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Abstract
This paper presents a review on getting a Weighted Multi-Objective Optimization (WMO) of Tuned Mass Damper (TMD) parameters based on Response Surface Methodology (RSM) coupled central composite design and Weighted Desirability Function (WDF) to attenuate the earthquake vibration of a jacket supported Offshore Wind Turbine (OWT). To optimize the parameters (stiffness and damping coefficient) of damper, the frequency ratio and damping ratio were considered as a design variable and the top displacement and frequency response were considered as objective functions. The optimization has been carried out under only El Centro earthquake results and after obtained the optimal parameters, more two earthquakes (California and Northridge) has been performed to investigate the performance of optimal damper. The obtained results also compared with the different conventional TMD\'s designed by Den Hartog\'s, Sadek et al.\'s and Warburton\'s method. From the results, it was found that the optimal TMD based on RSM shows better response than the conventional damper. It is concluded that the proposed response model offers an efficient approach regarding the TMD optimization.

Key Words
weighted multi-objective optimization; tuned mass damper; response surface methodology; weighted desirability function; offshore wind turbine

Address
Mohammad S. Rahman, Mohammad S. Islam: Civil and Environmental Engineering, Kunsan National University, 558 Daehak-ro, Gunsan-si 54150, Republic of Korea Jeongyun Do and Dookie Kim: Industry-University Cooperation Foundation, Kunsan National University, 558 Daehak-ro, Gunsan-si 54150, Republic of Korea

Abstract
This study presents optimum design of plane steel bridges considering corrosion effect by using teaching-learning based optimization (TLBO) method. Optimum solutions of three different bridge problems are linearly carried out including and excluding corrosion effect. The member cross sections are selected from a pre-specified list of 128 W profiles taken from American Institute of Steel Construction (AISC). A computer program is coded in MATLAB to carry out optimum design interacting with SAP2000 using OAPI (Open Application Programming Interface). The stress constraints are incorporated as indicated in AISC Allowable Stress Design (ASD) specifications and also displacement constraints are applied in optimum design. The results obtained from analysis show that the corrosion effect on steel profile surfaces causes a crucial increase on the minimum steel weight of bridges. Moreover, the results show that the method proposed is applicable and robust to reach the destination even for complex problems.

Key Words
optimum design; steel bridge; teaching-learning based optimization; MATLAB-SAP2000 OAPI

Address
Musa Artar : Department of Civil Engineering, Bayburt University, Bayburt 69000, Turkey Recep Catar : Department of Mechanical Engineering, Bayburt University, Bayburt 69000, Turkey Ayse T. Daloglu : Department of Civil Engineering, Karadeniz Technical University, Trabzon 61000,Turkey

Abstract
This paper presents the application of topology optimization as a design tool for a steel railway bridge. The choice of a steel railway bridge is dictated by the particular situation that it is suitable for topology optimization design. On the one hand, the current manufacturing techniques for steel structures (additive manufacturing techniques not included) are highly appropriate for material optimization and weight reduction to improve the overall structural efficiency, improve production efficiency, and reduce costs. On the other hand, the design of a railway bridge, especially at higher speeds, is dominated by minimizing the deformations, this being the basic principle of compliance optimization. However, a classical strategy of topology optimization considers typically only one or a very limited number of load cases, while the design of a steel railway bridge is characterized by relatively concentrated convoy loads, which may be present or absent at any location of the structure. The paper demonstrates the applicability of considering multiple load configurations during topology optimization and proves that a different and better optimal layout is obtained than the one from the classical strategy.

Key Words
topology optimization; SIMP; steel railway bridge; multiple load cases

Address
Arne Jansseune and Wouter De Corte: Department of Structural Engineering, Research group Schoonmeersen, Faculty of Engineering and Architecture, Ghent University, Valentin Vaerwyckweg 1, 9000 Ghent, Belgium

