• Structural Engineering and Mechanics
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• 제72권3호
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• pp.355-366
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• 2019

Self-centering wall (SCW) is a resilient and sustainable structural system which incorporates unbonded posttensioning (PT) tendons to provide self-centering (SC) capacity along with supplementary dissipators to dissipate seismic energy. Hysteretic energy dissipators are usually placed at two sides of SCWs to facilitate ease of postearthquake examination and convenient replacement. To achieve a good prediction for the skeleton curve of the wall, this paper firstly developed an analytical investigation on lateral load responses of self-centering walls with distributed vertical dampers (VD-SCWs) using the concept of elastic theory. A simplified method for the calculation of limit state points is developed and validated by experimental results and can be used in the design of the system. Based on the analytical results, parametric analysis is conducted to investigate the influence of damper and tendon parameters on the performance of VD-SCWs. The results show that the proposed approach has a better prediction accuracy with less computational effects than the Perez method. As compared with previous experimental results, the proposed method achieves up to 60.1% additional accuracy at the effective linear limit (DLL) of SCWs. The base shear at point DLL is increased by 62.5% when the damper force is increased from 0kN to 80kN. The wall stiffness after point ELL is reduced by 69.5% when the tendon stiffness is reduced by 75.0%. The roof deformation at point LLP is reduced by 74.1% when the initial tendon stress is increased from $0.45f_{pu}$ to $0.65f_{pu}$.

• Smart Structures and Systems
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• 제14권5호
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• pp.883-900
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• 2014

Shape memory alloys (SMA) can dissipate energy through hysteresis cycles without significant residual deformation. This paper describes the fabrication and testing of copper-based SMA hourglass-shaped plates for use in energy dissipation devices and the development of a numerical model to reproduce the experiments. The plates were tested under cyclic flexural deformations, showing stable hysteresis cycles without strength degradation. A detailed nonlinear numerical model was developed and validated with the experimental data, using as input the constitutive relationship for the material determined from cyclic tests of material coupons under tension loading. The model adequately reproduces the experimental results. The study is focused on the exploitation of SMA in the martensite phase.

• 한국안전학회지
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• 제33권5호
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• pp.134-140
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• 2018

Scour in the downstream of hydraulic structures such as apron induces to collapse due to abruptly increasing rainfall and discharge in streams and reaches. This is because the forcible jet from overflowing is not sufficiently dissipated by existing energy dissipators, and it continues to sweep the bed materials during flood events. In this study, a second stilling basin was proposed as a countermeasure and the energy dissipation efficiency of this structure was analyzed using 3D-dimensional numerical analysis. First, results from previous research and hydraulic tests were used to verify the accuracy of the numerical model. It showed that the second stilling basin played a definite role in reducing the bottom velocity, comparing with diminishing the energy dissipation when numerical tests were conducted under scaled field conditions in Korea. This means that the second stilling basin can be a countermeasure against scour in downstream. If more efficiency analysis of the second stilling basin would be performed in terms of energy dissipator for various types of hydraulic jump, it would be an alternative solution to scouring issues.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2000년도 추계 학술발표회 논문집 Proceedings of EESK Conference-Fall 2000
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• pp.399-406
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• 2000

Viscous dampers have been utilized as bearings and STU`s (Shock Transmission Unit) in earthquake resistant designs for bridges. Some viscous dampers are used as energy dissipators on one hand, but some dampers such as STU`s are used as fixing devices during an earthquake on the other hand. This paper discusses the effect of viscous dampers on the response of bridge with respect to the magnitude of damping coefficients. For this purpose, a typical bridge was taken as an example, and time-history dynamic analysis have been carried out. The input seismic data used in the analyses are relevant to the response spectra in the Koreans design code. The results show that there is an optimum value of coefficient considered most effective in the design. A STU with a large value of coefficient seems to make its support fixed. The response of the bridge is not much sensitive to the variation of the damping coefficients.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2001년도 춘계학술대회 논문집
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• pp.379-386
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• 2001

Fluid viscous dampers have been used as energy dissipators or STU's (Shock Transmission Unit) in earthquake resistant designs for bridges. Viscous dampers have many advantages compared to other friction type or visco-elastic type of dampers. They do neither increase internal pier forces due to their out of phase response, nor produce reaction forces at the low velocities associated with thermal movements. Therefore, they anable the super structure to restore itself perfectly after a severe movement dut to seismic excitations. This paper investigates the response of bridges designed with viscous dampers in regard to damping coefficients, properties of dampers, and arrangements of dampers. For this purpose, time-history dynamic analyses have been performed using a very simple model relevant to a typical bridge example. Based on the results, it presents some design duidelines on how to determine a proper damping ratio and on how to arrange dampers. In usual cases, damping coefficients corresponding to about 0.2-0.3 of damping ratios seem to be very effective in bridge designs.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2011년도 춘계학술대회 논문집
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• pp.165-170
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• 2011

A large number of seismic isolation systems have been developed since the early 1970s. They are basically a combination of elastomeric bearing and energy dissipators. The investigation described in this paper analyzes shear property and the frequency dependence of Lead Rubber Damper(LRD). Lead Rubber Damper is similar in shape and performance property to Lead Rubber Bearing. Experimental condition ranges from 20 to 200% in share strain and from 0.1 to 1.0Hz in frequency. When the shear strain is increased, effective stiffness and damping ratio are decreased. When the frequency is increased, change of the behavior characteristic is subtle.

