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Satsumasendai, Japan

Abukawa T.,CHODAI CO. | Hasegawa A.,Hachinohe Institute of Technology
Engineering for Progress, Nature and People | Year: 2014

Many bridges suffered serious damage in the 2011 Japan Tohoku Earthquake off the Pacific coast. In this earthquake, the damage to bridges caused by the tsunami was more serious than that due to the tremors themselves. In particular, the superstructures of large bridges were swept away by the tsunami. Kesen Bridge is one of the largest bridges damaged by the tsunami, having 5 spans, and with a total length of 181.5 m. All of the superstructures of the 5 spans were carried upstream approximately 300 m. Consequently, an important route for the region was blocked off, causing significant delays in the relief and restoration of the damaged area. The authors conducted hydraulic experiments in order to understand the forces that tsunami exert on bridges, and to consider corresponding measures for bridges that will be effective against tsunami. With respect to one such measure, an experimental study was performed to determine whether the force of a tsunami can be reduced by attaching fairings to a bridge, two types of fairing being investigated. Source


Abukawa T.,CHODAI CO. | Hasegawa A.,Hachinohe Institute of Technology
IABSE Conference, Nara 2015: Elegance in Structures - Report | Year: 2015

In the 2011 Japan Tohoku Earthquake off the Pacific coast, the superstructures of bridges were swept away by the tsunami. The authors conducted hydraulic experiments in order to understand the forces that tsunami exert on bridges, and to consider corresponding measures for bridges that will be effective against tsunami. With respect to one such measure, an experimental study was performed to determine whether the force of a tsunami can be reduced by attaching fairings to a bridge. From previous studies, it has been found that fairings are effective for horizontal drag, but it is not effective for vertical drag because of the buoyancy. Therefore, hydraulic experiments were conducted on the effect of having to open a slit in the fairing, to smooth the flow of water into the fairing within. Source


Ninomiya Y.,Office Ehime Prefecture | Okamoto M.,Office Ehime Prefecture | Tanaka G.,CHODAI CO.
IABSE Conference, Nara 2015: Elegance in Structures - Report | Year: 2015

The Ikina Bridge spans the strait between the islands of Ikina and Sashima in Ehime prefecture, Japan. Since the particular geographic conditions at the bridge site of the Ikina Bridge pose certain problems in terms of balancing the bridge dynamically across the span length, a composite cable- stayed bridge structure combining light-weight steel girders and heavy concrete girders is adopted to ensure the correct dynamic balance. While steel girders and prestressed concrete (PC) girders are joined near the main towers in conventional composite cable-stayed bridges, in the Ikina Bridge, the PC girder ranges are expanded to positions approximately 1/4 of the main span length from each of the main towers, where they are joined to the steel girders in order to improve not only the workability and economic efficiency of the Ikina Bridge, but also the wind resistance. A main girder design that achieves excellent economic efficiency by taking simple and rational wind- pressure countermeasures was selected, and the wind resistance was verified through wind-tunnel tests. In addition, H-shaped concrete main towers are adopted due to their excellent wind-resistance and durability as well as their conformance to the narrow road width condition. Sufficient aseismatic performance of the concrete main towers is ensured by reducing the self-weight by adopting a hollow cross-section and reducing cross-sectional forces by allowing minor plastic deformations in the connecting beams at the top of the H-shaped main towers. Note that this bridge is the first composite cable-stayed bridge in Japan in which stay-cables are anchored diagonally at both steel and concrete girders along the main span. Source


Abukawa T.,CHODAI CO. | Hasegawa A.,Hachinohe Institute of Technology
IABSE Conference, Geneva 2015: Structural Engineering: Providing Solutions to Global Challenges - Report | Year: 2015

The massive tsunami after the Great East Japan Earthquake in 2011 caused immense damage to people's lives and industries; some superstructures of long-span bridges were washed away. Even now, nearly four years after the tsunami, many people are still forced to live in temporary housing and other makeshift facilities. Because the major bridges had been on important roads in the tsunami-stricken areas, their loss caused significant delays to relief and restoration work. Taking measures to protect bridges from tsunamis is extremely important, as there are concerns that similar tsunami damage to bridges could occur in other areas of Japan. However, reliable technologies have yet to be established for protecting bridges from tsunamis. The authors' recent experiments have verified the effects of employing fairings, fairings with slits, and slabs with air holes as measures against tsunamis. This paper describes the outline of experiments, experimental results, and discussions on these experiments, as well as conclusions. Source


Miwa T.,EcoTopia Science Institute | Okada Y.,CHODAI CO. | Morikawa T.,Nagoya University
Transportation Research Record | Year: 2010

In recent practical transportation planning in Japan, the adoption of stochastic user equilibrium assignment models for traffic assessment has been discussed. Such models include a dispersion parameter that accounts for drivers' errors in perception of travel time at the time of route choice decision. In practice, setting a rational value for this parameter is an issue. Generally, the dispersion parameter is exogenously set to the same value for all origin-destination (O-D) pairs. However, it is not guaranteed that errors in drivers' perception of travel costs are equal for all O-D pairs. This study examines how the parameter is set and applies a multiclass stochastic user equilibrium assignment model to consider differences in drivers' errors in perception of travel costs in using an existing general-purpose road network. Results show that changes in the dispersion parameter affect the user class flows that make up the link flows rather than the link flows themselves. Setting a dispersion parameter according to the travel cost of an O-D pair rather than setting a constant parameter improves the reproducibility of the user class flows on each link. These findings encourage practical transportation planners to evaluate qualitative measures of traffic flows in the road network, such as the utilization of road links. Source

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