Abstract
Investigating the properties and durability of high-strength concrete exposed to sulfuric acid attack for the purpose of its application in structures exposed to this acid is of outmost importance. In this research, the resistance and durability of highstrength concrete containing macro-polymeric or steel fibers together with the pozzolans of silica fume or nano-silica against sulfuric acid attack are explored. To accomplish this goal, in total, 108 high-strength concrete specimens were made with 9 different mix designs containing macro-polymeric and steel fibers at the volume fractions of 0.5, 0.75, and 1.0%, as well as the pozzolans of silica fume and nano-silica with the replacement levels of 10 and 2%, respectively. After placing the specimens inside a 5% sulfuric acid solution in the periods of 7, 21, and 63 days of immersion, the effect of adding the fibers and pozzolans on the compressive properties, ultrasonic pulse velocity (UPV), and weight loss of high-strength concrete was investigated and the respective results were compared with those of the reference specimens. The obtained results suggest the dependency of the resistance and durability loss of high-strength concrete against sulfuric acid attack to the properties of fibers as well as their fraction in concrete volume. Moreover, compared with using nano-silica, using silica fume in the fibrous concrete mix leads to more durable specimens against sulfuric acid attack. Finally, an optimum solution for the design parameters where the crushing load of high-strength fibrous concrete is maximized was found using response surface method (RSM).

Key Words
sulfuric acid attack; fibers; silica fume; nano-silica; ultrasonic test; crushing load; high-strength concrete; response surface method; optimization

Address
Mahdi Nematzadeh and Saber Fallah-Valukolaee: Department of Civil Engineering, University of Mazandaran, Babolsar, Iran

Abstract
Modal expansion technique (MET) is a method to estimate the vibration fields of flexible structures by using eigenmodes of the structure and the signals of sensors. It is the useful method to estimate the vibration fields but has the truncation error since it only uses the limit number of the eigenmodes in the frequency of interest. Even though block-wise MET performed frequency block by block with different valid eigenmodes was developed, it still has the truncation error due to the absence of other eigenmodes. Thus, this paper suggested an improved block-wise modal expansion technique. The technique recovers the truncation errors in one frequency block by utilizing other eigenmodes existed in the other frequency blocks. It was applied for estimating the vibration fields of a cylindrical shell. The estimated results were compared to the vibration fields of the forced vibration analysis by using two indices: the root mean square error and parallelism between two vectors. These indices showed that the estimated vibration fields of the improved block-wise MET more accurately than those of the established METs. Especially, this method was outstanding for frequencies near the natural frequency of the highest eigenmode of each block. In other words, the suggested technique can estimate vibration fields more accurately by recovering the truncation errors of the established METs.

Key Words
modal expansion technique; vibration field; truncation error; modal assurance criterion; sensor placement optimization

Address
Byung Kyoo Jung and Weui Bong Jeong : School of Mechanical Engineering, Pusan National University, 2, Busan 46241, Republic of Korea Jinrae Cho : Department of Naval Architecture and Ocean Engineering, Hongik University, Sejong 339-710, Korea

Abstract
This study presents the Big Bang and Big Crunch (BB-BC) optimization algorithm for detection of structure damage in large severity. Local damage is represented by a perturbation in the elemental stiffness parameter of the structural finite element model. A nonlinear objective function is established by minimizing the discrepancies between the measured and calculated acceleration responses (AR) of the structure. The BB-BC algorithm is utilized to solve the objective function, which can localize the damage position and obtain the severity of the damage efficiently. Numerical simulations have been conducted to identify both single and multiple structural damages for beam, plate and European Space Agency Structures. The present approach gives accurate identification results with artificial measurement noise.

Key Words
damage detection; time domain; BB-BC algorithm; optimization

Address
J.L. Huang and Z.R. Lu : Department of Applied Mechanics, Sun Yat-sen University, Guangzhou, Guangdong Province, 510006, P.R. China

Abstract
The traditional design procedure of a prestressed concrete (PC) cable-stayed bridge is complex and time-consuming. The designers have to repeatedly modify the configuration of the large number of design parameters to obtain a feasible design scheme which maybe not an economical design. In order to efficiently achieve an optimum design for PC cable-stayed bridges, a multi-parameter optimization technique is proposed. In this optimization technique, the number of prestressing tendons in girder is firstly set as one of design variables, as well as cable forces, cable areas and cross-section sizes of the girders and the towers. The stress and displacement constraints are simultaneously utilized to ensure the safety and serviceability of the structure. The target is to obtain the minimum cost design for a PC cable-stayed bridge. Finally, this optimization technique is carried out by a developed PC cable-stayed bridge optimization program involving the interaction of the parameterized automatically modeling program, the finite element structural analysis program and the optimization algorithm. A low-pylon PC cable-stayed bridge is selected as the example to test the proposed optimization technique. The optimum result verifies the capability and efficiency of the optimization technique, and the significance to optimize the number of prestressing tendons in the girder. The optimum design scheme obtained by the application can achieve a 24.03% reduction in cost, compared with the initial design.

