• Computers and Concrete
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• 제30권2호
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• pp.127-141
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• 2022

In this paper, a numerical procedure is proposed for achieving the minimum cost design of reinforced concrete polygonal column cross-sections under compression and biaxial bending. A methodology is developed to integrate the metaheuristic algorithm Quantum Particle Swarm Optimization (QPSO) with an algorithm for the evaluation of the strength of reinforced concrete cross-sections under combined axial load and biaxial bending, according to the design criteria of Brazilian Standard ABNT NBR 6118:2014. The objective function formulation takes into account the costs of concrete, reinforcement, and formwork. The cross-section dimensions, the number and diameter of rebar and the concrete strength are taken as discrete design variables. This methodology is applied to polygonal cross-sections, such as rectangular sections, rectangular hollow sections, and L-shaped cross-sections. To evaluate the efficiency of the methodology, the optimal solutions obtained were compared to results reported by other authors using conventional methods or alternative optimization techniques. An additional study investigates the effect on final costs for an alternative parametrization of rebar positioning on the cross-section. The proposed optimization method proved to be efficient in the search for optimal solutions, presenting consistent results that confirm the importance of using optimization techniques in the design of reinforced concrete structures.

• Journal of Communications and Networks
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• 제11권2호
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• pp.134-147
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• 2009

Tracking and exploiting instantaneous spectrum opportunities are fundamental challenges in opportunistic spectrum access (OSA) in presence of the bursty traffic of primary users and the limited spectrum sensing capability of secondary users. In order to take advantage of the history of spectrum sensing and access decisions, a sequential decision framework is widely used to design optimal policies. However, many existing schemes, based on a partially observed Markov decision process (POMDP) framework, reveal that optimal policies are non-stationary in nature which renders them difficult to calculate and implement. Therefore, this work pursues stationary OSA policies, which are thereby efficient yet low-complexity, while still incorporating many practical factors, such as spectrum sensing errors and a priori unknown statistical spectrum knowledge. First, with an approximation on channel evolution, OSA is formulated in a multi-armed bandit (MAB) framework. As a result, the optimal policy is specified by the wellknown Gittins index rule, where the channel with the largest Gittins index is always selected. Then, closed-form formulas are derived for the Gittins indices with tunable approximation, and the design of a reinforcement learning algorithm is presented for calculating the Gittins indices, depending on whether the Markovian channel parameters are available a priori or not. Finally, the superiority of the scheme is presented via extensive experiments compared to other existing schemes in terms of the quality of policies and optimality.

• 한국소음진동공학회논문집
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• 제18권2호
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• pp.185-191
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• 2008

Optimal damping layout of the constrained viscoelastic damping layer on beam is identified with temperatures by using a gradient-based numerical search algorithm. An optimal design problem is defined in order to determine the constrained damping layer configuration. A finite element formulation is introduced to model the constrained layer damping beam. The four-parameter fractional derivative model and the Arrhenius shift factor are used to describe dynamic characteristics of viscoelastic material with respect to frequency and temperature. Frequency-dependent complex-valued eigenvalue problems are solved by using a simple re-substitution algorithm in order to obtain the loss factor of each mode and responses of the structure. The results of the numerical example show that the proposed method can reduce frequency responses of beam at peaks only by reconfiguring the layout of constrained damping layer within a limited weight constraint.

• Wind and Structures
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• 제18권1호
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• pp.1-20
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• 2014

Modern design of long suspension bridges must satisfy at the same time spanning very long distances and limiting their response against several external loads, even if of high intensity. Structural Control, with the solutions it provides, can offer a reliable contribution to limit internal forces and deformations in structural elements when extreme events occur. This positive aspect is very interesting when the dimensions of the structure are large. Herein, an updated numerical model of an existing suspension bridge is developed in a commercial finite element work frame, starting from original data. This model is used to reevaluate an optimization procedure for a passive control strategy, already proven effective with a simplified model of the buffeting wind forces. Such optimization procedure, previously implemented with a quasi-steady model of the buffeting excitation, is here reevaluated adopting a more refined version of the wind-structure interaction forces in which wind actions are applied on the towers and the cables considering drag forces only. For the deck a more refined formulation, based on the use of indicial functions, is adopted to reflect coupling with the bridge orientation and motion. It is shown that there is no variation of the previously identified optimal passive configuration.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2005년도 춘계 학술발표회 논문집
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• pp.704-711
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• 2005

Recently Life Cycle Cost Analysis for civil infrastructures such as pavements, bridges, and dams has been emphasized However, so far, there are few systems available for life cycle cost analysis of bridges at design stage. Therefore, the objective of this paper is to develop a user-friendly life-cycle cost analysis system for LCC-effective optimal design decision making at design stage. The program is based on the proposed LCC model, formulation, analysis modules and systematic procedure that suit Korean construction conditions. It is expected that the developed system can be effectively utilized for more LCC-effective design of bridges. It is applied to an actual bridge design project in order to demonstrate its effectiveness and applicability.

