Author Hideyuki Honda has experimented on actual modern timber bridges using glulam timber to investigate their structural rigidity as well as the static and dynamic characteristics of their structural performance for over 24 years. He has also evaluated the structural performance of modern timber bridges based on accumulated field test data and three-dimensional static and eigenvalue analyses. Atsushi Toyoda examined the structural performance of the static and dynamic characteristics based on those data. This study investigated the structural characteristics measured by field tests on 23 modern timber bridges immediately after completion, and then evaluated actual structural performance of those bridges based on the static and dynamic characteristics, such as static deflection, static rigidity, natural frequency, damping coefficient, dynamic increment factor (impact factor), vibration serviceability, and so on. The results clearly showed that the static flexural rigidity of modern timber bridges under actual service conditions was bigger than the rigidity in the design, and that the fundamental vertical natural frequency was almost equivalent to general highway bridges, such as steel and concrete bridges. New tables and figure have been added to the ones released in the past and an estimated equation of curve of the decrease of structural rigidity stiffness over time is proposed.
For paint-coated steel structures, corrosion tends to propagate not only from individual coating defects but also from a plurality of adjacent coating defects that, by interacting with each other, accelerates the corrosion process. However, the influence of size and proximity of the coating defect on corrosion behavior is ambiguous and unclear. In this research, combined cyclic corrosion tests were conducted over a prolonged period using paint-coated steel plates with single and two adjacent circular defects. The test results indicate that the mean and maximum corrosion depths increased when a single defect of the coated steel plate was larger. The corrosion growth rate for specimens with two adjacent circular defects was greater than the one with a single defect. Furthermore, in order to clarify the electrochemical mechanism between two adjacent circular defects, time-dependent corrosion current was measured using a model specimen with these defects.
In this study, a power generation-type Tuned Mass Damper (TMD) with an electromagnetic damping device that enables power generation and easier damping adjustment is proposed as an alternative to the conventional TMD with oil dampers installed on expressway bridges in service. A road traffic vibration test on an actual bridge in service was carried out to verify its damping effect and effect on reducing low-frequency noise. Numerical simulations were carried out to show that by changing the electric resistance of the electromagnetic damping device, various types of power-generating TMDs can be designed, which focus on vibration control, energy absorption or power generation. In the experiment, using an actual bridge, the damping effect of the power generation-type TMD was confirmed to, on the whole, agree with the numerical simulation and the electric resistance design was proven to be useful. The results indicates that it is possible to use the power generation-type TMD, with the same level of damping effect as that of the oil damper, on an actual bridge.
To clarify the mechanical behavior, peeling mechanism, and peeling strength of the adhesion layer inserted between a steel member and a carbon fiber-reinforced plastic (CFRP) sheet on reinforced steel structures, this study established a nonlinear theoretical analysis method with a CFRP-sheet-bonded steel plate under uniaxial tensile loading. The proposed analysis method considered the nonlinear material properties of all members of the analytical model. The material model of the adhesion layer was constructed based on the relationship between shear stress and relative displacement. To verify the accuracy of the proposed method, 2D geometric nonlinear finite element method (FEM) analyses were implemented. Comparison of the results of the theoretical and FEM analyses confirmed that accurate evaluation of the peeling strength of the analytical model and the mechanical behavior of all members is possible.
The steel plate bonding method has been widely adopted as a reinforcing method for deteriorated and damaged reinforced concrete (hereinafter referred to as RC) structures. This research presents a technique for the quantitative estimation of the thickness of water layer that has stagnated on the upper surface of a steel plate, debonded from a RC slab structure due to bonding re-degradation. The proposed technique is a non-destructive inspection that utilizes ultrasonic guided waves on the bottom side of a steel plate. The verification of the proposed technique has been conducted by comparing the results between the theoretical analysis and the experiments. In the verification, we examined various combinations of the thicknesses of steel plate and water layer, considering not only the steel plate bonding slab but also a steel plate-concrete composite slab and a concrete-filled I-beam grid deck, whose bottom surfaces are also covered with steel plates. The comparison provides a good agreement between the theoretical solutions and the experimental results and concludes that our proposed technique is a promising nondestructive testing for the detection and evaluation of the water ponding on the upper surface of the steel plates.
