High-strength bolted friction-type joints are often used for onsite maintenance and strengthening work for steel bridges. Abrasive blast-cleaning to prepare the surfaces of existing steel members may not be done depending on site conditions. In this paper, slippage tests were carried out for specimens with splice plates coated with inorganic zinc-rich paint on the surface and connected plates with varied surface roughness. The results of the slippage tests showed that the relationship between slip coefficient and surface roughness was linear up to 75 μm thickness of inorganic zinc-rich paint. Furthermore, a design slip coefficient is proposed for inorganic zinc-rich paint with thickness from 50 μm to 150 μm, considering Ra on the surface.
Wind loads, known to be an essential factors in the design of structures for photovoltaic arrays, are the products of kinetic pressure, wind-force coefficient CW and array area, under JIS C 8955. However, the use of CW is limited to an array angle-of-attack θ between 15° and 45°, and is not applicable where angle-of-attack is low at approximately 10°. However, such low θ have been used increasingly in recent years. In addition, the impact of the difference in the distance from the ground to array has not been investigated. When objects having a wing-form shape are moving close to the ground, a ground-effect may arise, resulting in an increase in lift power, and a similar increase is expected for arrays that have shapes similar to wings. If these wind loads can be evaluated properly, it is expected that the safety and economical performance of arrays can be further improved. In this research, the authors conducted a wind tunnel test using a 1/20 single-unit scale array model to estimate and refine wind-force coefficient CW taking into account the array's angle-of-attack and its structure height.
This paper shows the failure mechanism of steel-concrete composite bridge deck having studs and ribs subjected to repetitive moving loads. Three-dimensional nonlinear FE analysis was used. First, the property of interface element between steel and concrete was identified by sensitivity analyses. Next, the progress of strains of concrete and steel elements obtained in simulation were examined throughout all the loading programs of wheel running tests. In particular, special attention was devoted to the development of horizontal cracks inside the concrete. Furthermore, static analysis was performed to highlight the difference in the failure process given by the fixed point load and the one caused by the moving load. Considering a particular failure mechanism of the deck under moving load, setting a proper limit states and control level for engineering practice was strongly required.
Experimental researches have confirmed that UIT (Ultrasonic Impact Treatment) gives excellent fatigue strength enhancement in welded joints. The main factor in increasing the fatigue strength by UIT is the introduction of compressive residual stress rather than the improvement of weld toe shape. Further improvement of fatigue strength is expected by introducing high compressive residual stress which can be realized by increasing the static strength of steel. The purpose of the present study is to clarify the influence of static strength of steel on the fatigue strength of web-gusset welded joints with UIT. For this purpose, fatigue tests on the joint specimens made of SBHS400, SBHS500 and SBHS700 steel and treated by UIT have been performed, and fatigue crack initiation and propagation behavior and crack opening-closing behavior due to the compressive residual stresses have been examined.
The long-period ground motion scale of the Japan Meteorological Agency (JMA), which is divided into four classes depending on the maximum velocity response spectrum, is tried for long-period ground motion, although the seismic intensity scale with ten classes based on the instrumental seismic intensity is used. The present study proposes the long-period ground motion scale by using a long-period seismic intensity level with the intermediate characteristics of velocity and displacement. The long-period seismic intensity level based on the seismic intensity level is obtained for the maximum value to have a correlation between the long-period ground motion scale of the JMA. Not only the design of the long-period ground motion waveform, but also the observed seismic waves are used for comparison with the long-period seismic intensity level and various seismic intensity levels, as well as the maximum velocity response spectrum.
Along with the spread of steel bridges with I-shaped girders, the use of thick steel plates has been increasing in recent years. It is feared that residual stress in the thick plate affects the girder's load-carrying capacity, yet residual stress measurement data are insufficient. Consequently, the load-carrying capacity curves used in the Japan Highway Bridge Specifications are based on old data. In this study, a test specimen that simulates the welding section between the main girder web and thick flange is elaborated; the residual stress distribution is also measured in the flange plate width and thickness direction using a mechanical cutting method. In the plate thickness direction measurement, accuracy of the measurement is sacrificed in order to propose a simple and easy measurement method. It is found that the slope of stress distribution in the plate thickness direction increases as the thickness of the plate increases. Then, considering a three-dimensional equilibrium of residual stress, the intermediate support of an existing bridge is modeled. From the elasto-plastic finite element analysis, it is confirmed that the residual stress in the thick plate does not affect the load-carrying capacity for the bending of steel girders.
