• Journal of Korean Society of Steel Construction
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• v.20 no.5
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• pp.675-681
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• 2008

This study introduced a new steel-jacketing method to retrofit RC columns. It also estimated the performance of steel-jacketed concrete cylinders. Twelve concrete cylinders were fabricated with varying steel jacket thicknesses of 1.0, 1.5, and 2.0 mm. Lateral confining pressure was applied with three clamps and the performance of plain concrete cylinders was compared with that of steel-jacketed cylinders. Steel jacket proved to be effective in increasing the strength of the cylinder. Finally, Li's constitutive model was compared with that of the experimentalresults. However, Li's model showed incongruity in Region II, which indicates the region after the yield of steel jackets. Therefore, the modified value of n was used for the region and the model showed a good agreement.

• Journal of Korean Society of Steel Construction
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• v.21 no.2
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• pp.105-113
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• 2009

To improve braced frame performance, the connection strength, stiffness, and ductility must be directly considered in the frame design. The resistance of the connection must be designed to resist seismic loads and to help provide the required system ductility. In addition, the connection stiffness affects the dynamic response and the deformation demands on the structural members and connections. In this paper, current design models for gusset plate connections are reviewed and evaluated usingthe results of past experiments. Current models are still not sufficient to provide adequate connection design guidelines and the actual stress and strain states in the gusset plate are very nonlinear and highly complex. Design engineers want simple models with beam and column elements to make an approximate estimation of system and connection performance. The simplified design models are developed and evaluated to predict connection stiffness and system behavior. These models produce reasonably accurate and reliable estimation of connection stiffness.

• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.4 s.50
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• pp.55-66
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• 2006

This paper considers the nonlinear direct spectrum method to estimate seismic performance of mixed building structures without iterative computations, given dynamic property $T_1$ from stiffness skeleton curve and nonlinear pseudo acceleration $A_{1y}/g$ and/or ductility ratio p from response spectrum. Nonlinear response history analysis has been performed and analysed with various earthquakes for evaluation of correctness and confidence of nonlinear direct spectrum method. The conclusions of this study are as follows; (1) Nonlinear direct spectrum method is considered as a practical method which is applicable to compute the structural initial elastic period and the yielding strength from stiffness skeleton owe and calculate the nonlinear maximum response of structure directly from nonlinear response spectrum. (2) The comparison of the analysis results from NDSM and NRHA showed that the average errors were less than 20% in about 3/4 of the analysis cases, and that the results obtained from NDSM turned out to be generally larger than those from NRHA.

• Journal of the Korea Concrete Institute
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• v.20 no.1
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• pp.51-58
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• 2008

Analytical probabilistic vulnerability analysis requires extensive computing effort as a result of the randomness in both input motion and response characteristics. In this study, a new methodology whereby a set of vulnerability curves are derived based on the fundamental response quantities of stiffness, strength and ductility is presented. A response database of coefficients describing lognormal vulnerability relationships is constructed by employing aclosed-form solution for a generalized single-degree-of-freedom system. Once the three fundamental quantities of a wide range of structural systems are defined, the vulnerability curves for various limit states can be derived without recourse to further simulation. Examples of application are given and demonstrate the extreme efficiency of the proposed approach in deriving vulnerability relationships.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.2
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• pp.207-212
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• 2015

Bridges are designed and constructed as infrastructures in order to overcome topographical obstructions for fast and smooth transfer of human/material resources. Therefore the shape and size of piers constructed along the longitudinal bridge axis should be restricted by topographical conditions. Action forces of connections and piers are affected by pier shapes and sizes together with connection arrangement which decides load carrying path under earthquakes. In this study a typical bridge is modelled with steel bearings and reinforced concrete piers and seismic analyses are performed with analysis models with different arrangement of steel bearings and piers. From analysis results ductile failure mechanisms for all analysis models are checked based on strength/action force ratios of steel bearings and pier columns. In this way the influences of arrangement of connections and piers on the earthquake resistant capacity of typical bridges are figured out in view of forming ductile failure mechanism.

