Expansive and collapsing behaviour of volume change soils

This thesis is designed to achieve three goals: Goal One - to introduce the reader to soils exhibiting expansive and/or collapsing behaviour; Goal Two - to provide an in depth understanding of aspects of this behaviour, obtained from an extensive study of these soil types; and, Goal Three - to serve as a reference for future research work (a recommendation for further research proposed in Chapter Ten of this thesis). The thesis is divided in two main parts. In the first part representative soil types were selected on the basis of their properties and expected engineering behaviour. The soil structure and clay minerals were also studied in part one of this thesis. The second part of the thesis deals with aspects of expansive and collapsing behaviour of soils. Chapter three provides the introduction to the subsequent chapters on expansive and collapsing behaviour of volume change soils

Modelling the behaviour of reinforced concrete beams strengthened with FRP

Comunicação apresentada em III European Conference on Computational Mechanics Solids, Structures and Coupled Problems in Engineering, Lisbon, 5–8 June 2006The strengthening of reinforced concrete structures with fiber reinforced polymers (FRP) is particularly attractive due to their mechanical properties. The understanding of the premature failure modes is of great importance. Since rupture is frequently found to occur at the interface FRP concrete, there is a clear need to study the nature of the bonding so as to develop techniques to permit its design modeling. The stress distribution in shear test models does not precisely match the one obtained in flexural reinforcement; in the latter, according to various authors [1, 2], in addition to the stresses tangential to the interface, normal stresses are also important. In this paper, a numerical model is presented to describe the behavior of reinforced concrete beams strengthened with FRP. This model is based on previous studies focused both on: i) the distribution of shear stresses at the interface FRP concrete and on ii) the stress concentration at the plate ends in flexural models. Furthermore, the importance of the flexural cracks in the premature rupture of the element is also analyzed. The behavior of reinforced c concrete beams strengthened with both FRP laminates and sheets is considered. The FRP epoxy concrete arrangement and the flexural cracks are modeled with interface elements with initial zero thickness, using a discrete approach and a localized damage model. A softening behavior is adopted to simulate the stress transfer along the FRP- -concrete interface. The importance of considering the mixed mode of fracture is discussed. Mention is also made to some of the main mathematical models found in the literature

Approach of a class of discontinuous dynamical systems of fractional order: existence of the solutions

In this letter we are concerned with the possibility to approach the existence of solutions to a class of discontinuous dynamical systems of fractional order. In this purpose, the underlying initial value problem is transformed into a fractional set-valued problem. Next, the Cellina's Theorem is applied leading to a single-valued continuous initial value problem of fractional order. The existence of solutions is assured by a P\'{e}ano like theorem for ordinary differential equations of fractional order.Comment: accepted IJBC, 5 pages, 1 figur

Mixed-mode fracture and load misalignment on the assessment of FRP-concrete bond connections

Considerable dispersion is usually found in experimental data concerning the material properties of FRP-concrete bond connections. In pure shear models, the direction of FRP loading is assumed to be parallel to the axis of the concrete specimen. However, in practice, it is very difficult to prevent load misalignment. This fact can have important consequences on the derivation of material properties from experimental data. This is why a parametric study is herein undertaken to thoroughly identify the role of the load misalignment in the behaviour of the connection. It is concluded that the load capacity of the connection significantly decreases in the case of a misaligned load pointing outwards the reinforced surface. It is also found that this effect is less relevant for thick laminates when compared to thin FRP sheets.Australian Research Council Discovery Early Career Researcher Award (DE150101703); Faculty of Engineering & Information Technologie

The influence of the mode II fracture energy on the behaviour of composite plate reinforced concrete

Comunicação apresentada em Fifth International Conference on Fracture Mechanics of Concrete and Concrete Structures, Vail, Colorado, USA, 2004In this paper, the finite element method is used to analyse the behaviour of concrete externally strengthened by sheets of carbon fibre reinforced polymer (CFRP). The bond between concrete and CFRP is modelled by a discrete approach using interface elements. The mechanisms involved in the behaviour of externally reinforced concrete specimens are complex, the global strength of the specimen being governed by the strength of each individual material as well as by the adhesion properties conferred by the epoxy. It is observed in experiments that, in most cases, failure occurs due to the loss of cohesion of a portion or lamina of concrete attached to the epoxy-fibres layers, the latter remaining intact. In this paper, the results of numerical simulations of bond tests are presented, aiming to contribute for a better understanding, in qualitative and quantitative terms, of mode II fracture energy in concrete and its influence on the behaviour of the interface concrete-FRP

Study of the Van der Pol Oscillator with Fractional Derivatives

In this paper we propose a modified version of the classical Van der Pol oscillator by introducing fractional-order time derivatives into the state-space model. The resulting fractional-order Van der Pol oscillator is analyzed in the time and frequency domains, by using phase portraits, spectral analysis and bifurcation diagrams. The fractional-order dynamics is illustrated through numerical simulations of the proposed schemes by using approximations to fractional-order operators. Finally, the analysis is extended to the forced Van der Pol oscillator.N/

Análise das disposições do EC2 para a avaliação dos efeitos de 2ª ordem em estruturas de betão armado

Comunicação apresentada em Jornadas Portuguesas de Engenharia de Estruturas, Lisboa, 2006Na sequência da aprovação da última versão do EC2 é abordado o tema dos efeitos de 2ª ordem em estruturas de betão armado. Neste contexto, é realizada uma análise comparativa das diversas metodologias regulamentares, propostas pela nova versão do EC2 e pelo REBAP, com a exposição de conceitos úteis para uma correcta aplicação das disposições regulamentares