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Center for Advanced Engineering Structural Assessment and Research (CAESAR) is one of the four research institutes and centers of Japan's Public Works Research Institute (PWRI).
In Japan, the number of highway structures began increasing rapidly in the 1960s in response to the rapid economic growth of the time, and now a significant number of those structures are more than 50 years old. Over the years, many such Japanese highway structures, including bridges, have been subjected to heavy traffic loading and have suffered from exposure to severe environmental and seismic conditions.
Therefore, there are urgent needs that demand comprehensive technology development as well as fast action to ensure their continuing safety and utility.
In response to these urgent needs, the PWRI reorganized its institutes in April 2008 to establish CAESAR.
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Working together with highway administrators, CAESAR formulates remedial treatments for bridges with serious structural deficiencies in situations where the current practical levels of inspection, diagnostic examination, and prognosis are not necessarily sufficient to fully rectify their conditions. Should a disaster occur, the Center is responsible for providing immediate emergency countermeasure support. Needless to say, CAESAR conducts basic laboratory research to find more reasonable and practical applications to the results obtained from such trials.
The encourages and supports networking between highway administrators engaged in (or otherwise concerned with) the inspection and management of existing highway bridges. The Center also collaborates in voluntary research and development activities with organizations such as universities and companies, as well as those undertaken by other national and foreign highway administrators and research institutions.
As national codes and recommendations, the Center feeds back information on the state-of-the-art experiences, and the trial results obtained, in a way that ensures the lessons are put to practical use.
The Center also continues to develop, maintain, and renew human resource programs that will ensure the continuing development and excellence of the national highway bridge maintenance system.
Cover Photos: Upper left = Unseating of the Showa-Oh-Hashi bridge during the 1664 Niigata Earthquake, Upper right = Fatigue crack in a main girder, Lower left = Alkali silica reaction observed in an RC bridge, Lower right = Survey of an overpass that has suffered from salt corrosion
The Research Coordinator for Earthquake Engineering coordinates research on earthquake disaster prevention and mitigation for national infrastructure (including highway and river structures) while the Research Coordinator also covers Tsukuba Central Research Institute and Civil Engineering Research Institute for Cold Region in terms of earthquake engineering. When a large-scale earthquake occurs, the Research Coordinator will immediately organize an emergency investigation and support team from CAESAR researchers. The Research Coordinator also can ask researchers from the Tsukuba Central Research Institute and the Civil Engineering Research Institute for the Cold Region to work for the support team.
Bridges and Structures Research Group conducts research on improving highway bridge maintenance, disaster damage prevention and mitigation, and on design and construction methods. This group pays special attention to basic and applied inspection technology, structural condition assessment methods, object-related diagnostic examination methods, rehabilitation methods, and reinforcement methods. The Group is assisted by an ad hoc research unit flexibly composed of selected researchers whenever there is a need for CAESAR to focus intensively on an issue within their area of expertise.
|As of April 1, 2013
People: 23 in-house, 2 research specialists and 15 visiting researchers
Large-scale test facilities: 30 MN loading test machine, Large-scale continuous wheel load test machine, 1,000 kN fatigue test machine, Earthquake loading simulator and so forth.
|Acronym CAESAR — The acronym was inspired by Julius Caesar of the Roman Empire, who established and maintained the infrastructure of long empire-wide highway network – parts of which are still in use more than 2000 years later.|
In the US, vast numbers of highway bridges were constructed in the 1930s as part of that nation's New Deal public works program. Fifty years later, in the 1980s, infrastructure decay to such structures resulted in numerous traffic slowdowns and shutdowns – and emerged as an important social issue.
In Japan, a similar surge in infrastructure development took place alongside the nation's rapid economic growth period of the1950s through the 1970s. This statistic is already raising concerns about three major types of distress that severely impact bridge strength capacity. They are fatigue in steel structures and deck plates, salt corrosion and alkali silica reaction (ASR) to concrete structures. We have to rush to stay ahead of the problems caused by such decay.
