Papers - OBATA Makoto
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IMPROVEMENT OF STRESS-STRAIN RELATION UNDER MULTIAXIAL LOADING OF RUBBER FOR BEARINGS Reviewed
Makoto Obata, Takemasa Ebisawa, Yoshiaki Goto
Journal of Japan Society of Civil Engineers Ser A1 (Structural Engineering & Earthquake Engineering (SE/EE)) 76 ( 2 ) 320 - 330 2020.08
Authorship：Lead author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Japan Society of Civil Engineers
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Makoto Obata, Taro Murakami
Kozo Kogaku Ronbunshu. A (Journal of Structural Engineering. A) 60 ( A ) 596 - 604 2014.04
Authorship：Lead author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Japan Society of Civil Engineers
It is important to estimate corrosion environment of steel bridges for an appropriate corrosion prevention and maintenance program. Estimation of environment has heavily depended on insitu observation and many data have been collected. However, versatile numerical approaches to this problem has not fully pursued yet. To this end, observation of airborne sea salt particles was performed with a standard low volume sampler (JIS Z 8814) beginning from April, 2013 to August, 2013 in the city of Nagoya and compared analytical estimation. A meso scale meteorological analysis employed here is WRF-Chem Ver. 3.4. Although WRF uses land use and terrain data based on USGS by default, the data is sometimes incorrect in Japan and yields inaccurate results especially for wind. Introduction of more accurate land use and geographic data supplied by the Geospatial Information Authority of Japan improves accuracy of basic meteorological data and therefore concentration of airborne sea salt particles. Other factors affecting accuracy of airborne sea salt concentration will also be discussed.
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Global-local approach to numerical simulation of adhesion of seasalt particles on bridge girders Reviewed
Makoto Obata,Li Guotai, Yasunari Watanabe, Yoshiaki Goto
Journal of Structural Engineering A 58 668 - 678 2012.03
Authorship：Lead author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Japan Society of Civil Engineers
It is important to estimate corrosion environment of steel bridges for a proper corrosion prevention and maintenance program. Adhered sea-salt particulate matter (SSPM) is an influential factor especially in coastal areas. To this end, it is better to know the adhesion behavior of SSPM to bridge girders. The objective of this manuscript is to pursue numerical method to simulate the adhesion behavior of salt particles oriented from sea surface. Specifically, two scale approach is proposed. Mesoscale Meteorological Analysis and Lagrangian type two phase flow analysis are used in global and local analyses respectively. The comparisons between the numerical and observed results showed that the numerical analysis can reproduce essential behaviors of airborne SSPM.
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Numerical analysis of fracture phenomena observed in a locally buckled circular steel column Reviewed
Hideyuki Fujiwara, Makoto Obata, Yoshiaki Goto
Journal of Structural Engineering A 58 310 - 318 2012.03
Language：Japanese Publishing type：Research paper (scientific journal)
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Construction of a practical finite element model from point cloud data for an existing steel truss bridge Reviewed
Nao Hidaka, Naofumi Hashimoto, Kazuya Magoshi, Tetsuya Nonaka, Makoto Obata, Ei Watanabe
Proceedings of 23° International Conference on Construction Applications of Virtual Reality 1155 - 1166 2023.11
Language：English Publishing type：Research paper (international conference proceedings)
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Construction analysis model of steel bridge by using point cloud data and accuracy verification Reviewed
Hidaka Nao, Hashimoto Yoshifumi, Nakamura Masaki, Magoshi Kazuya, Nonaka Tetsuya, Obata Makoto
Journal of structural engineering 69A 637 - 647 2023.04
Language：Japanese Publishing type：Research paper (scientific journal)
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YIELDING STEEL DAMPERS TO REPLACE CONCRETE SHEAR KEYS FOR SEISMIC RETROFIT OF BRIDGES WITH UNEQUAL HEIGHT PIERS Reviewed International coauthorship International journal
Nailiang Xiang, Y Goto, Makoto Obata, M. Shahria Alam, Jianzhong Li
Proc. 17th World Conference on Earthquake Engineering 2020.09
Language：English Publishing type：Research paper (international conference proceedings)
Irregular multi-span continuous bridges with unequal height piers are commonly adopted in mountainous areas when crossing steep-sided valleys. As common practice, economical unbonded laminated rubber bearings and concrete shear keys are usually installed in such bridges as superstructure-to-substructure connections. In strong earthquakes, the sliding of rubber bearings and the shear key failure are mostly expected, which may weaken the seismic resistance of the irregular bridges. The current study is mainly divided into three parts: the first one investigates the effect of concrete shear keys on the transverse seismic performance of the irregular bridges by incorporating the potential sliding of laminated rubber bearings; the second part proposes the concept of using yielding steel dampers to replace shear keys for mitigating the irregular seismic responses of the unequal height bridges with the practical design method being developed; the third part demonstrates the retrofit effectiveness by conducting nonlinear time-history analyses. The results indicate that the existence of concrete shear keys increases the bridge irregularity by inducing a significant in-plane superstructure rotation response around the vertical axis, posing nonuniform displacement demands at the substructures. The shear keys also contribute to the unbalanced ductility demands on the unequal height substructures, rendering the taller piers more vulnerable to the seismic damages. This differs from the case with fixed bearings, where the shorter piers are more subjected to damages. Using yielding steel dampers that are appropriately designed as per the proposed method, the seismic rotations of the bridge superstructure can be considerably mitigated with a relatively uniform superstructure movement maintained. The steel dampers are also effective in distributing the inertia forces among the unequal height piers. The effectiveness of yielding steel dampers replacing concrete shear keys in unequal height irregular bridges is successfully verified by the results from the numerical simulation.
