Key historical events and technological developments in the field of structural engineering with emphasis on steel bridges for the past 50 years are reviewed in order to evaluate the present problems from four different perspectives, namely analysis, material, structural design, and measurement. The current state and future prospects are discussed to bring in a new future outlook on structural engineering field.
A perfobond strip is widely used as the validated shear connector in various steel-concrete hybrid structures. In general, the penetrating rebar is arranged in the perforation to suppress the brittle fracture of the perfobond strip due to the shear failure of the concrete at the perforation. However, the effect of the penetrating rebar on the shear resistance, and the effect of the perforation diameter, the penetrating rebar diameter, and the thickness of the steel plate on the behavior of the penetrating rebar have not been clarified until now. In this research, in order to investigate the effect of the penetrating rebar on the shear resistance of the perfobond strip, simple push-out tests were conducted paying attention to the relation between the perforation diameter and the penetrating rebar diameter, and the variations in the steel plate thickness. Furthermore, to obtain the shear contribution of the penetrating rebar to the shear resistance of the perfobond strip, a nonlinear numerical analysis was conducted. As a result, a design formula was constructed to evaluate the shear resistance of the perfobond strip with the penetrating rebar.
This paper proposes continuumnization for a set of regularly arranged spherical rigid bodies of identical radius. Motion of each rigid body, which is assumed to be infinitesimally small, is converted to a smooth function, and tensor quantities that correspond to material mechanical properties are derived from spring constants; one of them is a fourth-order elasticity tensor. For simplified two-dimensional setting, the characteristic equation of the continuumnized motion is studied. It is observed that there are high-frequency modes of local spin. Such high-frequency modes of local spin induce damping effects on translation.
This study aims to investigate the effects of very high strain rate on low-cycle fatigue behavior of structural steel under large plastic strain with strain rate order of 1.0 s-1 as expected during earthquakes. Low-cycle fatigue tests were conducted using compact-tension specimens at various strain rate levels. Fatigue life based on crack size indicated that the higher strain rate caused lower fatigue life in large plastic strain region. The energy approach was employed to clarify the low-cycle fatigue mechanism in this region. Finally, a prediction method for fatigue life regarding high strain rate effect in large plastic strain region is proposed in this study.
Energy loss at manholes under surcharged conditions is as important as the friction loss in pipes in the design of storm sewer networks and in flood analysis. Some researchers have already proposed the formula to calculate the energy loss at three-way manholes under surcharged conditions. However, in most of these proposed formulas, all variables of structural elements for the pipes and the manholes have not been considered enough yet. Therefore, development of the formula to exactly calculate the energy loss at three-way manholes is needed. In this paper, the effect of diameter ratios between inflow pipes and an outflow pipe, the ratios of flow rates between inflow pipes, connected angles among those pipes and drop gaps between inflow pipes and outflow pipe on the energy loss at three-way circular drop manholes were investigated. Based on the experimental results, a new formula that considers all structural elements and the ratios of flow rates between inflow pipes was proposed for the energy loss coefficients at the manholes. In the proposed formula, calculated energy loss coefficients reproduce measured values more exactly than existing formulas do.
We propose a simple numerical method to describe the air-water gas transfer at high Schmidt number. A numerical simulation is carried out in terms of the advection-diffusion equation using interfacial velocities obtained from a direct numerical simulation of open-channel turbulent flow. The present numerical method can describe the high Schmidt number air-water gas transfer driven by turbulence dynamics of the open channel flow. The numerical results show that the surface divergence effectively promotes the interfacial gas flux. Characteristics of surface-renewal eddies, such as surface divergence and vorticities, are found on the basis of cross-correlation coefficients between the interfacial gas flux and turbulent quantities.
This study clarifies the water quality characteristics of stagnant, eutrophic water bodies that freeze in winter, based on our surveys and simulations, and examines how climate change may influence those characteristics. The survey found that climate-change-related increases in water temperature were suppressed by ice covering the water area, which also blocked oxygen supply. It was also clarified that the bottom sediment consumed oxygen and turned the water layers anaerobic beginning from the bottom layer, and that nutrient salts eluted from the bottom sediment. The eluted nutrient salts were stored in the water body until the ice melted. Climate change was surveyed as having caused decreases in nutrient salts concentration because of the shortened ice-covered period; however, Biochemical Oxygen Demand (BOD) showed a tendency to increase because of the proliferation of phytoplankton that was promoted by the climate-change-related increase in water temperature in spring. To forecast the water quality by using these findings, particularly the influence of climate change, we constructed a water quality simulation model that incorporated the freezing-over of water bodies. The constructed model showed good temporal and spatial reproducibility and enabled water quality to be forecast throughout the year, including during the ice-covered period. The forecasts using the model agreed well with the survey results of the shortened ice period and climate-change-related increase in the BOD in spring.