Therefore CAESAR applies a scientific trial approach including anatomic and pathologic elements aimed at fighting decay in the nation's highway bridges and conducts its research projects using a microscopic level of management – that is, a customized diagnosis, prognosis, and rehabilitation for individual older bridges aimed at preventing critical failure.
In Japan, the 1995 Hyogo-ken Nanbu (Kobe) earthquake (Mj7.3) damaged infrastructure and a number of bridges were toppled. The urgent possibility of future large-scale earthquakes is a national concern, many of which are predicted to occur with a magnitude order of 7 to 8 on the intensity scale. The PWRI has been the center of excellence in disaster mitigation technology for highway bridges against large earthquakes. Now CAESAR will continue to develop new comprehensive technologies to make Japan resilient against earthquakes.
Currently, visual inspection is the standard used to make such determinations. This needs to be upgraded in order to locate problems in components which are not readily visible – such as those submerged in water.
In response, CAESAR has been testing nondestructive tools such as ultrasonic transducers (UTs) as part of efforts to detect defects in metal deck plates and a separate self-potential method to detect corrosion in concrete reinforcement bars.
CAESAR also has projects dedicated to studying the mechanism of damage occurrences. Such efforts are necessary in order to invent cutting-edge diagnostic examinations that will accurately reveal the current structural condition and remaining performance of an existing highway bridge. A separate CAESAR project aims at measuring the influence of a particular part's structural deficiency on the overall bridge behavior.
In terms of disaster mitigation, CAESAR supports national initiatives, including the development of a systematic upgrade program for the seismic performance of the highway bridge group on emergency transportation highway networks.
Seismic vulnerability assessment and retrofit techniques for existing bridges include structural dynamics, nonlinear soil-foundation interactions, soil liquefaction and liquefaction-induced lateral soil spreading – all of which must be considered when evaluating seismic performance.
Needless to say, CAESAR will disseminate the results of all its research, as well as the information gained from its past experience in earthquake damage control, into its practical application of seismic vulnerability assessments and disaster mitigations as well as in the design of new and replacement structures.
Still other CAESAR projects are aimed at developing reinforcements or rehabilitation techniques that will provide customized maintenance programs for individual bridges. CAESAR also has started a new project to conduct follow-up examinations for bridges that were rehabilitated or strengthened in the past in order to measure the effectiveness of such countermeasure works over time.
CAESAR also has projects for seeking bridge types and structural details for improving the long-term performance.
Another CAESAR's important goal is to provide post-earthquake emergency inspection and recovery tools for highway bridges that will allow them to return to emergency service quickly. This is necessary because, even though a large-scale earthquake causes damage to highway bridges, it is vital to return them to service as soon as possible in order to facilitate rescue efforts and transport emergency aid and supplies.
To ensure nation's bridges are structurally safe, the incorporation of ongoing technology developments from private and academic sectors is crucial.
To encourage such efforts, as well as to guarantee the quality level of individual technologies, the Center sets out not only the performance requirements, it also develops verification measures.
For example, the PWRI's standard tests for the fatigue durability of deck plates and the seismic ductility for piers have been gaining wide acceptance.
Furthermore, the Center has been preparing for the next revision of the Japanese Specifications for Highway Bridges, which will be based on a performance-based specification concept, involving a reliability design concept.
CAESAR serves as a portal site to facilitate the exchange of information and knowledge between Japan and international communities, as well as to collaborate with other foreign institutions. For example, under the framework of the Panel on Wind and Seismic Effects, UJNR (US-Japan Cooperative Program in Natural Resources), CAESAR co-organizes US-Japan Bridge Engineering Workshop with the US Federal Highway Administration and shares the knowledge, experience, initiatives, and research results with other US and Japanese highway administrators, national institutes, and academic and industry partners. CAESAR also has frequent communications with foreign government institutions and universities, in which some of them are under agreements. Furthermore, CAESAR also dispatches researchers and provides technical cooperation in response to requests from foreign highway administrators via the Japan International Cooperation Agency (JICA).
As the nation's primary promoter and guarantor of highway bridge excellence, the Center collaborates with voluntary public, academic and private sector organizations engaged in research activities.
Address: 1-6 Minamihara, Tsukuba, Ibaraki, Japan 305-8516