Estabilidade das abóbadas da igreja do Mosteiro dos Jerónimos

Apresenta-se um estudo relativo à avaliação da segurança das abóbadas da Igreja do Mosteiro dos Jerónimos e revê-se um estudo anterior sobre o comportamento sísmico global do conjunto. Descrevem-se os modelos, as acções e os materiais adoptados na análise e discutem-se os resultados obtidos. Atendendo à informação limitada sobre as propriedades dos materiais e às condicionantes de uma análise deste tipo, face à elevada complexidade da estrutura, os resultados deverão ser encarados como a melhor aproximação da resposta provável da estrutura

Safety assessment of the Jerónimos church in Lisbon

Advanced (non-linear) analysis of historical constructions represents a key contribution for the understanding of the architectural heritage. The safety of a famous Portuguese church is addressed using two different finite element models for the nave and the transept. The complexity of the ornaments of the vaults calls for a mix of volume, curved shell and beam elements. A sensitivity study and a simplified buckling analysis are also carried out to provide further insight in the results. The analysis indicates that the safety level of the structure is low, probably due to the uniqueness of the structural conception.Fundação para a Ciência e a Tecnologia - POCTI-ECM-38071-2001

Assessment of the mechanical microstructure of masonry clay brick by nanoindentation

Tese de doutoramento em Engenharia CivilThe work presented in this thesis aims to implement the recent advances in the material science into the field of structural clay products applied to masonry constructions. The experimental analysis carried out by the author is focused on the detailed description of the heterogeneous microstructure of the fired clay brick, as a function of its composition and processing conditions. Multi-field methods of investigation have been combined, from standard mechanical tests carried out on bulk material on the macro-scale to novel nanoindentation techniques, which infers the mechanical properties of the solids on the nanoand micro-scales. Moreover, the complex interplay between the different components of this heterogeneous solid is traced with Scanning Electron Microscopy methods or Mercury Intrusion Porosimetry. The existing hierarchical ordering of fired brick microstructure is framed in the multi-level model, where the building blocks are classified and described with reference to the type of morphology present and mechanical characteristics. The statistical indentation method, originally developed for cement based materials is extended to the field of structural ceramics. Such an experimental analysis of mechanical phase properties is carried out with the aid of Gaussian Mixture Modeling, which together with Maximum Likelihood concept and Expectation-Maximization algorithm, provides a robust and efficient deconvolution strategy. This deconvolution technique is validated on Ordinary Portland Cement, brass alloy and investigated fired brick. The relation between the characteristic scale of depth-sensing measurement and the mechanical characteristics inferred from the bulk of composite material is presented. Additionally, Buckle’s rule-of-thumb is approached with a probabilistic model of biphasic composite materials, which represent idealized microstructures. The mechanical properties of the ‘glassy’ matrix of the fired brick are investigated in the depth-sensing experiment. Different regimes of the indentation force are considered along the experimental campaign. The relation between the morphology of the ‘glassy’ matrix, its composition and measured indentation modulus, elastic modulus and indentation hardness is studied. Additionally, the composite ‘polycrystalline-amorphous’ nature of the matrix of the brick is corroborated and documented in detail. Mechanical properties of other mechanically active phases incorporated within the microstructure of the fired clay brick e.g. quartz, rutile etc. are assessed and reported.O trabalho apresentado nesta tese tem como objectivo a aplicação dos avanços recentes na ciência dos materiais aos produtos cerâmicos estruturais usados nas construções de alvenaria. A análise experimental realizada pelo autor está focada na descrição detalhada da microestrutura heterogénea do tijolo de barro cozido, em função da sua composição e condições de processamento. Foram combinados métodos de investigação multi-campo, desde ensaios mecânicos padrão realizados no material ao nível da macro-escala, até novas técnicas de nano-indentação que inferem as propriedades mecânicas dos sólidos ao nível das escalas nano e micro. Adicionalmente, a complexa interacção entre as diferentes componentes deste sólido heterogéneo é caracterizada com recurso aos métodos de Microscopia Electrónica de Varrimento ou Porosimetria por Intrusão de Mercúrio. O ordenamento hierárquico da microestrutura existente nos tijolos cozidos é enquadrado num modelo multi-nível, onde os elementos são classificados e descritos com referência ao tipo de morfologia presente e às características mecânicas. O método de indentação estatística, originalmente desenvolvido para materiais cimentícios, é alargado ao campo da cerâmica estrutural. Esta análise experimental das propriedades mecânicas da fase é realizada com o auxílio de um Modelo de Mistura de Gauss que, juntamente com os conceitos de máxima verosimilhança e algoritmo de Maximização da Expectativa, fornece uma estratégia de deconvolução robusta e eficiente. Esta técnica de deconvolução é validada em Cimento Portland corrente, em liga de latão e nos tijolos cozidos investigados. É apresentada a relação entre a escala característica na medição da profundidade e as características mecânicas inferidas a partir da massa de material compósito. Adicionalmente, a regra empírica de Buckle é abordada com um modelo probabilístico de materiais compósitos bifásicos, que inclui microestruturas idealizadas. As propriedades mecânicas da matriz ‘vítrea’ do tijolo cozido são investigadas no ensaio com medição da profundidade. Consideram-se diferentes regimes da força de indentação ao longo da campanha experimental. É estudada a relação entre a morfologia da matriz ‘vítrea’, composição e módulo de indentação medido, módulo elástico e dureza de indentação. Adicionalmente, a natureza do compósito ‘policristalino-amorfo’ da matriz do tijolo é corroborada e documentada em detalhe. As propriedades mecânicas das outras fases mecanicamente activas incorporados na microestrutura do tijolo de barro cozido, por exemplo quartzo e rútilo, são avaliadas e descritas.Fundação para a Ciência e a Tecnologia (FCT) - SFRH/BD/39232/200