To improve the fatigue life of welded joints in steel bridges, a series of experimental and analytical
investigations was conducted on a method of welding residual stress reduction by local heating with
an induction heating (IH) device. The IH coil of 110 mm x 40 mm was installed around the fillet weld
and heated to 350 °C. The tensile residual stress of about 340 MPa was reduced to under 30 MPa. The
local heating experiment was simulated by the thermal elasto-plastic analysis to examine the mechanism
of residual stress reduction. A four-point bending fatigue experiment was conducted. The fatigue
life of the locally heated joints became two to five times longer than that of the joints without heating
under the applied stress conditions of 70 to 100 MPa.
This study shows the applicability of using the posterior distributions of model parameters on the structural reliability analysis of existing bridges. The target here was a steel plate-girder bridge that showed corrosions and deterioration in its girders, bearings, and concrete slab. The mean and variance of resonant frequencies were acquired through multiple measurements of traffic vibration for use as observation data in the Bayesian inference. A nominal finite element (FE) model of the target bridge was then constructed. The prior distributions of model parameters that represented the uncertainties due to the deteriorations were then determined based on the inspection data, and the parameters that had sensitivities to resonant frequencies were extracted by the analysis of variance (ANOVA) to prevent ill-posedness. The posterior distributions of the spring stiffness at the ends of steel girders, which were given to represent performances of the corroded bearings in the FE model and the density of the concrete slab, were estimated by applying surrogate modeling and the Markov Chain Monte Carlo (MCMC). It was then recognized that the uncertainties of those model parameters could be reduced, and those posterior distributions could explain the actual deteriorations. The posterior distributions were used to calculate the structural reliability index β of the target bridge. The probability density functions of maximum Mises-stress on the steel girders under the design load were first obtained by the Monte Carlo FE model calculations using the prior and posterior distributions, respectively. In the results, the reliability index against the variability of steel yield stress in the case of posterior distributions became higher than that in the case of the prior. It was then concluded that the procedure presented in this study could provide an understanding of the structural reliability of existing bridges quantitatively.
Compared with the conventional HQ-curve method, the HK-curve method computes river discharge Q more accurately by considering hydrological data at water level H and water-surface slope i. In the analysis, the actual observed hydrological data during the flood is used, and the results indicated that the error of the computed Q by the HK-curve method for the observed value was less than almost 5%, while the error of the computed Q by the HQ-curve method occasionally exceeded 10%. Additionally, the results suggested that the HK-curve was almost identical to the one that considered the whole observed data from the river rising period to the river falling period via peak time during the flood although only the data in the period of drawdown were used. Thus, even when the data were observed only in the drawdown period of flood, the HK-curve method estimated highly accurate missing Q at the river rising period.
Water–level fluctuations resembling long period waves, which differ from normal wind waves, were observed immediately after the Tohoku earthquake of 2011 in multiple locations, such as lakes in Yamanashi Prefecture, the fjords of Norway, and other sites located far away from the epicenter. Not many research on similar abnormal water–level fluctuations have been conducted thus far and, in many cases, these studies have treated the phenomena as seiches. However, researchers have not established concrete wave generation mechanisms and evaluation methods, and their awareness of this phenomenon and disaster prevention remains low. In this study, the authors sought to select a quantitative impact assessment method and learn more about this phenomenon. The authors used previous research and eyewitness accounts to judge that onsite slosh dynamics caused the waves to generate, and the authors attempted to recreate this phenomenon using a 3-D slosh dynamic analysis. After comparing laboratory results to verify the validity of the analysis, the authors recreated past examples of waves and also made future predictions. As a result, the authors were able to recreate abnormal water–level fluctuations based on this method. In addition, the authors identified water damage risks to in-land lakes and waterways of inner parts of bays. These are different from risks posed by tsunamis. The waves are formed immediately after the onset of an earthquake.
