• Advances in concrete construction
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• 제8권3호
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• pp.173-185
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• 2019

This article presents a comparative study of the effect of steel layouts on the seismic behavior of transition steel-concrete composite connections, both experimental and analytical investigations of concrete filled steel tube-reinforced concrete (CFST-RC) and steel reinforecd concrete-reinforced concrete (SRC-RC) structures were conducted. The steel-concrete composite connections were subjected to combined constant axial load and lateral cyclic displacements. Tests were carried out on four full-scale connections extracted from a real project engineering with different levels of axial force. The effect of steel layouts on the mechanical behavior of the transition connections was evaluated by failure modes, hysteretic behavior, backbone curves, displacement ductility, energy dissipation capacity and stiffness degradation. Test results showed that different steel layouts led to significantly different failure modes. For CFST-RC transition specimens, the circular cracks of the concrete at the RC column base was followed by steel yielding at the bottom of the CFST column. While uncoordinated deformation could be observed between SRC and RC columns in SRC-RC transition specimens, the crushing and peeling damage of unconfined concrete at the SRC column base was more serious. The existences of I-shape steel and steel tube avoided the pinching phenomenon on the hysteresis curve, which was different from the hysteresis curve of the general reinforced concrete column. The hysteresis loops were spindle-shaped, indicating excellent seismic performance for these transition composite connections. The average values of equivalent viscous damping coefficients of the four specimens are 0.123, 0.186 and 0.304 corresponding to the yielding point, peak point and ultimate point, respectively. Those values demonstrate that the transition steel-concrete composite connections have great energy dissipating capacity. Based on the experimental research, a high-fidelity ABAQUS model was established to further study the influence of concrete strength, steel grade and longitudinal reinforcement ratio on the mechanical behavior of transition composite connections.

• Earthquakes and Structures
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• 제10권1호
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• pp.141-161
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• 2016

In seismic fragility and risk analysis, the definition of structural limit state (LS) capacities is of crucial importance. Traditionally, LS capacities are defined according to design code provisions or using deterministic pushover analysis without considering the inherent randomness of structural parameters. To assess the effects of structural randomness on LS capacities, ten structural parameters that include material strengths and gravity loads are considered as random variables, and a probabilistic pushover method based on a correlation-controlled Latin hypercube sampling technique is used to estimate the uncertainties in LS capacities for four typical reinforced concrete frame buildings. A series of ten LSs are identified from the pushover curves based on the design-code-given thresholds and the available damage-controlled criteria. The obtained LS capacities are further represented by a lognormal model with the median $m_C$ and the dispersion ${\beta}_C$. The results show that structural uncertainties have limited influence on $m_C$ for the LSs other than that near collapse. The commonly used assumption of ${\beta}_C$ between 0.25 and 0.30 overestimates the uncertainties in LS capacities for each individual building, but they are suitable for a building group with moderate damages. A low uncertainty as ${\beta}_C=0.1{\sim}0.15$ is adequate for the LSs associated with slight damages of structures, while a large uncertainty as ${\beta}_C=0.40{\sim}0.45$ is suggested for the LSs near collapse.

• Composites Research
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• 제34권4호
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• pp.226-232
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• 2021

본 논문에서는 전개장치용 복합재료 테이프 스프링 개발을 위해 테이프 스프링의 설계, 해석, 제작 및 기계적 특성을 검토하였다. 이를 위해 다양한 복합재료 소재를 선정하고 3개의 적층 패턴에 따라 제작하여 굽힘 시 파손여부를 구조해석과 실험적으로 검토하였다. 이중 파손이 발생하지 않고 잘 굽혀지는 소재와 적층 패턴을 선정하였다. 이렇게 확보된 정보를 이용해 전개구조물용 테이프 스프링을 개발하고 4점 굽힘 시험을 통해 구조적인 특성을 검토하였다. 시험 결과로부터 굽힘과 펴짐에 따라 모멘트-회전 곡선에서 테이프 스프링 고유의 비선형 히스테리시스 현상이 적절히 구현됨을 확인하였다. 따라서 복합재료 테이프 스프링이 적절히 개발된 것을 확인하였다.

