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In this study, the method of inscribed hyperspheres (IHS) is presented and applied for the optimal design of 2-D steel moment frame structures. The weight of the structures, which is a function of the design variables (cross-sectional areas), is optimized subject to stress, displacement, size limits, and the variables’ linkage constraints. The IHS approach is employed to find the acceptable centers. The basic idea of this method is to inscribe the largest possible sphere in a closed space that has been created by the objective function and linearized constraints in each step. The obtained results were presented in discrete and continuous variables and compared to the results reported in the literature. This comparison showed the efficiency of this method. Also, a new mixed method of combining the optimality criteria (OC) method and the IHS method is presented in this study. It was observed that the number of iterations needed to reach the optimal solution using this new method is less than that of the above two methods when used individually, and the problem is converged to the optimal answer with extremely low iterations.

Several self-centering systems have been developed and tested so far, and all of them confront problems. Several problems like stress relaxation, elongation capacity and high post-yield stiffness are some of the problems, which should be addressed. The aim of this study is to find a solution to these problems. To this end, a new pre-compressed self-centering system has been proposed, tested and studied. Pre-compressed springs have been used to provide the required restoring force. Since the spring is under pressure and it has a high elastic capacity, the problem related to limited elongation capacity no longer exists. The experimental result indicates that the proposed self-centering brace has complete self-centering behaviour and low postyield stiffness. The proposed self-centering system produces less secondary stiffness compared to other systems. The effect of secondary stiffness on the drift and base shear was studied. Results of the numerical models indicate that high secondary stiffness does not decrease the drift of the structure, it only increases the base shear. Therefore, to attain an economical design, using the proposed self-centering system with slight secondary stiffness is suggested.

High thermal conductivity in phase change materials (PCM) is preferred in thermal energy storage (TES) systems. Carbon additives are considered as suitable materials for this purpose; however, some important issues such as price and stability for these materials should be considered. In this study, graphite powder and multiwall carbon nanotubes as an inexpensive and a relatively expensive carbon additives were used to improve the thermal conductivity of a long-chain paraffin (P) with a melting peak point of 64 °C. Also an amine functionalization method was applied to enhance the dispersion of CNTs into the non-polar paraffin medium. At first, the thermal conductivity and stability of the materials, as important and critical properties, were evaluated. In the next step, atmospheric impregnation method was conducted to incorporate modified PCM into the expanded perlite (EP) particles and finally, a lightweight concrete was constructed by these form-stable EP/P composites. Thermal behavior of the final concrete sample was studied by a simple handmade apparatus. Also, DSC analysis was conducted to determine the melting/freezing point and latent heat value for modified paraffin and form-stable PCM composites. The maximum allowable volume percent of EP usage for having a structural concrete was also determined by compression strength analysis. Thermal behavior analysis showed promising results for TES of the concrete block containing modified paraffin as phase change materials; also it was found that in form-stable technique, the stability of the additives is not significantly effective due to the narrow pores and channels, which reduce the effect of particles precipitation.

In this paper the nonlinear analysis and design optimization of guyed masts is addressed. The mast is modeled as a 3D truss and is supported by catenary cable elements that have nonlinear elastic behavior. For nonlinear static analysis, an innovative procedure is proposed that divides the structure into linear and nonlinear parts and analyzes them separately. The proposed method satisfies the equilibrium and compatibility by establishing and solution of a set of nonlinear equations. The optimization problem employs the sizes of members, initial cable tensions and the positions of anchor on the ground and tie level of cables on the mast as design variables. To facilitate the optimization solution, a compatible sensitivity analysis procedure is proposed. Sensitivities of objective function, displacement and strength constraints in the mast and cables, subjected to a variety of load combinations including dead, wind and ice loads are calculated. Numerical examples are provided to show the nonlinear analysis procedure and the applicability of the algorithm to optimum design of practical guyed masts.

This paper aims to ponder the effect of fuzzy uncertainties on performance evaluation of steel moment frame structures. Since the performance evaluation of a structure depends on its seismic demand and capacity spectra, any uncertainties in these two spectra causes uncertainty in performance level and performance point. Among many sources of uncertainties in structural dynamic analysis, in this paper, the modulus of elasticity, gravity load on the structure, dynamic properties of structure and soil properties have been considered and treated as fuzzy variables. To investigate the effect of these uncertainties, first, a nonlinear static pushover analysis program was written in MATLAB medium. Then, fuzzy inference model was used for determination of the design spectrum for different kinds of soils and seismic zones. The Effects of fuzzy uncertainties on capacity curve and capacity spectrum have been investigated on a typical example based on a new fuzzy concept in construction of the capacity spectrum of structures. Finally, performance point and performance level of structure has been determined as a fuzzy output.

The design of reinforced concrete frameworks is a complex task. To produce an economic design of a reinforced concrete structure in traditional design practise requires the services of a competent structural engineer with years of experience in the field. With the current progress in computer technology, the development of computer-based design tools to aid the task of engineers is now possible and, indeed, needed in this era of strict time deadlines. This study addresses the problem of design of reinforced concrete building frameworks. The design problem is formulated in a relatively detailed manner with the width, depth and longitudinal reinforcement of members taken as the design variables, consideration of architectural and construction requirements, and account for the performance conditions imposed by the ACI 318-89 code of practice for reinforced concrete structures. The design is cast as an optimization problem involving the minimization of the overall cost of two-dimensional planar frameworks while satisfying all performance constraints concerning member strength, beam deflection and structure side-sway. The cost of the framework is considered to be the summed cost of concrete, reinforcement and formwork. Various load conditions at the service load level are considered for the beam deflection and structure-sway constraints, and several other load conditions at the ultimate load level are considered for the member strength constraints. Size limits are imposed on the dimensions of beams and columns to reflect architectural and construction requirements. As well, limitations are placed on the amount of reinforcement in accordance with the ACI 318-89 design code. To account for the slenderness effects of columns, both P- $\\Delta$analysis and an approximate 'moment magnification factor' method are separately considered. The design problem is formulated as a standard optimization problem by using first-order Taylor series expansions to express the performance constraints as explicit functions of the design variables. Sensitivities (derivatives) of the constraints with respect to the design variables are derived for all performance constraints, for both member responses and member capacities. Then, an efficient optimality criteria resizing technique based on the Kuhn-Tucker optimality conditions at the optimum point is formulated and implemented in an iterative design procedure. Several design examples, including a 23-story 4-bay frame under multiple load conditions, are solved and the features and capabilities of the design procedure are discussed. Overall, the design output meets the requirements of the ACI 318-89 design code and complies with the principles of good design practice.