• 대한토목학회논문집
• /
• 제10권1호
• /
• pp.47-56
• /
• 1990

본 연구에서는 FWD시험의 표면 처짐곡선으로부터 시멘트 콘크리트 포장구조체의 물성 및 응력을 추정할 수 있는 역산반복기법을 개발하였다. 국내에 가설되어 있는 시멘트 콘크리트 포장구조체에 대한 요소설계를 실시하여 구한 모형들에 대하여 유한요소와 층탄성이론을 조합한 해석방법을 적용하여 처짐 특성 및 탄성 계수 추정식을 구하였다. 추정식에 의한 각 층의 탄성계수를 초기 탄성계수로 하고, 탄성계수 변화율과 처침 변화율의 관계를 이용하여 반복역산시 탄성계수 보정에 사용하였다. 각 고속도로 노선별로 효율적인 역산반복기법을 전산화하였으며, 수치모델을 통하여 신뢰성 및 타당성을 검증하였다.

• 한국농공학회논문집
• /
• 제46권6호
• /
• pp.47-58
• /
• 2004

As concrete structures are getting larger, higher, longer and more specialized, it is more required to develop steel fiber concrete and apply to the real world. In this research, it is aimed to have fatigue strength examined, varying the steel fiber content of 0%, 0.75%, 1.00%, 1.25% by experimental study of fatigue behavior of the steel fiber reinforced concrete continuous beams under cyclic loading. The ultimate load and initial load of flexural cracking were measured by static test. In addition, the load versus strain relation, load versus deflection relation, crack pattern and fracture mode by increasing weight were observed. On the other hand, the crack propagation and the modes of fracture according to cycle number and the relation of cyclic loading to deflection relation and strain relation were investigated by fatigue test. As the result of fatigue test, continuous beam without steel fiber was failed at 60 ~ 70% of The static ultimate strength and it could be concluded that fatigue strength to two million cyclic loading was arround 67.2% by S-N curve. On the other hand, that with steel fiber was failed at 65 ~ 85% of the static ultimate strength and it could be concluded fatigue strength to two million cyclic loading around 71.7%.

• 대한조선학회지
• /
• 제20권1호
• /
• pp.11-20
• /
• 1983

In this paper elastic-plastic large deflection analysis of ship structural members, plates, stiffened plates and cylindrical shallow shell, are performed by the finite element method. And for the consideration of the yielded propagation through the depth of the member, the layered element approach is employed. The present method is justified by comparing its results with those of experiment and others. As results, the nonlinear behavior and the ultimate strength curves are shown, which can be used in the design of the plates and the stiffened plates under compression, and the applicability to the shell structures is suggested. The analysis results are as followings. (1) The results of the approximate equations as well as those of buckling analysis may not guarantee precisely the safety of the structures in some cases and the optimum in other cases. Therefore they may not show the design criteria for the optimal design. (2) As the initial deflection increases, its effects on the ultimate strength of the structure generally increases, and the ultimate load, therefore, decreases. (3) This approach can be applied to the shell type structures. (4) The present method can be applied to the various structures composed of plate and beam members, for example, plates with hole and the stiffened plates with hole stiffened by spigot, doubler and/or stiffener, for the optimal design.

• 한국안전학회지
• /
• 제14권1호
• /
• pp.129-140
• /
• 1999

This study presents test results of RC beams strengthened by steel plates, carbon fiber sheets(CFS) and aramid fiber sheets(AFS) for increasing flexural and shear resistance. The test was performed with different parameters including the type of strengthening materials, flexural-strengthening methods and shear-strengthening methods. In case of flexural test, RC beams are initially loaded to 70% of the ultimate flexural capacity and in case of shear test loaded to 60 or 80 percent of the ultimate shear capacity and subsequently reinforced with steel plates, CFS and AFS. Experimental data on strength, steel strain, deflection, and mode of failure of the reinforced beams were obtained, and comparisons between the different shear reinforced schemes and the non-strengthened control beams were made. The test results showed that damaged RC beams strengthened by steel plates, CFS and AFS have more improved the flexural and shear capacity. For the beams with external reinforcement by steel plates, aramid fiber sheets and carbon fiber sheets increases in ultimate strength of 4 to 21, 17 to 43 and 26 to 36 percent were respectively achieved. Initial load had small effect on strength after reinforcement, but an important influence on deflection. One sheet reinforced was stronger than two sheets reinforced but less deflected than two sheets reinforced.

