• Geomechanics and Engineering
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• 제6권2호
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• pp.99-115
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• 2014

Uncertainties in design variables and design equations have a significant impact on the safety of geotechnical structures like retaining walls and slopes. This paper presents a possible framework for obtaining the partial safety factors based on reliability approach for different random variables affecting the stability of a reinforced concrete cantilever retaining wall and a slope under static loading conditions. Reliability analysis is carried out by Mean First Order Second Moment Method, Point Estimate Method, Monte Carlo Simulation and Response Surface Methodology. A target reliability index ${\beta}$ = 3 is set and partial safety factors for each random variable are calculated based on different coefficient of variations of the random variables. The study shows that although deterministic analysis reveals a safety factor greater than 1.5 which is considered to be safe in conventional approach, reliability analysis indicates quite high failure probability due to variation of soil properties. The results also reveal that a higher factor of safety is required for internal friction angle ${\varphi}$, while almost negligible values of safety factors are required for soil unit weight ${\gamma}$ in case of cantilever retaining wall and soil unit weight ${\gamma}$ and cohesion c in case of slope. Importance of partial safety factors is shown by analyzing two simple geotechnical structures. However, it can be applied for any complex system to achieve economization.

• Elastomers and Composites
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• 제33권4호
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• pp.290-296
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• 1998

폐타이어는 현재 재활용 범위가 제한되어 있고, 매우 단순한 용도로 사용되고 있다. 본 연구에서는 이러한 폐타이어를 탄성과 투수성을 갖는 포장재로서 활용할 수 있는 지를 알아보았다. 도로포장재가 갖는 주요 인자인 압축강도 시험 결과 압축강도에 영향을 미치는 인자는 고무분말 크기, 골재 크기 및 바인더의 성질이 주요 인자임을 알 수 있었고, 또한 투수성은 골재의 크기와 분말의 크기에 의존하였다. 본 연구에서 시도된 탄성 투수성 도로 포장재는 기존의 다공성 콘크리트의 값보다 압축강도는 1.4배, 투수성은 최대 116배 향상된 결과를 나타냈다.

• Structural Engineering and Mechanics
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• 제68권6호
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• pp.677-689
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• 2018

Residual deformation is a crucial index that should be paid special attention in the performance-based seismic analyses of reinforced concrete (RC) structures. Owing to their superior re-centering capacity under earthquake excitations, the post-tensioned self-centering (PTSC) RC frames have been proposed and developed for engineering application during the past few decades. This paper presents a comprehensive assessment on the seismic fragility of a PTSC frame by simultaneously considering maximum and residual deformations. Bivariate limit states are defined according to the pushover analyses for maximum deformations and empirical judgments for residual deformations. Incremental Dynamic Analyses (IDA) are conducted to derive the probability of exceeding predefined limit states at specific ground motion intensities. Seismic performance of the PTSC frame is compared with that of a conventional monolithic RC frame. The results show that, taking a synthetical consideration of maximum and residual deformations, the PTSC frame surpasses the monolithic frame in resisting most damage states, but is more vulnerable to ground motions with large intensities.

• 대한건축학회논문집:구조계
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• 제35권11호
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• pp.129-136
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• 2019

Non-structural elements are vulnerable to earthquake ground motion. In this study, an experimental study for the electrical non-structural element was performed using tri-axial shaking table tests. A 100kVA UPS(Uninterruptible Power Supply system) was used as the test specimen. The test specimen was anchored to the concrete slab using the conventional installation detail. The input acceleration were generated in accordance with ICC-ES AC156 code. Scale factors of the input acceleration with respect to the required response spectrum defined in ICC-ES AC156 were from 25% to 600%. Based on the test results, damage and dynamic characteristics of UPS were evaluated and analyzed including natural frequency, damping ratio, acceleration time history response, dynamic amplification factor and relative displacement.

