جستجوی مقالات مرتبط با کلیدواژه "بهینه سازی توپولوژی" در نشریات گروه "عمران"

In this article, MMA which is a mathematical programing method is utilized for solving truss optimization problem. Although this method has been widely used in topology optimization problems of continuous structures, it has received less attention in the case of truss structures. The optimization problem considered here is the problem of minimizing the strain energy of the structure by considering the volume constraint. For the first time, the basics of the SIMP method and the application of the penalty exponent of the density function have been used for simultaneous optimization of topology and size of the truss members.To solve the optimization problem, analytical sensitivity analysis has been performed. Various problems have been solved at the end of the paper and the results have been discussed. The results show that if the appropriate penalty exponent is chosen, the correct optimal solution is obtained for the benchmark problems. Also, some more practical problems have been solved and the results have been discussed.

The current research seeks to present a novel method for numerical modeling of concrete behavior at meso-scale. In this method, as the stress distribution at the macro scale can be a suitable indicator for critical areas (crack propagate and growth), the areas under stress (critical areas) are identified through numerical modeling at the macro scale (coarse mesh) and using the extended finite element method and topology optimization. Macro-scale critical regions are considered cumulatively using topology optimization. Therefore, critical regions are modeled at the meso-scale, and the rest are modeled on the macro scale. At the meso-scale, the three phases including aggregate, mortar matrix, and ITZ were considered. The aggregate phase was distributed in the mortar matrix using a random algorithm and a Fuller curve. The accuracy of modeling concrete at the meso-scale using topology optimization was investigated by two examples, the results of which show the appropriate accuracy of the method. Furthermore, the method can reduce the computational cost and analysis time compared to modeling the whole sample at the meso-scale. In this research, the piecewise meshing method was used for numerical modeling. Using this method, traction-separation crack growth and expansion are modeled with appropriate accuracy.

A new formula based on strut and tie model to determine the shear strength of exterior beam-column joints without transverse reinforcement (stirrup) in the joint region under monotonic and seismic lateral loading is proposed in this paper. Based on the accomplished topology optimization to determine directions of the principal stresses of the joint region, the main shear transfer mechanism in beam-column joints without transverse reinforcement in the joint region is diagonal strut mechanism; therefore, the proposed strut and tie model is made up of a concrete bottle-shaped diagonal strut. Formulae available in published literature for calculating the diagonal strut angle of inclination was checked by finite element analysis results of two exterior joints, the results indicate that all formulae have good agreement. Various experimental data set of this kind of joints are collected from previous literature based on consistent and specified criteria for data selection. The accuracy of the proposed procedure and two approaches of determining the diagonal strut width was checked by comparing calculated shear strengths with experimental data. Based on the two introduced approaches for calculating the diagonal strut width, approach 1 which does not take into account the column axial load, has the best performance in the proposed model. The proposed formula, in addition to the specified compressive strength of concrete which is included in Iranian and American concrete codes, considers other effective parameters on exterior joints behavior such as the beam longitudinal tension reinforcement ratio and its strength, the intermediate column bars and the joint aspect ratio. Therefore, the proposed formula is able to estimate accurately the shear strength of exterior beam-column joints without transverse reinforcement in the joint region.

A suitable design is one design can achieve to its aims with minimum cost and needing to less computing time. In civil engineering due to survey of large scale structures and large number of design variables, it is so hard achieving to such design only based on experience and therefore optimization methods came to help designer as useful tools in order to find an economic and efficient design. Structural optimization can be defined as a process of dealing with the optimal design of various structures. Ausual objective function is the weight of the structure. In general, there are three main categories in structural optimization applications, namely, size, topology and geometry (shape) optimization.Cellular automata (CA) is a computationally efficient and robust tool to simply implement complex computations. As CA is simple to be implemented and can deal with complex problems without extensive mathematical computations, it is widely used in various fields of science and engineering.In recent years, various meta-heuristic inspired optimization methods have been developed.Almost all of metaheuristic algorithms come up with an idea of employing a particular process or event in nature as a source of inspiration for the development of optimization algorithm. The Cuttlefish algorithm is inspired based on the color changing behavior of cuttlefish to find the optimal solution. The patterns and colors seen in cuttlefish are produced by reflected light from different layers of cells including (chromatophores, leucophores and iridophores) stacked together, and it is the combination of certain cells at once that allows cuttlefish to possess such a large array of patterns and colors.In this article, cuttlefish algorithm (CFA)combined with cellular automata (CA) and were used for optimization truss structures.First, cellular automata and the Moor neighboring cells are defined and to the number ofsquares of the cell number ofcellular automata lattice( )is selected from the  best population. Then, the variables vector and their objective function of selected population are placed in each cell of the cellular automata.In a Moor neighboring, nine cells are compared to each other and the best answer ( )is selected and that is used to create new population.Finally, the best person in thenew population will be selected and itreplacedwith the worst person in the cellular automata, and thus the cellular automatais updated. Some benchmark numerical examples were solved using the CFA and CA-CFA algorithms, and the results of the numerical examples showed that the enhanced algorithm performancesbetter in size and topology optimization of truss structures than cuttlefish algorithm and other methods introduced in the literature. Finally, it can be concluded that the convergence speed of the improved algorithm compared with previous approaches is higher and its ability to achieve the desired values is better too.

