Young Joo Lee

Ulsan National Institute of Science and Technology | UNIST · School of Urban and Environmental Engineering

Structural redundancy acts as a safeguard against localized damage, but it may lead to a variety of potential overall failures. A system-level probabilistic failure path approach is necessary to identify system failure events and account for stress redistribution in structures prone to fatigue-induced damage. Incorporating such probabilistic constr...

As the threat of natural disasters to structures intensifies, risk assessment of infrastructure has gained much importance. Fragility curves are essential tools in predicting disaster-related losses and making disaster miti-gation decisions. In this paper, we propose a new method to efficiently derive accurate fragility curves for structures with h...

This study proposes a data-driven method for predicting the probabilistic response of cable-stayed bridges. The proposed method is used to construct an optimal prediction model based on a data-driven machine-learning method. In addition, the accuracy and efficiency of the prediction model are improved by considering the correlation coefficients bet...

The fatigue-induced sequential failure of a structure having structural redundancy requires system-level analysis to account for stress redistribution. System reliability-based design optimization (SRBDO) for preventing fatigue-initiated structural failure is numerically costly owing to the inclusion of probabilistic constraints. This study incor...

Despite the rapid development of sensors, structural health monitoring (SHM) still faces challenges in monitoring due to the degradation of devices and harsh environmental loads. These challenges can lead to measurement errors, missing data, or outliers, which can affect the accuracy and reliability of SHM systems. To address this problem, this stu...

Changes in a structure's use can have a significant impact on distribution of live loads, both in the plan and elevation of a building. Unevenly distributed live loads can introduce variations in mass, causing irregularities in the structure and making it more susceptible to damage during earthquakes. Previous studies have extensively investigated...

This study aims to develop a decision-making support system for managing aged road facilities in a target road network based on seismic performance evaluation. For this purpose, the seismic fragility considering aging effect is analyzed for bridges, tunnels, retaining walls, and slopes to assess the direct damage to individual road facilities, as d...

The extent of damage to a community from an earthquake depends on the existing road infrastructure and space for disaster response activities. The Bureau of Urban Development of the Tokyo Metropolitan Government has assessed the seismic vulnerability and risk to communities, and announced the results approximately every five years since 1975. The p...

Seismic fragility curves play a crucial role in assessing potential seismic losses and predicting structural damage caused by earthquakes. This study compares non-sampling-based methods of seismic fragility curve derivation, particularly the probabilistic seismic demand model (PSDM) and finite element reliability analysis (FERA), both of which requ...

A bridge transportation network supplies products from various source nodes to destination nodes through bridge structures in a target region. However, recent frequent earthquakes have caused damage to bridge structures, resulting in extreme direct damage to the target area as well as indirect damage to other lifeline structures. Therefore, in this...

This study incorporates the Branch-and-Bound method employing system reliability Bounds, which is a failure-path structural system reliability analysis approach and termed the B 3 method, with a metaheuristic optimization algorithm, namely grey wolf optimization, to obtain the optimal design of structures under fatigue-induced system failure. An ad...

Reliability analysis with unknown system event definition such as sequence of member failures requires a failure-path approach to determine the component events that will induce overall system failure. In particular, redundant structures prone to fatigue-induced sequential failure needs a system-level analysis employing a failure-path approach to a...

We evaluate seismic fragilities for cantilever retaining walls with three slope angles of backfill (i.e., 0, 10°, and 20°), subjected to the ground motions computed for four site classes (S2, S3, S4, and S5). We collect measured shear wave velocity profiles and select representative profiles. Using one-dimensional site response analyses, surface gr...

Any change in structure's occupancy or use can significantly impact the plan and elevation mass distributions, turning even regular structures into mass-eccentric structures with in-plan or vertical irregularities. Generally, irregular structures are more vulnerable to earthquake hazards because of the torsional effect, which causes non-uniform def...

The damage state assessment of buildings after an earthquake is an essential and urgent task that typically requires significant manpower and time for the resilience of a city-scale society. This study aims to develop machine learning (ML) models for the rapid seismic damage-state assessment of steel moment frames, which was never tried before to t...