• Earthquakes and Structures
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• 제20권3호
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• pp.337-351
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• 2021

On September 12, 2016, the Gyeongju earthquake occurred in the south-eastern region of the Korean peninsula. The event was ranked as the largest magnitude earthquake (=5.8) since instrumental recording was started by the Korean Metrological Administration (KMA) in 1978. The objective of this study is to provide information obtained from the 2016 Gyeongju earthquake and to propose a procedure estimating seismic risk of a typical old RC building for past and potential earthquakes. Ground motions are simulated using the point source model at 4941 grid locations in the Korean peninsula that resulted from the Gyeongju earthquake and from potential future earthquakes with the same hypocenter considering different soil conditions. Nonlinear response history analyses are conducted for each grid location using a three-story gravity-designed reinforced concrete (RC) frame that most closely represents conventional old school and public buildings. Then, contour maps are constructed to present the seismic risk associated with this building for the Gyeongju earthquake and potential future scenario earthquakes. These contour maps can be useful in the development of a mitigation plan for potential earthquake damage to school and public buildings at all grid locations on the Korean peninsula.

• Geomechanics and Engineering
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• 제29권3호
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• pp.359-368
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• 2022

Undercutting using an actuated disc cutter (ADC) involves more complex cutting mechanism than traditional rock cutting does, requiring the application of various new cutting parameters, such as eccentricity, cutter inclination angle, and axis rotational speed. This study presents cutting-edge laboratory-scale testing equipment that allows performing ADC tests. ADC tests were carried out on a concrete block with a specified strength of 20 MPa, using a variety of cutting settings that included penetration depth (p), eccentricity (e), and linear velocity (v). ADC, unlike pick and disc cutting, has a non-linear cutting path with a dynamic cutting direction, requiring the development of a new method for predicting cutting force and specific energy. The influence of cutting parameters to the cutter forces were discussed. The ratio of eccentricity to the penetration depth (e/p) was proposed to evaluate the optimal cutting condition. Specific energy varies with e/p ratio, and exhibits optimum values in particular cases. In general, actuated undercutting may potentially give a more efficient cutting than conventional pick and disc cutting by demonstrating reasonably lower specific energy in a comparable cutting environment.

• Structural Engineering and Mechanics
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• 제86권6호
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• pp.793-815
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• 2023

The current study looks at the experimental and numerical performance of ferrocement RC channel slabs reinforced with welded steel mesh, expanded steel mesh, and fiber glass mesh individually. Ten RC channel slabs with dimensions of 500 mm×40 mm×2500 mm were subjected to flexural loadings as part of the testing program. The type of reinforcing materials, the number of mesh layers, and the reinforcement volume fraction are the key parameters that can be changed. The main goal is to determine the impact of using new inventive materials to reinforce composite RC channel slabs. Using ANSYS -16.0 Software, nonlinear finite element analysis (NLFEA) was used to simulate the behavior of composite channel slabs. Parametric study is also demonstrated to identify variables that can have a significant impact on the model's mechanical behavior, such as changes in slab dimensions. The obtained experimental and numerical results indicated that FE simulations had acceptable accuracy in estimating experimental values. Also, it's significant to demonstrate that specimens reinforced with fiber glass meshes gained approximately 12% less strength than specimens reinforced with expanded or welded steel meshes. In addition, Welded steel meshes provide 24% increase in strength over expanded steel meshes when reinforcing RC channel slabs. In general, ferrocement specimens tested under flexural loadings outperform conventional reinforced concrete specimens in terms of ultimate loads and energy absorbing capacity.

• 한국공간구조학회논문집
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• 제24권1호
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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.

• 콘크리트학회논문집
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• 제27권2호
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• pp.185-193
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• 2015