In ultrasonic testing, SAFT (Synthetic Aperture Focusing Technique) is a signal processing technique used to reconstruct flaw images by the superposition of A-scan waveforms. However, an additional signal processing technique may also be integrated into SAFT algorithms to get clearer ultrasound images. Wave theory is one of the most significant keys in SAFT improvement because it can lead to a better understanding of the wave phenomenon. In this paper, approximate wave solution (AWS) based on a stationary phase method is used to calculate beam radiations inside a target of inspection. Multiplying A-scan waveforms by the ultrasonic beam radiations computed from the AWS, wave diffraction characteristics that are spatial functions between a transducer and a target are incorporated into the SAFT. Moreover, the AWS can be used to predict the Effective Region (ER) where high imaging capability can be obtained. The performance of the improved SAFT, namely AWS-SAFT, and the ER technique are experimentally tested in ultrasonic imaging for a side-drilled hole (SDH) in a steel plate. As a visualizing aid, Structural Similarity (SSIM) index is introduced and Structural Similarity Index Map (SSIM-MAP) is proposed instead of a SAFT image. It is shown that SSIM-MAP can improve a flaw image, especially in that the image is more focused on the location of a flaw, and artifacts due to a longitudinal wave mode are eliminated in a transverse wave mode SAFT image. The ER, where a high contrast flaw image can be definitely obtained, is defined quantitatively in advance of SAFT imaging. The preliminary study for the use of the proposed technique in a real problem is demonstrated using ultrasound imaging of a bottom defect of a steel plate to demonstrate the application of AWS-SAFT and ER.
The direction of the principal stress on web-gusset welded joint connected to a main girder web of steel girder bridges changes instantaneously so that the direction of shear stress reverses when a vehicle passes right above there. It is well known that the fatigue crack initiates and propagates in the direction perpendicular to the principal stress one, but fatigue crack propagation behavior and fatigue strength when the direction of principal stress changes have not been studied yet. In this study, to determine the propagation behavior and the fatigue strength in the stress field where the direction of the principal stress changes, fatigue tests on girder specimens and fatigue crack propagation analyses have been performed.
Due to the massive earthquakes and tsunami on March 11th, 2011 in Eastern Japan, Fukushima Daiichi nuclear power plant was severely damaged and some reactors were exploded. Then radioactive particles were widely spread out. In this study, we modified the stable isotope module of RSM (IsoRSM, Yoshimura et al.) to enable to simulate the transport of the radioactive tracers, namely iodine 131 and cesium 137, by including the dry and wet deposition processes. The control experiment with 10km resolution and the emission estimated by Chino et al. (2011) showed reasonable temporal results for Toukatsu area (eastern part of Tokyo metropolis and western part of Chiba prefecture), i.e., on March 22th, the tracers from Fukushima was reached and precipitated in a significant amount as wet deposition. Thus, we conducted 4 experimental simulations to analyze the uncertainty due to different meteorological patterns and different parameters for wet and dry deposition and diffusion. Though the temporal patterns of deposition of radioactive particles were moderately similar each other in all experiments, we revealed that the deposition parameters and boundary conditions can cause the uncertainties largely in the distribution of deposition.
A two-dimensional frequency-domain numerical analysis on the primary conversion efficiency of multi-chamber Oscillating Water Columns (OWCs) is presented. The numerical model is developed by combining the hydrodynamics of the interaction between the wave and the OWC and the thermodynamics of the air chambers. The wave-induced force is calculated using the boundary element method based on the velocity potential theory. The air flow is studied using mass and energy conservation equations and an equation of state. The air pressure in the air chambers, the reflection coefficient, and the primary conversion efficiency of each of the chambers, as well as the combined efficiency, are evaluated using the boundary integral equations. In addition, the behavior of these physical quantities, along with the variations in the nozzle ratio, the relative water depth, the depth of the curtain wall, and the width of the front-chamber are investigated using the calculated results.
In Japan, flooding damage in urban areas caused by local heavy rainfall has increased in recent years. It is of great importance to improve the precision of forecasting local heavy rainfall. However, the present weather forecasting system cannot forecast the local heavy rainfall well in advance since local heavy rainfall has small scale and builds up suddenly. In this study, therefore, we develop two early local heavy rainfall forecast techniques at Osaka City. One is the weather index technique, and the other is the numerical weather forecasting technique that assimilates the X-band multiparameter radar (X-MP). As a result, we can forecast local heavy rainfall earlier by the weather index technique, and we can express the movement, strength, and detailed structure of local heavy rainfall using the numerical weather forecasting technique by assimilating X-MP.
