• Structural Engineering and Mechanics
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• 제65권5호
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• pp.535-546
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• 2018

The objective of this study is to understand the behaviour of hollow core slabs strengthened with FRP and hybrid techniques through numerical and analytical studies. Different strengthening techniques considered in this study are (i) External Bonding (EB) of Carbon Fiber Reinforced Polymer (CFRP) laminates, (ii) Near Surface Mounting (NSM) of CFRP laminates, (iii) Bonded Overlay (BO) using concrete layer, and (iv) hybrid strengthening which is a combination of bonded overlay and NSM or EB. In the numerical studies, three-dimensional Finite Element (FE) models of hollow core slabs were developed considering material and geometrical nonlinearities, and a phased nonlinear analysis was carried out. The analytical calculations were carried out using Response-2000 program which is based on Modified Compression Field Theory (MCFT). Both the numerical and analytical models predicted the behaviour in agreement with experimental results. Parametric studies indicated that increase in the bonded overlay thickness increases the peak load capacity without reducing the displacement ductility. The increase in FRP strengthening ratio increased the capacity but reduced the displacement ductility. The hybrid strengthening technique was found to increase the capacity of the hollow core slabs by more than 100% without compromise in ductility when compared to their individual strengthening schemes.

• 한국구조물진단유지관리공학회 논문집
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• 제26권3호
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• pp.48-54
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• 2022

본 연구는 균열에 의한 콘크리트 전단벽 강성저하 영향 평가를 위해 수행되었으며, 극한 내지진 하중의 60%까지 재하한 비선형 해석 결과, 사전 균열효과에 의해 비손상 대비 진동수의 12%정도 진동수가 감소하였으며 강성 측면에서 23%정도의 감소현상을 나타냈다. 단계적으로 지진하중의 크기를 증가시킨 비선형 해석 결과, 지진하중의 세기가 커짐에 따라 콘크리트 전단벽체에 전단균열이 발생하여 진전함을 파악하고, 반복이력에 의한 에너지 손실과 강성 저하가 뚜렷하게 발생함을 알 수 있었다. 또한 두 가지 콘크리트 강도와 전단벽 제원에 대하여 지진하중의 크기가 극한 내지진 하중에 근접함에 따라 진동수의 감소량은 비손상 대비 10~40%정도로 나타났으며, 강성의 경우 비손상 대비 40%정도 수준까지 감소할 수 있는 것으로 나타났다.

• Computers and Concrete
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• 제21권4호
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• pp.399-406
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• 2018

The present study focuses on the performance of basalt fiber reinforced concrete (BFRC) lining in tunnel situated in sandstone rock when subjected to internal blast loading. The blast analysis of the lined tunnel is carried out using the three-dimensional (3-D) nonlinear finite element (FE) method. The stress-strain response of the sandstone rock is simulated using a crushable plasticity model which can simulate the brittle behavior of rock and that of BFRC lining is analyzed using a damaged plasticity model for concrete capturing damage response. The strain rate dependent material properties of BFRC are collected from the literature and that of rock are taken from the authors' previous work using split Hopkinson pressure bar (SHPB). The constitutive model performance is validated through the FE simulation of SHPB test and the comparison of simulation results with the experimental data. Further, blast loading in the tunnel is simulated for 10 kg and 50 kg Trinitrotoluene (TNT) charge weights using the equivalent pressure-time curves obtained through hydrocode simulations. The analysis results are studied for the stress and displacement response of rock and tunnel lining. Blast performance of BFRC lining is compared with that of plain concrete (PC) and steel fiber reinforced concrete (SFRC) lining materials. It is observed that the BFRC lining exhibits almost 65% lesser displacement as compared to PC and 30% lesser displacement as compared to SFRC tunnel linings.