• 한국농공학회지
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• 제13권1호
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• pp.2206-2217
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• 1971

본연구(本硏究)는 Dam 또는 여수토(餘水吐) 방수로등(放水路等) 급구배수로(急勾配水路)에 고속(高速)으로 유하(流下)되는 물을 감세처리(減勢處理)하기 (爲)한 감세공형식중(減勢工型式中) 보다도 구조(構造)가 간단(簡單)하고 시공(施工)이 용역(容易)하며 경제성(經濟性)이 높은 Flip Bucket 형감세공(型減勢工)에 의(義)하여 수리특성(水理特性)에 따른 일반적(一般的) 적용조건(適用條件)과 설계시공(設計施工)의 발전(發展)을 도모(圖謀)하기 위(爲)하여 연구(硏究)한 것으로서 그 결과(結果)를 요약(要約)하면 다음과 같다. 1. Flip Bucket의 수리특성(水理特性)과 일반적(一般的) 적용조건(適用條件) Flip Bucket는 일반적(一般的)으로 다음과 같은 조건(條件)을 갖일 때에 채용(採用)할 수 있다. 가. 하류하천(下流河川)의 수위(水位)가 얕어서 도수형(跳水型) 감세공법(減勢工法)을 이용(利用)하며는 막대(莫大)한 공사비(工事費)를 요(要)하게 될 때 나. 하류하천(下流河川)의 하상(河床)이 안정(安定)할 수 있는 양질(良質)의 암반(岩盤)일 경우 다. 하류하천(下流河川)은 여수토(餘水吐) 방수로(放水路)의 중심선(中心線)에 연(沿)하여 적어도 전수두(全水頭)의 $3{\sim}5$배(倍)되는 거리까지는 하심(河心)이 거이 직선(直線)인 여건(與件)에 있을 경우 라. 방사수맥(放射水脈)의 낙하지점(落下地點)을 중심(中心)으로 해서 주위(周圍)에 민가(民家), 경지(耕地), 중요시설물등(重要施設物等)이 없고 수맥낙하(水脈落下)로 인(因)하여 생기는 소음(騷音), 토사붕양(土砂崩壤), 물방울등(等)으로 피해(被害)를 받을 염려(念慮)가 없을 경우 2. 설계(設計) 및 시공상(施工上)의 적용사항(適用事項) 1항(項)과 같은 현지조건(現地條件)을 갖이고 실제(實際) Flip Bucket 형(型)으로 설계(設計) 또는 시공(施工)을 할 경우 고려(考慮)하여야 할 사항(事項)은 가. Bucket의 반경(半徑)(R)은 $R=7h_2$로 적용(適用)이 가능(可能)하다. ($h_2$: Bucket 시점(始點)의 평균수심(平均水深) 나. 본형식(本型式)은 한계지면이하(限界施面以下) 방수로(放水路)의 구배(勾配)가 $0.25<\frac{H}{L}<0.75$의 수로(水路)에서만 채용(採用)한다. 다. 방사수맥(放射水脈)은 가급적(可及的) 하상면(河床面)에 직각(直角)에 가까운 각도(角度)로 낙하(落下)시켜야 하며 그러기 위(爲)해서는 수맥(水脈)을 높이 또는 멀리 방사(放射)시켜야 한다. 상기목적(上記目的)을 만족(滿足)시키는 Flip의 앙각(仰角)은 $\theta=30^{\circ}{\sim}40^{\circ}$를 적용(適用)하는 것이 좋다. 라. 상기(上記) 가${\sim}$다항(項)을 적용(適用)했을 때 유량별(流量別) 방사수맥(放射水脈)의 낙하거리(落下距離)는 그림-4.1에 의(依)하여 쉽게 추정(推定)할 수 있다.(단 실물(實物)에 대(對)한 제량(諸量)의 환산(換算)은 표(表-3.2)에 제시(提示)된 Froude 상사율(相似律)을 적용(適用)할 것) 마. Bucket 부(部)에 Chute Blocks를 설치(設置)하는 것은 방사수맥(放射水脈)의 낙하범위(落下範圍)를 확장(擴張), Energy를 분배(分配)시켜 주므로 하류하상(下流河床)의 세굴심(洗掘深)을 감소(減少)시키는 이점(利點)은 있으나 소맥낙하거리(小脈落下距離)는 다소(多少) 단축(短縮)되는 경향(傾向)이 있다. 바. 수맥낙하점(水脈落下點)에는 세굴(洗掘)에 의(依)한 깊은 Water Cushion을 형성(形成)한다. 최종적(最終的)으로 도달(到達)하는 Water Cushion의 깊이는 하상구성재료(河床構成材料)의 조성(組成)과 재질(材質)에는 거이 무관(無關)하며 단위폭당(單位幅當)의 유량(流量)과 전수두(全水頭)에 따라 소요(所要) 깊이까지 세굴(洗掘)된다. 사. 빈도(頻度)가 잦은 소유량(小流量)에서는 수맥(水脈)의 낙하거리(落下距離)가 단축(短縮)되어 Flip Bucket 하류단(下流端) 직하류(直下流)를 세굴(洗掘)하게 되므 Bucket로 하류단(下流端)은 견고(堅固)한 암반(巖盤)에 충분(充分)한 깊이까지 삽입절연(揷入絶緣)시켜 수맥하부(水脈下部)의 공기유통(空氣流通)을 원활(圓滑)하게 하므로서 Cavitation을 방지(防止)할 수 있다. 지하벽(直下壁)은 보통(普通) Bucket 말단(末端)에서 약(約) $0.3{\sim}0.5m$ 정도(程度)는 수평(水平)으로 하고 수평(水平)과 내각(內角)이 $120^{\circ}{\sim}130^{\circ}$되게 절단(切斷)하여 적당(適當)한 곳에서 수직(垂直)으로 하여 암반(巖盤)에 견고(堅固)히 절연(絶緣)시킨다. 아. 하상(河床)에 돌입(突入)한 고속(高速) Jet는 수두(水頭)의 크기에 따라 막대(莫大)한 Energy의 일부(一部)를 함유(含有)한채 하상면상(河床面上)을 유하(流下)하게 되므로 이 영향(影響)을 받는 하류제방(下流堤防)에는 상당구간(相當區間)까지 사석(捨石) 또는 기타(其他)의 방호조치(防護措置)를 강구(講究)해야 한다. 자. 낙하지점(落下地點)의 조건(條件)으로 보아 자연낙하지점(自然落下地點)보다 더욱 양호(良好)한 지점(地點)이 주위(周圍)에 구비(具備)되어 있을 경우에는 별도(別途)로 수리실험(水理實驗)을 통(通)하여 수맥(水脈)의 변이방법(變移方法)을 강구(講究)해야 한다. 차. 수로(水路)의 중심선(中心線)이 만곡(灣曲)을 갖던가 또는 본연구(本硏究) 범위(範圍)에서 제외(除外)된 구조물(構造物)에서 본형식(本型式)을 계획(計劃)할 때는 별도(別途)로 수리실험(水理實驗)을 행(行)하여야 한다.

