• Journal of Korean Tunnelling and Underground Space Association
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• v.25 no.6
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• pp.525-540
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• 2023

Because of a new seismic design code has been enacted in 2023, there is a need to evaluate whether the road tunnels in operation satisfies the requirements of the new code. Four tunnels that are considered to be most susceptible to damage. Time history analyses are performed to quantify their seismic performances. The input ground motions generated to fit both 2007 and 2023 codes are used to evaluate the effect of the motions on the calculated responses. The analyses show that all tunnels perform favorably and satisfies the requirements successfully. Therefore, retrofit or reinforcement are deemed as unnecessary.

• Journal of Korean Association for Spatial Structures
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• v.15 no.2
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• pp.61-68
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• 2015

The performance enhancement of various structural building systems from natural hazards has become an inctreasingly important issue in engineering field. In this paper, visco-elastic(VE) CST30 damping systems were tested under cyclic loadings to evaluate their performance in terms of ductility and energy dissipation. Main test variables are relative shear stiffness, rate of loading frequency, and thickness of specimens to evaluate the seismic capacity based on the performance criteria. This experiment was performed using a total of 12 specimens, subjected to cyclic loadings up to a shear deformation of 500%. All the CST30 dampers provided a ductile and stable hysterestic behavior when subjected to the demands of large shear stiffness and different loading frequencies. The test results showed that the CST30 dampers are an effective damping systems to enhance the buildings performance for remodeling and retrofit of buildings.

• Journal of Korean Association for Spatial Structures
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• v.24 no.1
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• pp.29-36
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• 2024

The paper presents the experimental investigation of RC beams retrofitted with Textile Reinforced Mortar (TRM), featuring enhanced bond capacity. Anchoring systems, including an extension of retrofitting length and the use of chemical anchors, are newly employed to improve the structural performance of the RC beam retrofitted with TRM. For the experimental investigation, a total of seven shear-critical RC beams, with and without stirrups, were designed and constructed. The structural behaviors of specimens retrofitted with the proposed TRM methods were compared to those of non-retrofitted specimens or specimens strengthened with conventional TRM methods. Crack pattern, force-displacement relationship, and absorbed energy were evaluated for each specimen. The experimental results indicate a significant improvement in the shear capacity of the RC beam with the proposed retrofitting method. Therefore, it is concluded that the application of an extended retrofitting length and chemical anchors to the TRM retrofitting method can effectively enhance the bond capacity of TRM, thereby improving the shear performance of RC beams.

• Journal of the Earthquake Engineering Society of Korea
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• v.24 no.1
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• pp.29-37
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• 2020

This study is to investigate the effect of a retrofitted reinforced concrete frame with non-seismic details strengthened by embedded steel moment frames with an indirect joint, which mitigates the problems of the direct joint method. First, full-scale experiments were conducted to confirm the structural behavior of a 2-story reinforced concrete frame with non-seismic details and strengthened by a steel moment frame with an indirect joint. The reinforced concrete frame with non-seismic details showed a maximum strength of 185 kN at an overall drift ratio of 1.75%. The flexural-shear failure of columns was governed, and shear cracks were concentrated at the beam-column joints. The reinforced concrete frame strengthened by the embedded steel moment frames achieved a maximum strength of 701 kN at an overall drift ratio of 1.5% so that the maximum strength was about 3.8 times that of the specimen with non-seismic details. The failure pattern of the retrofitted specimen was the loss of bond strength between the concrete and the rebars of the columns caused by a prying action of the bottom indirect joint because of lateral force. Furthermore, methods are proposed for calculation of the specified strength of the reinforced concrete frame with non-seismic details and strengthened by the steel moment frame with the indirect joint.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2003.09a
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• pp.263-270
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• 2003

Before the implementation of the 1992 seismic design provisions in Korea, longitudinal steels of RC bridge piers were practically lap-spliced in the plastic hinge region. Experimental investigation was made to evaluate the seismic performance of RC bridge pier specimens in a flexure/shear mode. Six circular test specimens in an aspect ratio of 2.5 (600mm in diameter) were made with test parameters confinement ratio, lap splices, and retrofit FRP materials. They were damaged under a series of artificial earthquakes with 0.22g PGA, being compatible in Korean peninsula, through the pseudo-dynamic test. Probable damages were assessed by the Park and Ang damage index. Approximate 0.1 and 0.3 damage indices were obtained for RC specimens without lap splice and with lap splice, respectively. Directly after the pseudo-dynamic test, damaged test columns were laterally actuated under inelastic reversal cyclic loadings simultaneously under a constant axial load. Through curvature measurements, residual seismic performance was evaluated for test specimens. Test results show that RC pier specimens with lap-spliced appeared to fail at low ductility, but significant improvement was obtained for the ductility of these specimens if externally wrapped with FRP.