A multilevel grid-type turbulent shallow flow model combined with an equilibrium sediment transport model (KMR-MB: Kinematic Mesh Reconstruction for Movable Bed) is proposed. The KMR method is a kind of multilevel grid model with dynamic refinement that combines grid cells to efficiently capture the unsteady flow phenomena. Saito et al. (2012)1),2) have applied the KMR approach to open channel flows around a bridge pier and have shown the advantage of the model. They used the maximum value of the strain and rotation parameters for the threshold for quadtree and 3×3 grid divisions. We have extended the model for computations of morphological phenomena in rivers by incorporating an equilibrium sediment transport model as well as a bed continuity equation, and used new criteria for grid cell refinement. We used an average curvature of the bed surface as the criteria for refinement and combined quadtree-type grid cells. The present model has been applied to simulate the alternate bar formations. The experimental result by Akahori et al. (2011)3) was used to validate the model. The comparison between numerical and experimental results showed that the present KMR-MB can excellently simulate the phenomena with less CPU time than those computed with the fixed grid.
This study experimentally and numerically investigates the relationship between flow structure and the scour process around a slit weir. First, we carry out a movable bed experiment on the scour. In this experiment, a weir with a rectangular slit is used to simulate physically the scour induced by sediment releasing through a dam gate. The stereo PIV method is applied to measure spatially and temporally flow velocity fields on a movable bed. Next, we carry out three-dimensional numerical analyses using the bed topography measured in the scour experiment. The numerical analysis solves the Reynolds-averaged Navier-Stokes (RANS) equations coupled with the VOF method and the k-ω SST turbulence closure model. The analytical results agree well with the measurements. Both results show a tornado-like vortex near the slit. This vortex is found to contribute highly to the temporal evolution of the scour hole.
In major cities, large populations can hinder evacuation efforts in the event of a large-scale flooding. Therefore, for investigating evacuation strategies during large-scale flooding in such cities, population size and its impact must be considered. This study aims to examine the evacuation problems that arise when big cities are subjected to large-scale flood damage. In addition, it attempts to examine strategies that can overcome the evacuation problems. In this study, we developed a scenario simulator to elaborately simulate the flooding, evacuation of residents, and status of damage due to water exposure in the Edogawa Ward, which has a population of approximately 650,000. In addition, using a simulation that reflected the intended evacuation behaviors of the residents for a scenario in which the banks of the Arakawa River overflowed, we were able to identify the inherent evacuation problems of the city, including the damage caused by the presence of a large number of evacuees. Furthermore, we analyzed scenarios including measures to reduce the extent of damage. From this information, it became clear that countermeasures such as spatial and temporal dispersion of evacuees and a reduction in evacuation demand are necessary.
Although several physically based sediment runoff models have been proposed, sediment production and supply to river channels has not been considered in detail. In this paper, we introduce a freeze-thaw action model and gully erosion model for sediment production, and a talus erosion model for sediment supply. Each numerical model is connected to the sediment transport model proposed by Egashira and Matsuki (2000). Applying this combined model to a real mountainous basin, we confirm that this can express some sediment runoff characteristics in this geomorphological context; for example, seasonal variation of sediment runoff, temporal variation of the deposited sediment amount in the talus, and differences between upstream and downstream riverbed deformation.
In urban areas, there are inevitable interactions between existing structures and new constructions such as tunneling. A series of centrifuge model tests has been carried out to study the effects of tunnelling-induced soil movements on the adjacent pile group in sand. The tunneling process was simulated by reducing the diameter of the model tunnel for various ground loss values in 100g centrifugal acceleration. The tunneling machine is a mechanical type that can reduce diameter in co-axial direction to create a clear boundary condition. Two model pile groups consisting of four piles each with different lengths were embedded in dry sand at either side of the tunnel. The effects of horizontal distance between the pile and tunnel center (Xp), relative pile tip position to the tunnel center (Zpe), vertical loads on the pile groups, and cover depth ratio (C/D) were investigated in this study. Zones of influence were applied to investigate the area of large soil movements with the adjacent pile group. For small ground loss ratio (ΔV/V0), the pile group movements increased almost proportionally to ΔV/V0. While for the large ΔV/V0 over 3%, the pile movement increment gradually decreased with ΔV/V0, except for the pile group with the front pile resting in the large displacement zone, of which movement still proportionally increased with ΔV/V0. The effect of Xp and Zpe on the pile cap movement could be reasonably combined with the relative depth from the boundary of the less-movement zone to the pile length. Relative pile depth in the less displacement zone to the pile length and the horizontal position are the critical controlling factors of the profiles of pile bending moment and axial force.