Key Words
cable-stayed bridge; prestressed concrete; multi-parameter; optimization technique; prestressing tension

Address
Qiong Gao : School of Civil Engineering, Central South University, Changsha 410075, P.R. China Meng-Gang Yang : School of Civil Engineering, Central South University, Changsha 410075, P.R. China Jian-Dong Qiao : School of Civil Engineering, Central South University, Changsha 410075, P.R. China

Abstract
In this paper, an innovative procedure is proposed for the seismic design of reinforced concrete frame structures. The main contribution of the proposed procedure is to minimize the construction cost, considering the uniform damage distribution over the height of structure due to earthquake excitations. As such, this procedure is structured in the framework of an optimization problem, and the initial construction cost is chosen as the objective function. The aim of uniform damage distribution is reached through a design constraint in the optimization problem. Since this aim requires defining allowable degree of damage, a damage pattern based on the concept of global collapse mechanism is presented. To show the efficiency of the proposed procedure, the uniform damage-based optimum seismic design is compared with two other seismic design procedures, which are the strength-based optimum seismic design and the damage-based optimum seismic design. By using the three different seismic design methods, three reinforced concrete frames including six-, nine-, and twelve-story with three bays are designed optimally under a same artificial earthquake. Then, to show the effects of the uniform damage distribution, all three optimized frames are used for seismic damage analysis under a suite of earthquake records. The results show that the uniform damage-based optimum seismic design method renders a design that will suffer less damage under severe earthquakes.

Key Words
structural damage; collapse mechanism; seismic damage analysis; reinforced concrete; construction cost; optimization

Address
Sadjad Gharehbaghi: Department of Civil Engineering, Behbahan Khatam Alanbia University of Technology, Behbahan, Iran

Abstract
In this paper, finite element (FE) model updating based on multi-objective optimization with the surrogate model for a steel plate girder bridge is investigated. Conventionally, FE model updating for bridge structures uses single-objective optimization with finite element analysis (FEA). In the case of the conventional method, computational burden occurs considerably because a lot of iteration are performed during the updating process. This issue can be addressed by replacing FEA with the surrogate model. The other problem is that the updating result from single-objective optimization depends on the condition of the weighting factors. Previous studies have used the trial-and-error strategy, genetic algorithm, or user\'s preference to obtain the most preferred model; but it needs considerable computation cost. In this study, the FE model updating method consisting of the surrogate model and multi-objective optimization, which can construct the Pareto-optimal front through a single run without considering the weighting factors, is proposed to overcome the limitations of the single-objective optimization. To verify the proposed method, the results of the proposed method are compared with those of the single-objective optimization. The comparison shows that the updated model from the multi-objective optimization is superior to the result of single-objective optimization in calculation time as well as the relative errors between the updated model and measurement.

Key Words
FE model updating; surrogate model; multi-objective optimization; pareto-optimal front

Address
Yongmoon Hwang, Seung-seop Jin, Ho-Yeon Jung and Hyung-Jo Jung: Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea Sehoon Kim and Jong-Jae Lee: Department of Civil and Environmental Engineering, Sejong University, 209 Neungdong-ro, Gwangjin-gu, Seoul 05006, Republic of Korea

Abstract
In this paper, the Colliding Bodies Optimization (CBO), Enhanced Colliding Bodies Optimization (ECBO) and Vibrating Particles System (VPS) algorithms and the force method are used for the simultaneous analysis and design of truss structures. The presented technique is applied to the design and analysis of some planer and spatial trusses. An efficient method is introduced using the CBO, ECBO and VPS to design trusses having members of prescribed stress ratios. Finally, the minimum weight design of truss structures is formulated using the CBO, ECBO and VPS algorithms and applied to some benchmark problems from literature. These problems have been designed by using displacement method as analyzer, and here these are solved for the first time using the force method. The accuracy and efficiency of the presented method is examined by comparing the resulting design parameters and structural weight with those of other existing methods.

Key Words
force method; metaheuristic algorithms; analysis; design; optimization; truss; stress ratio; energy

Address
A. Kaveh and Sh. Bijari: Centre of Excellence for Fundamental Studies in Structural Engineering, School of Civil Engineering, Iran University of Science and Technology, Narmak, Tehran-16, Iran

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