Seung-Hee Kwon

Column Shortening of SRC Columns Considering the Differential Moisture Distribution

Steel reinforced concrete(SRC) columns, which have been widely employed in high-rise buildings, exhibit a time-dependent behavior because of creep and shrinkage of concrete. This long-term behavior may cause a serious serviceability problem in structural systems, so it is very important to predict the deformation due to creep and shrinkage of concrete. However, it was found from the previous experimental studies that the long-term deformation of SRC columns was quite dissimilar from that of RC columns. A new method is required to quantitatively predict the long-term deformation of SRC columns. In this study, the causes of the discrepancy between the behaviors of RC and SRC columns are investigated and discussed. SRC columns exhibit a time-dependent relative humidity distribution in a cross section differently from that of reinforced concrete(RC) columns owing to the presence of a inner steel plate, which interferes with the moisture diffusion of concrete. This relative humidity distribution may reduce the drying shrinkage and the drying creep in comparison with RC columns. Therefore it is suggested that the differential moisture distribution should be taken into account in order to reasonably predict column shortening of SRC columns.

Variation of Bilinear Stress-Crack Opening Relation for Tensile Cracking of Concrete at Early Ages

Dept. of Architecturaltural Engineering, Ewha Womans University, Seoul 120-750, KoreaABSTRACT One of the most vulnerable properties in concrete is tensile cracking, which usually happens at early ages due tohydration heat and shrinkage. In order to accurately predict the early age cracking, it needs to find out how stress-crack openingrelation is varying over time. In this study, inverse analyses were performed with the existing experimental data for wedge-splittingtests, and the parameters of the softening curve for the stress-crack opening relation were determined from the best fits of the mea-sured load-CMOD curves. Based on the optimized softening curve, variation of fracture energy over time was first examined, anda model for the stress-crack opening relation at early ages was suggested considering the found feature of the fracture energy. Themodel was verified by comparisons of the peak loads, CMODs at peak loads, and fracture energies obtained from the experimentsand the inverse analysis. Keywords : stress-crack opening relation, softening curve, cracking, ordinary concrete, wedge splitting test, inverse analysis

Long-term Behavior of Reinforced Concrete Wall under Axial Loading

The purpose of this study is to suggest a method to quantitatively predict long-term deformation of walls under an axial load concentrated to a part of the whole width. Four wall specimens were tested and three-dimensional finite element analyses were performed for these specimens. The finite element models established in this study were verified from the test results. On the basis of this verification, analysis parameters were selected considering various dimensions of walls and sectional area that a concentrated load is acting on, and finite element analyses for these parameters were carried out. The concept of the effective width coefficient was newly introduced as a method to predict the long-term behavior of walls, and a function that is able to optimally fit the effective width coefficients calculated from the analysis results for the selected parameters was found from regression analysis. The found function can be conveniently used in practice to predict the long-term behavior under loads concentrated to a local area of the whole width of walls.

Long-Term Behavior of Square CFT Columns with Diaphragm

This paper presents experimental and analytical studies on long-term behavior of square CFT columns with diaphragm. In order to investigate the effect of the diaphragm on the long~term behavior, experiments for six specimens with two diaphragms and three different column length, and three-dimensional finite element analysis for each specimen have been performed. The finite element models considering the interface behavior between the steel tube and the inner concrete were verified from comparison of the test results with the analysis results. From the test and the analysis results, the following conclusions were obtained. The confinement effect created by the diaphragm does not depends on column length and influences only a part of the whole column that is from the end to the depth which is the same to the width of the column. The shortening of the column with diaphragm which covers more than a half of the cross sectional area of the inner concrete is the same as that of the column under a load applied on the steel tube and the entire section of the inner concrete.