In the Higashi-Yokobori and Dotonbori Rivers, water quality is controlled by the inflow of relatively clean river water from above the upstream floodgate and outflowing polluted water to below the downstream floodgate. However, a hypoxic water mass occurs during high-temperature periods; therefore, there is room for further water quality improvement. In this study, field surveys, laboratory experiments, and simulations were conducted to determine the water quality characteristics of these two rivers.
The impacts of these water quality improvements resulting from the exchange of the water mass with water from outside the floodgates were evaluated, and more effective methods were proposed. It was shown that the main factor leading to hypoxia was dissolved oxygen (DO) consumption in the water. In order to maintain a satisfactory DO environment in the summer, it would be necessary to continuously allow water to enter from above the upstream floodgate at a rate of more than 2.0 m3/s.
We developed a real-time river stage prediction model using a hybrid deep neural network and physically based distributed rainfall-runoff model. The main component of the hybrid model was a four-layer feed-forward artificial neural network. Using the predicted flow of the rainfall-runoff model as the input data of the neural network, we integrated the two models into the hybrid model. The input data of the hybrid model included upstream water level, hourly change in water level, and estimated hourly change in catchment storage. The output was the change in water level at the prediction point. In the training phase, input data and supervised data were formed using the observed data. In the prediction phase, input data were formed using a combination of the observed data and flowrate calculated using the distributed mode.
The result of the hybrid model outperformed those of the ANN and distributed models. Especially in the largest flood event, the performance of the hybrid model was significantly stronger.
In recent years, levee breaches have occurred occasionally, requiring the development of technology to mitigate the damage caused by such breaches. Therefore, it is vital to clarify the levee breach phenomenon. Levee breach experiments have been performed using the Chiyoda Experimental Channel to obtain various data. However, those experiments were performed under limited river channel conditions. Using the numerical-computation model developed on the basis of the experiments performed so far, the effects of river width and riverbed slope on the levee breach phenomenon have been studied. A steep-slope riverbed develops, not depending upon the river width, but on the levee breach expansion in the longitudinal direction, whereas a gentle riverbed develops remarkable depressions, and wider river width causes flooding close to direct overflow. The characteristics of the river channel were classified into four categories to determine the different types of levee breaches and to show how to approach effective methods to reduce the risk of a disaster.
This research proposes a procedure to conduct climate change impact assessment on flood risks aimed at having smooth risk communication with river managers and citizens. The large ensemble database “d4PDF” was applied to flood runoff analysis model used to develop the flood prevention plan by the river manager. This method expresses the climate change impact in expressions that are easy for river managers to understand by applying the climate model product into the flood runoff model used in the official flood prevention planning. The proposed method was verified in the Nagara River basin, which has a basin population of about 830,000 in mainly the downstream area and no large dam in the upstream of main stream. The hydrological observation data were utilized for verification of the flood runoff model calculation results. The results of the flood runoff analysis by the annual maximum rainfall event extracted from d4PDF NHRCM 20 well represented the distribution of annual maximum flood observations. Although the influence of the spatial resolution of the climate model is still unclear, the assessment procedure presented by this research has versatility applicable to other river basins.
This paper analyzed the trend in long-term change in annual mean equilibrium water temperatures and air temperatures all over Japan for 50 years (1963–2012), and investigated their regional characteristics. To analyze the time series data of the temperatures, Mann-Kendall test was used to statistically detect the trend and Sen’s slope was used to quantitatively evaluate its significance. The results showed that a tendency for temperature to rise in the equilibrium water temperature was common in the coastal part of the Pacific Ocean in the western part from the Kanto region. In these areas, a positive correlation was found in the rising tendency between the equilibrium water temperature and the air temperature. Furthermore, a trend towards lowering of temperature in the equilibrium water temperature was detected more often in the northern part of Tohoku and Kyushu regions as well as the coastal part of the Sea of Japan. In these areas, there was a negative correlation between the equilibrium water temperature and the air temperature.