• 물과 미래
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• 제28권4호
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• pp.147-154
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• 1995

본 연구에서는 특별한 에너지 감세를 위한 수공구조물이 설치되지 않은 중 소규모 단락부 하류부에서 자유낙하하는 수맥으로 인하여 발생되는 비점착성 하상재료의 세굴특성을 수리모형실험을 통하여 분석하였다. 단락수맥 하류부에서의 세굴특성을 분석하기 위하여 먼저 직사각형 단락수맥의 흐름특성을 조사하였으며, 하상재료, 유량, 하류수심을 변화시키면서 세굴공의 직하류부에 생성되는 둔덕(mound)의 유무로 인한 세굴특성을 비교 분석하였다. 평형세굴심 뿐만 아니라 둔덕의 높이도 밀도 후르드수의 함수로 표시되며, 밀도 후르드수는 다른 무차원량 보다 평형세굴심과 비교적 깊은 관계가 있는 것을 확인하였다. 단락부 하류부 하상 보호공의 설계시 둔덕의 영향을 고려해야 한다는 결론을 얻었다.

• Earthquakes and Structures
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• 제15권6호
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• pp.639-654
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• 2018

Rocking motion have been used for achieving the 'resilient buildings' against earthquakes in recent studies. Low-rise buildings, unlike the tall ones, because of their small aspect ratio tend to slide rather than move in rocking mode. However, since rocking is more effective in seismic response reduction than sliding, it is desired to create rocking motion in low-rise buildings too. One way for this purpose is making the building's structure rock on its internal bay(s) by reducing the number of bays at the lower part of the building's skeleton, giving it a mushroom form. In this study 'mushroom skeleton' has been used for creating multi-story rocking regular steel buildings with square plan to rock on its one-by-one bay central lowest story. To show if this idea is effective, a set of mushroom buildings have been considered, and their seismic responses have been compared with those of their conventional counterparts, designed based on a conventional code. Also, a set of similar buildings with skeleton stronger than code requirement, to have immediate occupancy (IO) performance level, have been considered for comparison. Seismic responses, obtained by nonlinear time history analyses, using scaled three-dimensional accelerograms of selected earthquakes, show that by using appropriate 'mushroom skeleton' the seismic performance of buildings is upgraded to mostly IO level, while all of the conventional buildings experience collapse prevention (CP) level or beyond. The strong-skeleton buildings mostly present IO performance level as well, however, their base shear and absolute acceleration responses are much higher than the mushroom buildings.