• Journal of Korean Society of Steel Construction
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• v.24 no.4
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• pp.361-369
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• 2012

In this study, prefabricated composite columns using high-strength angles (PSRC composite column) was studied. Concentric axial loading tests were performed for 2/3 scale PSRC specimens and an conventional SRC specimen with H-steel at the center of the cross-section. The test parameters were the steel ratio of angles and the spacing of lateral re-bars. The test results showed that by placing the angles at the corners of the cross-section for confinement with provided for the core concrete, the PSRC column specimens exhibited greater load-carrying capacity and deformation capacity than those of the conventional SRC column. The axial load-carrying capacity of the PSRC columns was greater than the prediction by KBC 2009. Using existing stress-strain relationship of confined concrete, the axial load-deformation relationship of the specimens were predicted. The numerical predictions correlated well with the test results in terms of initial stiffness, load-carrying capacity, and post-peak strength- and stiffness-degradations.

• Journal of Korean Society of Steel Construction
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• v.27 no.4
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• pp.399-410
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• 2015

Concrete filled steel tube(CFT) has outstanding deformation capacity and strength in comparison with reinforced concrete or steel tube. CFT drilled shaft, which is developed large shear force due to seismic load and soil liquefaction, is designed as large diameter. However, shear design equations of the current standards do not consider bond stress of CFT and it results in extremely conservative design. Currently, previous studies for improving shear equations scarcely exist and are impossible applied to large CFT drilled shafts since these studies focus on only small scale experimental research. In this study, eventually to propose improving shear equation of large diameter CFT, it is preliminary research to compare and investigate the previous studies and current standards.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.73-76
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• 2008

The damage of earthquakes have to achieve by probabilistic evaluation because of uncertainty of earthquake. Fragility analysis is a useful tool for predicting the probability of damage induced by the probable earthquake. This paper presents the probability of damage as a function of peak ground acceleration and estimates the probability of five damage levels for the pier of prestressed concrete (PSC) bridge subjected to given ground acceleration. At each 100 artificial earthquake motions were generated in terms of soil conditions, and nonlinear time domain analyses were performed for the damage states of the pier of PSC bridge structures. These damage states are described by displacement ductility result from seismic performance based on existing research results. Using the damage states and ground motion parameters, five fragility curves for the pier of PSC bridges with five types of dominant frequencies were constructed assuming a log-nomal distribution. It was found that there was a significant effect on the fragility curves due to the dominant frequencies.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.5
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• pp.3602-3609
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• 2015

HPFRCC is characterized by a very low water-to-binder ratio which induce extremely large autogenous shrinkage at early age. The restriction of such autogenous shrinkage through the use of forms and reinforcing bars will increase substantially the risk of excessive residual stresses and shrinkage cracking. The exact understanding of the shrinkage behavior and studies on solutions to reduce shrinkage should be imperatively undertaken for further application of HPFRCC to real structures. Therefore, this paper investigated the mechanical properties of HPFRCC with respect to the eventual introduction of expansive admixture(EA) and shrinkage reducing agent (SRA) in the mixture. Autogenous shrinkage test was conducted considering the coefficient of thermal expansion (CTE) measured at early age so as to examine the effects of EA and SRA on the autogenous shrinkage behavior of HPFRCC.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.5
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• pp.119-126
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• 2022

This study proposed a BCM(Binding Column Method) that can reinforce the insufficient seismic force of piloti buildings that are not designed for seismic resistance. In addition, 4 reinforcement specimens and 1 reference specimen were manufactured for the proposed seismic reinforcement method. The effect of improving seismic performance before and after reinforcement was examined through repeated loading tests. As a result of experiment, seismic reinforcement specimen with BCM system showed hysteretic characteristics of a large ellipse with great energy dissipation ability and increased strength and stiffness, while reference specimen showed rapid reduction in strength and brittle shear failure column. In addition, it can be seen that the reinforcing effect is improved as the gap is narrow, the torque is large, and the thickness of the L-shaped steel sheet is thicker. The SC4 specimen showed the best seismic performance reinforcement effect.

