• Title/Summary/Keyword: Seismic retrofitted

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Seismic Capacity of Non-seismic Designed RC Framed Building Retrofitted by CBD System (CBD 시스템으로 보강된 비내진 RC 골조의 내진성능 평가)

  • Hur, Moo-Won;Lee, Sang-Hyun;Chun, Young-Soo
    • Journal of the Korea Concrete Institute
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    • v.27 no.6
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    • pp.625-632
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    • 2015
  • In this study, a comparative analysis have been conducted to examine seismic reinforcement effect of a school building that is designed with a CBD (Channel Beam Damper) system supported by H-frame with existing non-seismic RC frame. As a result of experiment, seismic reinforcement specimen with CBD system showed hysteretic characteristics of a large ellipse with great energy dissipation ability and increased strength and stiffness, while non-seismic design specimen showed rapid reduction in strength and brittle shear failure at top and bottom of the left and right column. In addition, comparing the stiffness reduction between the two specimens, CBD system was effective in preventing the reduction of stiffness. Energy dissipation ability of specimen reinforced by CBD system was about 4.0 times higher than the non-reinforced specimen. Such enhancement in energy dissipation ability could be considered as the result of improved strength and deformation for further application in designing of seismic reinforcement.

Seismic Performance Evaluation of Inverted V Braced Steel Frames with Considering P-Δ Effects: A Case Study (P-Δ 효과를 고려한 역 V형 철골 가새골조의 내진성능평가: 사례연구)

  • Lee, Cheol-Ho;Kim, Jeong-Jae
    • Journal of the Earthquake Engineering Society of Korea
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    • v.8 no.3
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    • pp.97-103
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    • 2004
  • Most of the columns in centrally braced steel frame buildings are usually designed as the gravity columns to reduce connection cost. For a rational seismic performance evaluation of centrally braced steel frame buildings, it is important to properly incorporate in the analysis  the P-${\Delta}$ effects arising from the gravity columns. An effective scheme for the P-${\Delta}$ effects modeling due to the gravity columns was illustrated based on the concept of fictitious leaning column. Seismic performance evaluation of inverted V braced steel frames with or without P-${\Delta}$ effects modeling was conducted by following the FEMA 273 NSP (Nonlinear Static Procedure). The problem in estimating dynamic P-${\Delta}$ modification factor (C3) in FEMA 273 was discussed. The results of this study indicated that the P-${\Delta}$ effects should be included in the seismic performance evaluation of centrally braced steel frames. This study also showed that the inverted V braced frames, retrofitted by applying the tie bars to redistribute the inelastic demand over the height of the building, exhibit significantly improved seismic performance.

Seismic Performance of RC Frame System Retrofitted with TS Seismic Strengthening Method (Part 1:Analytical Study) (TS 제진공법으로 내진보강된 철근콘크리트 골조의 내진성능(Part 1:해석적 연구))

  • Jung, Myung-Cheol;Song, Jeong-Weon;Song, Jin-Kyu
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.22 no.2
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    • pp.141-147
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    • 2018
  • In this study, a cyclic loading test was carried out for a reinforced concrete frame installed a TS(tension-spring) damper for the purpose of verifying the seismic strengthening effect of the TS seismic reinforcing method. The test specimens are four specimens of non - reinforced frame and three reinforced frame specimens. Experimental parameters are Shape of damper and construction method of damper. As a result, the construction method of inserting type inside window was twice as much in terms of strength and stiffness, and the method of externally attached type showed a performance improvement of about 2 times in terms of energy dissipation. From these results, it can be confirmed that the TS seismic reinforcing method is a superior method for field application and seismic strengthening.

