• Journal of the Earthquake Engineering Society of Korea
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• v.18 no.5
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• pp.241-251
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• 2014

In this study, shaking table test was carried out to evaluate the seismic behavior and performance of low-rise reinforced concrete (RC) piloti structures with and without retrofit. The specimens were designed considering the characteristics of existing building with pilotis such as natural period, distribution factor of strength and stiffness between columns and core wall on the first soft story. The test for the non-retrofit specimen showed that damage was concentrated on the stiffer member on the same floor as the core wall failed by shear fracture whereas columns experienced slight flexural cracks. Considering the failure mode of the non-retrofit specimen, the retrofit method using steel rod damper was presented for improving the seismic performance of piloti structures. The results of the test for retrofit specimen revealed that the retrofit method was effective for controlling the damage as the main RC structural members were not destroyed and most of input energy was dissipated by hysteretic behavior of the damper.

• Journal of the Earthquake Engineering Society of Korea
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• v.5 no.3
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• pp.29-36
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• 2001

Same as-built drawings in national roadway bridges in Korea were examined. As a result, many bridge piers were found whose aspect ratios are in the vicinity of 2.5. These columns are expected to do shear-flexure behaviour, but the previous research works considered flexure behaviour columns only. In the study, therefore, a shear-flexure behaviour column was selected as the model pier, and quasi static test on the full and 1/2 scale models was carried out. From the test results, the scale effect on the seismic performance evaluation was analyzed, and the seismic performance of the model bridge pier without seismic details was evaluated by the capacity spectrum method.

• Magazine of the Korea Concrete Institute
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• v.7 no.1
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• pp.156-164
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• 1995

P-${\Delta}$ analysis by use of the equivalent colurnn stiffness determined by Momcnt curvature-Thrust curves provides relatively precise analytical results for unbraced reinforced concrete columns, however it needs a complicated arialytical procedure. Equ~valent col~rnn stiffness equations are proposed for a simple analytical procedure which are ckterrnined by the Moment-Curvature Thrust curves of the practically useable sections. Thc proposed stiffness equations are appiled to P-${\Delta}$ analysis and rnornent magnifier method to compare with the selected test result. Use of the proposed stiffness equations may slrnplify the P-${\Delta}$ i.rialvtica1 procedure and improve the accuracy of moment magnifier niethod.

• Earthquakes and Structures
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• v.11 no.1
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• pp.141-163
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• 2016

Fiber models have been developed and applied to various structural elements such as shear walls, beams and columns. Only scarcely have fiber models been applied to circular foundation systems such as cast in drilled holes shafts (CIDH). In pile foundations with constraint head boundary conditions, shear deformations can easily contribute to the lateral pile response. However, soil structure interaction formulations such as the p-y method, commonly used for lateral pile design, do not include structural shear deformations in its traditional derivation method. A fiber model that couples shear and axial-bending behavior, originally developed for wall elements was modified and validated on circular cross sections (columns) before being applied to a 0.61 m diameter reinforced concrete (RC) pile with fixed head boundary conditions. The analytical response was compared to measured test results of a fixed head test pile to investigate the possible impact of pile shear deformations on the displacement, shear, and moment profiles of the pile. Results showed that shear displacements and forces are not negligible and suggest that nonlinear shear deformations for RC piles should be considered for fixed-head or similar conditions. Appropriate sensor layout is recommended to capture shear deformation when deriving p-y curves from field measurements.

• Earthquakes and Structures
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• v.7 no.5
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• pp.797-815
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• 2014

This research aimed to investigate retrofitting methods for damaged RC columns with SRF (Super Reinforced with Flexibility) and aramid composites and their impacts on the seismic responses. In the first stage, two original (undamaged) column specimens, designed to have a flexural- or shear-controlled failure mechanism, were tested under quasi-static lateral cyclic and constant axial loads to failure. Afterwards, the damaged column specimens were retrofitted, utilizing SRF composites and aramid rods for the flexural-controlled specimen and only SRF composites for the shear-controlled specimen. In the second stage, the retrofitted column specimens were tested again under the same conditions as the first stage. The hysteretic responses such as strength, ductility and energy dissipation were discussed and compared to clarify the specific effects of each retrofitting material on the seismic performances. Generally, SRF composites contributed greatly to the ductility of the specimens, especially for the shear-controlled specimen before retrofitting, in which twice the deformation capacity was obtained in the retrofitted specimen. The shear-controlled specimen also experienced a flexural failure mechanism after retrofitting. In addition, aramid rods moderately fortified the specimen in terms of the maximum shear strength. The maximum strength of the aramid-retrofitted specimen was 12% higher than the specimen without aramid rods. In addition, an analytical modeling of the undamaged specimens was conducted using Response-2000 and Zeus Nonlinear in order to further validate the experimental results.

