• Structural Engineering and Mechanics
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• 제49권3호
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• pp.395-410
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• 2014

Fiber Reinforced Elastomeric Bearings (FREBs) are a relatively new type of laminated bearings that can be used as seismic/vibration isolators or bridge bearings. In an unbonded (U)-FREB, the bearing is placed between the top and bottom supports with no bonding or fastening provided at its contact surfaces. Under shear loads the top and bottom faces of a U-FREB roll off the contact supports and the bearing exhibits rollover deformation. As a result of rollover deformation, the horizontal response characteristics of U-FREBs are significantly different than conventional elastomeric bearings that are employed in bonded application. Current literature lacks an efficient analytical horizontal stiffness solution for this type of bearings. This paper presents two simplified analytical models for horizontal stiffness evaluation of U-FREBs. Both models assume that the resistance to shear loads is only provided by an effective region of the bearing that sustains significant shear strains. The presented models are different in the way they relate this effective region to the horizontal bearing displacements. In comparison with experimental results and finite element analyses, the analytical models that are presented in this paper are found to be sufficiently accurate to be used in the preliminary design of U-FREBs.

• Geomechanics and Engineering
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• 제30권4호
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• pp.383-392
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• 2022

Although pipelines are composed of segmental tubes commonly connected by rubber gasket or push-in joints, current studies mainly simplified pipelines as continuous structures. Effects of joints on three-dimensional deformation mechanisms of existing pipelines due to tunnel excavation are not fully understood. By conducting three-dimensional numerical analyses, effects of pipeline burial depth, tunnel burial depth, volume loss, pipeline stiffness and joint stiffness on bending strain and joint rotation of existing pipelines are explored. By increasing pipeline burial depth or decreasing tunnel cover depth, tunneling-induced pipeline deformations are substantially increased. As tunnel volume loss varies from 0.5% to 3%, the maximum bending strains and joint rotation angles of discontinuous pipelines increase by 1.08 and 9.20 times, respectively. By increasing flexural stiffness of pipe segment, a dramatic increase in the maximum joint rotation angles is observed in discontinuous pipelines. Thus, the safety of existing discontinuous pipelines due to tunnel excavation is controlled by joint rotation rather than bending strain. By increasing joint stiffness ratio from 0.0 (i.e., completely flexible joints) to 1.0 (i.e., continuous pipelines), tunneling-induced maximum pipeline settlements decrease by 22.8%-34.7%. If a jointed pipeline is simplified as a continuous structure, tunneling-induced settlement is thus underestimated, but bending strain is grossly overestimated. Thus, joints should be directly simulated in the analysis of tunnel-soil-pipeline interaction.

• Steel and Composite Structures
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• 제47권3호
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• pp.375-382
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• 2023

The H-shaped steel beam is popular due to its ease of manufacturing and connection to the column. This profile, which is used as a shallow beam, needs the high weak-axis bending stiffness and torsional stiffness to meet the overall stability. Achieving the local beam flange stability, bearing capacity, bending stiffness, and torsional requirements need a great thickness and width of the beam flange, which causes, which will cause more uneconomical structural design. So, the box-section beam is the ideal alternative. However, the current design specifications do not have design rules for the bolt-and-welded connection of the box-section beam and box-section column. The paper proposes a novel bolt-and-welded connection of the box-section beams and box-section columns based on a high-rise structural design scheme. Three connection models, BASE, WBF, and RBS, are analyzed under cyclic loading in ABAQUS software. The failure modes, hysteresis response, bearing capacity, ductility, plastic rotation angle, energy dissipation, and stiffness degradation of all models are determined and compared. Compared with the other two models, the model WBF exhibited excellent seismic performance, ductility, and plastic rotation ability. Finally, model WBF was chosen as the connection scheme used in the project design.