Structural condition monitoring of railway bridges has been emphasized for guaranteeing the passenger comfort and safety. Various attempts have been made to monitor structural conditions, but many of them have focused on monitoring dynamic characteristics in frequency domain representation which requires additional data transformation. Occurrence o...

Any change in the structure occupancy or use can significantly affect mass distributions in plan and elevation. The mass-eccentric structures having in-plan or vertical irregularities can suffer from non-uniform deformation demands due to the torsional effect. The existing design practices recommend special design requirements for such irregular st...

Skewed bridges are commonly used in highway interchanges where the straight (unskewed) bridges are not suitable. There have been several observations of heavy damage of bridges that have geometric irregularities, especially significant skewness. Such damage severely disrupts transportation systems, leading to substantial economic consequences. Skew...

This study proposes a new hybrid method that uses both of post-earthquake reconnaissance data and numerical analysis results based on a finite element (FE) model. As the uncertainty of a capacity threshold for a structural damage state needs to be estimated carefully, in the proposed method, the probabilistic distribution parameters of capacity thr...

Many standards and studies have emphasized the importance of considering various uncertainty factors of material properties and corrosion in assessing the structural performance of bridges. In such an analysis, however, high computational cost is a major issue because a probabilistic structural analysis requires multiple structural analyses. In thi...

In this study, a new framework of seismic resilience estimation for urban water transmission networks was developed. The proposed resilience estimation model consists of three phases: input earthquake generation, hydraulic analysis, and recovery of network facilities. In the earthquake generation phase, the uncertainty of the ground motion is deter...

Transportation system management and traveler information systems evolve with the development of data communications and intelligence of traffic simulations. Variety of roadside and mobile sensing platforms will be deployed to allow communication between vehicles with Dedicated Short Range Communications (DSRC). Traffic data received from moving ve...

Traffic simulation tools are becoming more popular as complexity and intelligence are growing in transportation systems. The need for more accurate and intelligent traffic modeling is increasing rapidly as transportation systems are having more congestion problems. Although traffic simulation models have been continuously updated to represent vario...

Highway systems play a key role in providing mobility to society, especially during emergency situations, including earthquakes. Bridges in highway systems are susceptible to damage from earthquakes, causing traffic capacity loss leading to a serious impact on surrounding areas. To better prepare for such scenarios, it is important to estimate capa...

This paper provides an overview of theories and applications of structural system reliability (SSR). The paper defines SSR problems and discusses the growing needs for SSR analysis and technical challenges. Detailed literature reviews are provided for three subtopics: SSR methods for Boolean system events, SSR methods for sequential failures, and S...

In this study, a seismic risk assessment model was proposed to evaluate the seismic reliability of a water transmission network. The proposed risk assessment model involves earthquake generation and hydraulic analysis modules. To consider a comprehensive approach, the numerical simulation strategy includes probabilistic seismic hazard analysis, bur...

In this study, optimal post-hazard bridge recovery strategies were proposed for transportation networks under seismic conditions. To predict the performance of the transportation network, a robust performance measure, total system travel time (TSTT), was employed, and an artificial neural network (ANN)-based surrogate model was developed to enable...

In this study, an artificial neural network (ANN)-based surrogate model is proposed to evaluate the system-level seismic risk of bridge transportation networks efficiently. To estimate the performance of a network, total system travel time (TSTT) was introduced as a performance index, and an ANN-based surrogate model was incorporated to evaluate a...

The 2017 M5.4 Pohang, South Korea, earthquake damaged numerous buildings. Immediately after the main shock event, 1,880 professional engineers inspected the damaged buildings and assigned three damage grades (“Usable,” “Restricted use,” and “Unusable”). We investigate factors influencing the building damage. The built year, number of stories, and e...

The Republic of Korea has been considered to be relatively safe from earthquake hazards because of the geological location of the Korean Peninsula, which has a low level of intraplate seismic activity. However, an earthquake with a moment magnitude of 5.4 struck the city of Pohang on November 15, 2017, causing 90 casualties and 52 million USD in pr...