• Steel and Composite Structures
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• v.23 no.5
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• pp.571-583
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• 2017

A kind of accordion-web RBS connection, "Tubular Web RBS (TW-RBS)" connection is proposed in this research. TW-RBS is made by replacing a part of web with a tube at the desirable location of the beam plastic hinge. This paper presents first a numerical study under cyclic load using ABAQUS finite element software. A test specimen is used for calibration and comparison of numerical results. Obtained results indicated that TW-RBS would reduce contribution of the beam web to the whole moment strength and creates a ductile fuse far from components of the beam-to-column connection. Besides, TW-RBS connection can increase story drift capacity up to 9% in the case of shallow beams which is much more than those stipulated by the current seismic codes. Furthermore, the tubular web like corrugated sheet can improve both the out-of-plane stiffness of the beam longitudinal axis and the flange stability condition due to the smaller width to thickness ratio of the beam flange in the plastic hinge region. Thus, the tubular web in the plastic hinge region improves lateral-torsional buckling stability of the beam as just local buckling of the beam flange at the center of the reduced section was observed during the tests. Also change of direction of strain in arc shape of the tubular web section is smaller than the accordion webs with sharp corners therefore the tubular web provides a better condition in terms of low-cycle fatigue than other accordion web with sharp corners.

• Steel and Composite Structures
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• v.21 no.5
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• pp.1017-1029
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• 2016

When a welded circular hollow section (CHS) tubular joint is subjected to brace axial loading, failure position is located usually at the weld toe on the chord surface due to the weak flexural stiffness of the thin-walled chord. The failure mode is local yielding or buckling in most cases for a tubular joint subjected to axial load at the brace end. Especially when a cyclic axial load is applied, fracture failure at the weld toe may occur because both high stress concentration and welding residual stress along the brace/chord intersection cause the material in this region to become brittle. To improve the ductility as well as to increase the static strength, a tubular joint can be reinforced by increasing the chord thickness locally near the brace/chord intersection. Both experimental investigation and finite element analysis have been carried out to study the hysteretic behaviour of the reinforced tubular joint. In the experimental study, the hysteretic performance of two full-scale circular tubular T-joints subjected to cyclic load in the axial direction of the brace was investigated. The two specimens include a reinforced specimen by increasing the wall thickness of the chord locally at the brace/chord intersection and a corresponding un-reinforced specimen. The hysteretic loops are obtained from the measured load-displacement curves. Based on the hysteretic curves, it is found that the reinforced specimen is more ductile than the un-reinforced one because no fracture failure is observed after experiencing similar loading cycles. The area enclosed by the hysteretic curves of the reinforced specimen is much bigger, which shows that more energy can be dissipated by the reinforced specimen to indicate the advantage of the reinforcing method in resisting seismic action. Additionally, finite element analysis is carried out to study the effect of the thickness and the length of the reinforced chord segment on the hysteretic behaviour of CHS tubular T-joints. The optimized reinforcing method is recommended for design purposes.

• Journal of the Korean Geotechnical Society
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• v.15 no.6
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• pp.155-165
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• 1999

In completely weathered granite gneiss,8 of 40cm cast-in-situ concrete piles are constructed, and static pile load tests are executed on the piles to study the bearing behavior of rock-socketed piles. Subsurface explorations are carried out on the test site in three phases, in which 14 borehole investigations as well as the seismic investigation are performed. Rock socketd depths of the piles in the weathered rocks are varied as 3m, 6m and 9m to separate the shaft resistance from the end bearing resistance, and for a couple of piles, styrofoam of 10cm thickness is installed under the pile point to eliminate the effect of the end resistance. Strain gages are instrumented on re-bars to pick-up the transferred loads along the pile length. From the results of the pile load tests, the allowable shaft resistance and the allowable end bearing values of weathered rocks are proposed as $8.6t/m^2\;and\; 84t/m^2$, respectively. The empirical equation relating the elastic modulus of rock mass with the uniaxial compressive strength of the rock specimen is also proposed for the weathered rocks.

• Fire Science and Engineering
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• v.27 no.6
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• pp.21-25
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• 2013

Fire resistance steel, grading 490 MPa, had developed by using Thermo-mechanical control process (TMCP) and it has better performance at welding, seismic resistance than those of the ordinary structural steel, But the fire resistance performance is required to verify against the ordinary fire resistance, FR 490. Therefore this study was done to make database of mechanical properties at high temperature and to evaluate the structural stability at high temperature in terms of materials and structural member such as H-section from that of FR 490. The result of this study was that the structural stability of TMCP was lower than that of ordinary FR 490 at the range up about $700^{\circ}C$.

• Journal of Korean Society of Steel Construction
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• v.25 no.5
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• pp.497-507
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• 2013

This study investigated the tension-field action induced strip angle changes and deformed mode shapes of SPSW for high-rise structures subjected to lateral forces. Based on the numerical analysis 3, 9, 14 and 20 story structures, shear and flexural modes were identified by comparing the numerical analysis results to the predicted strength by theory. Shear deformation mode exhibited a constant angle in tension-field; whereas, flexural mode of the numerical results, differed from the tension-field action theory.