• 한국정밀공학회지
• /
• 제11권1호
• /
• pp.54-62
• /
• 1994

This paper presents active control methodologies to suppress structural deflections of a composite beam using a distributed piezoelectric-film actuator and sensor. Three types of different controllers are employed to achieve vibration suppression. The controllers are established depending upon the information on the velocity components of the structrue and on the deflection magnitudes as well. They are constant-amplitude controller(CAC), constant-gain mcontroller(CGC), and constant-amplitude-gain controller(CAGC). For the minimization of the residual vibration (chattering in a settled phase), which is the practical shortcoming of the conventional CAC dur to time delay phenomenon of the hardware system, a new control algoritym CAGCis designed by selecting switching constants in an optimal manner with respect to the initial tip deflection and the applied voltage. The experimental investigations of the transient and forced vibration control for the first vibrational mode are undertaken in order to compare the suppression efficiency of each control algorithm. Moreover, simultaneous controllability of various vibrational modes through the proposed scheme is also experimentally verified by pressenting both the transfer function and the phase.

• Structural Engineering and Mechanics
• /
• 제49권6호
• /
• pp.705-726
• /
• 2014

In general, cylindrically curved plates are used in ships and offshore structures such as wind towers, spa structures, fore and aft side shell plating, and bilge circle parts in merchant vessels. In a number of studies, it has been shown that curvature increases the buckling strength of a plate under compressive loading, and the ultimate load-carrying capacity is also expected to increase. In the present paper, a series of elastic and elastoplastic large deflection analyses were performed using the commercial finite element analysis program (MSC.NASTRAN/PATRAN) in order to clarify and examine the fundamental buckling and collapse behaviors of curved plates subjected to combined axial compression and lateral pressure. On the basis of the numerical results, the effects of curvature, the magnitude of the initial deflection, the slenderness ratio, and the aspect ratio on the characteristics of the buckling and collapse behavior of the curved plates are discussed. On the basis of the calculated results, the design formula was developed to predict the buckling and ultimate strengths of curved plates subjected to combined loads in an analytical manner. The buckling strength behaviors were simulated by performing elastic large deflection analyses. The newly developed formulations were applied in order to perform verification analyses for the curved plates by comparing the numerical results, and then, the usefulness of the proposed method was demonstrated.

• Structural Engineering and Mechanics
• /
• 제88권1호
• /
• pp.1-12
• /
• 2023

In this study, forced vibration behavior of a piezo magneto electric sandwich Timoshenko beam is investigated. It is assumed a sandwich beam with porous core and graphene platelet reinforced composite (GPLRC) in facesheets subjected to magneto-electro-elastic and temperature-dependent material properties. The magneto electro platelets are under linear function along with the thickness that includes a cosine function and magnetic and electric constant potentials. The governing equations of motion are derived using modified strain gradient theory for microstructures. The effects of material length scale parameters, temperature change, different distributions of porous, various patterns of graphene platelets, and the core to face sheets thickness ratio on the natural frequency and excited frequency of a sandwich Timoshenko beam are scrutinized. Various size-dependent methods effects such as MSGT, MCST, and CT on the natural frequency is considered. Moreover, the final results affirm that the increase in porosity coefficient and volume fractions lead to an increase in the amount of natural frequency; while vice versa for the increment in the aspect ratio. From forced vibration analysis, it is understood that by increasing the values of volume fraction and the length thickness of GPL, the maximum deflection of a sandwich beam decreases. Also, it is concluded that increasing the temperature, the thickness of GPL, and the initial force leads to a decrease in the maximum deflection of GPL. It is also shown that resonance phenomenon occurs when the natural and excitation frequencies become equal to each other. Outcomes also reveal that the third natural frequency owns the minimum value of both deflection and frequency ratio and the first natural frequency has the maximum.

