Pang-jo Chun

Bridge Damage Severity Quantification Using Multipoint Acceleration Measurement and Artificial Neural Networks

The deterioration of bridges as a result of ageing is a serious problem in many countries. To prevent the failure of these deficient bridges, early damage detection which helps us to evaluate the safety of bridges is important. Therefore, the present research proposed a method to quantify damage severity by use of multipoint acceleration measurement and artificial neural networks. In addition to developing the method, we developed a cheap and easy-to-make measurement device which can be made by bridge owners at low cost and without the need for advance technical skills since the method is mainly intended to apply to small to midsized bridges. In addition, the paper gives an example application of the method to a weathering steel bridge in Japan. It can be shown from the analysis results that the method is accurate in its damage identification and mechanical behavior prediction ability.

New Combined High and Low-Cycle Fatigue Model to Estimate Life of Steel Bridges considering Interaction of High and Low Amplitudes Loadings

A new model is proposed in this paper for the estimation of the life of bridges subject to damage caused by high cycle fatigue combined with low cycle fatigue taking account of the interaction of high and low amplitude loadings. High cycle fatigue is caused by normal routine traffic (low amplitude) loading while low cycle fatigue is caused by extreme (high amplitude) loading situations produced by such as earthquakes. The model mainly consists of a new damage indicator and a new strain-life fatigue curve. Total strain is treated as the damage variable. The proposed model predictions were verified by comparing with fatigue test results for four materials reported in the literature. The proposed model was then applied to estimate the fatigue life of a bridge member subject to combined high and low-cycle fatigue damage caused by normal traffic and by earthquake loadings. The results of the case study, confirm the importance and applicability of the proposed model.

Development of an Efficient Maintenance Strategy for Corroded Steel Bridge Infrastructures

The potential for structural capability degrading effects caused by corrosion is of profound importance and must be both fully understood and reflected in bridge inspection and maintenance programs. As the number of steel bridge infrastructures increases throughout the world, it is an exigent task to conduct regular and detailed corrosion surface investigations to evaluate their residual strength capacities and to develop analytical models to understand their current conditions and critical locations, as well as yield and ultimate behaviors. This paper presents a simple, accurate, and rapid assessment method and an effective maintenance management strategy developed by using the results of tensile coupon tests conducted on numerous corroded plates obtained from a steel plate girder used for about 100 years with severe corrosion and an finite element method (FEM) analytical approach proposed by measuring only the maximum corroded depth, which can be used to make reliable decisions affecting cost and safety.

Numerical Investigation of Residual Strength and Energy Dissipation Capacities of Corroded Bridge Members Under Earthquake Loading

Recent damage examples of aged steel bridge infrastructures around the world are so alarming. They intensified the importance of careful evaluation of existing structures for the feasibility of current usage and to ensure public safety. Corrosion and fatigue cracking may be the two most important types of damages in aging structures. Furthermore, recent earthquakes demonstrated potential seismic vulnerability of some types of steel bridges. Corrosion and its effects can trigger the damages caused by earthquakes, and it will be vital to understand the behavior of existing steel bridges which are corroding for decades in future severe seismic events as well. This article comprises the results of nonlinear FEM analysis of many actual corroded plates with different corrosion conditions and proposes a simple and reliable methodology to estimate remaining seismic strength and energy dissipation capacities by measuring only the minimum thickness of a corroded surface, which can be used to make rational decisions about the maintenance management plan of steel infrastructures.

Analytical Behavior Prediction for Skewed Thick Plates on Elastic Foundation

This paper presents analytical solutions for the problem of skewed thick plates under transverse load on a Winkler foundation, which has not been reported in the literature. The thick plate solution is obtained by using a framework of an oblique coordinate system. First, the governing differential equation in that system is derived, and the solution is obtained using deflection and rotation as derivatives of the potential function developed here. This method is applicable for arbitrary loading conditions, boundary conditions, and materials. The solution technique is applied to two illustrative application examples, and the results are compared with numerical solutions. The two approaches yielded results in good agreement.