• Journal of the Korean Geotechnical Society
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• v.26 no.11
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• pp.111-123
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• 2010

The steel pipe of steel-concrete composite drilled shafts increases the pile strength and induces the ductile failure by constraining the deformation of the inner concrete. In this research, pile loading tests were performed to analyze the field applicability of a steel-concrete composite drilled shafts. The test ground consisted of 5~7 m thick soil underlying rock mass. The test piles consisted of two steel-concrete composite drilled shafts, which were the concrete filled steel pipe piles with the diameter of 0.508 m, and a concrete pile with the same diameter. The test results showed that the boundary between the upper steel composite section and the lower concrete section was structurally weak and needs to be reinforced by using a inner steel cage. If the boundary is located in deep depth, which is not influenced by lateral load, the allowable strength of the lower concrete section increases, so an economical design can be performed by increasing the design load of steel-concrete composite drilled shafts.

• Journal of the Korea Concrete Institute
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• v.21 no.2
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• pp.187-197
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• 2009

This paper presents a systematic approach for estimating fragility curves and damage probability matrices for different frequencies. Fragility curves and damage probability indicate the probabilities that a structure will sustain different degrees of damage at different ground motion levels. The seismic damages are to achieved by probabilistic evaluation because of uncertainty of earthquakes. In contrast to previous approaches, this paper presents a method that is based on nonlinear dynamic analysis of the structure using empirical data. This paper presents the probability of damage as a function of peak ground acceleration and estimates the probability of five damage levels for prestressed concrete (PSC) bridge pier subjected to given ground acceleration. At each level, 100 artificial earthquake motions were generated in terms of soil conditions, and nonlinear time domain analyses was performed for the damage states of PSC bridge pier structures. These damage states are described by displacement ductility resulting from seismic performance based on existing research results. Using the damage states and ground motion parameters, five fragility curves for PSC bridge pier with five types of dominant frequencies were constructed assuming a log-normal distribution. The effect of dominant frequences was found to be significant on fragility curves.

• Journal of the Korea Concrete Institute
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• v.18 no.2 s.92
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• pp.161-168
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• 2006

An experimental investigation was conducted to examine the hysteretic behaviors of ultra-high strength concrete tied columns. The purpose of this study is to investigate the safety of ultra-high strength concrete columns with 100 MPa compressive strength for the requirement of ACI provisions. Eight 1/3 scaled columns were fabricated to simulate an 1/2 story of actual structural members with the cross section $300{\times}300mm$ and the aspect ratio 4. The main variables are axial load ratio, configurations and volumetric ratios of transverse reinforcement. The results show that the deformability of columns are affected by the configurations and volumetric ratios of transverse reinforcement. Especially, it has been found that the behavior of columns are affected by axial load ratio rather than the amounts and the configurations of transverse reinforcement. Consequently, to secure the ductile behavior of 100 MPa ultra-high strength concrete columns, ACI provisions for the requirement of transverse steel may considered axial load level and the details of transverse reinforcement.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.368-376
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• 2010

The bent foundation with single drilled shafts is suitable and economical in South Korea, which has good rock in a shallow depth. This foundation has been designed with an elastic design concept. To apply a plastic design concept written in Korea Bridge Design Criteria, a detail design regulation, which includes the method for a plastic hinge point to occur above the ground, rebar arrangement and soil modelling, should be defined. Soil modelling should be considered in the respect of structural engineer's practicality. In this paper, single drilled shaft piers with 1m diameter are constructed, and cyclic lateral load tests loaded at 4m above the ground are taken to examine the behavior. Reduced diameter shaft above the ground and remaining the steel casing under the ground were used to induce plastic hinge to occur above the ground. Simplified soil models such as elastic relation and p-y curve are adapted, and the prediction results are compared with test results. Prediction results of a model bridge were compared according to soil models with time domain analyses, and design criteria of soil were proposed.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.13 no.1
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• pp.13-24
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• 2000

Current specification prescribes that upper and lower reinforcement mat is required in the same amount to resist negative and positive moment in bridge decks. But the negative moment is much smaller than positive moment because the actual behavior of decks consists of local deflection of slab and global deflection of girder. From this study, the analysis method based on harmonic analysis and slope-deflection method was developed and verified by finite element method. The negative moment, obtained from this method, were smaller than those computed based on the KHBDC specifications as much as 40∼50% in the middle of bridge. The amount of reduction of the design negative moment was shown herein to be dependent on variable parameters as shape factor(S/L) of slab, relative stiffness ratio of girder and deck slab, and so on. This investigations indicate that the upper reinforcement mat to resist negative moment can be removed. But further experimental study is required to consider durability and serviceability. From this new design concept, the construction expense can be reduced and the problem of decreasing durability resulting from corrosion of upper reinforcement steel settled.