speeds of up to 130 km/h and is about a third the length of the present one.
The detection of high-resistance grounding faults in DC electric railways is difficult due to the impossibility of distinguishing fault current from load current in such systems. We therefore propose a new detection method to distinguish fault current from load current using the total feeding current of two substations. The technique takes advantage of the fact that the average load current is different from the average fault current. First, this paper describes the new method of detecting high-resistance grounding faults by using the total feeding current, then evaluates the length of time required for detection by simulation and shows the experimental results.
In the superconducting magnetically levitated transport (Maglev) system, the vehicles travel at high speeds of over 500 km/h and have car bodies that are light in weight, resulting in vibrations that affect the ride comfort. Vibration reduction methods discussed in this report include prior examinations of superconducting magnets resiliently mounted on to the bogie frame to reduce vibrations in the primary suspension, and semi-active vibration control of the secondary suspension. The authors performed simulations applying electromagnetic forces from a linear generator device to control the primary suspension between the bogies and guideway, and controlling actuators in the secondary suspension between the car body and bogies. The results verified the basic effectiveness of combining control methods of the primary and secondary suspension to reduce vehicle vibrations.
The superconducting magnetically levitated transportation (Maglev) system requires ground coils suitable for long-term outdoor use along the entire length of the guideway, meaning that the assurance of stable performance and high reliability is an important consideration in developing these coils. Durability verification testing from the level of the component materials to the actual product on the assumption of commercial service is therefore necessary to guarantee total reliability. We performed flexural fatigue tests using specimens made of the epoxy resin used for actual propulsion coils. The results were used to create a fatigue limit diagram as well as a diagram to verify Miner's Law. We then confirmed the correlation between the color difference and the flexural strength by comparing the outdoor exposure test results with those of accelerated artificial exposure testing.
Stable levitation or suspension of a heavy object in mid-air can be realized using a combination of a permanent magnet and a bulk superconductor with high critical current density, in that the force density has reached 100 kN/m2. The superconducting flywheel system for energy storage is attractive due to a great reduction in the rotational loss of the bearings So long as a permanent magnet is used as a magnetic source, however, the electromagnetic force (EMF) is essentially limited by its field strength. In order to overcome such a limitation, we employed a superconducting coil/magnet as a magnetic source and studied the EMF characteristics of bulk superconductors in high magnetic fields. We also measured the EMF between a bulk superconductor and a specially designed superconducting coil having a high field gradient, and confirmed that the EMF reached 9,000 N (force density: 1,190 k N/m2).