• Earthquakes and Structures
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• 제17권6호
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• pp.545-556
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• 2019

Bridge piers with bending failure mode are seriously damaged only in the area of plastic hinge length in earthquakes. For this situation, a modified method for the layout of longitudinal reinforcement is presented, i.e., the number of longitudinal reinforcement is increased in the area of plastic hinge length at the bottom of piers. The quasi-static test of three scaled model piers is carried out to investigate the local longitudinal reinforcement at the bottom of the pier on the seismic performance of the pier. One of the piers is modified by increased longitudinal reinforcement at the bottom of the pier and the other two are comparative piers. The results show that the pier failure with increased longitudinal bars at the bottom is mainly concentrated at the bottom of the pier, and the vulnerable position does not transfer. The hysteretic loop curve of the pier is fuller. The bearing capacity and energy dissipation capacity is obviously improved. The bond-slip displacement between steel bar and concrete decreases slightly. The finite element simulations have been carried out by using ANSYS, and the results indicate that the seismic performance of piers with only increasing the number of steel bars (less than65%) in the plastic hinge zone can be basically equivalent to that of piers that the number of steel bars in all sections is the same as that in plastic hinge zone.

• Structural Engineering and Mechanics
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• 제60권4호
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• pp.633-653
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• 2016

One of the major threats to the stability of classical columns and colonnades are earthquakes. The behavior of columns under high seismic excitation loads is non-linear and complex since rocking, wobbling and sliding failure modes can occur. Therefore, three dimensional simulation approaches are essential to investigate the in-plane and out-of-plane response of such structures during harmonic and seismic loading excitations. Using a software based on the Distinct Element Method (DEM) of analysis, a three dimensional numerical study has been performed to investigate the parameters affecting the seismic behaviour of colonnades' structural systems. A typical section of the two-storey colonnade of the Forum in Pompeii has been modelled and studied parametrically, in order to identify the main factors affecting the stability and to improve our understanding of the earthquake behaviour of such structures. The model is then used to compare the results between 2D and 3D simulations emphasizing the different response for the selected earthquake records. From the results analysis, it was found that the high-frequency motion requires large base acceleration amplitude to lead to the collapse of the colonnade in a shear-slip mode between the drums. However, low-frequency harmonic excitations are more prominent to cause structural collapse of the two-storey colonnade than the high-frequency ones with predominant rocking failure mode. Finally, the 2D analysis found to be unconservative since underestimates the displacement demands of the colonnade system when compared with the 3D analysis.

• 열처리공학회지
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• 제6권4호
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• pp.237-242
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• 1993

The fatigue behaviors of mechanically alloyed Al-4Mg alloys dispersed with either $Al_2O_3$ or $MgAl_2O_4$ oxide particles were investigated. This study maily concerned with the role of coherency of dispersed particles with the matrix on the fatigue behavior of the alloys. The $MgAl_2O_4$ which has a spinel structure with the lattice parameter of exactly the twice of Al showed the habit relation with the matrix. The mechanically alloyed Al-4Mg alloys showed stable stress responses with fatigue cycles from start to failure regadless of strain amplitudes and of existence of dispersoids. The Al-4Mg alloy dispersed with $MgAl_2O_4$ showed not only the better static mechanical properties but also the better low cycle fatigue resistance than that with $Al_2O_3$, i.e., much higher plastic strain energy dissipated to failure, at low strain amplitude. However, this alloy showed inferior fatigue resistance to that dispersed with $Al_2O_3$ or that without dispersion at high strain amplitude. These results imply that $MgAl_2O_4$ may promote lowering the stacking fault energy of the alloy inherited from the coherency with the matrix so that dislocations shuttle back and forth on the same slip plane without cross slipping to other planes during fatigue at low strain amplitude resulting in long fatigue life.

• 콘크리트학회논문집
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• 제17권6호
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• pp.903-910
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• 2005

최근 철근콘크리트 구조물의 보강 방법으로 고인장강도를 갖는 섬유복합체를 부재의 외부에 부착시켜 휨 내력을 증진시키는 부착식 보강공법이 널리 사용되고 있으나, 부착되는 섬유복합체의 박리에 의한 파괴강도를 예측하여 설계식에 반영하기 위한 연구는 미흡한 것이 사실이다. 보강재의 박리에 의한 파괴는 부재 전체의 취성적인 파괴를 유도하게 되므로, 부재의 보강설계를 위해서는 이에 대한 검토가 필수적으로 요구되어 진다. 본 연구에서는 보강재의 부착강도에 큰 영향을 미치는 유효부착길이의 개념을 도입하여, 기존 연구 결과로부터 부재의 부착강도를 좌우하게 되는 유효부착길이를 산정 하였으며, 이와 같은 유효부착길이에 의한 보강재의 박리하중을 산정할 수 있는 설계식을 제안하였다. 제안된 설계식은 기존 연구자들의 실험 연구결과와 비교하여 그 신뢰성을 검증하도록 하였으며, 기존 연구자들의 제안식과의 비교를 통하여 본 제안식의 타당성을 증명하였다.

