• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.6C
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• pp.295-304
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• 2012

In this study, a resonant column testing system which is the largest in Korea has been developed to evaluate the dynamic deformation characteristics of coarse granular geomaterials, and the performance and the applicability of the testing system have been verified. The system has been developed as a typical Stokoe type device whose boundary conditions are fixed bottom and free top with additional mass, and can adopt a large specimen with 200 mm in diameter and 400 mm in height. The driving and measurement instruments are configured as high performance and precision systems, hence the automated testing system is appropriate to drive enough stress and to measure the behavior precisely for the test in practical manner. The dynamic response of the mechanical components and the applicability of the system have been evaluated using metal specimens as well as polyurethane specimens, and its precision was verified by comparing its results with those from other equipment and/or methods. To confirm the applicability of the large system for coarse geomaterials, the resonant column test results from both large and normal scale apparatus for the same material were compared and it was found that the result can be partially affected by scale. Finally, the dynamic deformation characteristics of coarse geomaterial which is used for construction of large dam was evaluated using the large system and its practicality could be confirmed.

• 한국지구물리탐사학회:학술대회논문집
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• 2005.09a
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• pp.155-175
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• 2005

Soil and rock dynamic properties such as shear wave velocity (VS), compressional wave velocity (VP) and corresponding Poisson's ratio ( v ) are very important geotechnical parameters in predicting deformational behavior of structures as well as practicing seismic design and performance evaluation. In an effort to measure the parameter efficiently and accurately, various bore-hole seismic testing techniques have been, thus, developed and used during past several decades. In this study, cross-hole seismic testing technique which is known as the most reliable seismic method was adopted for obtaining geotechnical dynamic properties. To perform successfully the cross-hole test for rock as well as soil layers regardless of the ground water level, spring-loaded source which impact laterally a subsurface ground in vertical bore-hole was developed and applied at three study areas, which contain four sites composed of two existing port sites and two new LNG storage facility sites. The geotechnical dynamic properties such as VS, VP and v with depth were efficiently determined from the laterally impacted cross-hole seismic tests at study sites, and were provided as the fundamental parameters for the seismic performance evaluation of the existing ports and the seismic design of the LNG storage facilities.

• Advances in concrete construction
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• v.14 no.1
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• pp.45-55
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• 2022

In this article, the flexural and shear capacity of ultra-high-performance fiber-reinforced concrete beams (UHPFRC) using two kinds of rebars, including GFRP and steel rebars, are experimentally investigated. For this purpose, six UHPFRC beams (250 × 300 × 1650 mm) with three reinforcement ratios (ρ) of 0.64, 1.05, and 1.45 were constructed using 2% steel fibers by volume. Half of the specimens were made of UHPFRC reinforced with GFRP rebars, while the other half were reinforced with conventional steel rebars. All specimens were tested to failure in four-point bending. Both the load-deformation at mid-span and the failure pattern were studied. The results showed that utilizing GFRP bars increases the flexural strength of UHPFRC beams in comparison to those made of steel bars, but at the same time, it reduces the post-cracking strain hardening. Furthermore, by increasing the percentage of longitudinal bars, both the post-cracking strain hardening and load-bearing capacity increase. Comparing the experiment results with some of the available equations and provisions cited in the valid design codes reveals that some of the equations to predict the flexural strength of UHPFRC beams reinforced with conventional steel and GFRP bars are reasonably conservative, while Khalil and Tayfur model is un-conservative. This issue makes it essential to modify the presented equations in this research for predicting the flexural strength of UHPFRC beams using GFRP bars.

• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.4 s.50
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• pp.1-13
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• 2006

Soil and rock dynamic properties such as shear wave velocity $(V_s)$, compressional wave velocity $(V_p)$ and corresponding Poisson's ratio (v) are very important geotechnical parameters in predicting deformational behavior of structures as well as practicing seismic design and performance evaluation. In an effort to measure the parameter efficiently and accurately, various bore-hole seismic testing techniques have been, thus, developed and used during past several decades. In this study, cross-hole seismic testing technique which is known as the most reliable seismic method was adopted for obtaining geotechnical dynamic properties. To perform successfully the cross-hole test for rock as well as soil layers regardless of the ground water level, spring-loaded source which impact laterally a subsurface ground in vertical bore-hole was developed and applied at three study areas, which contain four sites composed of two existing port sites and two new LNG storage facility sites. The geotechnical dynamic properties such as $V_s,\;V_p$ and v with depth from the soil surface to the engineering and seismic bedrock were efficiently determined from the laterally impacted cross-hole seismic tests at study sites, and were provided as the fundamental parameters for the seismic performance evaluation of the existing ports and the seismic design of the LNG storage facilities.

