Jong Seh Lee

Buckling of orthotropic plates under various inplane loads

When a laminated composite plate is subjected to a compressive edge force lying in the plane of the plate, failure can occur by buckling at a stress below the strength of the material. Critical buckling loads of orthotropic plates are usually calculated using the analytical solutions which are based on the assumption of uniform end loads, despite the fact that real structures are subjected to various non-uniform inplane loads. This paper examines the buckling behavior of the orthotropic plates under non-uniform inplane loads with different boundary conditions (all edges simply supported, two loaded edges clamped and others simply supported, andall edges clamped) using the finite element method (FEM). Numerical results show that the existing formulas for buckling load basedon the uniform load assumption leads to overestimation of buckling loads.

Vertical vibration analysis of soil-pile interaction systems considering the soil-pile interface behavior

A numerical method is presented herein to study soil-pile interaction systems in a stratified media. The method is based on a coupling of the finite element method and the boundary element method. The near field is modeled by the finite elements whereas the far field is modeled by the boundary element formulation using the multi-layer dynamic fundamental solution that satisfies the radiation condition of the waves. The two fields are coupled by imposing the displacement compatibility conditions at the interface between the near and far fields. Special attention is paid to the soil-pile interface using elastic springs to model the discontinuity at the interface. In order to validate the analytical approach, a forced vibration test is simulated and the response under vertical harmonic loads at the pile cap in the layered half plane is calculated. The results are compared with the published theoretical and experimental results. Finally, numerical analyses of various soil-pile systems are performed to examine the dynamic behavior of the system depending on parameters such as the elastic modulus of the pile and the stiffness of the interface springs.

Advanced Robot System for Automated Bridge Inspection and Monitoring

Conventional bridge inspection process is time consuming, hazardous, and may be affected by environmental conditions. It is of great interest, therefore, that an automated and/or teleoperated inspection robot be developed to replace the manual inspection procedure. An advanced robot system for automated bridge inspection and monitoring is developed at the Bridge Inspection Robot Development Interface (BIRDI) at Hanyang University in Korea. The advanced robot inspection system consists of three parts; a modified crane truck with a robotic arm, a robot platform and control system, and a machine vision system for an automatic detection of cracks and other damages. The advanced robot crane truck looks similar to the conventional bucket crane, but is much smaller in size, light-weight and equipped with multi-linkage mechanism of seven degrees-of-freedom with hydraulic actuators. The inspection robot platform consists of rotary joint mechanisms for both pan and tilt motions for the machine vision system and a prismatic (up/down) joint mechanism for the gravitational direction movement. The machine vision system is developed to detect automatically the cracks and other damages on the underside of the bridge deck from the captured images. The developed robot system can allow remote inspection of bridges while reducing human risks and improving efficiency and data reliability, thereby enabling more rational bridge maintenance practice. The advanced robot inspection system is expected to contribute to advancement of infrastructure maintenance technology and enhancement of construction industry competitiveness.

New lumped-mass-stick model based on modal characteristics of structures: development and application to a nuclear containment building

In this study, a new lumped-mass-stick model (LMSM) is developed based on the modal characteristics of a structure such as eigenvalues and eigenvectors. The simplified model, named the “frequency adaptive lumped-massstick model,” hasonly a small number of stick elements and nodes to provide the same natural frequencies of the structure and is applied to a nuclear containment building. To investigate the numerical performance of the LMSM, a time history analysis is carried out on both the LMSM and the finite element model (FEM) for a nuclear containment building. A comparison of the results shows that the dynamic responses of the LMSM in terms of displacement and acceleration are almost identical to those of the FEM. In addition, the results in terms of fl oor response spectra at certain elevations are also in good agreement.

A Damper System for Mitigation of Suspension Bridge Flutter

This paper describes a floating system that uses a continuous girder between two anchor blocks for increasing the span length of suspension bridges. The flutter instability of the floating system due to winds is of great critical interest. This paper proposes a new control system that is designed to mitigate the flutter of the floating-type suspension bridge. The proposed control system consists of vertical dampers installed between the pylons and the bridge deck. The linear evaluation model is developed using the equations of motion generated around the deformed equilibrium position. Using the analytical model, performance of the proposed control systems is studied and compared to a traditional system with joints at the pylons. The paper shows that the proposed control system improves the overall stiffness and stability of the bridge. A control strategy using semi-active or active dampers is also proposed to enhance the controllability of the floating-type suspension bridge against flutter instability.

Hydroelastic Responses of Floating Structure by Modeling Dimensions

In this study, FE-BE direct coupling methods of 1D and 2D problems are considered for the pontoon-type floating structure and the difference of the modeling dimensions is investigated for the hydroelastic response. The modeling dimensions are defined as the 1D problem consisting 1D beam-2D fluid coupling and the 2D problem consisting 2D plate-3D fluid coupling with zero-draft assumption. For case studies, hydroelastic responses of the 1D Problem are compared to those of the 2D Problem for a wide range of aspect ratio and regular waves. It is shown that the effects of the elastic behavior are increased by decreasing the incident wavelength, whereas the effects of the rigid behavior are increased by increasing the incident wavelength. In 2D problem, the incident wave angle can be considered, and slightly more accurate results can be obtained, but the computational efficiency is lower. On the other hand, in 1D problem with plate-strip condition, the incident wave angle cannot be considered, but when the aspect ratio is large, the overall responses can be analyzed through a simplified model, and the computational efficiency can be improved.

Dynamic Amplification of Tied-Arch Girder due to Variations of Rise Ratio and Vehicle Moving Speed

In this paper the effect of rise ratio on the dynamic amplification (DA) of the tied-arch girder is investigated through a finite element analysis. Equivalent nodal loads are considered for the modeling of moving vehicle loads, and several vehicle speeds ranged between 60 km/hr and 120 km/hr are applied for the DA investigation. For detailed investigation, the relationship between the first mode frequency of the girder and the DA at the middle of the girder is investigated. The results show that the DA of the girder sensitively varies according to the rise ratio; especially when the rise ratio is more than 0.03, the maximum DA is relatively larger than the cases of the smaller rise ratio. Such result is appeared since the girder becomes more flexible and the developing time of the maximum DA is close to the first natural period of the girder.

Development of Advanced Robot System for Bridge Inspection and Monitoring

Conventional bridge inspection involves the physical positioning of an inspector by the hydraulic telescoping boom of a “snooper truck” thereby providing visual access to bridge components. The process is time consuming, hazardous, and may be affected by lighting conditions. Therefore, it is of great interest that an automated and/or teleoperated inspection robot be developed to replace the manual inspection procedure. This paper describes the advanced bridge inspection robot system under development and other related activities currently undergoing at the Bridge Inspection Robot Development Interface. Its primary goal is to develop advanced robot systems for bridge inspection and monitoring for immediate field application and commercialization. This research project will contribute to advancement of infrastructure maintenance technology, enhancement of construction industry competitiveness, and promotion of national capacity for technology innovation.