• Earthquakes and Structures
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• v.8 no.1
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• pp.37-56
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• 2015

The Emilia, May-July 2012, earthquake has dramatically highlighted the only the hazards facing the people in insufficiently secured workplaces, but also the socio-economic consequences of interruption of production activities. After the event, in order to guarantee suitable safety levels, the Italian government asked for a generalized seismic retrofit of buildingsaffected by the earthquake under consideration. Considering that Emilia is one of the most industrialized Italian region, the number of the industrial buildings to be verified could however lead to not acceptable resumption of production time. So, with the aim to speed up the recovery, were leaved out from this request the buildings which had undergone a strong enoughshaking without any damage. In practice, the earthquakes were being used as a "test" to evaluate the seismic structural strength. Besides, the Italian government provision specifies also the zones, within which buildings that escaped evident damage are exempt from obligatory checks, and termed "exclusion zones", shall be individuated using the data provided by the Italian National Institute of Geophysics and Volcanology in the form of so-called "shakemaps". Obviously, the precision of such data greatly influences the determination of the exclusions zones and so all the economic issues related to them. Starting from these considerations, the present paper describes an evaluation of the reliability of the procedure of shakemap generation with specific regard to the seismic events that struck the Emilia region on May 20 and 29, 2012.

• Journal of the Korean Society of Industry Convergence
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• v.23 no.5
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• pp.789-798
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• 2020

This paper considers the development of the dynamic analysis model and simulation-based operation safety estimation of A-Frame to be applied to the test evaluation support vessel for real sea test. The support vessel will be manufactured by modifying the existing offshore support vessel. Also, development and installation of various sensors and supporting facilities for test evaluation are under preparation. Among these facilities, A-Frame is an equipment that transfers marine equipment from ship deck to the sea floor, and is being designed to transfer up to 50 ton class equipment. However, the A-Frame is a moving equipment using hydraulic cylinders. When the 50 ton equipment is attached and transferred to A-Frame, the buckling of cylinders may occur or A-Frame becomes inoperable due to the influence of huge inertia. For this reason, safety verification should be performed using dynamic analysis techniques that can take into account huge inertia forces in the design of A-Frame. Therefore, in this study, A-Frame and ship behavior were modeled using dynamic analysis method, and the applied loads of various equipment including hydraulic cylinder of A-Frame was measured and the operation safety review was performed.

• 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.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.1A
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• pp.237-246
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• 2006

In order to evaluate the seismic performance of damaged reinforced concrete members, particularly bridge piers, an inelastic time-dependent element is proposed. The proposed element enables increased characteristics due to structural intervention(i.e., repair or retrofitting) to be accurately reflected to the degraded strength and stiffness of the members. The inelastic time-dependent element having both birth and death time can freely be activated within the user-defined time intervals during static and dynamic time-history analysis. Comparative studies are carried out for reinforced concrete bridge piers that are repaired and retrofitted. Analytical predictions using the developed element show reasonable correlation with experimental results. Also conducted is a nonlinear time-history analysis of a reinforced concrete bridge under multiple earthquakes. The comparative analytical results prove the validation of current development. In all, it is concluded that the present element is capable of providing salient features for the healthy evaluation of seismic performance and hence seismic stability assessment of RC bridge piers being repaired and retrofitted.

• Journal of the Korea Concrete Institute
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• v.21 no.3
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• pp.327-335
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• 2009

In the seismic region, non-ductile structures often form soft story and exhibit brittle collapse. However, structure demolition and new structure construction strategies have serious problems, as construction waste, environmental pollution and popular complain. And these methods can be uneconomical. Therefore, to satisfy seismic performance, so many seismic retrofit methods have been investigated. There are some retrofit methods as infill walls, steel brace, continuous walls, buttress, wing walls, jacketing of column or beam. Among them, the infilled frames exhibit complex behavior as follows: flexible frames experiment large deflection and rotations at the joints, and infilled shear walls fail mainly in shear at relatively small displacements. Therefore, the combined action of the composite system differs significantly from that of the frame or wall alone. Purpose of research is evaluation on the seismic performance of infill walls, and improvement concept of this paper is use of SHCCs (strain-hardening cementitious composites) to absorb damage energy effectively. The experimental investigation consisted of cyclic loading tests on 1/3-scale models of infill walls. The experimental results, as expected, show that the multiple crack pattern, strength, and energy dissipation capacity are superior for SHCC infill wall due to bridging of fibers and stress redistribution in cement matrix.