Bernardo Horowitz

Performance of a physical surrogate in the sequential approximate optimization of space trusses

Purpose – The purpose of this paper is to propose physically based varying fidelity surrogates to be used in structural design optimization of space trusses. The main aim is to demonstrate its efficiency in reducing the number of high fidelity (HF) runs in the optimization process.Design/methodology/approach – In this work, surrogate models are built for space truss structures. This study uses functional as well as physical surrogates. In the latter, a grid analogy of the space truss is used thereby reducing drastically the analysis cost. Global and local approaches are considered. The latter will require a globalization scheme (sequential approximate optimization (SAO)) to ensure convergence.Findings – Physically based surrogates were proposed. Classical techniques, namely Taylor series and kriging, are also implemented for comparison purposes. A parameter study in kriging is necessary to select the best kriging model to be used as surrogate. A test case was considered for optimization and several surrog...

Efficient Analysis of Beam Sections Using Softened Truss Model

In this paper, an efficient solution procedure is proposed to compute the pre-peak behavior of reinforced concrete (RC) beam cross sections under torsion and shear. This calculation procedure is based on the combined-action softened truss model (CA-STM), which idealizes rectangular RC cross sections as the association of four cracked panels. The proposed solution procedure formulates the problem as a system of nonlinear equations with constraints to be solved using optimization algorithms. The previsions obtained from this technique are compared with some experimental results of RC cross sections under pure torsion and torsion combined with shear, where good agreement was observed. Moreover, this procedure showed good computational efficiency, depicted by its ability to compute the load-deformation curves in few seconds. An analysis of a statically indeterminate structure incorporating beams under torsion and shear is also presented, for which a considerable decrease of the beam’s torsional stiffness is observed under the combined actions.

Modelação da flexibilidade de nós concentricos de pórticos em concreto armado

The intersections between beams and columns in a reinforced concrete building structure are called frame joints. It is a region with significant bending stiffness but subjected to large shear stresses. Appropriate modeling of the flexibility of reinforced concrete frames is essential to its design, in service limit states as well as in ultimate limit states. It has been shown, theoretically as well as experimentally, that the influence of joint flexibility may account for 20% of total structural lateral displacement. Models using only bar elements and rotational springs are proposed to consider the joint flexibility in linear analyses of building structures. In order to validate the proposed model, comparisons with experimental results found in the literature are made. Finally, the results of second order analyses using the proposed model are compared with those obtained by finite elements.

A Concurrent Efficient Global Optimization Algorithm Applied to Engineering Problems

One of the major difficulties in applying optimization to real engineering problems is that each function evaluation requires a complete model simulation which is in general computationally expensive. Moreover, some problems are known to be multimodal with several local minima. A common approach to tackle these problems is to construct cheap global approximation models of the responses often called metamodels or surrogates. These are based on simulation results obtained for a limited number of designs using global data fitting such as DACE. The optimization algorithm repetitive analysis needs are all performed using the cheap metamodels. In this study a two-stage approach is employed based on the Efficient Global Optimization algorithm, EGO, due to Jones. First an initial sample of designs is obtained using some Design of Experiments (DOE) technique such as Latin Hypercube. Parallel simulation runs for the initial sample are used to construct a kriging metamodel. In the second stage the metamodel is used to guide the search for promising designs which are added to the sample in order to update the model until a suitable termination criterion is fulfilled. The selection of designs which are adaptively added to the sample should balance the need for improving the value of the objective function with that of improving the quality of the prediction so that one does not get trapped in a local minimum. In the EGO algorithm this balance is achieved through the use of the Expected Improvement merit function. In this study the original EGO algorithm is modified to exploit parallelism. The algorithm is also modified to include general nonlinear constraints. The modified algorithm is applied to two example problems. The first is a small multimodal, two-variable structural design problem that can be graphically represented. The second is an eight-variable polymer injection problem in oil reservoir engineering.

Shear strength of hollow circular sections

The number of buildings higher than 30 floors has shown remarkable growth; many of them are supported on foundations of hollow circular piles. This increasing of height of constructions causes an increment of the shear stresses that are transmitted to their foundations, however these elements are more shear critical due to the hollow core. Most of the existing codes are based on shear models for rectangular sections, and guidelines for assessment of shear strength of members with hollow circular cross sections are practically non-existent. This study evaluates, on a comparative basis, the shear strength of elements with hollow circular cross sections, obtained from experimental tests, with values computed using the Canadian Code (CSA A23.3) and using a proposed simple procedure based on the Brazilian standard (NBR 6118).

Adaptive procedure for camber control of forward cantilever structures

In forward cantilever structures, segments are built from previous ones, therefore construction loads must be carried by the partly completed structure. As the cantilever is moved forward deformations increase and corrections must be made during the construction phase. In camber control, corrective displacements are applied to compensate for deformations. The proposed procedure assimilates topographical survey data collected at each construction stage to update the structural model by minimizing the differences between real and computed displacements. Concrete material properties are used as design variables in an optimization process that drives them to values that better represent the material actually used in construction. This is an iterative process where new data are assimilated at each new structural deformed configuration. New camber values are computed and applied to segments that will be cast in the future in order to reach the desired final design profile. The use of the procedure leads to residual displacements of no greater than 5% of the total deformation without camber.

Momentos fletores em vigas de edifícios de concreto armado

Edificios residenciais compostos de sistema de lajes macicas apoiadas em vigas de concreto armado sao largamente utilizados na industria da construcao civil. Na pratica, o calculo das reacoes destas lajes sobre as vigas e feito atraves de processos simplificados, nos quais os paineis de laje sao analisados de forma isolada. A NBR 6118 [1] mantem em seu texto o mesmo teor da antiga NB-1 [2] permitindo que, no caso de lajes macicas retangulares com carga uniforme, as reacoes possam ser calculadas admitindo-se que elas correspondem as cargas atuantes nos triângulos ou trapezios determinados atraves do metodo das charneiras plasticas. De maneira aproximada, a norma brasileira permite ainda que estas reacoes possam ser consideradas como uniformemente distribuidas sobre as vigas de apoio. O trabalho demonstra atraves de exemplos praticos que tal recomendacao pode conduzir a resultados contrarios a seguranca e propoe uma correcao para o calculo das reacoes de apoio em lajes macicas sobre as vigas de concreto armado.