• Steel and Composite Structures
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• 제48권1호
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• pp.59-71
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• 2023

Corrosion of the headed studs shear connectors is an important factor in the reduction of the durability and mechanical properties of the steel-concrete composite structure. In order to study the effect of stud corrosion on the mechanical properties in the negative moment region of steel-concrete composite beams, the corrosion of stud was carried out by accelerating corrosion method with constant current. Static monotonic loading was adopted to evaluate the cracking load, interface slip, mid-span deflection, and ultimate bearing capacity of four composite beams with varying corrosion rates of headed studs. The effect of stud corrosion on the stiffness of the composite beam's hogging moment zone during normal service stage was thoroughly examined. The results indicate that the cracking load decreased by 50% as the corrosion rate of headed studs increase to 10%. Meanwhile, due to the increase of interface slip and mid-span deflection, the bending stiffness dropped significantly with the same load. In comparison to uncorroded specimens, the secant stiffness of specimens with 0.5 times ultimate load was reduced by 25.9%. However, corrosion of shear studs had no obvious effect on ultimate bending capacity. Based on the experimental results and the theory of steel-concrete interface slip, a method was developed to calculate the bending stiffness in the negative bending moment region of composite beams during normal service stage while taking corrosion of headed studs into account. The validity of the calculation method was demonstrated by data analysis.

• 대한통합의학회지
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• 제7권3호
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• pp.159-169
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• 2019

Purpose: The purpose of this study was to provide an effective method of exercise therapy for patients with cervicogenic headache. Methods: The subjects were divided into the following three groups according to the intervention received: cervix-stabilizing exercise (n=12, group 1), transcranial direct current stimulation (n=12, group 2), and cervix-stabilizing exercise combined with transcranial direct current stimulation (n=12, group 3). The intragroup and intergroup differences in muscle characteristics and neck disability index were compared and analyzed. Results: The comparison and analysis of the changes in muscle tone and post hoc analysis revealed statistically significant intragroup decreases in the upper trapezius and suboccipitals in groups I and III, and statistically significant intergroup differences in the upper trapezius, with greater changes in group III than in group II, and in the suboccipitals, with greater changes in groupIII than in groups Iand II. The comparison and analysis of the change in muscle stiffness and post hoc analysis revealed a statistically significanti ntra group decrease in the upper trapezius in group Iand suboccipitals in group III, and a statistically significant intergroup difference in both muscles, with greater change in group III than in group II. The comparison and analysis of change in neck disability index and post hoc analysis revealed a statistically significant intragroup decrease in all the three groups and a statistically significant intergroup difference, with greater change in group III than in groups I and II. Conclusion: The neck-stabilizing exercise and transcranial direct current stimulation were shown to be effective in decreasing the tone of the cervical muscles by stabilizing the cervical bone and improving muscle durability, and in improving the movement and limitation of joint range of motion by decreasing muscle tone and stiffness.

• Earthquakes and Structures
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• 제12권3호
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• pp.333-347
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• 2017

Masonry infill walls are unavoidable parts of any building to create a separation between internal space and external environment. In general, there are some prevalent openings in the infill wall due to functional needs, architectural considerations or aesthetic concerns. In current design practice, the strength and stiffness contribution of infill walls is not considered. However, the presence of infill walls may decisively influence the seismic response of structures subjected to earthquake loads and cause a different behavior from that predicted for a bare frame. Furthermore, partial openings in the masonry infill wall are significant parameter affecting the seismic behavior of infilled frames thereby decreasing the lateral stiffness and strength. The possible effects of openings in the infill wall on seismic behavior of RC frames is analytically studied by means of pushover analysis of several bare, partially and fully infilled frames having different bay and story numbers. The stiffness loss due to partial opening is introduced by the stiffness reduction factors which are developed from finite element analysis of frames considering frame-infill interaction. Pushover curves of frames are plotted and the maximum base shear forces, the yield displacement, the yield base shear force coefficient, the displacement demand, interstory drift ratios and the distribution of story shear forces are determined. The comparison of parameters both in terms of seismic demand and capacity indicates that partial openings decisively influences the nonlinear behavior of RC frames and cause a different behavior from that predicted for a bare frame or fully infilled frame.

• Steel and Composite Structures
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• 제28권5호
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• pp.617-628
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• 2018

Steel shear wall possesses priority over many of the current lateral load-bearing systems due to reasons like higher elastic stiffness, desirable ductility and energy absorption, convenience in construction and implementation technology, and economic criteria. Besides these advantages, this system causes increase in the dimensions of other structural elements due to its high stiffness as one of its intrinsic characteristics. One of the methods for stiffness reduction is perforating the wall panel and creating openings in the wall that can also be used as windows or ducts in buildings service period. The aim of the present study is probing the appropriate geometric shape and location of opening to fulfil economic criterion plus technical and seismic design criteria. In the present research, a number of possible while reasonable opening shapes and locations are defined in various sizes for some steel shear wall specimens. The specimens are modelled in ABAQUS finite elements software and analyzed using nonlinear pushover analysis. Finally, the analyses' results are reported as force-displacement diagrams and the strength, the initial stiffness and the energy absorption are calculated for all specimens and compared together. The obtained results show that both shape and location of the openings affect the seismic parameters of the shear wall. The specimens in which the openings are further from the center and closer to the columns possess higher stiffness and strength while the specimens in which the openings are closer to the center show more considerable changes in their seismic parameters in response to increase in opening area.

