Abstract of Special Research Report (RR-2004)
National Institute of Occupational Safety and Health, Japan
An Inquiry into Basic Safety Requirements of Field-bus Network for Safety Control
RR-2004-1 |
Tsuyoshi SAITO, Hideo NAKAMURA and Masaki MIURA |
: In the bottom layer of a hierarchized computer network for manufacturing in a factory, serial communication networks, in which sensors, actuators and logic controllers are connected to a single wire (the bus) that has two endpoints, are collectively termed "Field Buses". Recently, application of the field bus technology to transmission of safety-related information from protective sensing devices for human safety to control parts of industrial machinery shows rapid progress. However, dangerous transmission errors on field buses and preventive measures against them have still not been investigated enough. The safety-related information transmission requires special considerations to ensure the promptness and inerrancy as well as the conventional hard-wired failsafe interlock system. |
Method for Characterizing Fracture Surface by using Two-Dimensional Local Hurst Exponent and its Application to the Quantative Evaluation of Stretched-Zone Width and Estimation of JIc
RR-2004-2 |
Kenta YAMAGIWA and Takashi HONDA |
: Fractal analyses have been widely used to characterize the fracture surface. It has been recognized that the local Hurst exponent, which is based on the concept of self-affine fractal, is useful to detect the transition point of fracture surface. For the calculation of the local Hurst exponent, a high resolution profile is needed. To measure the profile, however, much time and effort are needed. Therefore, it is difficult to calculate all profiles of fracture surface and evaluate the feature of fracture surface in detail. |
Study on the Mechanism of Generating Lateral Earth Pressures using Centrifuge with Movable Earth Support Equipmen
RR-2004-3 |
Yasuo TOYASAWA, Kazuya ITOH and Surendra B. TAMRAKAR |
: To prevent the accidental collapse of earth supports in construction work, knowledge about collapse mechanisms, collapse precursors, and so forth are needed. However, the interaction between the generation of lateral earth pressures, deformation of soil, movement of retaining walls and the behavior that leads to collapse are very complicated. Therefore, it is difficult to predict accurately whether the observed movement at a construction site will result in a collapse, or whether the movement will stop. Further research is required to take account of wall movement, deformation in the soil, and the phenomena that lead to collapse. This research investigates the interaction between the generation of earth pressures and soil deformation due to wall movement. Centrifuge experiments were carried out using the newly developed movable earth support equipment, which controls the wall movements with high precision in a 50g centrifugal field. For the analysis of soil deformation, an image-processing system was utilized. |
Tensile Strength of Soil Measured using Newly Developed Tensile Strength Apparatus
RR-2004-4 |
Surendra B. TAMRAKAR, Yasuo TOYASAWA and Kazuya ITOH |
: Recently, many soil-slopes get failed during the excavation or trimming process of slopes. In case of circular slope failure, it is generally thought that the failure is occurred due to shearing of soil layers. In such case, shearing surfaces are also seen at the failure sites. But in some failure excavation sites, such types of shearing surfaces are not seen. Instead soil layers seem to be detached from each other. The cause of such failure could be due to the development of tensile cracks. Also, many earth dams, embankments, pavements, etc. are failed due to the development of tensile cracks. In addition, location of the development of ice lens in freezing soils is also related with tensile strength. In order to understand the development of tensile crack, it is necessary to know the exact value of tensile strength that the particular soil consists of. Several methods of tensile testing of soils have been used in the past. But up to now, due to limitations of the existing test methods, the earlier tests were focused on to the more brittle and elastic materials (stiff, compacted and cement mixed soils) which have higher tensile strengths rather than for ductile (soft, saturated and clayey soils) materials which have lower tensile strength. |
Experimental Study to Reduce the Damage in Both Quay Walls and River Dikes related to the Lateral Flow of the Ground
RR-2004-5 |
Satoshi TAMATE, Ikuo TOHATA and Tsuyoshi HONDA |
: Liquefaction-induced flow causes severe damage to offshore structures and embankment of river dikes. It became important to assess safety of existing structures against a strong earthquake after Kobe earthquake 1995. Reinforcement of the ground is needed to ensure stability of the cranes on quay walls. Many researchers have studied mitigation techniques to reduce the damage. For example, installation of underground walls such as resistance piles, sheet piles and grouting was proposed to restrict ground flow behind quay walls and in subsoil of river dikes. This study aims to estimate the effects of underground walls on the reduction of ground movement. Centrifuge model tests of quay walls and river dikes were carried out. Additionally, laboratory shear tests and numerical analysis with distinct element method were conducted to investigate deformation mechanism. |
Study on Earthquake Resistibility of Container Cranes and Jib Cranes
RR-2004-6 |
Seiji TAKANASHI and Yasumichi HINO |