• Steel and Composite Structures
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• 제14권2호
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• pp.121-132
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• 2013

This paper deals with multiobjective optimization of symmetrically laminated composite angle-ply annular sector plates subjected to axial uniform pressure load and thermal load. The design objective is the maximization of the weighted sum of the critical buckling load and fundamental frequency. The design variable is the fibre orientations in the layers. The performance index is formulated as the weighted sum of individual objectives in order to obtain the optimum solutions of the design problem. The first-order shear deformation theory is used for the mathematical formulation. Finally, the effects of different weighting factors, annularity, sector angle and boundary conditions on the optimal design are investigated and the results are compared.

• Computers and Concrete
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• 제24권2호
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• pp.117-123
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• 2019

Optimization is an important subject which is widely used in engineering problems. In this paper, an analytical method is developed for optimum design of reinforced concrete beams considering both flexural and shear effects. A closed-form formulation is derived for optimal height and rebar of beams. The total material cost of steel and concrete is considered as the objective function which is minimized during the optimization process. The ultimate flexural and shear capacities of the beam are considered as the main constraints. The ultimate limit state is considered for deriving the relations for flexural capacity of the beam. The design requirements are considered according to the item 9 of the Iranian National Building. Analytical formulas and some curves are proposed to be used for optimum design of RC beams. The proposed method can be used to perform the optimization of RC beams without the need of any prior knowledge in optimization. Also, the results of the studied numerical example show that the proposed method results in a better design comparing with the other methods.

• 대한토목학회논문집
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• 제34권6호
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• pp.1845-1850
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• 2014

철도 운영측면에서 비용을 최소화하는 최적노선을 설계하기 위해서는 다양한 지형 위에 설계기준에 맞는 노선을 배치하여야 하며, 절토량과 성토량을 최소화 하거나 이 둘의 합을 균형화 하여 공사비용을 최소화하고 있다. 열차의 효율적인 운행을 가능하게 하는 노선의 설계는 다양한 변수의 해 공간을 모두 고려하여야하기 때문에 조합최적화의 문제라고 할 수 있다. 본 연구에서는, 공사비를 최소화 하는 최적 철도 노선을 설정하기 위한 수리적 모형을 개발하였으며, Genetic Algorithm을 사용한 문제의 해석을 하였고, Algorithm과 결과를 활용한 철도 최적 노선 설계 개념을 정립하였다. 그리고 가상의 구간에 대한 사례적용을 통하여 본 연구에서 제시하고 있는 방법론에 대하여 평가하여 성토량과 절토량을 균형화 할 수 있음을 확인하였다. 이러한 결과는 실제적으로 수명 동안의 에너지 비용이 공사비보다 높은 현실에서 철도노선설계의 최적화 과정에서 중요하게 활용될 수 있을 것이다.

• 전산구조공학
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• 제7권1호
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• pp.117-124
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• 1994

본 논문에서는 다단계다목적함수 최적화(MLMO)를 통해 철근콘크리트 뼈대구조의 최적해를 일단계단일 목적함수 최적화(SLSO)에 의한 결과와 비교하였다. MLMO방법에 의해서 간단히 가중치(Weighting factor)를 도모함으로써 경비와 처짐의 두가지 목적함수를 만족시키는 것이 가능했으며, 단계별로 제약조건식의 수를 감소시키고, 문제형성의 비선형성을 감소시킴으로써 최적화의 과정을 효율적으로 수행할 수 있었다. 또한 각 부구조물간의 설계변수의 변화에 의한 부재력의 변화를 제약조건에 반영하기 위하여 부재력변화량 추정을 하였고 부구조물의 최적화시 부재감 결합(coupling)이 가능하도록 하였다. 부구조물의 최적화시 선형화된 구조시스템의 선형화된 목적함수와 제약조건식을 사용하여 재해석 과정을 효율적으로 감소시킬 수 있었다. 최적화 과정중 초기에는 설계변수에 대한 비교적 큰 이동한계의 사용이 가능하였으며 반복회수 4호 정도에 최적해로의 효율적인 수렴이 이루어졌다.

• 한국전산구조공학회논문집
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• 제18권3호
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• pp.219-226
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• 2005

본 연구에서는 휠체어의 경량화를 위해 기존의 강관으로 제작된 휠체어를 피로파괴 및 손상에 강하고 방진 특성이 우수하며 유지 및 보수가 용이한 복합재료 중공빔으로 구성된 복합재료 휠체어로 대체하기 위하여 복합재료 중공빔 이론과 유전자 알고리즘을 적용하여 최적화된 등가 강성을 가지는 복합재료 중공빔의 최적의 단면 치수를 제시하였다. 제시한 최적의 단면치수를 가지는 복합재료 중공빔으로 구성된 휠체어 전체 구조에 Tsai-Wu 파손이론을 이용해 과하중이 가해지는 경우에 대하여 구조해석을 수행한 결과, 휠체어의 파손 유무를 나타내는 Makimum Tsai-Wu Failure Criteria Index가 파손이 발생하는 1.00보다 현저히 낮은 $0.192\times10^{-3}$을 나타내고 있음을 알 수 있었다. 또한 기존의 강관을 동일한 강성을 가지는 복합재료 증공빔으로 대체하였을 경우 중공빔 중량을 최대 45%감소하는 효과를 얻을 수 있음을 확인할 수 있었다.