Home Member Research Achievement Access Link English

Research
 
A large-scale computational model for deteriorated reinforced concrete structure
(3D RBSM and Truss Network)

Aging of infrastructure has become a social problem in Japan because the year for maintenance will be reached soon since the post-war reconstruction in the past half century. In addition, it was predicted that an enormous earthquake will occur in the future and the response prediction of the existing deteriorated structures due to this enormous earthquake is necessary.

Numerical simulation can be a beneficial tool for this purpose. In our research group, a simulation system of 3D Rigid Body Spring Model (RBSM) has been developed. As a continuation of the current active research on 3D RBSM, the future research will be focused on the application to the real reinforced concrete structures which are the deteriorted RC structures at site. In reality, RC structures are subjected no only to mechanical loading but also to environmental conditions. To broaden the applicability of 3D RBSM, "Truss-network" is being developed in our research group for modeling substance movement due to the environmental exposure. A combination of both simulations could be a powerful tool for assessing the deteriorated RC structures at site and predicting the life span of the deteriorated structures.

 



Conversion of Concrete to Sludge around Deformed Bars due to Liquid Water and Repeated Loads and Its Effect on Pull-out Failure

In the actual environments, civil engineering structures are frequently subjected to various repeated loading and at the same time are subjected to liquid water from the external surface (hereafter referred to as external liquid water), such as rainwater or snow water. In Japan, problems of fatigue in the RC deck slabs of road bridges have become serious since the 1960s, especially in the Tohoku Region, and in recent years a granulation phenomenon has been found in which the cementitious component of concrete is washed out and separated from the aggregates. Against this background research has been carried out on the fatigue properties of reinforced concrete (RC) deck slabs focusing on the effect of external liquid water.

Research into the effect of external liquid water on the fatigue properties at the material level in the past was carried out, in which the fatigue properties in water have been investigated, and it has been reported that the fatigue life of concrete in water is greatly reduced compared with the properties in air. On the other hand, no research could be found investigating the effect of external liquid water on the bond fatigue properties of reinforcement. In our research group, In this research, fatigue pull-out tests of deformed bars have been carried out using the presence or absence of external liquid water, matrix type and strength, loading method, and the presence or absence of a mechanical anchorage as experimental parameters, in order to determine the effect of external liquid water on the bond fatigue properties of deformed bars in concrete. The characteristics of the pull-out failure mode of deformed bars associated with formation of sludge were investigated by measuring the load, the pull-out displacements, and the strain distribution of deformed bars.

 



Cross-ministerial Strategic Innovation Promotion Program (SIP)

The Cross-ministerial Strategic Innovation Promotion Program (SIP) is a Japanese project led by the Cabinet Office's Council for Science, Technology and Innovation. The project was founded to promote scientific and technical innovation through management that extends beyond the boundaries of existing fields and government departments, ministries and agencies. The project will tackle ten major global issues that are also social issues of truly critical importance to the Japanese people and issues that can help to revitalize the Japanese economy. Each issue will have a Program Director (PD) who will exercise firm leadership and play a central role in promoting collaboration among industry, academia, and government, as well as pursue comprehensive research and development that takes into consideration the entire process from basic research through practical application and commercial development. SIP will provide a powerful impetus to the scientific and technical innovation that is the driving force behind economic growth and dramatic change in society.

Scientific and technical innovation are essential for revitalizing the Japanese economy and achieving sustainable economic growth. Under the leadership of the Prime Minister and the ministers in charge of science and technology policy, the Council for Science, Technology and Innovation plans and coordinates policy for basic and comprehensive science, technology, and innovation based on a broad perspective of science and technology in Japan. The Cross-ministerial Strategic Innovation Promotion Program (SIP) was established as part of this effort with the aim of strengthening the management functions (headquarter's functions) of the Council for Science, Technology and Innovation. It is designed to be one of the three main pillars of policy along with the Strategic Formulation of Overall Governmental Science and Technology Budget program and the Innovative Research and Development Promotion Program (ImPACT) program.

Our research group participates of international activities of "Infrastructure maintenance, renewal, and management". The following activites have been conducted.
(1) Development of educational programs of engineers for infrastructure maintenance in Vietnam
(2) SIP Special Session held in EASEC-14
(3) The 3rd SIP International Seminar in Phnom Penh, Cambodia

 



Science and Technology Research Partnership for Sustainable Development (SATREPS)

With Myanmar and its cities under large-scale development, the risk of disasters increases due to expansion of the urban population and climate change. This project monitors changes in the ground, terrain, and urban environment associated with the development process, and develops a system for assessing vulnerabilities to potential disasters in Myanmar. The project aims to identify disaster risks in advance to contribute to the formulation of regional development planning and disaster prevention countermeasures as well as to support the strengthening of the Myanmar government's disaster response capabilities.