Numerical modelling for monitoring the hysteretic behaviour of CFRP-retrofitted RC exterior beam-column joints

  • Mahini, Seyed S.;Ronagh, Hamid R.
    • Structural Engineering and Mechanics
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    • v.38 no.1
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    • pp.27-37
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    • 2011
  • This paper presents the results of a study on the capability of nonlinear quasi-static finite element modelling in simulating the hysteretic behaviour of CFRP and GFRP-retrofitted RC exterior beam-column joints under cyclic loads. Four specimens including two plain and two CFRP/GFRP-strengthened beam-column joints tested by Mahini and Ronagh (2004) and other researchers are modelled using ANSYS. Concrete in compression is defined by the modified Hognestad model and anisotropic multi-linear model is employed for modelling the stress-strain relations in reinforcing bars while anisotropic plasticity is considered for the FRP composite. Both concrete and FRP are modelled using solid elements whereas space link elements are used for steel bars considering a perfect bond between materials. A step by step load increment procedure to simulate the cyclic loading regime employed in the testing. An automatically reforming stiffness matrix strategy is used in order to simulate the actual seismic performance of the RC concrete after cracking, steel yielding and concrete crushing during the push and pull loading cycles. The results show that the hysteretic simulation for all specimens is satisfactory and therefore suggest that the numerical model can be used as an inexpensive tool to design of FRP-strengthened RC beam-column joints under cyclic loads.

Ultimate shear strength prediction model for unreinforced masonry retrofitted externally with textile reinforced mortar

  • Thomoglou, Athanasia K.;Rousakis, Theodoros C.;Achillopoulou, Dimitra V.;Karabinis, Athanasios I.
    • Earthquakes and Structures
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    • v.19 no.6
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    • pp.411-425
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    • 2020
  • Unreinforced masonry (URM) walls present low shear strength and are prone to brittle failure when subjected to inplane seismic overloads. This paper discusses the shear strengthening of URM walls with Textile Reinforced Mortar (TRM) jackets. The available literature is thoroughly reviewed and an extended database is developed including available brick, concrete and stone URM walls retrofitted and subjected to shear tests to assess their strength. Further, the experimental results of the database are compared against the available shear strength design models from ACI 549.4R-13, CNR DT 215 2018, CNR DT 200 R1/2013, Eurocode 6 and Eurocode 8 guidelines as well as Triantafillou and Antonopoulos 2000, Triantafillou 1998, Triantafillou 2016. The performance of the available models is investigated and the prediction average absolute error (AAE) is as high as 40%. A new model is proposed that takes into account the additional contribution of the reinforcing mortar layer of the TRM jacket that is usually neglected. Further, the approach identifies the plethora of different block materials, joint mortars and TRM mortars and grids and introduces rational calibration of their variable contributions on the shear strength. The proposed model provides more accurate shear strength predictions than the existing models for all different types of the URM substrates, with a low AAE equal to 22.95%.

Experimental Study on Shear Retrofitting of Concrete Columns Using Iron-Based Shape Memory Alloy (철계 형상기억합금을 이용한 콘크리트 기둥의 전단보강 실험연구)

  • Jung, Donghuk;Jeong, Saebyeok;Choi, Jae-Hee;Kim, Geunoh
    • Journal of the Earthquake Engineering Society of Korea
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    • v.28 no.1
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    • pp.41-46
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    • 2024
  • The current study investigates the seismic performance of shear-dominant RC columns retrofitted with iron-based shape memory alloy (Fe SMA). Three RC columns with insufficient transverse reinforcement were designed and fabricated for lateral cyclic loading tests. Before testing, two specimens were externally confined with carbon fiber-reinforced polymer (CFRP) sheets and self-prestressed Fe SMA strips. The test results showed that both CFRP and Fe SMA performed well in preventing severe shear failure exhibited by the unretrofitted control specimen. Furthermore, the two retrofitted specimens showed ductile flexural responses up to the drift ratios of ±8%. In terms of damage control, however, the Fe SMA confinement was superior to CFRP confinement in that the spalling of concrete was much less and that the rupture of confinement did not occur.

Seismic Behavior of Reinforced Concrete Moment Frames Retrofitted by Toggle Bracing System with High Density Friction Damper (토글 가새-고집적 마찰댐퍼를 설치한 철근콘크리트 모멘트 골조의 성능 평가)

  • Han, Sang Whan;Kim, Ji Yeong;Moon, Ki Hoon;Lee, Chang Seok;Kim, Hyung Joon;Lee, Kang Seok
    • Journal of the Earthquake Engineering Society of Korea
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    • v.18 no.3
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    • pp.133-140
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    • 2014
  • The friction damper can be used for improving the seismic resistance of existing buildings. The damper is often installed in bracing members. The energy dissipation capacity of the damping systems depends on the type of the structure, the configuration of the bracing members, and the property of dampers. In Korea, there are numerous low- to mid-rise reinforced concrete moment frames that were constructed considering only gravity loads. Those frames may be vulnerable for future earthquakes. To resolve the problem, this study developed a toggle bracing system with a high density friction damper. To investigate the improvement of reinforced concrete frames after retrofit using the developed damped system, experimental tests were conducted on frame specimens with and without the damped system. The results showed that the maximum strength, initial stiffness and energy dissipation capacity of the framed with the damped system were much larger than those of the frame without the damped system.

