• Structural Engineering and Mechanics
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• 제34권1호
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• pp.61-84
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• 2010

Presented in this paper is the behaviour of asymmetric building isolated by the double variable frequency pendulum isolator (DVFPI). The DVFPI is an adoption of single variable frequency pendulum isolator (VFPI). The geometry and coefficient of friction of top and bottom sliding surfaces can be unequal. The governing equations of motion of the building-isolation system are derived and solved in incremental form. The analysis duly considers the interaction of frictional forces in the two principal directions developed at each sliding surface of the DVFPI. In order to investigate the behaviour of the base isolation using the DVFPI, the coupled lateral-torsional response is obtained under different parametric variations for a set of six far-fault earthquake ground motions and criterion to optimize its performance is proposed. Further, influences of the initial time period, coefficient of friction and frequency variation factors at the two sliding surfaces are investigated. The numerical results of the extensive parametric study help in understanding the torsional behaviour of the structure isolated with the double sliding surfaces as in the DVFPI. It is found that the performance of the DVFPI can be optimized by designing the top sliding surface initially softer and smoother relative to the bottom one.

• Structural Engineering and Mechanics
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• 제78권4호
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• pp.387-401
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• 2021

This paper provides a methodology to analyze the seismic performance of different component designs in hybrid masonry structures (HMS). HMS, comprised of masonry panels, steel frames and plate connectors is a relatively new structural system with potential applications in high seismic areas. HMS dissipate earthquake energy through yielding in the steel components and damage in the masonry panels. Currently, there are no complete codes to assist with the design of the energy dissipation components of HMS and there have been no computational studies performed to aid in the understanding of the system energy dissipation mechanisms. This paper presents parametric studies based on calibrated computational models to extrapolate the test data to a wider range of connector strengths and more varied reinforcement patterns and reinforcement ratios of the masonry panels. The results of the numerical studies are used to provide a methodology to examine the effect of connector strength and masonry panel design on the energy dissipation in HMS systems. We use as test cases two story structures subjected to cyclic loading due to the availability of experimental data for these configurations. The methodology presented is however general and can be applied to arbitrary panel geometries, and column and story numbers.

• Steel and Composite Structures
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• 제38권4호
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• pp.399-414
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• 2021

This paper aims to verify the feasibility of rubber rings to mitigate the shear concentration in perfobond connector (PBL) groups. Firstly, modified push-out tests for five specimens with four holes were conducted to investigate the effects of rubber rings on the shear mechanism of PBL groups. The test results showed that by employing rubber rings on partial holes, more shear forces were distributed to the holes without rubber rings. The rubber rings significantly improved the slip ability of the specimens, and the ductility of PBL groups is dependent on the number and thickness of rubber rings. Subsequently, three-dimensional numerical models were established and validated by the experimental results. According to the plastic strain distribution in concrete dowels, the action principle of rubber rings in PBL groups was explained. Furthermore, the parametric study was conducted to investigate the influential factors on shear distributions, including the width of steel plates, the hole spacing, the number of holes, the rubber ring thickness, and the positions of rubber rings. The parametric analysis results showed that the redistribution of shear forces is significantly affected by the rubber rings with the smallest thickness. By properly employing rubber rings in PBL groups, the shear forces of holes are more even. Finally, an analytical model for PBL groups with rubber rings was proposed to predict the shear distribution at the serviceability stage.

• International Journal of Concrete Structures and Materials
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• 제8권3호
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• pp.239-249
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• 2014

In this paper, the analysis of a numerical study of pile-soil interaction subjected to axial and lateral loads is presented. An analysis of the composite pile-soil system was performed using the finite difference (FD) software LPILE. Two three dimensional, finite element (FE) models of pile-soil interaction have been developed using Abaqus/Cae and SAP2000 to study the effect of lateral loading on pile embedded in clay. A lateral displacement of 2 cm was applied to the top of the pile, which is embedded into the concrete pile cap, while maintaining a zero slope in a guided fixation. A comparison between the bending moments and lateral displacements along the depth of the pile obtained from the FD solutions and FE was performed. A parametric study was conducted to study the effect of crucial design parameters such as the soil's modulus of elasticity, radius of the soil surrounding the pile in Abaqus/Cae, and the number of springs in SAP2000. A close correlation is found between the results obtained by the FE models and the FD solution. The results indicated that increasing the amount of clay surrounding the piles reduces the induced bending moments and lateral displacements in the piles and hence increases its capacity to resist lateral loading.