Our research group participates of international activities as "Infrastructure Group" for SATREPS project. The primary activities can be clasified into:
(1) Proposal of simple monitoring systems
(2) Deterioration mechanism and countermeasures for the bolt-ruptured bridge
(3) Evaluation of road roughness in Yangon
(4) Development of the existing bridge database with GPS
(5) Verification of infrastructure management system

 



A Study on Retrofitted Damaged Reinforced Concrete Corbel Using Various Methods

Reinforced Concrete (RC) corbel is low span cantilever structure used basically to support direct vertical load, and horizontal load (lower than vertical load) due to thermal shrinkage. It is recommended that outer edge of bearing pad should not be projected beyond the straight portion of main tension bar of corbel and depth of corbel at corresponding position should never be less than half of its depth at the base (BS, 1997 & ACI, 2008). Mainly these provisions are provided to ensure desired failure modes in corbel avoiding premature failures. But to such tiny details, it might be common not to obey such provisions, which may lead to unsatisfactory structural performance. Design and construction with poor structural detail is more likely to be seen in underdeveloped countries with exception in developed one.

In a field study, several corbels were found to be failed at lower load than their corresponding design values due to faulty design of bearing pads. Bearing pad in such typical case was found to be extended to the edge of corbel resulting premature outward splitting parallel to the bent bar. Such case resulting premature local failure in corbel is targeted in this study and scenario is termed as 'Local Failure Criterion'. Practically, we can't simply demolish such corbels considering its structural importance and cost. Hence, it is necessary to propose appropriate retrofitting solution for such corbels, and equally important to identify parameters that governs the behavior of retrofitted corbels. In our research group, further retrofitting method which is eficient, simple, and easy is proposed throught simulations and experiments.

 



繊維補強コンクリートの多軸応力下における力学性能

引張に弱いというコンクリートの欠点を、セメントに繊維を混入することで引張性能を高める繊維補強コンクリートがある。 その中でも近年注目されている材料に高性能セメント複合材料(HPFRCC)があり、複数ひび割れの発生により優れた靱性能を発揮する。 しかし、ひび割れ発生後のせん断性能は低く、現在は補修・補強等限定的な用途に留まっており、構造性能には未解明な点が多い。 そこで、本研究では、せん断性能を高める材料の考案・開発から、構造レベルでの実験、さらには数値解析を通し研究を進めており、HPFRCCの実構造物への適用を目指している。
The Mechanical Performance of High-Performance Fiber-Reinforced Cementitious Composite Concrete under Multiaxial Stress Conditions

In Japan, concrete is a dominant structural material in the engineered construction. It is well known that concrete has more advantages than other materials. Concrete is strong in compression but weak in tension. Thus, cracks develop whenever the tensile stresses, caused by loads, excess the tensile strength of the concrete and the brittle failure mechanism tends to develop while concrete is subjected to the tensile stress. Generally, steel reinforcements are used to improve the tensile performance of the concrete. In recent years, fiber-reinforced cementitious composites (FRCC) has been developed as an alternative for the replacement of conventional steel reinforcements.

High-Peformance fiber-reinforced cementititous composite (HPFRCC) is a class of fiber-reinforced cementitious composites (FRCC) that exhibits multiple cracks and pseudo-strain-hardening behaviour under tension stress. One example of the HPFRCC is Engineered Cementitious Composite (ECC) that contains fine-graded materials and a moderate amount (2-3%) of short random polymeric fibers. Many experiments have been conducted to investigate the tensile behaviour of ECC and prove that the ductile failure mechanism can be achieved, due to the occurance of multiple cracks. In the other hand, the performance of the crack-shear transfer of ECC is low. As the result, the use of ECC is still limited in retrofitting. Therefore, some researches are still needed to improve the shear performance of ECC. Further research through experiment and numerical analysis is developed in our laboratory.