Effect of Fiber Diameter on Fatigue Strength of Fiber Reinforced Concrete and its Design

This paper describes the effect of fiber diameter of fiber reinforced concrete (FRC) under fatigue behavior and its design method. Some researchers showed that the fatigue behavior of FRC is mainly governed by the bridging stress degradation, but little information is still available so far. We conducted fatigue tensile experiments of the FRC under constant strain amplitude first and the degradation of bridging stress was measured experimentally. Then, the micromechanics-based theoretical model is also developed, and the model is verified by the test results. The model accounts for the loss of fatigue ruptured fibers of which fatigue rupture is based on S-N relationships. The parametric study from the micromechanics-based theoretical model indicates that the best fiber diameter varies according to the number of cycles and strain level applied to the FRC specimen. The result suggests that we need to design FRC with considering the application and its loading conditions to utilize the capacity of FRC.

Optimal Design of DFRCC Subjected to Fatigue Loading

This paper describes the optimal design of ductile fiber reinforced cementitious composite (DFRCC) under fatigue loading. First of all, fatigue tensile experiments of the DFRCC under constant strain amplitude were conducted, and the degradation of bridging stress was measured. The test results were employed to verify the micromechanics-based theoretical model developed in this research. The model accounts for the loss of fatigue ruptured fibers of which fatigue rupture is based on S-N relationships. According to the parametric study from the theoretical model, we found that the optimal choice of design variables, such as fiber length, is varied according to the maximum strain level and the number of cyclic loading. Therefore, it is required to design DFRCC optimally under given loading conditions to make the most of its excellent material properties and the developed model enables such a design.

ONE APPROACH ON FORECASTING METHODS FOR POTHOLES TRIGGERED BY THE DETERIORATION OF THE COURSES DEEPER THAN BINDER COURSE OF POROUS ASPHALT PAVEMENT

With an aim to grasp the damage progress on porous asphalt pavement, those data has been measured every other month using the high-accuracy pavement-condition measuring vehicle at the sites. Afterwards, it is confirmed that the cracks have progressed to potholes in a short time at the concerned place. Such the damages could not be detected and forecasted at their early stage with the traditional evaluation indicators (cracks, rutting, and surface roughness) and the conventional frequency of investigations. This paper is to propose (i) the new evaluation factors, the partial settlement values specific to porous asphalt pavement, based on the analysis of the high-accuracy surface profile, and (ii) the forecasting method of potholes occurrence, introducing the growth curve models for the damage progresses specific to the damage factors. 排水性舗装の損傷進行の把握を目的として，高精度な路面性状車両で，同一箇所の隔月計測を実施した結果，この場所では短期間でひび割れ発生からポットホールへ進展する事象を確認した．この様な損傷は従来の評価（ひび割れ，わだち，平坦性）指標や調査頻度では早期に発見，予測できない．本論文は，高精度で取得した路面の高さ情報を解析することで，排水性舗装特有の局所沈下量という新たな評価指標を提案するとともに，損傷要因に応じた損傷進行における成長曲線モデルを導くことで，ポットホール発生予測を提案するものである．

Tensile Behavior Prediction of Steel Plates with Pitting Corrosion

We report the tensile behavior of corroded steel plates with huge corrosion pit. The behavior of corroded steel plates is not easy to predict because of its surface roughness. We therefore conducted tensile tests first to understand the behavior experimentally using the corroded steel plates taken from plate girder bridge. Before the testing, a 3D laser prove system was employed to measure the surface irregularity. In addition, finite element model was developed here to predict the behavior numerically. The model was validated by the tensile test results so that the finite element model can be reliably used for the parametric study. It is found from the parametric study that the location of huge corrosion pit affects the tensile strength, at most 15%.

Sensored Elastomeric Bridge Bearing and its Application

A prototype of sensored bridge bearing was developed, fabricated, tested and planned to be applied in two bridge structures for sensing and monitoring of construction process and service condition. Besides, numerical modeling of the prototype was performed using the finite element method with ABAQUS, and meanwhile the testing results were calibrated. Numerical simulation results of the selected two bridge structures show that certain bearing reactions are sensitive to the interested behaviors and performances. This kind of sensored bearing is considered feasible for monitoring construction, damage scenario, and applied loads.