• 터널과지하공간
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• 제14권1호
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• pp.26-34
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• 2004

국내의 경우 UAM에 관한 체계적인 연구가 부족하여 역학적 보강 메커니즘에 관한 이론정립이 되어 있지 않음은 물론 설계변수에 따른 보강효과에 관한 정성적, 정량적인 관계정립이 아직 부족한 관계로 대부분의 경우 공학적 근거보다는 외국자료나 현장 지질조건에 따른 경험적 방법에 의존한 시공이 이루어지고 있다. 이러한 실정을 감안할 때 합리적이고 이론적 인 설계 및 해석기법의 도입이 요구되어지고 있다. 따라서, 본 연구에서는 유한요소법을 이용하여 UAM의 보강 메커니즘에 관여할 것으로 판단되는 지반물성, 상부지반의 두께, 삽입강관의 사이즈, 강관의 중첩길이, 강지보의 적용 유$.$무에 대하여 굴착 진행에 따른 강관의 거동 분석을 통해 UAM의 보강 메커니즘을 알아보기 위한 해석을 수행하였다. 본 연구를 통해 강관이 삽입된 지반의 하부를 굴착하면서 강관에 발생하는 부재력을 분석함으로써 UAM적용 시 강관의 보강 메커니즘을 확인하였다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 추계 학술발표회
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• pp.683-690
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• 2008

Steel-concrete composite columns are popular for superstructures of bridges, and the outside steel attached to the shaft increases the shaft resistance due to confining concrete. In this study, lateral resistance of steel-concrete composite drilled shafts was evaluated quantitatively based on numerical analysis when steel casings are used as structural elements like composite columns. Ultimate lateral resistance of composite drilled shafts with various diameters was numerically calculated through 3D finite element analysis. For that, elasto-plastic model with perfectly plasticity is involved to capture the ultimate load. A commercial FEM program, MIDAS-GTS, is used in this study. Real field conditions of the West Coast, Korea were considered to set up the ground conditions and pile lengths required for this parametric studies. Detailed characteristics of the stress and displacement distributions are evaluated for better understanding the mechanisms of the composite shaft behavior.

• Steel and Composite Structures
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• 제22권6호
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• pp.1417-1443
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• 2016

Cellular and castellated steel beams are used to obtain higher stiffness and bending capacity using the same weight of steel. In addition, the beam openings may be used as a pass for different mechanical fixtures such as ducts and pipes. The aim of this study is to investigate the effect of different parameters on both elastic and inelastic critical buckling stresses of steel web plates with openings. These parameters are plate aspect ratio; opening shape (circular or rectangular); end distance to the first opening; opening spacing; opening size; plate slenderness ratio; steel grade; and initial web imperfection. The web/flange interaction has been simplified by web edge restraints representing simply supported boundary conditions. A numerical parametric study has been performed through linear and nonlinear finite element (FE) models, where the FE results have been verified against both experimental and numerical results in the literature. The web plates are subject to in-plane linearly varying compression with different loading patterns, ranging from uniform compression to pure bending. A buckling stress modification factor (${\beta}$-factor) has been introduced as a ratio of buckling stress of web plate with openings to buckling stress of the corresponding solid web plate. The variation of ${\beta}$-factor against the aforementioned parameters has been reported. Furthermore, the critical plate slenderness ratio separating elastic buckling and yielding has been identified and discussed for two steel grades of DIN-17100, namely: ST-37/2 and ST-52/3. The FE results revealed that the minimum ${\beta}$-factor is 0.9 for web plates under uniform compression and 0.7 for those under both compression and tension.