Existing empirical relations for gas transfer velocity at wind-wave interface are expressed in terms of wind speed only, and so the difference in their estimated values may be caused by wave parameters such as wave age. A new model of transfer velocity describing the effects of wave breaking is formulated on the basis of the hybrid models of Woolf (2005) and Soloviev et al. (2007). The model expression and the values of parameters are examined in comparison with existing empirical relations. The present model can estimate wave-dependent gas transfer velocities and shows that wind-speed dependence in empirical relations is probably based on wave age. Also, the present model may be used to describe the behaviors of laboratory data with wave age.
This study suggests a novel 3D numerical model for simulating the flow and bed deformation around hydraulic structures, considering the transition process from bed-load motion to suspension. The numerical analysis of the fluid is carried out by solving the Reynolds-averaged Navier-Stokes (RANS) equations coupled with the Volume of Fluid (VOF) method. The temporal change in bed topography is calculated by coupling a stochastic model of sediment pickup, deposition, and transition and a momentum equation of sediment particles to account for the effect of non-equilibrium and transition from bed load to suspension. The numerical model was applied to an experimental scour phenomenon upstream of a slit weir, in which the initial bed elevation was lower than the crest elevation of the slit (i.e., all eroded particles experienced the transition process from bed load to suspension around the slit). A comparison between the numerical results and experimental data indicated that the model could reproduce the scour geometry around the slit weir with sufficient accuracy.
The combined sewer improvement projects dealt with in advanced sewer areas have issues in flowing water splitting accuracy in a rainwater discharge chamber, which is an important point in the combined sewer system. It is also pointed out that this measure has low improvement effect as well as complicated maintenance and management. The flowing water splitting function is made by organically combining the hydraulic phenomena of an overflow weir and an orifice. While the conventional technology directly controls the flow rate by splitting one time, this study proposes indirect control of the flow rate of suppressing water level fluctuation by splitting multiple times. This study has proven validity from the viewpoint of practical management through numerical analysis of the splitting phenomenon and careful examination of the data of a hydraulic model experiment to verify the technical theories of the conventional direct control and the new indirect control in flowing water splitting. The result of this study has confirmed the improvement effect where an error in the 45% level in the conventional technology can be reduced to 3% or less by the technology used in this study in the numerical analysis and the hydraulic model experiment focusing on the excessive interception error. It has also shown that the immediate issues in the combined sewer can be solved.
Deep mixing columns have been widely used to support embankments constructed on soft ground condition. A layer of shallow mixing is proposed to fix and reinforce these columns to increase their stability and the loading capacity of columned improved area. This study focuses on the external failure pattern of deep mixing columns reinforced by a stabilized shallow layer where the high strength columns fail due to large deformation without any failure inside the columns. Centrifuge model tests were carried out to investigate the effect of shallow layer on reducing embankment displacement and on the failure mechanism of deep mixing columns. High and low strength bottom layers where the columns deposit on were also considered. Acrylic pipes were used as deep mixing columns in the centrifuge tests to avoid unexpected internal failure. As a result, the tilting and sliding failures were observed as two main failure patterns of the improved ground in term of external stability. The tilting failure was found as the main failure pattern of the isolated columns. The stabilized shallow layer can significantly reduce the tilting displacement of improved area while the sliding displacement is considerably influenced by the bottom layer's strength. The effect of the shallow layer on the embankment displacement and the stability of the columned improved ground are also discussed in this study.
The ground anchoring method is a prevention work for maintaining the stability of slopes. Periodic inspections of ground anchor (hereinafter, anchor) are important to ensure slope stability. The residual tensile load of anchor is confirmed by lift-off tests. However, a unified method of the lift-off test has not been established so far. A concern is that the measured value may vary depending on the engineer carrying out the work. It is also possible that proper maintenance is not being carried out at present. In this paper, we will report on our studies of lift-off test methods. The lift-off tests were performed on working anchorsinstalled in the cut slopes of an expressway. Lift-off tests varying the displacement positions, loading methods, and other conditions were performed. At the end of our study, a lift-off test method will be proposed based on our findings.
Ground anchoring is one method for maintaining the stability of slope. When under construction, the tension of the anchor is usually managed by a load meter. At that time, the stability of slope is evaluated by checking the tension of ground anchor. However, there are cases where the measurements of a loadcell do not show a constant value even on stable ground. In addition, it is difficult to set a loadcell to a working anchor. Appropriate monitoring methods have not been established to date as well. In this paper, we have analyzed the characteristics of the measured loadcell values, looking at loadcell data collected on multiple slopes. Moreover, we have developed two new technologies. One is the technology to confirm functions of the loadcell. Another is a method for attaching loadcell to working anchors. Finally, we propose a monitoring method for the residual tensile load.