The assessment of fault activity is necessary to mitigate against damaging earthquakes. To adequately assess long-term fault activity, a new technique that complements chronological investigations is required. Here we examine the applicability of the slip tendency (ST) method, based on physical models, to assess fault activity in Japan. We computed the ST using a friction coefficient of 0.6 for the faults, a common friction coefficient for rocks, and the stress state estimated from earthquake focal mechanisms in north-eastern Japan. Calculated ST values are high for the most active faults (e.g., the Senya segment) and are low for inactive fault (e.g., the Sakunami—Yashikidaira segment). Therefore, we propose that the ST method can be applied in assessments of fault activity. However, the ST method sometimes underestimates fault activity, and we have explored the necessary input parameters to obtain reliable results. To use the ST method, the determination of these parameters is critical for the robust assessment of fault activity based on physical models.
High-density, low-permeability uniform layers of bentonite are required in radioactive waste disposal facilities to prevent the migration of such waste into the biosphere via ground water. Against such a background, the applicability of high-density compacted bentonite for the construction of low-permeability layers has become a subject of international consideration. However, the construction of these layers involves major technical challenges because the limited space available means that heavy machinery cannot be used. The authors developed a method for the construction of high-density low-permeability layers using a wet spraying approach that enables work to be performed in restricted spaces. This paper reports on research performed to verify the method, to investigate a water content adjustment technique for the bentonite used, and to study a measurement technique for bulk density, and also outlines construction quality control criteria.
A countdown timer can reduce startup delays and improve queue discharge; however, many researchers have reported an increased occurrence of red light violations with the use of such timers. We conducted an experiment to examine whether it is possible to retain the benefits of the countdown timer while limiting the problem of red light violations at startup when the signal switched from red to green. This experiment investigated the impacts of different settings of the countdown timer (10 different patterns for timer display) and without the timer on drivers (mainly young male drivers) and on two types of vehicles (with and without the idling stop system). We determined their influences on the startup delay and the proportion of red light violations at startup. Based on the findings, the extent of the reduction in startup delay is more apparent for vehicles with the idling stop system. In the presence of the countdown timer, drivers with the idling stop system responded 65% quicker than in the absence of the timer. The pattern that had the best overall performance in reducing startup delay without increasing drivers' tendency to violate red lights at startup, was to count down by seconds, then to stop the timer and keep the number unchanged for a short period (approximately 3 seconds) before the green phase. These findings may benefit the implementation or modification of countdown-signalized intersections to improve the safety of crossing pedestrians as well as driver satisfaction.
A huge deposit of buton natural asphalt in Buton island of South East Sulawesi, Indonesia, has not been fully utilized for asphalt concrete mixture. This is because the asphalt of buton granular asphalt is trapped in mineral, and currently the modifier to rejuvenate buton granular asphalt has not resulted in road pavement that can bear heavy daily traffic. This study aims to examine the performance of bio-flux oil as modifier of buton granular asphalt to determine its asphalt mixture requirement properties. This bio-flux oil consists of the oil derived from the seeds of the oil nut tree (Calophyllum inophyllum L.), crude pine resin from pine tree (Pinus merkusii), and other ingredients in certain composition.
This paper aims to develop a new method for shear reinforcing concrete beams by using the ultrahigh performance PBO fiber mesh as a replacement for conventional stirrups inside a concrete structural member. The elementary test was performed first to investigate the general behavior of the internal reinforcing PBO fiber mesh as a fundamental objective of this study. Then, nine RC beams with and without internal PBO fiber mesh were conducted in the RC beam test. The parameters in the RC beam test were the number of internal PBO mesh layers, the width of internal PBO mesh in the shear span, and the reinforcing configuration of the internal PBO mesh. The experimental results showed that the shear capacity and the shear carried by internal PBO fiber mesh increased significantly with a higher number of the internal mesh layers; however, the shear capacity decreased when the width of internal mesh in the shear span was expanded. Besides, the difference in reinforcing configuration of the internal PBO mesh showed a great impact on the shear capacity of concrete beams reinforced with internal PBO fiber mesh. Furthermore, an empirical method for evaluating shear carried by internal PBO fiber mesh was modeled and a moderate agreement between values from the model and values from the experiment was obtained.