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Shake-table tests of an innovative structural fusing system for small to medium-span highway bridges
Nailiang Xiang, Y Goto, Makoto Obata, M. Shahria Alam, Jianzhong Li
Proc. 17th World Conference on Earthquake Engineering 2020.09
Language：English
Irregular multi-span continuous bridges with unequal height piers are commonly adopted in mountainous areas when crossing steep-sided valleys. As common practice, economical unbonded laminated rubber bearings and concrete shear keys are usually installed in such bridges as superstructure-to-substructure connections. In strong earthquakes, the sliding of rubber bearings and the shear key failure are mostly expected, which may weaken the seismic resistance of the irregular bridges. The current study is mainly divided into three parts: the first one investigates the effect of concrete shear keys on the transverse seismic performance of the irregular bridges by incorporating the potential sliding of laminated rubber bearings; the second part proposes the concept of using yielding steel dampers to replace shear keys for mitigating the irregular seismic responses of the unequal height bridges with the practical design method being developed; the third part demonstrates the retrofit effectiveness by conducting nonlinear time-history analyses. The results indicate that the existence of concrete shear keys increases the bridge irregularity by inducing a significant in-plane superstructure rotation response around the vertical axis, posing nonuniform displacement demands at the substructures. The shear keys also contribute to the unbalanced ductility demands on the unequal height substructures, rendering the taller piers more vulnerable to the seismic damages. This differs from the case with fixed bearings, where the shorter piers are more subjected to damages. Using yielding steel dampers that are appropriately designed as per the proposed method, the seismic rotations of the bridge superstructure can be considerably mitigated with a relatively uniform superstructure movement maintained. The steel dampers are also effective in distributing the inertia forces among the unequal height piers. The effectiveness of yielding steel dampers replacing concrete shear keys in unequal height irregular bridges is successfully verified by the results from the numerical simulation.
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Passive seismic unseating prevention strategies implemented in highway bridges: A state-of-the-art review Reviewed International coauthorship International journal
Nailiang Xiang , Yoshiaki Goto, Makoto Obata, M. Shahria Alam
Engineering Strucures 194 77 - 93 2019.09
Language：English Publishing type：Research paper (scientific journal) Publisher：Elsevier
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Analysis of rubber bearing behavior with material deterioration Reviewed International journal
Makoto Obata, Yoshiaki Goto
Proceedings of ICASS2018 2018.12
Language：English Publishing type：Research paper (international conference proceedings)
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Analysis of rubber bearings with mullins effect uner cyclic loading Reviewed
Makoto Obata, Chisa Koiwa, Yoshiaki Goto
１ ( １ ) 335 - 338 2017.07
Authorship：Lead author Language：Japanese Publishing type：Research paper (conference, symposium, etc.)
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Ultimate Behavior of Steel and CFT Piers in Two-Span Continuous Elevated-Girder Bridge Models Tested by Shake-Table Excitations Reviewed International journal
Yoshiaki Goto, Takemasa Ebisawa, Makoto Obata, Jianzhong Li, Yan Xu
JOURNAL OF BRIDGE ENGINEERING 22 ( 5 ) 2017.01
Language：English Publishing type：Research paper (scientific journal) Publisher：ASCE-AMER SOC CIVIL ENGINEERS
Bidirectional shake-table tests were performed on two types of relatively large two-span continuous elevated-girder bridge models. One was supported on thin-walled hollow steel (HT) piers, and the other was supported on concrete-filled tubular (CFT) piers. The CFT piers were made by filling the hollow columns of the HT piers with normal concrete. One objective of the shake-table tests was to acquire basic data to establish an advanced seismic design method of the HT and CFT piers under bidirectional horizontal seismic accelerations, considering the interaction between the piers, rubber bearings, and a superstructure. The other objective was to experimentally confirm the effectiveness of upgrading the elevated-girder bridges with the HT piers by using CFT piers. It was shown by the present tests that the ultimate state of the respective HT piers in the bridge model was predicted reasonably well by the interaction equation expressed in terms of the multiaxial force and moment components acting at the top of the columns. As soon as all the piers reached their ultimate states, the entire physical bridge model with the HT piers started to collapse in the transverse (TR) direction. Because of the load redistribution between the HT piers in the bridge model during the shake-table test, the energy dissipation capacity of the piers increased considerably compared with that evaluated by the conventional shake-table test on single cantilever column models with a mass fixed to their top. The physical bridge model with the CFT piers exhibited an excellently upgraded seismic performance (i.e., small local buckling deformations of the piers and negligibly small residual sway displacements of the bridge system) despite the increased input acceleration wave with an amplitude 1.5 times larger than that used for the physical bridge model with the HT piers. This upgraded performance of the CFT piers was due to their enhanced energy dissipation capacity and unique local buckling restraining and/or restoring behavior.