Conventional Monte Carlo simulation-based methods for seismic risk assessment of water networks often require excessive computational time costs due to the hydraulic analysis. In this study, an Artificial Neural Network-based surrogate model was proposed to efficiently evaluate the flow-based system reliability of water distribution networks. The s...

Civil infrastructures experience long-term deflection as a result of persistent and transitory loadings, including self-weight, pre-stress, traffic, temperature variation, and stress redistributions due to damage. Thus, long-term displacement is an important safety indicator that can be widely employed in structural health monitoring. However, its...

In this paper, an optimal system design for the seismic performance enhancement of a water transmission network was proposed. The main purpose of the optimal design is to maximize the system performance within a limited construction cost. The proposed model evaluates network performance through the spatially correlated seismic attenuation law, dete...

p>Structural health monitoring (SHM) of civil engineering structures often requires displacement information to assess structural integrity. An unexpected large displacement can be an indication of lurking structural damage. Although structural displacement is a useful physical quantity for SHM purposes, the measurement on full-scale structures is...

Measurement of stress levels from an in-service structure can provide important and useful information regarding the current state of a structure. The stress relaxation method (SRM) is the most conventional and practical method, which has been widely accepted for measuring residual stresses in metallic materials. The SRM showed strong potential for...

Vertical deflection has been emphasized as an important safety indicator in the management of railway bridges. Therefore, various standards and studies have suggested physics-based models for predicting the time-dependent deflection of railway bridges. However, these approaches may be limited by model errors caused by uncertainties in various facto...

Steel strands are widely used as important structural members of bridges. Their failure can be detrimental to the structure; therefore, various studies on predicting their mechanical characteristics have been conducted. However, explaining the mechanical characteristics of steel strands is difficult because of geometric complexity, difficulty in co...

The number of cable-stayed bridges being built worldwide has been increasing owing to the increasing demand for long-span bridges. As the stay-cable is one of critical load-carrying members of cable-stayed bridges, its maintenance has become a significant issue. The stay-cable has an inherently low damping ratio with high flexibility, which makes i...

Many structures are subjected to the risk of fatigue failure. For their reliability-based design, it is thus important to calculate the probability of fatigue failure and assess the relative importance of the involved parameters. Although various studies have analyzed the fatigue failure, the stage of fracture failure has been less focused. In part...

Earthquakes can have significant impacts on transportation networks because of the physical damage they can cause to bridges. Hence, it is essential to assess the seismic risk of a bridge transportation network accurately. However, this is a challenging task because it requires estimating the performance of a bridge transportation network at the sy...

The mechanical properties of lightweight aggregate concrete (LWAC) depend on the mixing ratio of its binders, normal weight aggregate (NWA), and lightweight aggregate (LWA). To characterize the relation between various concrete components and the mechanical characteristics of LWAC, extensive studies have been conducted, proposing empirical equation...

Liquid-containing storage tanks are important structures in industrial complexes. Because earthquake damages to liquid storage tanks can cause structural collapse, fires, and hazardous material leaks, there have been continuous efforts to mitigate earthquake damages using seismic fragility analysis. In this regard, this study focuses on the seismic...

Concrete gravity dams are widely constructed owing to their advantages of low maintenance cost and relatively low risk of sudden failure. However, the structural failure rate has been reported to be higher than other dam types. Although various studies have been conducted to assess the structural fragility of concrete gravity dams, not enough empha...

As the construction of long-span bridges such as cable-stayed bridges increases worldwide, maintaining bridge serviceability and operability has become an important issue in civil engineering. The stay cable is a principal component of cable-stayed bridges and is generally lightly damped and intrinsically vulnerable to vibration. Excessive vibratio...

This paper proposes an estimation technique of fatigue crack length for an aluminum 6061-T6 plate structure with a notch using a stress-life (S-N) curve. First, an S-N curve is obtained from multiple specimen tests by applying constant-amplitude cyclic loading with different stress levels. Next, the parameters of the Paris’ law are estimated from t...

The determination of Paris’ law parameters based on crack growth experiments is an important procedure of fatigue life assessment. However, it is a challenging task because it involves various sources of uncertainty. This paper proposes a novel probabilistic method, termed the S-N Paris law (SNPL) method, to quantify the uncertainties underlying th...