Nonlinear earthquake capacity of slender old masonry structures prestressed with steel, FRP and NiTi SMA tendons

  • Preciado, Adolfo;Ramirez-Gaytan, Alejandro;Gutierrez, Nayar;Vargas, David;Falcon, Jose Manuel;Ochoa, Gil
    • Steel and Composite Structures
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    • v.26 no.2
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    • pp.213-226
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    • 2018
  • This paper focuses on the seismic protection of slender old masonry structures by the implementation of prestressing devices at key locations. The devices are vertically and externally located inside the towers in order to be reversible and calibrated. An extensive parametric study on a selected slender tower is carried out based on more than 100 nonlinear static simulations aimed at investigating the impact of different parameters on the seismic performance: (i) different prestressing levels; (ii) shape memory alloy superelasticity and (iii) changes in prestressing-forces in all the stages of the analysis until failure and masonry toe crushing. The tendon materials under analysis are conventional prestressing steel, fiber-reinforced polymers of different fibers and shape memory alloys. The parametric study serves to select the most suitable prestressing device and optimal prestressing level able to dissipate more earthquake energy. The seismic energy dissipation is evaluated by comparing the structural capacity curves in original state and retrofitted.

Design of a bracing-friction damper system for seismic retrofitting

  • Lee, Sung-Kyung;Park, Ji-Hun;Moon, Byoung-Wook;Min, Kyung-Won;Lee, Sang-Hyun;Kim, Jinkoo
    • Smart Structures and Systems
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    • v.4 no.5
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    • pp.685-696
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    • 2008
  • This paper deals with the numerical model of a bracing-friction damper system and its deployment using the optimal slip load distribution for the seismic retrofitting of a damaged building. The Slotted Bolted Connection (SBC) type friction damper system was tested to investigate its energy dissipation characteristic. Test results coincided with the numerical ones using the conventional model of a bracing-friction damper system. The placement of this device was numerically explored to apply it to the assumed damaged-building and to evaluate its efficiency. It was found by distributing the slip load that minimizes the given performance indicies based on structural response. Numerical results for the damaged building retrofitted with this slip load distribution showed that the seismic design of the bracing-friction damper system under consideration is effective for the structural response reduction.

Fragility Assessment of Damaged Piloti-Type RC Building With/Without BRB Under Successive Earthquakes (연속 지진에 의하여 손상된 필로티 RC 건축물의 BRB 보강 전/후의 취약성 평가)

  • Shin, Jiuk;Kim, JunHee;Lee, Kihak
    • Journal of the Earthquake Engineering Society of Korea
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    • v.17 no.3
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    • pp.133-141
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    • 2013
  • This paper presents the seismic evaluation and prediction of a damaged piloti-type Reinforced Concrete (RC) building before and after post-retrofitting under successive earthquakes. For considering realistic successive earthquakes, the past records measured at the same station were combined. In this study, the damaged RC building due to the first earthquake was retrofitted with a buckling-restrained brace (BRB) before the second earthquake occurred. Nonlinear Time History Analysis (NTHA) was performed under the scaled intensity of the successive ground motions. Based on the extensive structural response data obtained form from the NTHA, the fragility relationships between the ground shaking intensity and the probability of reaching a pre-determined limit state was were derived. In addition, The the fragility curves of the pre-damaged building without and with the BRBs were employed to evaluate the effect of the successive earthquakes and the post-retrofit effect. Through the seismic assessment subjected to the successive records, it was observed that the seismic performance of the pre-damaged building was significantly affected by the severity of the damage from the first earthquake damages and the hysteresis behavior of the retrofit element.