인장강도 및 휨강도가 낮고 취성파괴의 특성을 가지는 일반적인 콘크리트의 단점을 극복하기 위하여 최근에는 압축강도가 180 MPa이상인 고성능 콘크리트에 강섬유를 혼입한 강섬유 보강 초고성능 콘크리트(UHPC)에 대한 연구가 활발히 진행되고 있다. UHPC 바닥판과 강재 거더를 이용하여 합성보를 구성할 때, UHPC 바닥판의 높은 강도와 강성으로 인하여 강재거더 상부 플랜지의 역할이 거의 불필요할 것으로 예상된다. 이러한 점을 착안하여 본 논문에서는 합성보 구성 시에 강재 거더의 상부플랜지를 없앤 역T형 거더를 적용하였다. 역T형 거더에 UHPC바닥판을 합성하여 합성보를 구성할 경우, 상부플랜지가 없는 이유로 전단연결재의 설치 위치가 상부플랜지 대신에 강재 거더 복부에 설치해야하는 문제점이 발생되며, 강재 복부에 설치되는 전단연결재에 대한 거동, 역T형 강거더 합성보의 휨거동 특성 등은 현재까지 실험 및 이론적으로 평가된 적이 거의 없는 실정인 이유로 이에 대한 연구가 절실하다. 이를 위하여 본 논문에서는 전단연결재 간격, 바닥판 두께 등을 변수로 하여 역T형 거더와 UHPC바닥판을 합성한 합성보를 8개 제작하여 전단연결재의 거동, 휨거동 특성 등을 파악하고자 하였다. 또한, 강섬유 보강 초고성능 콘크리트의 인장연화거동을 고려한 재료모델링 및 이를 적용한 보 부재 단면의 변형률 적합조건을 이용한 해석모델을 제안하였다. 실험결과 및 해석결과를 기준으로 볼 때, UHPC 콘크리트의 경우 전단연결재의 간격은 100 mm에서 바닥판 두께의 2~3배 사이로 규정함이 적절한 것으로 나타났다. 실험결과와 해석결과를 종합적으로 비교하면, 강섬유 보강 초고성능 콘크리트 합성보의 실험결과와 해석결과는 비교적 잘 일치하고 있으므로 재료 실험으로부터 산정된 인장연화곡선은 강섬유 보강 초고성능 콘크리트의 실제 거동을 합리적으로 반영한다고 판단된다. 따라서, 본 연구에서 제시한 인장연화거동 특성을 반영한 강섬유 보강 초고성능 콘크리트의 재료모델링 및 휨거동 해석기법은 적절하며, 제시기법에 의해 강섬유보강 초고성능 콘크리트 합성 부재의 휨 내력을 합리적으로 예측할 수 있을 것으로 예상된다.

• 콘크리트학회논문집
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• 제26권6호
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• pp.761-769
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• 2014

인장강도 및 휨강도가 낮고 취성파괴의 특성을 가지는 일반적인 콘크리트의 단점을 극복하기 위하여 최근에는 압축강도가 180 MPa이상인 고성능 콘크리트에 강섬유를 혼입한 강섬유 보강 초고성능 콘크리트(UHPC)에 대한 연구가 활발히 진행되고 있다. UHPC 바닥판과 강재 거더를 이용하여 합성보를 구성할 때, UHPC 바닥판의 높은 강도와 강성으로 인하여 강재거더 상부 플랜지의 역할이 거의 불필요할 것으로 예상된다. 이러한 점을 착안하여 본 논문에서는 합성보 구성 시에 강재 거더의 상부플랜지를 없앤 역T형 거더를 적용하였다. 역T형 거더에 UHPC바닥판을 합성하여 합성보를 구성할 경우, 상부플랜지가 없는 이유로 전단연결재의 설치 위치가 상부플랜지 대신에 강재 거더 복부에 설치해야하는 문제점이 발생되며, 강재 복부에 설치되는 전단연결재에 대한 거동, 역T형 강거더 합성보의 휨거동 특성 등은 현재까지 실험 및 이론적으로 평가된 적이 거의 없는 실정인 이유로 이에 대한 연구가 절실하다. 이를 위하여 본 논문에서는 전단연결재 간격, 바닥판 두께 등을 변수로 하여 역T형 거더와 UHPC바닥판을 합성한 합성보를 8개 제작하여 전단연결재의 거동, 휨거동 특성 등을 파악하고자 하였다. 실험결과를 기준으로 볼 때, 향후 UHPC의 경우 스터의 간격은 100 mm에서 바닥판 두께의 2~3 배 사이로 규정함이 적절할 것으로 예상된다. 또한 실험 부재의 특성 상대변위는 Eurocode-4의 연성거동 기준에 의하면 충분한 연성 거동을 하는 것으로 판정되었으며, 바닥판이 지나치게 얇고 전단연결재의 간격이 지나치게 넓은 경우를 제외한 대부분의 부재들은 일반 콘크리트보다 UHPC의 성능이 우수하여 기존의 AASHTO LRFD 및 Eurocode-4의 식과 실험결과간의 차이가 있음을 알 수 있다.