 



鉄筋コンクリート部材定着機構の解明と設計の合理化

鉄筋コンクリート構造物の耐震性能への要求が高まり,構造物中の鉄筋量は増加している。結果,多方向からの部材が集中する柱梁接合部などで鉄筋が集中(過密配筋)し,鉄筋組立時間の増大や施工不良による品質低下といった問題が生じている。しかし,多方向かつ複雑に配置された鉄筋とコンクリート間での挙動は未だ明確ではなく,過密配筋を生じさせる現状の設計基準を変更できずにいる。この研究では,実験・数値解析を通して複雑な配筋状態でのコンクリート構造部材の内部挙動を解明し,過密鉄筋の解消をしうる合理的な設計法の提案を目指している。
A Rational Design Method for Reinforced Concrete Beam-Column Joint

As many buildings experienced failures due to the previous earthquakes, the performance requirements of the building in the seismic code are more stringent than the requirements in the previous code. To satisfy the requirements, a large number of steel reinforcements must be placed in the concrete member. As the result, a reinforcement congestion, especially in beam column joints where reinforcements meet from many directions, is occurred. A reinforcement congestion can cause difficulties during the compaction of the concrete and furthermore it can result a poor quality of construction. In the other hand, the behaviour of reinforced concrete where the reinforcements are arranged multidimensional that cause the complex stress condition and crack propagation, has not been clarified well yet. So that, there is still a possibility to reduce the reinfocement congestion, especially in the beam column joints. Our laboratory conducts the research by numerical simulation at meso scale to propose a more rational design method in reducing reinforcement congestion based on the mechanical behavior..

 



杭圧入施工中の地盤内挙動の解明と施工の合理化

圧入工法は杭施工方法の一つであり、杭を油圧力により静的に貫入させる。低振動、低騒音、省スペース施工が可能であるという利点から、主に都市部などの狭隘な空間における利用が盛んである。一方で、圧入工法が周辺地盤に与える影響は未だ解明されていない。既往の研究では、土圧計を用いた矢板圧入実験により、 地盤内構造物への影響が検討されているが、特に礫を含む多層地盤における圧入過程の地盤内変形や応力状態は十分に把握されていない。 この研究では、離散的数値解析手法を用いt均質場・非均質場における圧入中の地盤内部の変形や応力状態を把握することを試みている。また、貫入中の地盤内変形計測技術の開発も進めている。 数値解析と計測を通し、貫入中の地下空間の状態を可視化し、効率的な圧入施工法の提案と合理的な地盤性能評価を可能とすることを目指している。

Press-in method is a revolutionary technique in pile installation technology. It uses hydraulic rams to ‘push’ piles/sheet piles into the ground; enabling the piles to be installed with minimal noise and vibration compared to traditional dynamic methods. The compact-size of the machine and its self-moving feature allow the construction work to be carried out in places with limited access or in the areas where environmental disruption is prohibited. However, since the method allows the piles to be installed near existing structures, an impact on the structures in terms of earth pressure will be the matter of concern. This study measure soil displacement during pressing-in installation with inclinometer, which is mainly used for measuring the land slide. This research presents an approach by discrete analysis model to estimate the internal deformation and stress condition in soil during the press-in driving in homogeneous and heterogeneous layers. Rigid Body Spring Model (RBSM), which is one of discrete and static analysis methods, is adopted for the simulation in this study. Analysis results are compared with the experiment in sand layer and in aggregate layer.

 


 

少子高齢化が進む中山間地域の生活と社会基盤の維持管理


日本では、1970年に高齢化率が7%を超え、高齢化社会に突入し、現在では高齢化率は21%を超え、世界一の高齢化国となっている。この高齢化の傾向は、特に中山間地域で顕著であり、「限界集落」と呼ばれる高齢化率50%を超える地域が増えている。そのような地域では、自治体の財政悪化、社会基盤の維持管理の問題が生じ、その結果、住民の日常生活に支障が出ている。  この問題を都道府県別にみると、高知県は28.2%(全国平均;23.1%、ともに2010年)と特に高い高齢化率を示している。高知県内でも、県庁所在地である高知市に人口が集中し、その他の地域は急速に少子高齢化・過疎化が進行している。  本研究では、高知県吾川郡仁淀川町を対象地とし、住民にとっての道路の重要性と危険性や住民の買い物行動と移動、住民同士の繋がりと豊かさに関する調査などを行っている。 今後更に深刻化すると予想される少子高齢化・過疎化問題を抱える地域のあり方を提示することを目標としている。

English version is under construction.

 

 


Copyright(c) 2013- Nagai Laboratory, Institute of Industrial Science,The University of Tokyo. All rights reserved.
サイトの内容を無断で複写・複製することを禁じます.
東京大学生産技術研究所 長井研究室