• Journal of the Korea Concrete Institute
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• v.24 no.1
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• pp.3-14
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• 2012

This paper describes experimental results on the seismic performance of SHCC (strain-hardening cement composite) infill wall for improving damage tolerance capacity of non-ductile frame. To investigate the effect of tensile strain capacity and cracking behavior of SHCC materials on the shear behavior of SHCC infill wall, three infill walls were fabricated and tested under cyclic loading. The test parameter in this study is a type of cement composites; concrete and SHCCs. The two types of SHCC materials were prepared for infill walls. In order to induce crack damages into the mid-span of the infill wall, each infill wall had two 100-mm-deep-notches on both sides. Test results indicated that SHCC infill walls showed superior crack control capacities and much larger drift ratios at the peak loads than RC (reinforced concrete) infill wall, as expected. In particular, due to the bridging actions of the reinforcing fibers, SHCC matrix used in this study would delay the stiffness degradation of infill wall after the first inclined cracking. Moreover, from the damage classes based on the cracks' maximum width in the infill walls, it was observed that PIW-SHD specimen possessed nearly threefold seismic capacities compared to PIW-SLD specimen. Also, from the results on the strain of diagonal reinforcements, it can be concluded that the SHCC matrix would resist a part of tensile stresses transferred along steel rebar in the infill wall.

• Journal of the Korea Concrete Institute
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• v.28 no.1
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• pp.85-94
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• 2016

In this study, the hydrophilic chemical grout using silanol (HCGS) was introduced to overcome the limitations of conventional epoxy resin which have been used for strengthening reinforced concrete (RC) structures. Then, flexural tests on the RC slabs strengthened by FRP sheets were conducted. Three slab specimens were tested in this study; a control specimen with no strengthening, and two specimens strengthened by a typical epoxy resin or HCGS, respectively, as a binder between the slabs and the FRP sheets. In addition, an analytical model was developed to evaluate the flexural behavior of strengthened slab members, considering the horizontal shear force at the interface between concrete slabs and FRP sheets. The analysis results obtained from the proposed model indicated that the strengthened specimens showed fully composite behavior before their flexural failure. Especially, the specimen strengthened by HCGS, which can overcome the limitations of conventional epoxy resin, showed a similar flexural performance with that strengthened by a conventional epoxy resin.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.29-32
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• 2008

The renewal of existing buildings rather than new construction has increased due to it's cost effective characteristics. Remodeling is also an environmentally-friendly approach that reduces the amount of waste in construction site. Remodeling can sometimes include partial destruction of the structural members of a building. In addition it is important that the buildings under going remodeling retrofitted to make themselves stable and meet up with the future demands for better structural performance. The objective of this paper is to present the test results and structural behavior of RC walls that are perforated and to introduce effective retrofitting methods by evaluating efficacy of passive retrofit and active retrofit. Passive retrofit and Active retrofit using carbon fiber sheets, steel plates and wire that are widely used for strengthening the main members of existing buildings. The test results showed that the failed specimens had shear fractures and that two different types of retrofit method had different effects on the strengths of each specimen.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.2
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• pp.24-33
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• 2017

Domestic urban railway underground station structures, which were built in the 1970s ad 1980s, had been constructed as Cut-and-Cover construction system without seismic design. Because the trends of earthquake occurrence is constantly increasing all over the world as well as the Korean Peninsula, massive human casualties and severe properties and structures damage might be occurred in an non-retrofitted underground station during an earthquake above a certain scale. Therefore, to evaluate the retrofit effect and soil-structure interaction of seismic retrofitted underground station, a centrifugal shaking table test with enhanced stiffness on its structural main member are carried out on 1/60 scaled model using the Kobe and Northridge earthquakes. The seismic retrofitted members, which are columns, side walls, and slabs, are evaluated to comparing with existing non-retrofitted centrifuge test results Also, to simulate the scaled ground using variation of shear velocity according to site conditions such as ground depth and density, resonant column test is performed. From the test results, the relative displacement behavior between ground and structures shows comparatively similar in ground, but is increased on ground surface. The seismic retrofit effects were measured using relative displacements and moment behavior of column and side walls rather than slabs. Additionally, earthquake wave can be used to main design factor due to large structural deformation on Kobe earthquake wave than Norhridge earthquake wave.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.2 s.72
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• pp.151-160
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• 2006

In this study, we propose a new efficient 2-noded hybrid-mixed element for curved beam vibrationshaving a uniform and non-uniform cross section. The present element considering transverse shear strain is based on Hellinger-Reissner variational principle and introduces additional nodeless degrees for displacement field interpolation in order to enhance the numerical performance. The stress parameters are eliminated by the stationary condition and then the nodeless degrees are condensed out by the Guyan reduction. In the performance evaluation process of the present field-consistent higher-order element, we carefully examine the effects of field consistency and the role of higher-order interpolation functions on the hybrid-mixed formulation. Several benchmark tests confirm e superior behavior of the present hybrid-mixed element for curved beam vibrations.

• Journal of Korean Society of Steel Construction
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• v.25 no.1
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• pp.81-92
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• 2013

The objective of conventional seismic design is to ensure an acceptable safety level while avoiding catastrophic failures of structures and loss of life. Over the last many years, a large amount of research has been devoted into developing effective earthquake resistant systems in order to raise the seismic performance level of structures. The purpose of this study is to propose a new damping system, which realize not only increasing seismic performance but also easy repairing after an earthquake. The proposed damping system is slit in the bottom of wall with damping devices installed in the slit horizontally aiming to dissipate energy during earthquakes. Cyclic loading tests were conducted to investigate hysteretic behavior and energy dissipation capacity. Test results show that the proposed systems exhibit a stable hysteretic response and the energy dissipation in this system is concentrated on the damping devices.