• Earthquakes and Structures
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• 제20권2호
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• pp.149-160
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• 2021

Buildings made using the locally available clay materials are amongst the least expensive forms of construction in many developing countries, and therefore, widely popular in remote areas. It is despite the fact that these low-strength masonry structures are vulnerable to seismic forces. Since transporting imported materials like cement and steel in areas inaccessible by motorable roads is challenging and financially unviable. This paper presents, and experimentally investigates, adobe masonry structures that utilize the abundantly available local clay materials with moderate use of imported materials like cement, aggregates, and steel. Shake-table tests were performed on two 1:3 reduce-scaled adobe masonry models for experimental seismic testing and verification. The model AM1 was confined with vertical lightly reinforced concrete columns provided at all corners and reinforced concrete horizontal bands (i.e., tie beams) provided at sill, lintel, and eave levels. The model AM2 was confined only with the horizontal bands provided at sill, lintel, and eave levels. The models were subjected to sinusoidal base motions for studying the damage evolution and response of the model under dynamic lateral loading. The lateral forcedeformation capacity curves for both models were developed and bi-linearized to compute the seismic response parameters: stiffness, strength, ductility, and response modification factor R. Seismic performance levels, story-drift, base shear coefficient, and the expected structural damages, were defined for both the models. Seismic performance assessment of the selected models was carried out using the lateral seismic force procedure to evaluate their safety in different seismic zones. The use of vertical columns in AM1 has shown a considerable increase in the lateral strength of the model in comparison to AM2. Although an R factor equal to 2.0 is recommended for both the models, AM1 has exhibited better seismic performance in all seismic zones due to its relatively high lateral strength in comparison to AM2.

• 한국지진공학회논문집
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• 제26권1호
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• pp.13-22
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• 2022

This study proposes a low-cycle fatigue life derived from measurement points on pipe elbows, which are components that are vulnerable to seismic load in the interface piping systems of nuclear power plants that use seismic isolation systems. In order to quantitatively define limit states regarding leakage, i.e., actual failure caused by low-cycle fatigue, in-plane cyclic loading tests were performed using a sine wave of constant amplitude. The test specimens consisted of SCH40 6-inch carbon steel pipe elbows and straight pipes, and an image processing method was used to measure the nonlinear behavior of the test specimens. The leakage lines caused by low-cycle fatigue and the low-cycle fatigue curves were compared and analyzed using the relationship between the relative deformation angles, which were measured based on each of the measurement points on the straight pipe, and the moment, which was measured at the center of the pipe elbow. Damage indices based on the combination of ductility and dissipation energy at each measurement point were used to quantitatively express the time at which leakage occurs due to through-wall cracking in the pipe elbow.

• Steel and Composite Structures
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• 제44권2호
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• pp.199-210
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• 2022

This study build finite element analysis (FEA) models describing the bending events of coiled tubing (CT) at the wellhead and trips into the hole, accurately provide the state of stress and strain while the CT is in service. The bending moment and axial force history curves are used as loads and boundary conditions in the diametrical growth models to ensure consistency with the actual working conditions in field operations. The simulation diametrical growth results in this study are more accurate and reasonable. Analysis the factors influencing fatigue and diametrical growth shows that the internal pressure has a first-order influence on fatigue, followed by the radius of the guide arch, reel and the CT diameter. As the number of trip cycles increase, fatigue damage, residual stress and strain cumulatively increase, until CT failure occurs. Significant residual stresses remain in the CT cross-section, and the CT exhibits a residual curvature, the initial residual bending configuration of CT under wellbore constraints, after running into the hole, is sinusoidal. The residual stresses and residual bending configuration significantly decrease the buckling load, making the buckling and buckling release of CT in the downhole an elastic-plastic process, exacerbating the helical lockup. The conclusions drawn in this study will improve CT models and contribute to the operational and economic success of CT services.