Existing literature on the psychological approach to traveler's mode choice behavior has underlined two main streams of traveler motivation for using transport mode. Those are self-interest motive and pro-environmental motive. Travelers are assumed to consider cost-benefit mechanism when deciding on mode choice in the self-interest motive, whereas environmental obligation has been cited for deciding travelers' behavior with respect to the pro-environmental motive. Self-interest-based models were commonly found to be better compared to pro-environmental-based models in predicting travelers' behavior; however, conventional studies seem to ignore the important role of trip purposes towards travelers' mode-choice behavior. This study, therefore, aims at investigating travelers' mode-choice motive under different trip purposes. Results from 270 respondents in Saitama City, Japan, showed that travelers have different motives according to different trip purposes. In particular, travelers use cost-benefit perception to decide on bus use when going to work and going shopping. Regarding intention to take the bus to go to social events, travelers' perception were found to be driven by social-environmental obligation. Further efforts on combined models which integrate both self-interest motives and pro-environmental motives, suggested that travelers do not completely ignore pro-environmental motives in self-interest trips.
This paper studies the streetscapes of George Town (Malaysia) and Hanoi (Vietnam) through typology classification of tourist-oriented activity in these historic cities. The typology classification is based on a combination of the following criteria to define the type of tourist-oriented activity, which is considered a factor in the transformation of historic quarters' streetscapes: business activity elements, primary target market, secondary target market, and additional services provided. The study then examines the sustainable planning strategies and streetscape guidelines of rapidly changing historic quarters in Asian countries caused primarily by tourism activities. Thus, it is necessary to determine the current condition of historic quarters' streetscapes through the view of tourism-oriented activities. This study has two objectives: (1) propose a unique typology composed of various business elements and current activities, and (2) identify the current condition of two streetscapes in historic quarters (George Town and Hanoi) according to this typology. Results revealed that there were both similarities and differences between George Town and Hanoi, as evidenced by the use of the proposed typology based on streetscape elements. Differences were found to be due to the application of the conservation methods, as well as implementation of policies related to each quarter's tourism economy. Both areas have been similarly impacted by tourism activities, which are considered the main factors for streetscape formation, directly reflected by current activity and façade elements.
With increased awareness of the importance of land use change at both local and regional scales within watershed-based planning, the study of land use analysis has become the focus of several international scientific endeavors. Since land use change has become a major issue in this century due to global urbanization, the study of watershed-based land use analysis will play an important role in a sustainable future. This paper undertakes a comprehensive review of watershed-based land use analysis to clarify the research trends in this area, including basic tools, factors, methodologies, study regions, scales and areas. Land use detection methods, land use modeling and thresholds in watershed delineation were identified as the fundamental tools, while land use policies, water quality, surface runoff, flooding control, land use suitability and land allocation analysis, and landscape structure were identified as the main factors in watershed-based land use planning.
Although externally bonded carbon fiber-reinforced polymer (CFRP) sheets have been used more commonly for the strengthening of existing reinforced concrete (RC) structures, the effects of this strengthening method on prestressed concrete (PC) beams have not been well clarified. In this study, an experiment was conducted to investigate the behaviors of pre-tensioned PC beams without shear reinforcement strengthened in shear using externally bonded CFRP sheets with the consideration of CFRP reinforcement ratio, stiffness and prestressing level in strands. The results implied that the shear resistance in the strengthened PC beams depended on maintaining the combination of beam action, arch action, and the bonded sheets. The failures and the increase in shear capacity of the strengthened PC beams were strongly affected by the amount, thickness of the CFRP sheets, and the effective prestress in the strands. The higher effectiveness of strengthening could be obtained in the beams strengthened with a higher CFRP reinforcement ratio of the same thickness, higher elastic modulus sheets or having higher prestressing level. Nevertheless, the increase in the thickness of the sheets did not provide a better performance. Moreover, the high inaccuracy in the calculations using the equations stipulated in the recent design guidelines compared to the increment of the shear strength obtained by the experiment was explained by the shear-resisting mechanisms.
Recently, various strengthening methods have been utilized to enhance the structural performance and extend the life cycle of RC structures. However, the existing strengthening methods still have some drawbacks especially in the durability aspect. In this study, with the outstanding properties of UFC (i.e., high strength, ductility, and durability), a new flexural strengthening method using precast UFC panels was used to strengthen the RC beams. However, to obtain greater strengthening effect and durability, PC strands were pre-tensioned to the panel and this panel was subjected to a heat curing procedure to supplement a hydration procedure and eliminate the effect of shrinkage. Using this novel technology, this research was conducted to investigate the flexural enhancement and corresponding behavior of RC beams strengthened by pre-tensioned UFC panel. Five pre-tensioned UFC panels and eight strengthened RC beams were prepared and investigated using the bending test. Two different experimental parameters, i.e., prestressing level and amount of PC strands, were used. The undercut anchor bolts were applied for sufficient bonding between interfaces. The bending results of panels were investigated to compute the exact prestressing level in order to determine the calculation of prestressing losses. The results of the strengthened beams revealed that the pre-tensioned UFC panel drastically enhanced the loading capacity of RC beams, and each variable parameter affected the different structural characteristics. To ensure compatibility along a cross-section of the strengthening system, the compatibility along panel specimens and strengthened RC beams was investigated. Finally, the strain compatibility was satisfied at the mid-span of beams where the calculation of load-carrying capacity in strengthened beams could be carried out by using conventional flexural section analysis.