• Steel and Composite Structures
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• 제23권6호
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• pp.647-656
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• 2017

This paper presents an experimental study on the behaviour of steel beams with different types of web openings. Steel beams with web openings became progressively more accepted as a well-organized structural form in steel construction since their existence. Their complicated design and profiling method provides better flexibility in beam proportioning for strength, depth, size and location of holes. The objective of this study is to carry out the experiments on steel beams with different types of web openings and performed non-linear finite element (FE) analysis of the beams that were considered in the experimental study in order to determine their ultimate load capacity and failure modes for comparison. Ten full scale models of steel beam with web openings have been tested in the experimental investigation. The finite element method has been used to predict their entire response to increasing values of external loading until they lose their load carrying capacity. FE model of each specimen that is utilized in the experimental studies is carried out. These models are used to simulate the experimental work to verify test results and to investigate the nonlinear behaviour of failure modes such as local buckling, lateral torsional buckling, web-post buckling, shear buckling and Vierendeel bending of beams.

• 한국자동차공학회논문집
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• 제11권4호
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• pp.125-134
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• 2003

In this study, Mooney-Rivlin 1st model and Mooney-Rivlin 3rd model are adopted as strain energy density functions of the rubber compounds of a radial tire. It is shown that the FE analysis using Mooney-Rivlin models for rubber compounds may provide good approximations by employing the appropriate strain range of experimental stress-strain data in a way to describe the stress-strain relationship accurately. Especially, Mooney-Rivlin 3rd model gives an accurate stress-strain relationship regardless of the fitting strain range used within the strain of 100%. The static nonlinear FE analysis of a tire inflation is performed by employing an axisymmetric model, which shows that the outside shapes of the tire before and after inflating the tire agree well with those of the real tire. Additionally, the deformations at crown center and turning point on sidewall, distribution of belt cord force, interlaminar shear strain are predicted in terms of variation of belt cord angle which is known as the most influential factor in inflation behavior of a tire.

• 한국강구조학회 논문집
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• 제29권2호
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• pp.123-134
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• 2017

풍력발전 타워용 종방향 보강 원형단면 강재 쉘에 대하여 재료 및 기하학적 비선형 유한요소법(GMNIA)으로 극한압축강도 해석을 수행하였다. 보강 쉘의 반경 대 두께비, 초기변형 형상 및 진폭, 종방향보강재의 면적 및 간격 등의 주요 설계 파라미터가 압축력을 받는 보강 쉘의 극한강도에 미치는 영향을 분석하였으며, DNV 설계기준에 의한 설계좌굴강도와 유한요소해석으로 구한 극한압축강도를 비교하였다. 기하학적 초기결함의 형상은 선형 좌굴해석으로부터 구한 좌굴모드 및 제작 과정에서 용접으로 발생하는 딤플 변형을 고려하였다. 해석 대상 보강 쉘의 반경 대 두께비는 50~200이며, 종방향보강재는 횡비틀림좌굴과 국부좌굴이 발생하지 않도록 DNV 설계기준에 따라 두께와 돌출폭을 결정하였다.

• Structural Engineering and Mechanics
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• 제12권2호
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• pp.201-214
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• 2001

Four finite element (FE) models are examined to find the one that best estimates moment-rotation characteristics of top- and seat-angle with double web-angle connections. To efficiently simulate the real behavior of connections, finite element analyses are performed with following considerations: 1) all components of connection (beam, column, angles and bolts) are discretized by eight-node solid elements; 2) shapes of bolt shank, head, and nut are precisely taken into account in modeling; and 3) contact surface algorithm is applied as boundary condition. To improve accuracy in predicting moment-rotation behavior of a connection, bolt pretension is introduced before the corresponding connection moment being surcharged. The experimental results are used to investigate the applicability of FE method and to check the performance of three-parameter power model by making comparison among their moment-rotation behaviors and by assessment of deformation and stress distribution patterns at the final stage of loading. This research exposes two important features: (1) the FE method has tremendous potential for connection modeling for both monotonic and cyclic loading; and (2) the power model is able to predict moment-rotation characteristics of semi-rigid connections with acceptable accuracy.