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鋼製橋脚で支持された連続高架橋における積層ゴム支承の水平2方向地震動下の挙動特性 Reviewed
奥村徹，海老澤健正，後藤芳顯，小畑誠，Jianzhong Li, Yan Xu
第１８回性能に基づく橋梁等の耐震設計に関するシンポジウム論文集 1 49 - 56 2015.07
Language：Japanese Publishing type：Research paper (other academic)
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円形断面鋼製橋脚を持つ連続高架橋模型の２方向加振実験のFE解析と終局挙動特性 Reviewed
海老澤健正，後藤芳顯，小畑誠，Jianzhong Li，Yang Xu
第１８回性能に基づく橋梁等の耐震設計に関するシンポジウム論文集 1 ( 1 ) 57 - 64 2015.07
Language：Japanese Publishing type：Research paper (other academic)
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Effects of land use data on numerical simulation of corrosive environment caused by airborne sea salt particles Reviewed
Makoto Obata, Masato Fukushima, Seiya Suzuki
Proc. the 7th ISSS 1 ( 1 ) 228 - 229 2013.11
Authorship：Lead author Language：English Publishing type：Research paper (international conference proceedings)
Corrosion of steel bridges in a coastal area is mainly caused by sea salt particles coming from ocean. Appropriate estimation of such airborne sea salt particles is critically important for a proper anticorrosion management program. At present, the most reasonable simulation of sea salt concentration can be performed as a part of meso scale meteorological analysis. However, accuracy of such simulation is not verified well so far. The objective of this work is to verify and to improve the accuracy of numerical simulation of airborne sea salt particles by introducing enhanced land use data. Other factors affecting accuracy of airborne sea salt concentration will also be discussed.
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Numerical simulation of adhesion of sea-salt particles Reviewed
Makoto Obata, Li Guotai, Yasunari Watanabe, Yoshiaki Goto
Structure and Infrastructure Engineering 52 398 - 408 2013.01
Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)
It is important to estimate corrosion environment of steel bridges for a proper corrosion prevention and maintenance
program. The governing factors of corrosion are temperature, humidity and various dusts on the surfaces. Among them, the
adhered sea-salt particulate matter (SSPM) is most important and therefore airborne SSPM near a bridge site must be
considered in its design. To prevent degradation of protective paint, removal of adhered SSPM by wash out has been tried in
some bridges. To this end, it is better to know the adhesion behaviour of SSPM to bridge girders. The objective of this
manuscript is to pursue numerical method to simulate the adhesion behaviour of salt particles oriented from sea surface.
Specifically, two scale approach is proposed. Mesoscale meteorological analysis and Lagrangian type two phase flow
analysis are used in global and local analyses respectively. The comparisons between the numerical and observed results
showed that the numerical analysis can reproduce essential behaviours of airborne SSPM.DOI： 10.1080/15732479.2012.757328
Other Link： http://www.tandfonline.com/action/showAxaArticles?journalCode=nsie20
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Numerical Estimation of Corrosion Environment by Airborne Sea Salt Particles Reviewed
Liu Chen Chen, Makoto Obata
Advanced Materials Research 599 220 - 223 2012.11
Language：English Publishing type：Research paper (scientific journal)
Anticorrosion of steel bridges has been an increasingly important problem in Japan. For a proper anticorrosion
and maintenance program, it is important to estimate corrosion environment of steel bridges. In Japan, airborne
sea salt generated from ocean is a predominant factor. Authors have been working on establishing a consistent
framework to estimate corrosion environment numerically. It consists of a local and a global approach. While
adhesion of airborne sea salt particles to bridge structures are simulated locally by a CFD analysis, the large
scale analysis yields a boundary conditions of the local analysis and is given by a part of a mesoscale
meteorological analysis. The objective of this work is to numerically investigate reliability of such large scale
analysis in estimation of corrosion environment caused by airborne sea salt particles. -
Numerical Prediction of Ductile Crack Initiation in a Steel Column under Cyclic Loading Reviewed
Makoto Obata, Hideyuki Fujiwara, Yoshiaki Goto
Proc. of the 10th international conference on advances in steel concrete composite and 1 ( 1 ) 207 - 214 2012.07
Language：English Publishing type：Research paper (international conference proceedings)
DOI： 10.3850
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Numerical simulation of adhesion of sea salt particles for anticorrosion of steel bridges Reviewed
Makoto Obata, Shunya Yokoi, Li Guotai, Yoshiaki Goto
Proceeings of ASEM 1 ( 1 ) 5262 - 5269 2011.09
Authorship：Lead author Language：English Publishing type：Research paper (international conference proceedings)
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Investigation of corrosion environment of a steel bridge for effective washing of girders Reviewed
Kazutoshi Nagata, Kota Ito, Jin Yamada, Makoto Obata and Shigenobu Miyamoto
Journal of Structural Engineering 57 2011.03
Language：Japanese Publishing type：Research paper (scientific journal)
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