Graciela Doz

Towards the numerical simulation of seismic excitation

Recent advances in the numerical simulation of the rupture process in solids, namely mode I fracture propagation, are extended to account for sliding with friction along pre-existing fracture surfaces, with the final objective of analyzing seismic fault motions. The procedure is applied to the study of the resulting stick-slip motion of a prismatic block resting by gravity on a flat rigid surface. The result, although not yet confronted with experimental observations, suggests that the basic assumptions are correct and permits drawing a number of conclusions on the characteristics and evolution of stick-slip motion.

Plataforma de ensaios dinâmicos: Estudos preliminares, projeto e construção

This paper is about the design and construction of a platform for dynamic tests especially with people jumping, walking, etc. Initially it was tried to find out projects already implemented in platforms and dynamic tests and to study the loads produced by movement of people on slabs and the structural response to these loads. The limits established by different standards have been also studied for these dynamic responses, taking into account the ultimate limit state, as well as the structure in service, since the human body is very sensitive to structural vibrations. Parametric studies were performed considering various configurations of slabs (different spans, thicknesses and conditions of support) have been done, looking for a configuration that could have natural frequency close to the frequencies of the human loads. The slab should have dimensions compatible with the available physical space, fundamental frequency below 5 Hz and maximum immediate deflection compatible with the indications of the Brazilian standard NBR6118: 2007. Based on these criteria was chosen a rectangular structure consists of a solid reinforced concrete rectangular slab studded in two opposite edges of steel beams with shear connectors type U. The other two edges are free. The steel beams supporting the slab, in turn, are supported on eight metal profiles (two in each corner of the slab) that are supported on two to two short columns of steel profile H. Profiles U in steel are welded to four columns, forming a horizontal frame. Numerical analysis of the dynamic test platform have been performed for free and forced vibration, for obtaining the natural frequencies and corresponding vibration modes, considering the self-weight of the structure and the load that simulates people’s weight. After obtaining a structural configuration that fulfilled the stipulated requirements, the design of the slab taking into account the recommendations of the Brazilian standard NBR6118: 2007. The platform was built and has been done a preliminary experimental study to obtain the first natural frequencies.

Cracking Influence on Dynamic Parameters of Reinforced Concrete Floors

In view of the need to satisfactorily provide good performance of structures in their service situations, it is desired to understand the influence of some reinforced concrete particularities on the dynamic parameters of the structure. These particularities are fundamental in static analysis of pavements design. Starting from spans, geometry, and structural typologies common in real buildings, this paper studies the influence of cracking and non-constant reinforcements on the vibration frequency of concrete floors. It is shown that the reinforced concrete properties significantly impact the floor’s dynamic parameters; this impact is stronger when the floor is slender and deformable. Some of the common structural typologies, as the ribbed/waffle slabs, are even more susceptible to those influence. Knowing the main variables that may be responsible for excessive vibration phenomenon, it was possible to prevent issues during the design process.

Study of blast wave overpressures using the computational fluid dynamics

Resumo The threats of bomb attacks by criminal organizations and accidental events involving chemical explosives are a danger to the people and buildings. Due the severity of these issues and the need of data required for a safety design, more research is required about explosions and shock waves. This paper presents an assessment of blast wave overpressures using computational fluid dynamics software. Analyses of phenomena as reflection of shock waves and channeling effects are done and a comparison between numerical results and analytical predictions has been executed, based on the simulation of several models. The results of this paper suggest that the common analytical predictions aren’t accurate enough for an overpressure analysis in small stand-off distances and that poorly designed buildings may increase the shock wave overpressures due multiple blast wave reflections, increasing the destructive potential of the explosions.

CONTROL METHOD FOR ADJACENT BUILDINGS CONSIDERING SOIL-STRUCTURE INTERACTION

Abstract. In recent years a vibration control technique, called structural coupling, has been studied. This technique consists on linking two neighboring buildings, through a coupling device, with the purpose of reducing dynamic response. It is possible to control both structures response simultaneously, which is precisely the attractiveness of the technique. Several researchers explored the effectiveness of various seismic control devices, in connecting two adjacent buildings, considering they are supported on a fixed base. However, in general, all structures interacts with the surrounding soil, what substantially affects the dynamic response, it is called soil-structure interaction (SSI). Considering SSI on structural coupling is still incipient in literature. This work aims to evaluate SSI influence on the performance of this control technique, besides of presenting a simple analysis methodology to this type of problem. The results found show that SSI effects cannot be neglected on dynamic analysis of coupled structures. It was verified that changes on system natural frequencies due to SSI are important since, depending on earthquake frequency components, it modifies also the dynamic response of the system. All analysis were performed using MATLAB software.

Seismic Response Control of Adjacent Buildings Connected by Viscous and Hybrid Dampers

This paper discusses the seismic response control of a building by connecting it to another adjacent building. Coupled buildings have demonstrated to be an attractive method to mitigate excessive dynamic responses. This paper studies the behavior of two structures connected by passive dampers and also considering local feedback control systems installed in each structure, an hybrid strategy. These feedback control systems are designed and operated independently using active devices with limited actuation capacity like force actuators. The governing differential equations of motion of the coupled system are derived and solved for relative displacement. The advantages and disadvantages of each control strategy are examined in order to determine the more appropriate one. Based on the present research results, general conclusions and recommendations are given for further studies.

Locating damages in beams with artificial neural network

Despite the significant advance of new technologies applied in civil engineering, the structures continue subjected to the occurrence of faults which are produced in normal conditions of use. The detection of these faults may be done by the analysis of some dynamic characteristics as frequencies and mode shapes. This fact implies that such characteristics must be identified accurately in order to produce reliable results about structural health. Artificial neural network may be also used as an important tool in the evaluation of structural integrity. This work presents an experimental analysis, in which a laboratory beam was submitted to different vibration tests. In the attempt to establish a suitable methodology for structural evaluation, the method of artificial neural network was applied in order to identify the damage location and the obtained results were very satisfactory.

Estudo do comportamento dinâmico de uma passarela de pedestres da cidade de Brasília

O avanco das tecnologias construtivas e o uso de materiais de alta resistencia tem possibilitado o projeto de estruturas cada vez mais leves e flexiveis. Dessa forma, essas estruturas sao mais sensiveis a vibracoes em baixas frequencias. Essa tendencia tem se apresentado tambem nos projetos de passarelas de pedestres nos ultimos anos. Os carregamentos produzidos por movimentos humanos caracterizam-se por funcoes periodicas de baixas frequencias que podem provocar desconforto e ate problemas de seguranca, uma vez que essas baixas frequencias podem resultar proximas das frequencias naturais dessas estruturas. No presente trabalho estuda-se o comportamento dinâmico de uma passarela de pedestres localizada na cidade de Brasilia quando submetida as acoes humanas de caminhar e correr. Para isso, foi realizada uma avaliacao numerica de seu desempenho, utilizando os limites de servico referentes a vibracoes, aplicaveis a passarelas de pedestres, encontrados na literatura.