• Computers and Concrete
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• 제22권2호
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• pp.167-182
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• 2018

The modeling of loss of bond between reinforcing bars (rebars) and concrete due to corrosion is useful in studying the behavior and prediction of residual load bearing capacity of corroded reinforced concrete (RC) members. In the present work, first the possibility of using different methods to simulate the rebars-concrete bonding, which is used in three-dimensional (3D) finite element (FE) modeling of corroded RC beams, was explored. The cohesive surface interaction method was found to be most suitable for simulating the bond between rebars and concrete. Secondly, using the cohesive surface interaction approach, the 3D FE modeling of the behavior of non-corroded and corroded RC beams was carried out in an ABAQUS environment. Experimental data, reported in literature, were used to validate the models. Then using the developed models, a parametric study was conducted to examine the effects of some parameters, such as degree and location of the corrosion, on the behavior and residual capacity of the corroded beams. The results obtained from the parametric analysis using the developed model showed that corrosion in top compression rebars has very small effect on the flexural behaviors of beams with small flexural reinforcement ratio that is less than the maximum ratio specified in ACI-318-14 (singly RC beam). In addition, the reduction of steel yield strength in tension reinforcement due to corrosion is the main source of reducing the load bearing capacity of corroded RC beams. The most critical corrosion-induced damage is the complete loss of bond between rebars and the concrete as it causes sudden failure and the beam acts as un-reinforced beam.

• 지질공학
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• 제31권3호
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• pp.269-281
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• 2021

Land creeping is the imperceptibly slow, steady, downward movement o f slope-forming soil or rock. Because creep-related failures occur frequently on a large scale without notice, they can be hazardous to both property and human life. Korea Forest Service has operated the prevention and response system from land creeping which has been on the rise since 2018. We categorized and proposed three survey steps (e.g., preliminary, regional, detailed) for investigation of creeping susceptibility site with a focus on geophysical mapping of a selected test site, Yongheung-dong, Pohang, Korea. The combination of geophysical (dipole-dipole electrical resistivity tomography and reciprocal seismic refraction technique, well-logging), geotechnical studies (standard penetrating test, laboratory tests), field mapping (tension cracks, uplift, fault), and comprehensive interpretation of their results provided the reliable information of the subsurface structures including the failure surface. To further investigate the subsurface structure including the sliding zone, we performed high-resolution geophysical mapping in addition to the regional survey. High-resolution seismic velocity structures are employed for stability analysis because they provided more simplified layers of weathering rock, soft rock, and hard rock. Curved slip plane of the land creeping is effectively delineated with a shape of downslope sliding and upward pushing at the apex of high resistive bedrock in high-resolution electrical resistivity model with clay-mineral contents taken into account. Proposed survey steps and comprehensive interpretation schemes of the results from geological, geophysical, and geotechnical data should be effective for data sets collected in a similar environment to land-creeping susceptibility area.

• Steel and Composite Structures
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• 제46권4호
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• pp.497-512
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• 2023

Using light weight concrete as infill material in conventional cold-formed steel (CFS) shear wall systems can considerably increase their load bearing capacity, ductility, integrity and fire resistance. The compressive strength of the filler concrete is a key factor affecting the structural behaviour of the composite wall systems, and therefore, achieving maximum compressive strength in lightweight concrete while maintaining its lightweight properties is of significant importance. In this study a new type of optimum polystyrene lightweight concrete (OPLC) with high compressive strength is developed for infill material in composite CFS shear wall systems. To study the seismic behaviour of the OPLC-filled CFS shear wall systems, two full scale wall specimens are tested under cyclic loading condition. The effects of OPLC on load-bearing capacity, failure mode, ductility, energy dissipation capacity, and stiffness degradation of the walls are investigated. It is shown that the use of OPLC as infill in CFS shear walls can considerably improve their seismic performance by: (i) preventing the premature buckling of the stud members, and (ii) changing the dominant failure mode from brittle to ductile thanks to the bond-slip behaviour between OPLC and CFS studs. It is also shown that the design equations proposed by EC8 and ACI 318-14 standards overestimate the shear force capacity of OPLC-filled CFS shear wall systems by up to 80%. This shows it is necessary to propose methods with higher efficiency to predict the capacity of these systems for practical applications.

