• Steel and Composite Structures
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• 제30권6호
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• pp.591-601
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• 2019

This research study investigates experimentally and analytically the axial compressive behaviour of Concrete Filled Fiber Reinforced Polymer Tube (CFFT) columns with and without Fiber Reinforced Polymer (FRP) bars. The experimental program comprises five circular columns of 204-206 mm outer diameter and 800-812 mm height. All columns were tested under concentric axial compressive loads. It was found that CFFT columns with and without FRP bars achieved higher peak axial compressive loads and corresponding axial deformations than conventional steel reinforced concrete (RC) column. The contribution of FRP bars was about 12.1% of the axial compressive loads carried by CFFT columns reinforced with FRP bars. Axial load-axial deformation ($P-{\delta}$) curves of CFFT columns were analytically constructed, which mapped well with the experimental $P-{\delta}$ curves. Also, an equation was proposed to predict the axial compressive load capacity of CFFT columns with and without FRP bars, which adequately considers the contributions of the circumferential confinement provided by FRP tubes and lower ultimate strength of FRP bars in compression than in tension.

• Geomechanics and Engineering
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• 제11권4호
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• pp.553-570
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• 2016

A series of three-dimensional (3D) parametric finite element analyses have been performed to study the influence of the relative locations of pile tips with regards to the tunnel position on the behaviour of single piles and pile groups to adjacent tunnelling in weathered soil. When the pile tips are inside the influence zone, which considers the relative pile tip location with respect to the tunnel position, tunnelling-induced pile head settlements are larger than those computed from the Greenfield condition. However, when the pile tips are outside the influence zone, a reverse trend is obtained. When the pile tips are inside the influence zone, the tunnelling-induced tensile pile forces mobilised, but when the pile tips are outside the influence zone, compressive pile forces are induced because of tunnelling, depending on the shear stress transfer mechanism at the pile-soil interface. For piles connected to a cap, tensile and compressive forces are mobilised at the top of the centre and side piles, respectively. It has been shown that the increases in the tunnelling-induced pile head settlements have resulted in reductions of the apparent factor of safety up to approximately 43% when the pile tips are inside the influence zone, therefore severely affecting the serviceability of the piles. The pile behaviour, when considering the location of the pile tips with regards to the tunnel, has been analysed in great detail by taking the tunnelling-induced pile head settlements, axial pile forces, apparent factor of safety of the piles and shear transfer mechanism into account.

• 대한조선학회논문집
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• 제33권3호
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• pp.66-80
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• 1996

최근 고장력강(高張力鋼)이 구조물에 폭넓게 사용되고 있어서 판두께가 얇아지고 있다. 판두께가 얇아지므로해서 좌굴(座屈)이 발생하기 쉽다. 그러므로 좌굴(座屈)발생후 판의 거동(擧動)을 정확하게 파악하는 것은 중요하다. 좌굴(座屈) 발생후 2차좌굴(次座屈)이라고 하는 하중하(荷重下)에서는 판(板)의 처짐모드가 갑자기 변한다. 전체구조물의 붕괴강도(崩壞强度)를 고려할 때 2차좌굴(次座屈)은 매우 중요하다. 이런 관점에서 본 연구에서는 면내압축하중(面內壓縮荷重)을 받는 판(板)의 2차좌굴거동(次座屈擧動)에 관하여 연구하였다. 초기처짐을 갖는 판(板)을 대상으로 하여 탄성대변형해석(彈性大變形解析)을 실시하여, 2차좌굴(次座屈)의 영향을 검토하였다. 그 결과로서 다음과 같은 결론(結論)을 얻었다. 즉, 정사각형판은 대칭의 처짐성분은 영향이 있으나 비대칭의 처짐성분은 영향이 전혀 없다. 또한, 종횡비(縱橫比)를 갖는 판(板)은 모든 처짐성분의 영향이 있으며 초기좌굴(初期座屈)후 면내강성(面內剛性)이 계속적으로 감소한다.

