The heavy rainfall that occurred in western Japan in July 2018 caused massive and widespread damage to social infrastructures and lifelines. Certain cases that can be used to specifically and quantitatively analyze the damage situation and the cause of the damaged bridge groups are valuable for overcoming structural and complex engineering problems. Such cases can be used to identify the causes of the failure and the analysis progress, and they will help improve the design elements and construction method of bridges in the future. They could also yield such measures as washing out of the bridge at the time of flood. In this study, we conducted a field survey of the washed out Misasa railway bridge, and we evaluated the conditions that caused the failure based on hydrological, hydraulic, and structural analyses at the time of the flood, based on a field survey of the affected bridge. These analyses will help obtain design elements for small and medium bridge structures and countermeasures in the future. We focus on the collapse issue of the 1st Misasa Railway Bridge, wherein the collapse trigger of structural stability can be evaluated through its collapse mechanism. The structural analysis reveals the flood hydrodynamic force on the bridge girder during the flood that caused the collapse. In particular, when the hydrodynamic force of the water flow acts on the bridge girder part, the flood hydrodynamic force that led to the collapse of the bridge is estimated from the engineering point of view of structural stability. Based on the failure processes and conditions revealed by the analyses, we identified design elements that can help increase the resistivity of bridge structures on small rivers against floods with effective methods.

This paper was accepted for publication in the journal Automation in Construction and the definitive published version is available at http://dx.doi.org/10.1016/j.autcon.2016.05.007Mobile Bridge™ is a deployable bridge that uses a scissors mechanism to achieve its useful structural form. The bridge has a compact size in its undeployed state and can be transported easily to where it is needed. Its rapid deployment makes this type of bridge very useful in areas struck by natural disasters by enabling vehicles to cross terrain that has been made impassable. In previous research, experiments and analyses were conducted on a small-scale bridge designed for pedestrians. In order to consider a bridge of increased size, it is necessary to assess whether design and analysis techniques of the small scale bridge are applicable to the full-scale one. In this paper, we consider a full-scale deployable bridge with a lower deck and two scissor units, that allows for a light vehicle to pass across. We have carried out a light vehicle loading test in order to investigate its basic structural characteristics. Furthermore, the paper presents the theoretical design method and numerical models based on the experimental work followed by validation and comparison with the obtained experimental values

Scissors mechanisms are commonly used in safety engineering during the construction of temporary structures, owing to their inherent advantages of foldability, transformability, and reusability. We effectively utilized these scissors mechanism features to develop a lightweight, deployable emergency Mobile Bridge (MB) based on optimization, and control of the folding structure. Here, we discuss the problems of optimal reinforcement layout for the MB by formulating and solving three optimization problems, namely: (a) the load capacity maximization problem, (b) the weight minimization problem, and (c) coupling the load capacity maximization problem and the weight minimization problem. The potential benefits resulting from the application of reinforcement were evaluated using a combination of finite element analysis and an optimization algorithm based on the differential evolution method. The results demonstrate the significant positive influence of the additional reinforcing members. In particular, the limit load was increased by over 10 times, while the weight was decreased to approximately half. The proposed methodology enabled the development of a substantially improved version of the MB characterized by a higher load capacity and lower weight in comparison to the initial bridge design.