nedushan

In this paper, the bi-directional evolutionary structural optimization (BESO) method is used to find optimal layouts of 3D prestressed concrete beams. Considering the element sensitivity number as the design variable, the mathematical formulation of topology optimization is developed based on the ABAQUS finite element software package. The surface-to-surface contact with a small sliding between concrete and prestressing steels is assumed to accurately model the prestressing effects. The concrete constitutive model used is the concrete damaged plasticity (CDP) model in ABAQUS. The integration of the optimization algorithm and finite element analysis (FEA) tools is done by using the ABAQUS scripting interface. A pretensioned prestressed simply supported beam is modeled to show capabilities of the proposed method in finding optimal topologies of prestressed concrete beams. Many issues relating to topology optimization of prestressed concrete beams such as the effects of prestressing stress, geometrical discontinuities and height constraints on optimal designs and strut-and-tie models (STMs) are studied in the example. The results show that the proposed method can efficiently be used for layout optimization of prestressed concrete beams.

This article investigates the effect of the roof cover and the stressed skin action on the optimal design of curved portal frames. According to stressed skin effect, diaphragm is carrying part of the horizontal force of structure and the remaining part is carried out by the frames. Therefore, interior frames are designed for lower forces which, in turn, results in a lighter structure. Stressed skin effect is modelled using the equivalent spring theory. A program which links Sap2000 and genetic algorithm was developed that provides the best sections which result in the minimum weight of structure. Designs are performed by using the allowable stress design and stress skin effect. Seven curved portal frames with different span dimensions, lengths, number of frames and column heights are considered and optimally designed for roof cover with thickness of 0.5 mm and 0.7mm. The objective function is defined as the weight of the structure and the problem consists of eight design variables. The results show that consideration of the stressed skin effect results in a reduction of weight by more than 20% and that increasing the height of column results in 10% reduction of the weight. Moreover, it was observed that increasing the length of the span results in a 5% reduction in weight. Effects of increasing the number of frames and changing the length of the structure are negligible and are only about 1 or 2 percent of reduction in weight. Increase in the thickness of the roof cover sheet about 0.2 mm results in a decrease of the weight by about 3%.

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.