This study was conducted to understand asphalt concrete (AC) behavior using finite element method (FEM) modeling considering wet and dry aggregate-binder mixture. A small-scale FEM model of AC was developed considering an aggregate coated with matrix materials. Maximum stress criteria and surface-based traction-separation law were applied on matrix materials and matrix-aggregate interface, respectively, using ABAQUS. Results indicated that shear stress reached its capacity and damage initiated earlier in wet matrix materials due to moisture and caused higher damage. Moisture caused 62.80% more damage in matrix materials when compared with dry matrix materials. Damage occurred at the matrix-aggregate interface when shear contact stress reached its capacity and interfacial debonding occurred at the damaged locations. Moisture caused 17.45% more debonding at the interface region compared to the dry matrix. However, wet aggregate did not change the damage scenario at the matrix-aggregate interface when compared with dry aggregate. Matrix materials slid horizontally (i.e., relative displacement) and moved vertically (i.e., contact opening) at the debonding locations. The strong rebound effect of dry matrix was the reason for the higher relative displacement and contact opening at the damaged locations.
This study aims to clarify the shear resistance mechanism of reinforced concrete haunched beams (RCHBs). Four series of ten RCHBs with different parameters (positions of haunched portions, thickness of the concrete cover, presence of stirrups and the arrangement of the tensile rebar) were tested. The results demonstrated that the bending position of the tensile rebar as well as the different arrangement of the tensile rebar highly influenced the crack propagations which caused the variation in the shear capacities due to different contributions of the arch action. Different diagonal crack angles also resulted in different contributions by stirrups in RCHBs with stirrups. The thicker concrete cover at the mid span affected the crack propagation but had almost no effect on the shear capacity. Nonlinear FEM analyses were also conducted to complement the experiments and verify the results, which showed a good agreement including load-deflection curves, load capacities and crack patterns. The shape of the compression zone, which dominates the arch action in RC beams, was also evaluated by the analyses.
This paper presents the history of the application of a pavement management system (PMS) in Vietnam and the background to the successful development of a new PMS system that was customized from the Kyoto Model1), 2) to make it suitable for local application. In addition, we report on a scheme for road asset management with sustainable cooperation between Japan and Vietnam, realized through the support of the Japan International Cooperation Agency as well as the contributions of many Japanese researchers and experts over a long period of time. Numerous efforts, both personal voluntary-based and organizational-based, have been made to enable the adequate transfer of technologies and knowledge, and to ensure that the capacity for road asset infrastructure management and maintenance is enhanced in a sustainable way. We are pleased to say that fruitful outcomes have been made from the perspectives of circumstance, location, and enhancement of human capacity. The approach adopted is also expected to be expanded to other fields, regions, and nations in a wider scope.
OSV (On-Site Visualization) monitoring is a system that measures information which is shared visually in real time at site. It was introduced by Akutagawa in 2006 and has been effectively applied at various construction sites since then. The basic function of the OSV is to show changes in deformation, pressure, inclination, etc. of structures as well as ground movement using colored lights, namely blue, yellow and red through light-emitting converter and LED lights electrically. Through these previous site experiences, the OSV performance has been reassessed; it has been recognized that a major problem with the system is the cost of the number of electrically driven OSV devices needed to cover many locations for a more effective OSV operation. More simple mechanical monitoring devices have now been devised which do not require electricity and are sufficient and reliable enough to monitor structure and ground movement. These low-cost OSV devices have been introduced at the Bai Chay Road project in Vietnam as the first trial of low-cost OSV on an overseas project. Finally we propose a basic strategy for evaluating the performance of the OSV system and improving construction safety, utilizing low-cost OSV.
In our previous studies, a series of laboratory experiments were performed in order to evaluate the feasibility of applying the freshwater bivalve Sinanodonta woodiana as a Microcystis blooms removal tool. The results suggested that S. woodiana could greatly graze both the pure cultured Microcystis aeruginosa and the natural blooms of toxic Microcystis spp. in unicellular and colonial forms. Furthermore, in the subsequent long-term grazing experiment, the bivalves themselves demonstrated strong survival ability during exposure to natural eutrophic water containing microcystins (MCs) for 12 days. In order to clarify the survival mechanisms (selective feeding and detoxification mechanisms), we summarized all the conducted experiments and made a correlation analysis between the diet characters and the bivalves' physiological rates. The results showed that (1) MCs did not restrain the feeding behavior of S. woodiana; instead, the exorbitant initial food concentration could inhibit the filtration rates; (2) the absorption efficiency increased with the elevation of the toxic algae Microcystis concentration; (3) there was an obvious positive correlation between ammonia excretion rates and microcystin concentrations. Finally, combined with the phenomena in the long-term grazing experiment, the possible detoxification mechanism in this bivalve was inferred.