• Geomechanics and Engineering
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• 제28권2호
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• pp.117-133
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• 2022

Determination of the mechanical behaviour of jointed rock masses has been a challenge for rock engineers for decades. This problem is more pronounced for non-persistent jointed rock masses due to complicated interaction of rock bridges on the overall behaviour. This paper aims to study the effect of a non-persistent joint set configuration on the mechanical behaviour of rock materials under both uniaxial and biaxial compression tests using a discrete element code. The numerical simulation of biaxial compressive strength of rock masses has been challenging in the past due to shortcomings of bonded particle models in reproducing the failure envelope of rock materials. This problem was resolved in this study by employing the flat-joint contact model. The validity of the numerical model was investigated through a comprehensive comparative study against physical uniaxial and biaxial compression experiments. Good agreement was found between numerical and experimental tests in terms of the recorded peak strength and the failure mode in both loading conditions. Studies on the effect of joint orientation on the failure mode showed that four zones of intact, transition to block rotation, block rotation and transition to intact failure occurs when the joint dip angle varies from 0° to 90°. It was found that the applied confining stress can significantly alter the range of these zones. It was observed that the minimum strength occurs at the joint dip angle of around 45 degrees under different confining stresses. It was also found that the joint orientation can alter the post peak behaviour and the lowest brittleness was observed at the block rotation zone.

• Computers and Concrete
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• 제27권2호
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• pp.99-109
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• 2021

Experimental and discrete element methods were used to investigate the effects of echelon non-persistent joint on the failure behaviour of joint's bridge area under uniaxial compressive test. Concrete samples with dimension of 150 mm×100 mm×50 mm were prepared. Uniaxial compressive strength and tensile strength of concrete were 14 MPa and 1MPa, respectivly. Within the specimen, three echelon non-persistent notches were provided. These joints were distributed on the three diagonal plane. the angle of diagonal plane related to horizontal axis were 15°, 30° and 45°. The angle of joints related to diagonal plane were 30°, 45°, 60°. Totally, 9 different configuration systems were prepared for non-persistent joint. In these configurations, the length of joints were taken as 2 cm. Similar to those for joints configuration systems in the experimental tests, 9 models with different echelon non-persistent joint were prepared in numerical model. The axial load was applied to the model by rate of 0.05 mm/min. the results show that the failure process was mostly governed by both of the non-persistent joint angle and diagonal plane angle. The compressive strengths of the specimens were related to the fracture pattern and failure mechanism of the discontinuities. It was shown that the shear behaviour of discontinuities is related to the number of the induced tensile cracks which are increased by increasing the joint angle. The strength of samples increase by increasing both of the joint angle and diagonal plane angle. The failure pattern and failure strength are similar in both methods i.e. the experimental testing and the numerical simulation methods.

• Computers and Concrete
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• 제29권1호
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• pp.31-45
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• 2022

Experimental and numerical simulation were used to investigate the effects of angle and number of T shape non-persistent crack on the shear behaviour of crack's bridge area under uniaxial compressive test. concrete samples with dimension of 150 mm×150 mm×40 mm were prepared. Within the specimen, T shape non-persistent notches were provided. 16 different configuration systems were prepared for T shape non-persistent crack based on two and three cracks. In these configurations, the length of cracks were taken as 4 cm and 2 cm based on the cracks configuration systems. The angle of larger crack related to horizontal axis was 0°, 30°, 60° and 90°. Similar to cracks configuration systems in the experimental tests, 28 models with different T shape non-persistent crack angle were prepared in numerical model. The length of cracks were taken as 4 cm and 2 cm based on the cracks configuration systems. The angle of larger crack related to horizontal axis was 0°, 15°, 30°, 45°, 60°, 75° and 90°. Tensile strength of concrete was 1 MPa. The axial load was applied to the model. Displacement loading rate was controlled to 0.005 mm/s. Results indicated that the failure process was significantly controled by the T shape non-persistent crack angle and crack number. The compressive strengths of the specimens were related to the fracture pattern and failure mechanism of the discontinuities. Furthermore, it was shown that the compressive behaviour of discontinuities is related to the number of the induced tensile cracks which are increased by increasing the crack number and crack angle. The strength of samples decreased by increasing the crack number. In addition, the failure pattern and failure strength are similar in both methods i.e. the experimental testing and the numerical simulation methods (PFC2D).

• Advances in concrete construction
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• 제13권 2호
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• pp.199-213
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• 2022

