• Steel and Composite Structures
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• 제43권3호
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• pp.327-340
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• 2022

A vast amount of experimental and analytical research has been conducted related to the seismic behavior and performance of concrete filled steel tubular (CFT) columns. This research has resulted in a wealth of information on the component behavior. However, analytical and experimental data for structural systems with CFT columns is limited, and the well-known behavior of steel or concrete structures is assumed valid for designing these systems. This paper presents the development of an analytical model for nonlinear analysis of composite moment resisting frame (CFT-MRF) systems with CFT columns and steel wide-flange (WF) beams under seismic loading. The model integrates component models for steel WF beams, CFT columns, connections between CFT columns and WF beams, and CFT panel zones. These component models account for nonlinear behavior due to steel yielding and local buckling in the beams and columns, concrete cracking and crushing in the columns, and yielding of panel zones and connections. Component tests were used to validate the component models. The model for a CFT-MRF considers second order geometric effects from the gravity load bearing system using a lean-on column. The experimental results from the testing of a four-story CFT-MRF test structure are used as a benchmark to validate the modeling procedure. An analytical model of the test structure was created using the modeling procedure and imposed-displacement analyses were used to reproduce the tests with the analytical model of the test structure. Good agreement was found at the global and local level. The model reproduced reasonably well the story shear-story drift response as well as the column, beam and connection moment-rotation response, but overpredicted the inelastic deformation of the panel zone.

• Composites Research
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• 제36권4호
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• pp.259-263
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• 2023

This study investigated the open hole tensile (OHT) properties of carbon fiber/epoxy composites and compared them to bolt joint tensile (BJT) properties. The net nominal modulus and strength (1376 MPa) were found to be higher than the gross nominal strength (1041 MPa), likely due to increasing hole size. The OHT and BJT specimens exhibited similar stiffness, as expected without bolt rotation causing secondary bending. OHT specimens experienced a sharp drop in stress indicating unstable crack propagation, delamination, and catastrophic failure. BJT specimens failed through shear out on the bolt side and bearing failure on the nut side, involving fiber kinking, matrix splitting, and delamination, resulting in lower strength compared to OHT specimens. The strength retention of carbon fiber/epoxy composites with open holes was 66%. Delamination initiation at the hole's edge caused a reduction in the stress concentration factor. Filling the hole with a bolt suppressed this relieving mechanism, leading to lower strength in BJT specimens compared to OHT specimens. Bolt joint efficiency was calculated as 15%. The reduction in strength in bolted joints was attributed to fiber-matrix splitting and delamination, aligning with Hart Smith's bolted joint efficiency diagram. These findings contribute to materials selection and structural reliability estimation for carbon fiber/epoxy composites. They highlight the behavior of open hole and bolt joint configurations under tensile loading, providing valuable insights for engineering applications.

• Computers and Concrete
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• 제31권3호
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• pp.207-221
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• 2023

In this investigation, the interaction between opening space and neighboring joint has been examined by experimental test and Particle flow code in two dimension (PFC2D) simulation. Since, firs of all PFC was calibrated using Brazilian experimental test and uniaxial compression test. Secondly, diverse configurations of opening and neighboring joint were provided and tested by uniaxial test. 12 rectangular sample with dimension of 10 cm*10 cm was prepared from gypsum mixture. One quarter of tunnel and one and or two joint were drilled into the sample. Tunnel diameter was 5.5 cm. The angularities of joint in physical test were 0°, 45° and 90°. The angularities of joint in numerical simulation were 0°, 30°, 60°, -30°, -45°, -60° and its length were 2cm and 4cm. Loading rate was 0.016 m/s. Tensile strength of material was 4.5 MPa. Results shows that dominant type of crack which took place in the model was tensile cracks and or several shear bands develop within the model. The Final stress is minimum in the cases where oriented angle is negative. The failure stress decrease by decreasing the joint angle from 30° to 60°. In addition, the failure stress decrease by incrementing the joint angle from -30° to -60°. The failure stress was incremented by decreasing the number of notches. The failure stress was incremented by decreasing the joint length. The failure stress was incremented by decreasing the number of notches. Comparing experimental results and numerical one, showed that the failure stress is approximately identical in both conditions.