Hydraulics of sharp-crested weirs is investigated in order to obtain the base data for flood control planning in rivers with weir(s). A unique relationship between the dimensionless critical depth and the upstream head from the crest was obtained on the basis of momentum theorem, then the formulas for both discharge and upstream head were derived. In applying the momentum theorem, results of the previous experimental studies on the pressure distribution in the upstream face of the weir and in the flow section immediately behind the weir where the lower nap becomes highest were taken into account. The obtained formulas are much more hydraulically rational than the previous ones, and showed good agreement with experimental data for upstream head up to four times the weir height, which is far wider than the application limit of the previous formulas.
When using a groyne for bank protection purposes, obtaining a smooth reduction of velocity from the mainstream to the bank with less turbulence around the structure is ideal. This can be achieved by applying modifications to groyne permeability or layout. Obviously, pile-arrangement type in a pile-group groyne significantly affects the downstream flow structure. However, these effects have not been sufficiently studied. In this study, the effects of different pile-group groynes on the flow characteristics were investigated experimentally. This research aimed to find an efficient design of pile arrangement in a pile-group groyne in order to produce a smooth flow reduction with low turbulence around the structure. Two types of pile arrangements, namely in-line and staggered arrays, were considered. The findings demonstrated that the staggered type caused a gradual deceleration of flow from the mainstream toward the bank, longer low-velocity field behind the structure, and drastic reduction in the turbulence around the structure when compared with the in-line type.
Waterside space provides a good landscape and a relaxing space in urban areas. However, some people are vulnerable to the reflected light from the water surface. Some children have a weak tolerance to scattering light, and some elderly people are vulnerable to glare from strong light. The only medical advice to the weak in response to such light could be to teach them not to approach waterside spaces. At present, there is no fundamental solution, and the situation requires assistance from engineering technology. In this study, we tried to obtain basic knowledge to control the characteristics of reflected light from the water surface by conducting hydraulic experiments. Also, we investigated the condition of waterside space using a structure with water flow in urban space. Based on the results, a method for designing waterside space was considered from the viewpoint of human visual effects.
We developed a new surface flow direction dataset named “Japan Flow Direction Map (J-FlwDir)” at 1-sec (~30 m) resolution for the entire Japan domain, using “Kiban Chizu Joho” digital elevation model and “Kokudo Suchi Joho” water body layers. The calculation of flow directions for a large domain used to be difficult due to errors in the input elevation data. We solved this problem by developing a new algorithm, which first calculates the initial-guess flow directions by the steepest slope method, and then ensures river connectivity by reversing the initial-guess flow directions when needed. The new flow direction data shows better consistency with the actual river networks compared to the previous HydroSHEDS flow directions. We also generated supplementary data layers such as flow accumulation area, adjusted elevation, and river width. The new flow direction dataset will be published online, and is expected to enhance any geoscience studies which rely on flow direction data.
In 2017, heavy rains upstream of sabo dams in northern Kyushu, Japan, caused several disasters downstream due to debris-wood flow. These disasters demonstrated the necessity of protective measures against debris-wood flow throughout the entire river basin area. Therefore, it is necessary to examine the potential effects of such measures on the function of concrete slit Sabo dams, which are installed in regions of low-gradient flow. Based on our experimental results, we propose a technique to capture debris-wood in the backwater of concrete slit Sabo dam pools. We further propose the installation of wire-net counter-measures against debris-wood spill-out, and provide detailed diagrams illustrating the mechanisms of these countermeasures.
Due to the Kanto-Tohoku torrential rain in September 2015, one-third of the area of Joso City was flooded, and numerous evacuation delays and isolations occurred. In view of this incident, the authors developed a planning process named My-TimeLine with the aim of achieving zero evacuation delays by allowing residents to grasp information, judgments, and actions necessary for evacuation and obtain evacuation methods suitable for their family composition and living environment. My-TimeLine was developed with the participation of a total of 165 Joso-City residents. The results of the questionnaire survey of the participating residents showed that the knowledge and preparedness for flood risks were shared in the process of the planning and that the residents themselves could organize and prepare their own specific disaster prevention actions for crisis management, such as evacuation, in advance.