Experimental and discrete element approaches were used to examine the effects of F shape non-persistent joints on the failure behaviour of concrete under uniaxial compressive test. concrete specimens with dimensions of 200 cm×200 cm×50 cm were provided. Within the specimen, F shape non-persistent joint consisting three joints were provided. The large joint length was 6 cm, and the length of two small joints were 2 cm. Vertical distance between two small joints change from 1.5 cm to 4.5 cm with increment of 1.5 cm. In constant joint lengths, the angle of large joint change from 0° to 90° with increments of 30°. Totally 12 different models were tested under compression test. The axial load rate on the model was 0.05 mm/min. Concurrent with experimental tests, numerical simulation (Particle flow code in two dimension) were performed on the models containing F shape non-persistent joint. Distance between small joints and joint angles were similar to experimental one. the results indicated that the failure process was mostly governed by both of the Distance between small joints and joint angles. The axial loading rate on the model was 0.05 mm/min. The compressive strengths of the samples were related to the fracture pattern and failure mechanism of the discontinuities. Furthermore, it was shown that the compressive behaviour of discontinuities is related to the number of the induced tensile cracks which are increased by increasing the joint angle. In the first, there were only a few acoustic emission (AE) hits in the initial stage of loading, and then AE hits rapidly grow before the applied stress reached its peak. Furthermore, a large number of AE hits accompanied every stress drop. Finally, the failure pattern and failure strength are similar in both approaches i.e., the experimental testing and the numerical simulation approaches.

• 한국구조물진단유지관리공학회 논문집
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• 제28권3호
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• pp.19-26
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• 2024

본 연구에서는 풍력타워 지지구조 연결부 1/12.5 축소모형 실험체의 압축거동을 실험적으로 분석하였다. 압축강도 140MPa의 고성능 시멘트계 그라우트를 연결부에 충전하였으며, 전단키 간격, 형상과 연결부 길이를 변수로 하여 실험을 수행하였다. 연결부 내의 전단키의 개수가 동일한 경우 연결부 길이보단 전단키의 간격이 작을수록 부착전단강도가 높게 나타났으며, 동일한 간격과 연결부 길이에서는 전단키의 높이가 높을수록 강도가 높게 나타났다. 또한 연결부 슬립량 1.0mm 내외까지 선형거동을 한 후 하중이 증가함에 따라 비선형 거동을 한후 7.0mm 내외의 슬립에서 최대 강도에 도달하는 것으로 나타났다. 전단키의 형상과 간격 등에 따라 강도가 증가함에 따라 파괴형태는 계면전단파괴에서 그라우트 파괴로 변화하는 것으로 나타났으며, 강섬유에 의해 취성적인 파괴는 발생하지 않는 것으로 나타났다.

• 터널과지하공간
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• 제2권2호
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• pp.224-236
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• 1992

It is very important to determine the thermo-mechanical characteristics of the rock mass surrounding the repository of radioctive waste and the LPG storage cavern. In this study, Hwasoon-Shist. Dado-Tuff adn Chunan-Tonalite were the selected rock types. Temperature dependence of the mechanical properteis such as uniaxial compressive strength, tensile strength, Young's modulus was investigated by measuring the behaviour of these properties due to the variation of temperature. Also, the characteristics of strength and deformation of these rocks were examined through high-temperature triaxial compression tests with varing temperatures and confining pressures. Important results obtained are as follows: In high temperature tests, the uniaxial compressive strength and Yong's modulus of Tonalite showed a sligth increase at a temperature up to 300$^{\circ}C$ and a sharp decrease beyond 300$^{\circ}C$, and the tensile strength showed a linear decrease with increasing heating-temperature. In high-temperature triaxial compression test, both the failure stress and Young's modulus of Tonalite increased with the increase of confining pressure at constant heating-temperature, and the failure stress decreased at 100$^{\circ}C$ but increased at 200$^{\circ}C$ under a constant confining pressure. In low temperature tests, the uniaxial compressive and tensile strengths and Young's modulus of these rocks increased as the cooling-temperature is reduced. Also, the uniaxial compressive and tensile strengths of wet rock specimens are less than those of dry rock specimens.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2005년도 추계학술발표대회 논문집
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• pp.61-65
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• 2005

Existing test methods for thick-section specimens ( 4mm) have not provided precise compressive properties to date for the analysis and design of thick structure. A survey of the failure behaviour of such thick specimens revealed that the failure initiated at the top corner of the specimen and propagated down and across the width of the specimen as premature failure, not typically reported for thin compression specimens. In the current study, the premature failure was successfully avoided during compressive testing and the failure mode was quite similar regardless of increasing specimen thickness and specimen volume. Failure mode was similar regardless of increasing specimen thickness and specimen volume, i.e. brooming failure mode combined with longitudinal splitting, interlaminar cracking, fibre breakage and kinkband formation (fibre microbuckling). Nevertheless, average failure strengths of the specimens decreased with increasing specimen thicnkiness from 2mm to 8mm with the T800/924C system (36% strength reduction) and specimen volumes from scaling factor I to scaling factor 4 with the IM7/8552 system (46% strength reduction). It was revealed from the literature$^{11}$ that the thickness effect and scaling effect arc caused by manufacturing defects such as void content and fibre waviness.