• 대한토목학회논문집
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• 제5권4호
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• pp.1-8
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• 1985

수위변화(水位變化)에 따른 상이(相異)한 자유수면(自由水面)으로 인(因)하여 제체내부(堤體內部)에 응력상태(應力狀態)가 달라지므로 제체(堤體)의 안정해석(安定解析)이 필요(必要)하다. 수위(水位)가 급강하(急降下)할 경우 상류측(上流側) 사면(斜面)에서의 자유수면방향(自由水面方向)이 기초(基礎)쪽으로 바뀌어질 때, 상류측(上流側) Fill의 안전율(安全率)을 찾아 보았다. 여기서 하강(下降)하는 자유수면(自由水面)과 파괴형태(破壞形態)를 찾았으며, 또 안전율(安全率)을 구(求)하였고. 이로 강하속도(降下速度) 및 동수경사(動水傾斜)를 비교(比較)하였다. 실험(實驗)에 의한 결과(結果)는 다음과 같다. 1. 자유수면(自由水面)의 강하(降下)로 인(因)하여 상류측(上流側) Fill에 침투류(浸透流)에 의한 골동파괴(滑動破壞)가 일어나고, 파괴고(破壞高)는 각(各) 각(各)의 모형(模型)에 따라, 5~10, 9~15, 13~21(cm)이다. 2. 침투류(浸透流)에 의한 간극수압(間隙水壓)의 영향(影響)을 고려(考慮)하여 안전율(安全率)을 구하였으며, 이때 강하속도(降下速度)와 안전율(安全率)과의 관계(關係)에서 제체(堤體)의 안전상(安全上) 강하속도(降下速度)는 0.21~0.28(cm/sec)이어야 하고, 동수경사(動水傾斜)와 안전율(安全率)과의 비교(比較)에서 동수경사(動水傾斜)는 각(各) 모형(模型)에서 0.36~0.43 값보다 적어야 함을 실험상(實驗上) 알았다.

• 한국강구조학회 논문집
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• 제21권1호
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• pp.63-70
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• 2009

파괴모드는 저항력과 비탄성 변형 능력의 저하를 일으키는 균열이나 파단으로 귀결된다. 특수중심가새골조의 잠재적 파괴모드는 가새의 균열이나 파단, 가새나 거싯 플레이트의 순단면 파단, 거싯 플레이트용접의 균열, 볼트의 전단균열, 블록전단파단, 그리고 거싯 플레이트의 좌굴 등을 포함하고 있다. HSS 튜브가새는 특수중심가새골조에 자주 사용되고, 가새의 순단면 파단은 거싯 플레이트가 가새로 삽입되는 홈의 끝부분에 가새의 순단면을 통해 발생한다. 이 파괴모드는 인장파괴모드로 분류되고 급격한 강도저하와 취성적인 거동을 보인다. AISC 디자인 규준에선 순단면 보강을 요구하고 있다 (AISC 2001). 이 논문에서, 순단면 보강의 필요성에 대해 논의한다. 먼저, 미국 버클리대학교에서 수행됐던 순단면 파단실험을 유한요소모델을 이용한 이 실험의 모델링을 통해 소개한다. 실제 골조에서의 순단면 파단의 가능성을 조사하기 위해, 홈이 있는 중심가새골조를 유한요소법을 이용 모델링 하고, 인장지배의 근거리지진 이력을 적용시킨다. 이는 이력이 순단면 파단의 가장 중요한 인자라는 이전 해석 결과에서 기인한 것이다. 순단면 보강의 필요성과 인장지배의 근거리지진 이력의 영향에 대해 조사한다.

• 한국재료학회지
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• 제10권2호
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• pp.111-116
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• 2000

니켈기 주조용 합금 738LC를 816$^{\circ}C$와 982$^{\circ}C$에서 크리프 파단 시험과 열간 노출시험을 통해 온도와 응력 변화에 따른 파단양상, 탄화물과 $\sigma$상의 석출 거동에 대해 조사하였다. 816$^{\circ}C$/440MPa에서는 크리프 파단양상이 전단변형에 의한 입내파괴를 나타내었으나, 982$^{\circ}C$/152MPa에서는 표면과 접하는 결정입계에서 입계산화에 의해 표면에너지의 감소로 균열이 나타나 진행되는 입계파괴가 나타났다. M(sub)23C(sub)6 탄화물이 816$^{\circ}C$에서는 주로 결정입계에서와 전단변형에 의한 입내균열을 따라 석출하였으나, 982$^{\circ}C$에서는 결정입계 뿐만 아니라 입내에서는 석출하였으며 석출양은 증가하였다. $\sigma$상은 Cr(sub)23C(sub)6 탄화물에서 핵생성 후 기지로 성장하며, 온도가 높고 응력이 주어지면 Cr(sub)23C(sub)6 탄화물의 양이 증가하여 $\sigma$상의 석출도 많아졌다.