• 한국지반공학회논문집
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• 제22권7호
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• pp.13-21
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• 2006

최근 보강토는 토지활용의 극대화 방법의 일환으로 토목구조물에 다양하게 이용되고 있다. 일반적으로 보강토를 축조하는 과정에서 높이 약 $20{\sim}50cm$ 내외로 다짐을 실시하고 있으며, 이러한 다짐과정에서 기계진통이 보강토에 영향을 미치고 있는 상태이다. 본 연구에서는 토목섬유(부직포)로 보강된 화강풍화토에 대한 정적하중 및 동적하중에 의한 비압밀비배수 삼축압축시험을 실시하여 무보강 및 보강화강풍화토의 응력-변형특성 등에 대한 분석을 실시하였다. 즉 비압밀비배수 조건하에서 토목섬유로 보강된 화강풍화토의 전단장도는 주로 점착력성분 증가는 뚜렷하게 나타났으며, 내부마찰각 성분의 증가는 무보강에 비해 다소 작게 나타났다.

• Composites Research
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• 제20권4호
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• pp.1-8
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• 2007

본 연구에서는 에폭시 수지조합에 따른 탄소섬유강화 복합재 프리프레그 제작 및 극저온 인장시험을 통해 극저온에서 우수한 기계적 물성을 갖는 복합재 수지조합을 제시하였다. 환경챔버를 이용하여 상온으로부터 $-150^{\circ}C$ 까지 6회의 열-하중 사이클을 수행한 일방향 복합재 시편에 대하여 $-150^{\circ}C$에서 복합재의 인장강도와 강성을 측정하였다. 또한, $-150^{\circ}C$에서 복합재의 섬유수직방향 인장물성 및 면내 전단물성과 같은 모재 지배적인 물성 측정을 통해 수지조성변화가 섬유와 모재의 계면에 미치는 영향을 고찰하였다. 그 결과, bisphenol-A 형의 에폭시와 CTBN 고무 변성 형 필러를 비교적 다량으로 함유한 수지조성을 갖는 복합재 시편이 극저온에서 우수한 기계적 물성을 보임을 확인하였다.

• Geomechanics and Engineering
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• 재33권6호
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• pp.597-609
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• 2023

The instability and failure of engineered rock masses are influenced by crack initiation and propagation. Uniaxial compression and acoustic emission (AE) experiments were conducted on cracked sandstone. The effect of the crack's dip on the crack initiation was investigated using fracture mechanics. The crack propagation was investigated based on stress-strain curves, AE multi-parameter characteristics, and failure modes. The results show that the crack initiation occurs at the tip of the pre-fabricated crack, and the crack initiation angle increases from 0° to 70° as the dip angle increases from 0° to 90°. The fracture strength k_cr is derived varies in a U-shaped pattern as β increased, and the superior crack angle β_m is between 36.2 and 36.6 and is influenced by the properties of the rock and the crack surface. Low-strength, large-scale tensile cracks form during the crack initiation in the cracked sandstone, corresponding to the start of the AE energy, the first decrease in the b-value, and a low r-value. When macroscopic surface cracks form in the cracked sandstone, high-strength, large-scale shear cracks form, resulting in a rapid increase in the AE energy, a second decrease in the b-value and an abrupt increase in the r-value. This research has significant theoretical implications for rock failure mechanisms and establishment of damage indicators in underground engineering.