• 한국지반환경공학회 논문집
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• 제24권2호
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• pp.25-30
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• 2023

본 연구에서 개발하고자 하는 고강도 포획망은 심선 직경 3.2mm, 인장강도 290~540MPa급 강선으로 제작되는 일반 PVC 코팅망을 활용한 낙석방지망 공법을 대체하기 위함이다. 일반 PVC 코팅망은 그 성능이 낮아 낙석이나 표층유실이 발생할 경우 그 하중을 버티지 못하고 찢어지며 오히려 피해가 가중된다. 따라서 심선 직경 2.8~3.2mm, 인장강도 1,000~2,000MPa급 강선을 활용하여 고강도 포획망을 제작하였다. 시험 방법은 국제 기준인 Steel wire rope net panels and rolls-Definitions and specifications(ISO 17746:2016)을 참조하였으며, 펀칭시험에 대한 사항의 규정을 따라 실시하였다. 실내펀칭시험을 통해 일반 PVC 코팅망과 개발한 고강도 포획망(1,000MPa, 2,000MPa)의 하중-변위 곡선을 비교하였으며, 최대 인발력이 324.47%(고강도 포획망 2,000MPa)가 향상되는 것으로 분석되었다.

• 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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• 제26권1A호
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• pp.155-162
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• 2006

본 연구에서는 납면진받침(LRB)이 설치된 중경간 엑스트라도즈드교에서 교각의 파손, 상부구조의 이동변위, 그리고 케이블의 항복에 대한 지진위험도를 평가하였다. 지진위험도는 다수의 지진자료를 이용하여 지진에 대한 구조적 취약성을 평가한 지진취약도와 지진재해지도를 이용하여 해당지역에서의 지진재해도를 산정하여, 이들을 조합함으로써 평가할 수 있었다. 지진시 교각에서 소성힌지의 발생을 고려하기 위해 SAP2000을 사용하여 비선형 지진해석을 수행하였다. 지진자료는 암반노두에서 설계응답스펙트럼을 만족하는 인공지진을 작성한 후, SHAKE91을 사용하여 해당지역의 지반증폭효과를 고려하여 지진 가속도 시간이력을 구하여 사용하였다. 교각의 비선형 응답은 연성도를 사용하여 나타내었고, 2선형 직선의 모멘트-곡률 곡선으로 작성하였다. 본 연구에서는 대수정규분포함수로 지진취약도를 표현하였으며, 한반도를 대상으로 작성된 지진재해지도를 이용하여 지진재해도를 산정하였다. 해석결과 엑스트라도즈드교에서는 케이블과 거더보다는 교각하단에서 면진장치가 더 효과적인 것을 알 수 있었다.

• Earthquakes and Structures
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• 제26권5호
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• pp.383-400
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• 2024

For a conventionally repaired frame-supported-transfer-slab (FSTS) reinforced concrete (RC) structure, both the transfer slab and the beam-to-column and transfer slab-to-column joints remain vulnerable to secondary earthquakes. Aimed at improving the seismic performance of a damaged FSTS RC structure, an innovative retrofitting scheme is proposed, which adopts the sector lead rubber dampers (SLRDs) at joints after the damaged FSTS RC structure is repaired by conventional approaches. In this paper, a series of quasi-static cyclic tests was conducted on a large-scale retrofitted FSTS RC structure. The seismic performance was evaluated and the key test results, including deformation characteristics, damage pattern, hysteretic behaviour, bearing capacity and strains on key components, were reported in detail. The test results indicated that the SLRDs started to dissipate energy under the service level earthquake, and thus prevented damages on the beam-to-column and transfer slab-to-column joints during the secondary earthquakes and shifted the plastic hinges away from the beam ends. The retrofitting scheme of using SLRDs also achieved the seismic design concept of 'strong joint, weak component'. The FSTS RC structure retrofitted by the SLRDs could recover more than 85% bearing capacity of its undamaged counterpart. The hysteresis curves were featured by the inverse "S" shape, indicating good bearing capacity and hysteresis performance. The deformation capacity of the damaged FSTS RC structure retrofitted by the SLRDs met the corresponding codified requirements for the case of the maximum considered earthquake, as set out in the Chinese seismic design code. The stability of the FSTS RC structure retrofitted by the SLRDs, which was revealed by the developed stains of the RC frame and transfer slab, was improved compared with the undamaged FSTS RC structure.