: The Hyogoken-nambu earthquake, which occurred on January 17, 1995, caused damage not only to buildings but also to a number of large cranes. The collapse of these large cranes did not cause human casualties because the earthquake occurred early in the morning. However, their collapse could have harmed many workers at the harbor. It was also pointed out that the problems with material-handling machinery caused delays in delivering relief goods such as medical products, foodstuffs, and water. In particular, transportation by ship was necessary because damage to roads was severe. This paper deals with the seismic response characteristics of container cranes and jib cranes. Damage observed in container cranes can be classified into two types. One type is damage due to opening of legs by the liquefaction of the ground. The other is buckling of crane legs due to rocking. We researched the damage caused by rocking of the crane with shaking table tests and numerical analysis simulations. We used a 1/15 crane model for the shaking table tests. We presumed that the marks of damage on the pier were due to the rocking of the cranes, and we confirmed that marks of damage were due to such behavior of the cranes by the shaking table tests. The crane response acceleration that can be used as an index for seismic intensity in the design was greatest with the maximum input acceleration of 8.5 m/s2. We found that the response acceleration remained constant even if the input acceleration increased further. The maximum axial force in the legs showed similar characteristics, but the maximum bending moment in the legs grew larger as the input acceleration grew. As we were sure that test results could be obtained through numerical analysis simulation, we carried out simulation analyses using seismic waves with various characteristics. We obtained the same results as from the shaking table tests regardless of seismic characteristics. Our test and analysis results show that the axial force and bending moment in the legs can be estimated without non-linear calculation. These stresses obtained by linear calculation give safer side results than the results obtained by non-linear calculation. In addition, we proved with numerical analysis simulations that seismic resistibility can be improved by lowering the container crane's center of gravity. |
Development of Passive-Type Electrostatic Eliminator for Pneumatic Powder Transport
RR-2004-7 |
Tsutomu KODAMA, Mizuki YAMAGUMA, Teruo SUZUKI and Tomofumi MOGAMI |
:In order to prevent a dust explosion caused by electrostatic discharges in a silo during loading of particulate products via a pneumatic transport system, we have developed a novel passivetype electrostatic charge eliminator to reduce the static charge on products before they enter a silo. The eliminator is installed at the end of the loading pipe inside the silo. It consists of a short length of plastic pipe and air-nozzle ionizers without a power supply mounted on it. Each ionizer is equipped with a grounded needle electrode within an insulated nozzle. Instead of a high-voltage power supply, the eliminator utilizes the electrostatic field strength resulting from the electrification of the plastic pipe as the energy source for the corona discharge at the needle electrode to produce air ions for reducing the static charge. The inside wall of the plastic pipe is electrified as particulate products pass through it. The charge elimination performance of the eliminators with plastic pipes of different materials was evaluated using a real-size experimental apparatus and 350-400 kg of polypropylene pellets. The eliminator used in the experiment consisted of a plastic pipe with an inner diameter of 10 cm and a length of 20 cm, as well as six air-nozzle ionizers arranged along the circumference of the plastic pipe. PTFE, PVC, PP, PE, and Nylon were used as the material for the plastic pipe. Two types of ionizers with different nozzles, i.e., insulated metal and PVC, were used. The air ions produced by corona discharges were blown inside the plastic pipe by compressed air at a pressure of 250-300 kPa to neutralize the static charge on the pellets within it. The experimental apparatus consisted of an SUS silo with a diameter of 1.5m and a capacity of 4.8m3, an SUS pipeline with a diameter of 10 cm and a length of approximately 20m, an air blower with an air volume of 10m3/min, and an air conditioning unit. Incendiary discharges, which occurred along the pellet-heap surface in the silo, were observed using a camera/CCD camera with an image intensifier set on the window of the silo roof. The charging tendencies of the pellets before and after elimination were evaluated using two air-blow-type electrostatic field sensors set on each sidewall of the silo and the pipe. It was found that effective elimination was achieved by electrifying the plastic pipe with the same polarity as the pellets and that the pipe was electrified due to the triboelectrification between the pipe and the pellets. The eliminator using PTFE for the pipe material was practically effective for reducing the static charge on the pellets. |
An Inspection of Contact Failure of Connector on the Electric Circuit for Signal Use
RR-2004-8 |
Tatsuo MOTOYAMA, Hajime TOMITA and Kenji NAKATA |
: One of the biggest weaknesses in an electric line is the connector. The connector for a signal transportation line use is particularly likely to lead to contact failure because of its low signal energy. |
Theoretical Evaluation of Electrostatic Properties of Thin Materials with Grounded Backing Conductor
RR-2004-9 |
Atsushi OHSAWA |
:This paper derives analytical expressions for surface potential distributions on thin materials having a grounded backing conductor from using the model of a distributed resistor-capacitor network. In this paper, their steady-state and transient solutions for disk and rectangular thin materials are applied for determining the resistance to ground and charge relaxation, which characterize their antistatic properties. |
Measurement and Countermeasures of Induced Electromagnetic Field on a Rough-Terrain Crane due to Medium Frequency
RR-2004-10 |
Hajime TOMITA |
: The sum length of the boom, jib, and wire of a large-scale crane may reach about 1/4 of the medium frequency wavelength. Such cranes may be effective medium frequency receiving antennas. Thus, the induced voltage at the hook of a crane located near a medium frequency broadcasting station may become high, which may result in electric shock to workers. |