• Steel and Composite Structures
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• 제51권3호
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• pp.225-241
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• 2024

For several reasons, cold-formed steel (CFS) beams are often manufactured with holes. Nevertheless, because of holes, the reduction in the web area causes a decrease in the bending strength. Edge stiffeners are presently added around the holes to improve the bending strength of flexural members. Therefore, this research studies CFSZ-beams with stiffened holes and investigates how edge stiffener affects bending strength and failure modes. Nonlinear analysis was carried out using ABAQUS software and the developed finite element (FE) model was verified against tests from previous studies. Using the verified FE model, a parametric study of 104 FE models was conducted to investigate the influence of key parameters on bending strength of Z- sections. The results indicated that the effect of holes is less noticeable in very thin Z-sections. Moreover, adding edge stiffeners around the holes improves the flexural capacity of Z-beams and sometimes restores the original bending capacity. Because the computational techniques used to solve the CFS buckling mode with stiffened holes are still unclear, a numerical method using constrained and unconstrained finite strip method (CUFSM) software was proposed to predict the elastic distortional buckling moment for a wide variety of CFSZ-sections with stiffened holes. A numerical method with two procedures was applied and validated. Upon comparison, the numerical method accurately predicted the distortional buckling moment of CFS Z-sections with stiffened holes.

• 한국전산구조공학회논문집
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• 제25권2호
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• pp.163-173
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• 2012

이 연구에서는 프리스트레싱용 고강도 강연선의 정착장치 중 강연선을 직접 정착하는 앵커헤드(anchor head)에 대해 거동특성을 분석하고, 앵커헤드의 제원을 결정하는 단계에 있어서 해석적 검토에 요구되는 프로세스에 대해 정립하였다. 앵커헤드는 쐐기와의 접촉(contact)을 통해 강연선으로부터의 힘이 전달되고 거동변화에 따라 접촉상태 또한 변하게 된다. 이를 고려한 상세 거동분석을 위해 쐐기와 헤드 사이의 접촉(contact)조건을 설정하였으며, 앵커헤드의 비선형 재료모델을 적용하여 기하 및 재료 비선형성을 고려한 구조해석을 수행하였다. 해석결과로부터 다음의 결과를 얻을 수 있었다. 앵커헤드의 거동은 앵커헤드와 쐐기 간의 상호거동에 크게 영향을 받기 때문에 초기 설계단계부터 상대 영향을 고려해야 한다. 쐐기홀(wedge hole)의 배치는 층배열(layered) 보다는 원형배열(circular)이 보다 응력분배에 효과적이고, 쐐기홀의 간격을 증가시키고 헤드 하면 구멍의 크기를 줄여 구멍사이 강재의 두께를 다소 늘이는 것이 구조거동에 효과적이다.

• 한국전산구조공학회논문집
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• 제29권6호
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• pp.499-512
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• 2016

경계반력법은 일반적인 복합법에서 필요한 진동수영역과 시간영역의 반복 작업이 필요없는 두 단계의 시간수영역 부구조법이다. 경계반력법은 다음의 두 단계로 나누어진다: (1) 진동수영역에서 선형구간과 비선형구간 경계에서 경계반력계산, (2) 시간영역에서 경계반력을 이용한 파동방사형문제 해석. 이때 시간영역에서는 파동방사형문제를 모사하기 위해 근역지반을 모델링한다. 이 연구에서는 면진원전구조물의 비선형 SSI 해석을 위한 BRM 해석의 근역지반 모델링 범위에 따른 응답을 평가하였다. 이를 위해 등가선형 SSI 문제를 이용하여 매개변수해석을 수행하였다. BRM 응답의 정확성을 평가하기 위해 BRM 응답은 재래의 SSI 해석의 응답과 비교하였다. 수치해석결과 BRM 해석을 위한 근역지반 모델링 범위는 기초의 크기뿐만 아니라 지반조건의 영향을 받았다. 마지막으로, BRM 해석을 면진원전구조물의 비선형 SSI 해석에 적용하므로 BRM의 정확성과 효율성을 입증하였다.