Yoshito Itoh

Multiobjective optimization of bridge deck rehabilitation using a genetic algorithm

The solution methods of multiobjective optimization have undergone constant development over the past three decades. However, the methods available to date are not particularly robust. Because of the complicated relationship between the rehabilitation cost and deterioration degree of infrastructure systems, it is difficult to find a near-optimal solution using common optimization methods. Since genetic algorithms work with a population of points, they can capture a number of solutions simultaneously and easily incorporate the concept of Pareto optimality. In this paper a simple genetic algorithm with two additional techniques, Pareto optimality ranking and fitness sharing, is implemented for the deck rehabilitation plan of network-level bridges, aiming to minimize the total rehabilitation cost and deterioration degree. This approach is illustrated by a simple example and then applied to a practical bridge system with a large number of bridges.

Using CO2 emission quantities in bridge lifecycle analysis

Abstract In recent years, new types of bridges have continued to appear with the development of new construction technologies and functional requirements in Japan. However, lifecycle analysis was rarely used to evaluate such new types of civil infrastructures. In this research, a general lifecycle assessment methodology is modified for evaluating new types of civil infrastructures. Furthermore, this modified methodology is applied in comparing the lifecycle performance of a conventional bridge and a minimized girder bridge, which is a new type of bridge constructed in the second Tokyo–Nagoya–Osaka expressway. Finally, accelerated exposure tests of steels and seismic isolation bearings are addressed and test results on the durability of these materials are used to perform the lifecycle analysis.

Accelerated cyclic corrosion testing of structural steels and its application to assess steel bridge coatings

Purpose – The purpose of this study was to determine correlation between an accelerated cyclic corrosion test (S6‐cycle test) specified in Japanese Industrial Standards K5621 and field exposure tests, and to open up applications of the accelerated tests in various regional environments.Design/methodology/approach – The S6‐cycle corrosion test was carried out on structural steels for 30, 60, 90, 120 and 150 days and metal coating films for 100, 200 and 300 days. Comparing the weight loss of the steels with 1‐, 3‐, 5‐ and 9‐year field exposure test data at 31 sites in Japan. Correlation of the S6‐cycle tests to the field exposure tests was determined by acceleration coefficients.Findings – The correlation between the S6‐cycle test and the field test on uncoated structural steels can be determined by acceleration coefficients based on flying salt amount. The coefficients were applicable for durability prediction of uncoated, zinc hot‐dip galvanized and painted steels.Research limitations/implications – In de...

Information technology applications for bridge maintenance management

Infrastructure maintenance management has become a challenge field for civil engineers and government managers because of the increasing number of deteriorated structures, their complicated spatial locations, the improved service requirements, the limited maintenance budgets and so on. Therefore, maintenance management approaches have been developed for civil infrastructures such as bridges and roads over the past several decades, but most of such approaches focused on one specific structure only – project‐level maintenance management. Now, there are increasing demands and appropriate conditions for network‐level maintenance management for civil infrastructure systems. Aims to explore such a maintenance management approach by integrating and applying the current information technologies, which include the database management system, geographic information system, genetic algorithm and the Internet. Several possible applications of each technology are discussed for solving real‐world problems.

Comparative study of optimized and conventional bridges: Life cycle cost and environmental impact

In recent years, environmental problems have become serious issues in the whole world. Researchers and practical engineers in civil engineering have to pay enough attention to the environmental impacts as well as to the function, safety, cost and aesthetics at all lifecycle stages of civil infrastructures. In this study, the estimation is made for the lifecycle CO2 emission, and the lifecycle cost of both the conventional bridges and the minimum maintenance bridges. According to the results concluded from this research, the lifecycle environmental analysis and the lifecycle cost analysis may deduce various conflicting bridge design and management schemes, therefore, the bridge engineers and government managers should consider the environmental impact as a fundamental criterion in addition to the lifecycle cost during the decision-making process for the bridge lifecycle management. In addition, the characteristics of lifecycle environmental impact and lifecycle cost of bridges using new technologies have advantages compared with those of the conventional bridges.

Aging Behaviors of Natural Rubber in Isolation Bearings

This paper attempts to reveal the aging behaviors of natural rubber (NR) used in isolation bearings. Using various degradation factors like thermal oxidation, ultraviolet, ozone, low temperature ozone, salt water and acid rain, a series of environmental accelerated aging tests were conducted to investigate the aging characteristics. From the test results, it was clarified that the thermal oxidation is the dominant degradation factor, which hardens the rubbers and results in a significant drop of performance. This study is fundamental to predicting the lifecycle of NR isolation bearings.

Anticorrosive performance of repair painting as remedy for deterioration in metallised steel

Abstract When the various metallic coating systems applied on steel bridges deteriorated, they may need to be repaired by painting because onsite metallic recoating is very difficult. In order to examine the performance of repaired painting on steel plates with the remains of four types of deteriorated metallic coating systems, cyclic corrosion tests were performed in combination with exposure to an acid rain spray. It was found that a residual coating of zinc hot dip galvanising acted as a helpful substrate for the repair painting. Residual coatings of a zinc–aluminium thermal spray and of a zinc–aluminium pseudoalloy did not have such an effect. The residue of an aluminium thermal spray had a positively harmful influence on the repair painting over it. The degree of this influence was correlated with the thickness of the residual coating.

Minimum Thickness of Welding Patches to Recover Structural Performance of Steel Pipe Piles under Compression

This paper presents an analytical study on a minimum patch thickness necessary to fully recover structural performance of corrosion-damaged pipe piles under axial compressive loads using welding repair. Load transfer mechanism, the repaired stiffness and strength of pipe piles are examined. An accurate calculation of load share ratio of patch plates considering weld stiffness is derived, and the results are compared with experimental results and finite element analysis results. The minimum thickness of patch plates to fully recover the stiffness and the design strength of the corrosion-damaged piles to their intact state considering the existing loads is proposed.

Study on environmental durability of rubber bearing for bridges

IABSE Symposium, Towards a Better Built Environment-Innovation, Sustainability, Information Technology, Melbourne, Australia, September 11-13, 2002（CD-ROM). 2002, p.268-269

Experimental and numerical analysis database on structural stability

Test data are an invaluable resource for structural engineering research. In this paper, a numerical database system is built for material properties of steels, steel columns, steel beams and unstiffened steel plates, etc. The database is used to clarify the strength variations of material properties and to obtain the mean value and the coefficient of variation of each member strength. In addition, these values are compared with existing design formulas. The database is further developed in the shape of a structural test information-based system. This system includes database functions, test data evaluation functions, reference retrieval functions and technical terms explanation functions. The usefulness of the knowledge base approach for representing the test data is proved and the potential and problems of the system are clarified.