• 대한의용생체공학회:의공학회지
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• 제30권2호
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• pp.129-134
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• 2009

The ideal method which measures a blood vessel of senility and degree of arteriosclerosis is to measure compliance of arterial and condition of blood circulation at the periphery. In these days vascular stiffness have been assessed by analyzing PTT (pulse transit time) from ECG and PPG. PTT is that between toe and finger each subject estimated through ECG and PPG signals. Two parameters, which are related to PWV, were tested with the time delay between the finger and toe. PWV is a variation of quantity which is associated with vascular stiffness. These researches which use PTT and PWV don't consider the blood vessel characteristic of an individual. In this current research, we have used with the blood vessel characteristic of an individual. That is an assessment of vascular stiffness using the variation of quantity in PWV with the changes of position in the subject. PWV variation increased as functions of the subject's age. The increase of the PWV variation parameters with age is attributed to the direct decrease of the blood vessel compliance with different position. The quantity of variation estimated by experimental results is that old age's (75.78${\pm}$7.75) case is 113.68% and young age's (26.47${\pm}$2.04) case is 85.69%. We proved and presented about estimation of vascular stiffness of possibility by this result.

• 한국강구조학회 논문집
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• 제16권5호통권72호
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• pp.671-682
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• 2004

본 연구는 부분 전단연결을 가지는 강-콘크리트 합성보의 처짐에 미치는 전단슬립의 영향을 조사하는 것이다. 현재 각국의 설계규준에서는 합성보의 처짐 계산시 전단연결재의 강도와 관련되어 있지만, 본 연구에서는 하중조건에 상관없는 전단연결재의 강성에 기반을 둔 정확한 해를 유도하였다. 우선, 평형조건, 곡률의 적합조건에 기반을 둔 3가지 하중조건에서의 합성보의 등가강성을 유도하고, 이로부터 하중조건에 상관없이 슬립의 영향을 적용할 수 있는 간편한 제안식을 유도하였다. 이러한 제안식의 타당성을 검증하기 위해서 현재 AISC에서 사용하고 있는 합성보의 유효강성 및 Nie가 제안한 식과 비교하였다. 일반적으로 사용되는 보의 경우, 전단슬립의 영향은 스팬이 짧을 경우, AISC에 비해서 최대 18%까지의 강성의 감소를 나타냄을 알 수 있었다. 완전합성보의 경우, AISC의 제안 값이 본 연구의 결과 보다 크게 나타났는데, 이는 안전측이 되지 못함을 알 수 있었으며, 불완전 합성보의 경우, AISC 제안식이 본 연구보다 강성을 과소 평가하는 결과를 나타내었다.

• 한국지반신소재학회논문집
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• 제2권2호
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• pp.13-24
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• 2003

본 논문에서는 유한요소해석을 통해 기초지반의 강성과 상재하중이 블록식 보강토 옹벽에 미치는 영향을 고찰한 내용을 다루었다. 이를 위해 기초지반의 강성과 상재하중의 위치를 변화시키며 매개변수 연구를 수행하였으며 해석결과에서는 벽체의 변위와 보강재의 유발인장력은 기초지반의 강성이 감소함에 따라 증가하는 것으로 나타났다. 한편, 해석결과에 따르면 현재 설계기준에서 적용되고 있는 상재하중 처리 방법은 경우에 따라서 상재하중의 영향을 지나치게 과대평가 하는 것으로 나타났으며 상재하중이 보강영역에 근접하여 작용할 경우 외적안정성 검토시 주의를 요하는 것으로 나타났다. 본 논문에서는 본 연구를 통해 얻어진 결과가 실무적 측면에서 의미하는 바를 심도 있게 고찰하였다.