• 대한토목학회논문집
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• 제28권6C호
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• pp.359-366
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• 2008

말뚝의 하중전이거동 및 변형특성 해석을 위해 하중전이함수법이 널리 사용된다. 본 연구에서는 말뚝-지반의 상효작용 즉, 지반의 연속성을 고려한 하중전이해석에 고찰하였으며, Mindlin 해를 이용하여 이를 고려함으로써 말뚝의 실제 거동에 보다 부합되도록 수정된 하중전이 해석방법을 제안하였다. 이를 통해 말뚝-지반 상호작용의 영향인자인 말뚝직경-지반계수의 비$(D/E_s)$과 주면마찰력-재하하중의 비$(R_s/Q)$를 고려할 수 있었다. 제안된 하중전이함수법의 타당성을 검증하기 위하여 현장재하시험 사례와의 비교분석 결과, 제안된 해석방법은 암반 근입 현장타설말뚝의 하중-침하 거동 및 하중전이특성을 적절히 예측함을 알 수 있었다.

• 대한토목학회논문집
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• 제30권6C호
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• pp.241-253
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• 2010

본 연구에서는 응답변위법을 수직구 내진설계에 적용하고 구조물의 응답을 정확하게 구할 수 있는 방법을 제시하고자 기반면, 지반의 상대변위 산정 방법, 하중 산정 및 적용 방법에 따른 3차원 유한요소해석을 수행하였다. 그 결과, 수직구 내진설계를 위한 기반면은 전단파속도가 1500m/s를 초과하는 지반을 선정하는 것이 가장 적합하며, 지반변위 산정 방법은 다층지반의 특성을 반영할 수 있는 double cosine이 가장 적합하다. 또한 응답변위법 해석을 위한 동토압 및 주면전단력 산정 시 구조물의 단면형상효과를 고려하는 것이 실제 수직구의 동적거동을 적절히 반영하며 경제적인 설계를 할 수 있음을 알 수 있었다.

• Structural Engineering and Mechanics
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• 제84권3호
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• pp.345-360
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• 2022

In this paper, the impact on seismic performance of an economical effective technique for retrofitting reinforced concrete (RC) columns using high-strength steel strips under high axial compression ratios was presented. The experimental program included a series of cyclic loading tests on one nonretrofitted control specimen and three retrofitted specimens. The effects of the axial compression ratio and spacing of the steel strips on the cyclic behavior of the specimens were studied. Based on the test results, the failure modes, hysteretic characteristics, strength and stiffness degradation, displacement ductility, and energy dissipation capacity of the specimens were analyzed in-depth. The analysis showed that the transverse confinement provided by the high-strength steel strips could effectively delay and restrain diagonal crack development and improve the failure mode, which was flexural-shear failure controlled by flexural failure with better ductility. The specimens retrofitted using high-strength steel strips showed more satisfactory seismic performance than the control specimen. The seismic performance and deformation capacity of the retrofitted RC columns increased with decreasing axial compression ratio and steel strip spacing. Based on the test results, a hysteretic model for RC columns that considers the transverse confinement of high-strength steel strips was then established. The hysteretic model showed good agreement with the experimental results, which verified the effectiveness of the proposed hysteretic model. Therefore, the aforementioned analysis can be used for the design of retrofitted RC columns.

• 한국전산구조공학회논문집
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• 제37권4호
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• pp.283-293
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• 2024

본 논문에서는 지진 하중으로 인한 급격한 구조손상탐지를 수행하기 위해 분산점 칼만필터(Unscented Kalman Filter, UKF)와 파티클 필터(Particle Filter)를 소개하고 지진 손상 시나리오에 적용 및 비교·검토하였다. 이때, 비선형 전단 빌딩을 모사하기 위해 Bouc-Wen 모델을 사용하였고, 급격한 변화를 추정하기 위해 추가적으로 적응형 기법(Adaptive rule)인 Adaptive Jumping Method를 두 필터 모두에 적용하였다. 적용 결과 두 오리지날 필터 모두 급격한 손상 시점과 정도를 파악하지 못하였고, 적응형 기법을 반영하였을 경우에만 시점 파악이 가능하였다. 하지만, 여전히 손상 정도를 정확히 파악하지 못하였고, 두 방법 모두 제안된 적응형 기법을 새로이 조정하였을 경우에 정확한 추정이 가능함을 확인하였다. 최종적으로 계산시간을 고려하였을 때, 새로운 형태의 적응형 기법을 적용한 UKF 사용을 제안하는 것으로 비교 검토를 수행하였다.