• 대한치과교정학회지
• /
• 제37권6호
• /
• pp.432-439
• /
• 2007

초탄성 니켈-티타늄 호선의 하중값은 온도 변화에 따라 변화함이 보고된 바 있다. 따라서 본 연구에서는 온도가 변화함에 따라 니켈-티타늄 합금 호선의 하중값이 어떻게 변화하는지 알아보고자 하였다. $37^{\circ}C$ 항온 상태에서 $0.016"{\times}0.22"$ 니켈-티타늄 호선을 3.1 mm까지 변위시키는 3점 굴곡 실험을 시행하여 하중 시와 탈하중 시의 1.5mm 변위지점의 하중값을 측정하고 이 지점에서 구강내 온도 변화를 고려한 온도 변화 실험을 시행하였다. $20^{\circ}C$ 저온수 또는 $50^{\circ}C$ 고온수를 호선에 흘려보냄으로써 온도 변화를 주었다. 저온 실험은 저온수로 온도 변화를 주고 $37^{\circ}C$ 항온 온도로 회복된 후에 다시 저온수를 흐르게 하는 방법으로 10회 시행하였고 고온 실험도 동일한 방법으로 시행하였다. 그 결과 하중 시 1.5mm 변위지점의 하중값은 저온 실험 및 고온 실험 후 $37^{\circ}C$로 회복된 후에도 모두 감소된 값을 유지하였다. 반대로 실제로 치아에 가해지는 교정력으로 생각되는 탈하중 시 1.5 mm 변위 지점의 하중값은 저온 실험 및 고온 실험 후 온도가 $37^{\circ}C$로 회복되어도 모두 증가된 값을 유지하였다. 이상의 결과를 종합해 볼 때 온도변화를 거친 후 초탄성 니켈-티타늄 합금 호선의 하중 시 힘은 감소하였고 탈하중 시 힘은 증가되므로, 임상에서 니켈-티타늄 호선을 적용 시에는 $37^{\circ}C$에서의 하중-변위 곡선에서 나타나는 힘에 비해 더 작은 하중 시 힘과 더 큰 탈하중 시 힘이 적용될 수 있음에 유의하여야 한다.

• 한국정밀공학회지
• /
• 제22권3호
• /
• pp.146-153
• /
• 2005

In this paper, a multi-step optimization using genetic algorithm with variable penalty function is introduced to the structural design optimization of a grinding machine. The design problem, in this study, is to find out the optimum configuration and dimensions of structural members which minimize the static compliance, the dynamic compliance, and the weight of the machine structure simultaneously under several design constraints such as dimensional constraints, maximum deflection limit, safety criterion, and maximum vibration amplitude limit. The first step is shape optimization, in which the best structural configuration is found by getting rid of structural members that have no contributions to the design objectives from the given initial design configuration. The second and third steps are sizing optimization. The second design step gives a set of good design solutions having higher fitness for lightweight and minimum static compliance. Finally the best solution, which has minimum dynamic compliance and weight, is extracted from the good solution set. The proposed design optimization method was successfully applied to the structural design optimization of a grinding machine. After optimization, both static and dynamic compliances are reduced more than 58.4% compared with the initial design, which was designed empirically by experienced engineers. Moreover the weight of the optimized structure are also slightly reduced than before.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2000년도 봄 학술발표회 논문집
• /
• pp.393-398
• /
• 2000

To use concrete box culverts effectively, precast goods are manufactured at a factory, then linked and anchored with prestressing tendon at a field. However, the corrosion of rebar and prestressing tendon in the box culverts utilizing portland cement concrete is issued when the cracks occur at a underground water level. It has been reported that reported that expansive concrete, compared with portland cement concrete, has many structural advantages such as increasing capacity of watertight, controling initial crack and improving durability due to its property of expansion. During flexure test with RC beam made from expansive concrete, in the case of a constant section of concrete element, the lower steel ratio is, and in the case of a constant steel ratio, the more incremental the section of concrete element, the more incremental the amount of chemical prestress by expansive concrete is. At the segment of the box culverts using expansive concrete, the numbers of crack and its gap is reduced, and ultimate load and initial crack load is much larger than the segment at which expansive concrete is nor used. Also lay-out of tendon with a curvature generate upward force so that deflection is reduced. Through the whole procedure, it could be confirmed that performance precast box culvert by means of using expansive concrete is improved.