• 한국전산구조공학회논문집
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• 제33권3호
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• pp.153-158
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• 2020

본 논문에서는 부분 CFST (concrete-filled steel tube) 기둥에 대한 수치해석적 저항력 평가 방법에 대해 소개하고 있다. 기존 RC(reinforced concrete) 기둥에서 소성힌지가 발생할 것으로 예상되는 부분을 강관으로 보강함으로써 완전 CFST 기둥보다는 적은 재료를 사용하여 비슷한 휨 모멘트 저항력을 가지는 부분 CFST 기둥의 디자인 컨셉을 제시하였다. 부분 CFST 기둥에서 외부 강관과 내부 콘크리트 사이의 계면에서 거동을 수치해석적으로 모사하기 위해 개선된 부착슬립모델을 적용한 유한요소모델을 구축하고, 이중곡률 휨-압축시험결과와 비교를 통해 타당성을 검증하였다. 검증된 수치모델을 바탕으로 매개변수 연구를 통해서 P-M 상관도를 그려 단면 조건에 따른 최대 저항력을 평가하였다. 또한, 강관 두께별로 필요 보강길이를 산출하고, 보강 조건에 따른 부분 CFST 기둥에서의 파괴메커니즘을 분석하였다.

• Steel and Composite Structures
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• 제36권1호
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• pp.103-118
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• 2020

The static behavior of grouped large-headed studs (d = 30 mm) embedded in ultra-high performance concrete (UHPC) was investigated by conducting push-out tests and numerical analysis. In the push-out test, no splitting cracks were found in the UHPC slab, and the shank failure control the shear capacity, indicating the large-headed stud matches well with the mechanical properties of UHPC. Besides, it is found that the shear resistance of the stud embedded in UHPC is 11.4% higher than that embedded in normal strength concrete, indicating that the shear resistance was improved. Regarding the numerical analysis, the parametric study was conducted to investigate the influence of the concrete strength, aspect ratio of stud, stud diameter, and the spacing of stud in the direction of shear force on the shear performance of the large-headed stud. It is found that the stud diameter and stud spacing have an obvious influence on the shear resistance. Based on the test and numerical analysis results, a formula was established to predict the load-slip relationship. The comparison indicates that the predicted results agree well with the test results. To accurately predict the shear resistance of the stud embedded in UHPC, a design equation for shear strength is proposed. The ratio of the calculation results to the test results is 0.99.

• Geomechanics and Engineering
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• 제16권6호
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• pp.643-654
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• 2018

Tunnel excavation leads to a disturbance on the initial stress balance of surrounding soils, which causes convergences around the tunnel and settlements at the ground surface. Considering the effective impact of settlements on the structures at the surface, it is necessary to estimate them, especially in urban areas. In the present study, ground settlements due to the excavation of East-West Line 7 of the Tehran Metro (EWL7) and the Abuzar tunnels are evaluated and the effect of the lateral earth pressure coefficient ($K_0$) on their extension is investigated. The excavation of the tunnels was performed by TBMs (Tunnel Boring Machines). The coefficient of lateral earth pressure ($K_0$) is one of the most important geotechnical parameters for tunnel design and is greatly influenced by the geological characteristics of the surrounding soil mass along the tunnel route. The real (in-situ) settlements of the ground surface were measured experimentally using leveling methods along the studied tunnels and the results were compared with evaluated settlements obtained from both semi-empirical and numerical methods (using the finite difference software FLAC3D). The comparisons permitted to show that the adopted numerical models can effectively be used to predict settlements induced by a tunnel excavation. Then a numerical parametric study was conducted to show the influence of the $K_0$ values on the ground settlements. Numerical investigations also showed that the shapes of settlement trough of the studied tunnels, in a transverse section, are not similar because of their different diameters and depths of the tunnels.