• KIEAE Journal
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• v.7 no.6
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• pp.113-118
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• 2007

The composite beam adopted in the study was designed to reduce the floor height as well as to embed the top flange of steel frame into the slab that will enable to avoid applying the fire-resistant coating and to unify the joint method with a steel frame-type. As the steel frame and bottom concrete of the beam is pre-fabricated at the factory it could reduce the overall schedule at the jobsite. Applying such composite beam system to the work is expected to provide the efficient and enhanced performance, given the current tendency of the building construction that tends to be getting higher, larger and dense. The study focused on combining the composite beam with various column systems in a bid to propose the details thereof. A desirable composite girder can be adopted depending on site conditions through the evaluation of various beam and jointing approaches. Among the column systems applied to the study are steel column, SRC column, RC-PC column and RC column. The ways of combining with the columns addressed in the study were categorized into the rigid joint, pin joint, steel frame joint and bracket type joint. Besides, the instruction for site fabrication of beam-column was added in an effort to help set up the site fabrication procedures.

• Structural Monitoring and Maintenance
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• v.2 no.2
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• pp.165-180
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• 2015

In this paper lead zirconate titanate transducers (PZT) are employed for damage detection of four reinforced concrete (RC) column specimens retrofitted with carbon fiber reinforced polymer (CFRP) jackets. A major disadvantage of FRP jacketing in RC members is the inability to inspect visually if the concrete substrate is damaged and in such case to estimate the extent of damage. The parameter measured during uniaxial compression tests at random times for known strain values is the real part of the complex number of the Electromechanical Admittance (Conductance) of the sensors, obtained by a PXI platform. The transducers are placed in specific positions along the height of the columns for detecting the damage in different positions and carrying out conclusions for the variation of the Conductance in relation to the position the failure occurred. The quantification of the damage at the concrete substrate is achieved with the use of the root-mean-square-deviation (RMSD) index, which is evaluated for the corresponding strain values. The experimental results provide evidence that PZT transducers are sensitive to damage detection from an early stage of the experiment and that the use of PZT sensors for monitoring and detecting the damage of FRP-retrofitted reinforced concrete members, by using the Electromechanical Admittance (EMA) approach, can be a highly promising method.

• Structural Engineering and Mechanics
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• v.37 no.1
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• pp.111-129
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• 2011

This paper presents a nonlinear analysis of reinforced concrete column with lap splice confined by FRP wrapping in the critical hinging zone. The steel stress-slip model derived from the tri-uniform bond stress model presented in the companion paper is included in the nonlinear frame analysis to simulate the response of reinforced concrete columns subjected to cyclic displacement reversals. The nonlinear modeling is based on a fiber discretization of an RC column section. Each fiber is modeled as either nonlinear concrete or steel spring, whose load-deformation characteristics are calculated from the section of fiber and material properties. The steel spring that models the reinforcing bars consists of three sub-springs, i.e., steel bar sub-spring, lap splice spring, and anchorage bond-slip spring connected in series from top to bottom. By combining the steel stress versus slip of the lap splice, the stress-deformation of steel bar and the steel stress-slip of bars anchored into the footing, the nonlinear steel spring model is derived. The analytical responses are found to be close to experimental ones. The analysis without lap splice springs included may result in an erroneous overestimation in the strength and ductility of columns.

• Earthquakes and Structures
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• v.7 no.3
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• pp.251-269
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• 2014

To investigate the seismic performance and to obtain quantitative parameters for the requirement of performance-based bridge seismic design approach, 12 reinforced concrete (RC) hollow rectangular bridge column specimens were tested under constant axial load and cyclic bending. Parametric study is carried out on axial load ratio, aspect ratio, longitudinal reinforcement ratio and transverse reinforcement ratio. The damage states of these column specimens were related to engineering limit states to determine the quantitative criteria of performance-based bridge seismic design. The hysteretic behavior of bridge column specimens was simulated based on the fiber model in OpenSees program and the results of the force-displacement hysteretic curves were well agreed with the experimental results. The damage states of residual cracking, cover spalling, and core crushing could be well related to engineering limit states, such as longitudinal tensile strains of reinforcement or compressive strains of concrete, etc. using cumulative probability curves. The ductility coefficient varying from 3.71 to 8.29, and the equivalent viscous damping ratio varying from 0.19 to 0.31 could meet the requirements of seismic design.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.6
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• pp.59-66
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• 2020

Two octagonal RC bridge columns of small scale model were tested under cyclic lateral load with constant axial load. One in two specimens was solid cross section, the other was hollow cross section. The volumetric ratio of transverse spiral hoop of all specimens is 0.00206. The columns showed flexure-shear failure. Failure behavior and seismic performance were investigated. The test results showed that the structural performance of the hollow specimen such as initial crack pattern, initial stiffness, and energy dissipation performance was comparable to that of the solid specimen, but the lateral strength, ultimate displacement, energy dissipation performance of hollow specimen noticeably decreased after drift ratio of 3%.