Large-scale spatial skeletal structures belong to a special kind of 3D structures widely used in exhibition centers, supermarkets, sport stadiums, airports, etc., to cover large surfaces without intermediate columns. Space structures are often categorized as grids, domes and barrel vaults. Double layer grid structures are classical instances of prefabricated space structures and also the most popular forms which are frequently used nowadays.Topology optimization of large-scale skeletal structures has been recognized as one of the most challenging tasks in structural design. In topology optimization of these structures with discrete cross-sectional areas, the performance of meta-heuristic optimization algorithms can be increased if they are combined with continuous-based topology optimization methods. In this article, a hybrid methodology combining evolutionary structural optimization (ESO) and harmony search algorithm (HSA) methods is proposed for topologyoptimization of double layer grid structures subject to vertical load. In the present methodology, which is called ESO-HSA method, the size optimization of double layer grid structures is first performed by the ESO. Then, the outcomes of the ESO are used to improve the HSA. In fact, a sensitivity analysis is carried out using an optimization method (ESO) to determine more important members based on the cross-sectional areas of members. Then, the obtained optimum cross-sectional areas of members are used to enhance the HSA through two modifications. Structural weight is minimized against constraints on the displacements of nodes, internal stresses and element slenderness ratio. In topology optimization of double layer grid structures, the geometry of the structure, support locations and coordinates of nodes are fixed and this structure is assumed as a ground structure. Presence/absence of bottom nodes, and element cross-sectional areas are selected as design variables. In topology optimization of the ground structure, tabulating of nodes is carried out based on structural symmetry: this leads to reduce complexity of design space and nodes are removed in groups of 8, 4 or 1. The presence or absence of each node group is determined by a variable (topology variable) which takes the value of 1 and 0 for the two cases, respectively. The ground structure is assumed to be supported at the perimeter nodes of the bottom grid. Therefore, these supported nodes will not be removed from the ground structure. In order to achieve a practical structure, the existence of nodes in the top grid will not be considered as a variable. This causes the load bearing areas of top layer nodes to remain constant. Also, discrete variables are used to optimize the cross-sectional area of structural members. These variables are selected from pipe sections with specified thickness and outer diameter. Therefore, in topology optimization problem, the number of design variables is the summation of the number of compressive and tensile element types and the number of topology variables. The proposed approach is successfully tested in topology optimization problem of double layer grid structure. In particular, ESO-HSA is very competitive with other metaheuristic methods recently published in literature and can always find the best design overall. Also, it is determined that HSA method can find better answer in the topology optimization of large-scale skeletal structures, in comparison to optimum structures attained by the GSA and ICA.

Reliability-based topology optimization (RBTO) results in an optimal topology satisfying given constraints with consideration of uncertainties in the variables. Due to inherent uncertainties, including external loading, material properties, and the quality of construction, prototypes and products may not satisfy the essential functions required. In RBTO, each of these uncertain parameters are treated as random variables and reliability constraints are used in the formulation of the topology optimization problem to obtain a more reliable structure. In this article, RBTO was applied to obtain reliable topologies for two bridge structures using the Solid Isotropic Microstructure with Penalization (SIMP). The first and second order reliability methods are used as reliability analysis methods to take into account the uncertainties of the load, Young's modulus and thickness. It was found that in optimal topologies obtained by RBTO, the corresponding compliance values are higher than values obtained by deterministic topology optimization (DTO) and increase the number of uncertain parameters which results in softer structures with higher compliances.

In the last two decades, strut-and-tie model (STM) has been the most widely used method for design of reinforced concrete disturbed regions. Continuum topology optimization is the latest method for determining appropriate STM. This method does not have limitations of conventional methods.In this article, an efficient methodology is presented for development of STM for reinforced concrete members under multiple loading conditions. Solid isotropic material with penalization (SIMP) topology optimization algorithm is employed to minimize elastic strain energy of the models. In order to prevent checkerboard patterns and mesh dependency, the sensitivity filtering was applied and design variables were updated using the optimality criteria.Two numerical examples were used to investigate the effectiveness of the proposed methodology. The first example is a shear wall with asymmetric opening under reversed static loading. The ultimate load to steel weight ratio was used as the criteria to compare the models with different volume fractions. CAST software was used for analysis and design of models. Nonlinear Finite Element models were developed to obtain load-deflection curves for different models.In the second example, a new criterion was used to compare the STM of a corbel under horizontal and vertical static loads. Effects of different filtering radii were also investigated. The results of this example show that models obtained from topology optimization are efficient and require the minimal steel reinforcement when compared with conventional models. The results indicate that a volume fraction in the range of 0.35-0.45 leads to efficient and optimum models. A low filtering radius results in models with redundant members and a high filtering radius results in removal of members from model. It should be noted that using topology optimization under multiple loads also results in saving the CPU time for analysis and design.

Determination of optimal steel reinforcement layout for shear wall with opening is an important topic in designing this structural member.Strut-and-Tie Method (STM) is one way to design such members, where steel reinforcement is arranged based on the selected model.In this study, a strategy was introduced to determine optimal Strut-and-Tie model by selecting a good volume fraction in continuum topology optimization problem.The elastic strain energy was selected as the objective function to achieve the optimal pattern, and the modified Solid Isotropic Material with Penalization (SIMP) with continuous penalty function was used to prevent local minimum solution. Finally, By using Nonlinear Finite Element and defining qualitative and quantitative conditions for optimal STM, the resulting models, obtained with topology optimization for three shear wall with various opening, were compared with previous models and models with manufacturing constraint.The results show that, topology optimization models have the best ultimate load to steel weight ratio and get the optimal steel reinforcement layout for shear wall with opening.