Earthquakes are natural disasters which human beings cannot control, causing significant damage to the economy and society as a whole. In particular, earthquakes affect not only buildings but also lifeline structures such as water distribution, electric power, transportation, and telecommunication networks. The interruption of these networks is cri...

Construction activities, involving cutting, drilling, and grinding of materials, often produce toxic respirable dust that can cause fatal diseases and illnesses. To protect workers from breathing excessive amounts of respirable dust at job sites, superintendents should continuously monitor the level of respirable dust in workspaces and make timely...

Because significant damages to structures having structural irregularity in their plans were repeatedly observed during many past earthquakes, there have been great research efforts to evaluate their seismic vulnerability. Although most of the previous studies used simplified structural representations such as one-dimensional or two-dimensional mod...

This paper investigates roundabout capacity analysis using mathematical modelling and microscopic simulation. The capacity in approach section in roundabout is calculated by estimating the number of vehicles that can enter a roundabout for a given approach given a certain circulating volume. Since roundabouts are working with only yield conditions,...

Management of the vertical long-term deflection of a high-speed railway bridge is a crucial factor to guarantee traffic safety and passenger comfort. Therefore, there have been efforts to predict the vertical deflection of a railway bridge based on physics-based models representing various influential factors to vertical deflection such as concrete...

With the rapid advancement of sensing technologies, it has been feasible to collect various types of traffic data such as traffic volume and travel times. Vision-based approach is one of the major scheme actively used for the automated traffic data collection, and continues to gain traction to a broader utilization. It collects video streams from c...

This paper proposes a novel method termed the S-N Paris law (SNPL) method to quantify the uncertainties lying in the Paris law parameters, by finding the best estimates of their statistical parameters from the S-N curve data using a Bayesian approach. Through a series of steps, the SNPL method helps determine the statistical parameters (e.g., mean...

Railway bridges are exposed to repeated train loads, which may cause fatigue failure. As critical links in a transportation network, railway bridges are expected to survive for a target period of time, but sometimes they fail earlier than expected. To guarantee the target bridge life, bridge maintenance activities such as local inspection and repai...

Bridges are one of the most important infrastructure systems that provide public and economic bases for humankind. It is also widely known that bridges are exposed to a variety of flood-related risk factors such as bridge scour, structural deterioration, and debris accumulation, which can cause structural damage and even failure of bridges through...

This paper proposes a framework for a reliability-based flow analysis for a water pipe network after an earthquake. For the first part of the framework, we propose to use a modeling procedure for multiple leaks and breaks in the water pipe segments of a network that has been damaged by an earthquake. For the second part, we propose an efficient sys...

Since the structural damage due to earthquakes has continuously increased all over the world, estimating seismic fragility of structures effectively is emphasized so as to take emergency actions properly. A fragility curve is widely used as a probabilistic measure representing the failure probability of structures caused by earthquakes. For example...

As the structural damage caused by earthquakes has been gradually increasing, estimating the seismic fragility of structures has become essential for earthquake preparation. Seismic fragility curves are widely used as a probabilistic indicator of structural safety against earthquakes, and many researchers have made efforts to develop them in a more...

Fatigue life prediction for a bridge should be based on the current condition of the bridge, and various sources of uncertainty, such as material properties, anticipated vehicle loads and environmental conditions, make the prediction very challenging. This paper presents a new approach for probabilistic fatigue life prediction for bridges using fin...

Floods have been knownto be one of the main causes of bridge collapse. Contrary to earthquakes, flood events tend to occur repeatedly and more frequently in rainfall areas; flood-induced damage and collapse account for a significant portion of disasters in many countries. Nevertheless, in contrast to extensive research on the seismic fragility anal...

There are continuous efforts to mitigate structural losses from earthquakes and manage risk through seismic risk assessment; seismic fragility curves are widely accepted as an essential tool of such efforts. Seismic fragility curves can be classified into four groups based on how they are derived: empirical, judgmental, analytical, and hybrid. Anal...