The anticorrosion functions of ground anchors (hereinafter anchors) have been strengthened after the revision of standards by the former Japanese Society of Soil Mechanics and Foundation Engineering (present Japanese Geotechnical Society) in 1988. However, some old-type anchors constructed before the revision have failed to achieve the prescribed function due to corrosion of steel materials. Therefore, the three NEXCO companies have indicated in their expressway policy that they will install a new type of anchor in the specific renewal and other works, which were approved in 2016. In installing additional anchors as a measure to supplement existing old anchors, some issues remain. For example, there is no concrete method developed to manage the tensile force when unloading tensile force of existing anchors. This paper examines the handling of existing anchors at the sites where special anchor renewal works were carried out and, based on the findings, proposes a tensile force management method to be used in countermeasures for anchor deterioration.
Local governments manage 70% of all bridges in the Japan. One-half of the number of bridges will reach their service lifetime in the near future. However, local governments have insufficient financial resources, specialists, and technologies to maintain these bridges. Therefore, it is necessary to develop a practical method for the evaluation of bridge soundness to assess the degree of the structural health of a bridge’s superstructure. In this paper, the maintenance priority evaluation of bridge integrity of small and medium span bridges is examined using the support vector machines (SVM) of artificial intelligence (AI) techniques. Based on the model, an algorithm is proposed as a useful feature to provide the engineering expertise for the inspection of bridges. This proposed method was able to substitute engineer judgement to distinguish the health rating of I. The input data were the degrees of deterioration of the structural parts and the output data were the soundness of the structure. As inspection example, 971 inspection data on bridges in Gifu prefecture were used. The results showed that adding the inspection item of exposed direction of steel bars gives good assessment on whether bridge maintenance works are needed or not.
Climate change, which directly impacts human and animal life, is one of the current critical issues worldwide. In Afghanistan, climate change has begun to impact its already limited water resources. This study was conducted using data gathered from the Investigation and Development of Water Resources sector in Afghanistan, which focus on the contributions of the water sector in alleviating poverty as the country strives for the return of peace and stability. A survey of the current state of surface water resources in the Northern River basin of Afghanistan shows that discharge from this basin is 12% higher than in the late 20th century, even though annual precipitation has decreased. The increase in surface temperatures causes an increase in snowmelt volume, and the main source of inputs in this basin has shifted to snowmelt due to climate change.
Vehicular collisions with Amami rabbits (Pentalagus furnessi), an endemic species on Amami-Oshima Island, Kagoshima Prefecture, Japan, is a serious issue. One measure that can decrease the number of road kills is to reduce vehicle speed. We evaluated the effectiveness of a new Wildlife Detection System (WDS), which consists of a sign and light, compared to a passive warning sign only. To determine the effect of the combined sign and light on vehicle speed reduction, we recorded vehicle speeds in three experiments: control, sign only, and WDS. Vehicle speeds were significantly reduced in the sign only and WDS experiments. However, the lighting of the WDS facilitated the visibility of wildlife from a distance. Therefore, we believe that WDS is an effective method to prevent vehicular collisions with Amami rabbits.
Batik is an Indonesian technique of wax-resist dyeing applied to whole cloth. The designation of the Indonesian batik as a UNESCO Intangible Cultural Heritage has increased demand for batik. Consequently, Indonesia faces severe environmental problems caused by waste/wastewater generated by batik enterprises. However, current circumstances in batik and textile wastewater treatment have not been fully reported. This paper reports the current situations in three wastewater treatment plants (WWTPs) for batik wastewater in Pekalongan City based on field survey and data analysis. Jenggot Village has used a horizontal subsurface flow constructed wetland. Kauman Village has used an activated sludge process. Banyuurip Village has used anaerobic biological treatment followed by constructed wetland. Those WWTPs have conformed to effluent quality standards for temperature, biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids, total chrome, total ammonia, and pH, except for BOD and COD concentrations at Jenggot Village WWTP during maintenance period. Influent and effluent quality scores of those WWTPs were evaluated through the effluent quality index (EQI). The respective EQI scores of influent and effluent of the WWTPs were comparable to water resource class III and II scores in Indonesia. The EQI scores suggest that the Banyuurip Village WWTP was the most effective at batik wastewater treatment.