Seungjun Kim

A Study on Behavior Characteristics of Precast Coping Part under Axial Load

Recently, bridge construction technology has made great progress from development of high performance materials and new bridge types. However, most technology are based on methods of cast-in-place and material cost saving. The method of cast-in-place concrete causes environmental damages and costumer complaints. Especially, under bad weather conditions, the construction can not proceed. To overcome these disadvantages, new construction methods were developed to reduce construction time. These methods are called precast method. Most prefabricated methods have been applied to superstructure constructions of bridges, but very minutely applied to substructure constructions. The most important agendas on precast method are light weight and transportability of the precasted members, because very strict transporting specifications exist for road transportation of the precasted members. For example, the weight and length of coping members may be larger than the available transporting vehicles. Although column is constructed by precast method to save construction time, if coping member is constructed by cast-in-place method, then the column construction time reduction becomes meaningless. Therefore, in this study, a new precast coping member and a connecting system of column-coping member are proposed. The proposed method is verified by analyzing their ultimate performance through analysis and experimental study.

Performance Evaluation of the Column-Coping Joint for Prefabricated DSCT Pier

Recently, Technology of bridge construction has made great progress for reduction of construction period and Green Growth. The construction period of Pier had about 50% in construction period of entire bridge. Therefore, construction method of prefabricated piers have researched by many researchers, lately. In this paper, we suggested the joint of coping-column for prefabricated DSCT pier and verified by experimental study. To experimental study, the test methods had proposed for the performance characteristics evaluation of coping-column joint. Test methods were made up cyclic eccentricity loading test and static compressive loading test. We had produced the major parameters and suggested the standard model for joint of coping-column through the experimental study.

Buckling Behavior of Circular Steel Tubes under Fire

Recently, several lives were lost because of the collapse of structures under fire. Steel members are mainly used in the columns and beams of buildings for improving construction efficiency. The fire resistance of steel structure is very important because when it don’t have fire resistive covering, it rapidly changes with high temperature. In fire resistance design of steel, steel structure must have fire resistive covering. But many facilities as temporary facilities, parking lot don’t have it. The buckling behavior of steel structures under fire is also significant because it can cause local buckling failure through the reduction in structural material properties by temperature. In this study, the elastic buckling behavior of a circular steel tube under fire was investigated using finite element analysis. The parameters for this analysis used were, diameter–thickness ratio, fire exposure area, and fire scenarios. The elastic buckling strength of circular steel tube rapidly decreased when subjected to the fire curve. Local buckling occurred and this can lead to global failure. When fire resistance design of circular steel tube was performed, buckling behavior must be considered.

Concrete strength reduction of DSCT member by welding heat

Strength reduction was investigated when a double-skinned composite tubular (DSCT) member was exposed to welding heat. And a method for a DSCT member to maintain its original strength against the welding heat when modular DSCT members are composed. Welding causes the heat of 20,000 °C on the weld zone and the heat of 1,300°C around the weld zone. The strength of concrete nearby the weld zone decreases by high temperature. In this study, the concrete strength cases were investigated when arc welding and electro slag welding were used as the welding methods. Through heat transferring analysis of welded DSCT members, a preventing method preventing concrete strength reduction was proposed. The proposed method showed it prevented concrete strength reduction and it was verified by finite element analysis (FEA).

Study of the Structural Displacement Estimation by the Acceleration Measurement with an Effective Noise Filtering Method

In this study, the estimation method for the structural displacements by the acceleration measurement is investigated for effective real-time structural monitoring. Theoretically, the velocity and displacement data during the specific period can be obtained by integration of the measured acceleration. But, the integrated data is highly affected by unexpected error sources such as noise signal. So, the effective and rational method for the noise elimination or minimization should be suggested and used. In this study, an effective noise filtering method for an useful displacement estimation by double integration is suggested based on the characteristics of structural dynamics. For the rational noise filtering technique applied to the measured acceleration data, the multi bandpass filter, which allows the signals nearby the peak frequencies of measured data, is newly suggested. By the suggested filtering and double integration method, the estimation method of structural displacements using an acceleration measurement is suggested in this study. The accuracy and rationality of the suggested method was validated using the numerical example obtained by finite element analysis. In the validation, the displacement data estimated by the suggested method was directly compared with those obtained by highpass filter and bandpass filter, formerly well known methods.

Tangential Modulus Equation of the Steel Axial Member with I-section Considering the Pattern and the Maximum Value of the Residual Stress

This paper suggests a reasonable tangential modulus equation of a steel I-section member subjected the axial force considering residual stress. In general, there are three analyses methods which can be used to inelastic analysis using a beam element, a plastic zone analysis, an elastic-plastic hinge analysis, and a refined plastic hinge analysis. Among these three analysis methods, a refined plastic hinge analysis has been performed by many researchers because of its efficiency as well as reasonability. In a refined plastic hinge analysis, the CRC tangential modulus equation is adopted to consider a gradual yielding effect when the member is applied the axial force. But, this CRC tangential modulus equation can consider only restricted residual stress pattern and maximum value of the residual stress which is a half of a yield stress. By inelastic finite element analysis in this research, this limitation of the CRC tangential modulus revealed. In this research, new tangential modulus equation of a steel I-section member subjected the axial force was derived. This equation can consider different residual stress patterns, maximum value of the residual stress, the geometry of the section, and the direction of applied axial force. And this equation is validated by the inelastic finite element analysis using ABAQUS V6.9.