Modelling of masonry creep and damage

The problems related to the analysis of ancient constructions are gigantic due to the difficulties in characterizing the geometry, the materials, the sequence of construction, the existing damage and the building processes. A difficult aspect in the repair and strengthening of existing structures is the long-term behaviour of masonry. Safety assessment has been greatly influenced by the collapse of monumental buildings in the last decade, where creep behaviour and creep-fatigue interaction proved to be of relevance for massive masonry walls. Experimental testing on the creep of regular and rubble ancient masonry together with numerical modelling is currently under investigation by the authors. In a first stage, the research is primarily focused on the monotonic behaviour. This represents a contribution for understanding creep behaviour, providing insight into the basic phenomena that occur in masonry upon increasing loading. The results obtained using a continuous model to represent the masonry components largely overestimated the experimental strength and peak strain. Alternative modelling approaches seem, thus, to be needed and a discontinuous model in which a fictitious micro-structure was given to the components was considered. Clear advantages were shown by this last model. In the present paper, the results obtained using these models are briefly reviewed. The results from the ongoing simulations on the long-term behaviour of masonry assemblages will be presented in the oral communication.(undefined

The multi-scale approach of masonry, paradigm of clay brick

Recent progress in nanoscience and engineering allows advanced characterization of materials. This type of characterization includes investigations revealing the scale dependent microstructure and mechanical as well physical properties of each component incorporated in the heterogeneous material. Its applicability and efficiency is confirmed in the field of cement based materials where the paradigm of these materials is solved, and universal buildings blocks and the multi-scale nature are well described. As a consequence, material researchers and engineers have knowledge about the impact of basic constituents and microstructure on macro behaviour of cement based materials. In the masonry field, a quite diverse situation is found. Although clay brick is among the oldest building materials, the main building blocks are still unknown. This knowledge gap is apparent in structural masonry, since the present homogenization and upscaling techniques consider only mortar joints, brick units and interface as a basic units. Here, the mechanical properties and elementary arrangement of these three components in the representative volume element (RVE) are assumed to govern the behaviour of masonry as a composite. But, it is understood that mortar may be broken down to lower scales, and its macro mechanical properties considered in the already developed approaches are governed by the lover scale components and its microstructure. Similarly, as it is shown by the authors in this contribution the brick unit may be broken down to lower scales, in which the basic material components and theirs properties are inherent. Therefore, the macro behaviour of composite masonry wall and its durability is considered to be ruled by the phenomena from the much lower scales present in the mortar, clay brick and the interface of these two

Multitechnique investigation of extruded clay brick microstructure

Despite the omnipresence of clay brick as construction material since thousands of years, fundamental knowledge about the link between composition, microstructure and mechanical performance is still scarce. In this paper, we employ a variety of advanced techniques of experimental mechanics and material characterization for extruded clay brick for masonry, that range from Scanning Electron Microscopy (SEM) coupled with Energy-dispersive X–ray Spectroscopy (EDX), Mercury Intrusion Porosimetry (MIP), to Instrumented Nanoindentation and macroscopic strength and durability tests. We find that extruded clay brick possesses a hierarchical microstructure: depending on the firing temperature, a “glassy” matrix phase, which manifests itself at sub-micrometer scales in form of neo-crystals of mullite, spinel-type phase and other accessory minerals, forms either a granular or a continuum matrix phase that hosts at sub-millimeter scale the porosity. This porous composite forms the backbone for macroscopic material performance of extruded brick, including anisotropic strength, elasticity and water absorption behavior.Authors gratefully acknowledge Portuguese Foundation for Science and Technology (FCT) for providing doctoral scholarship under the reference SFRH/BD/39232/2007 for Konrad J. Krakowiak. Special thanks to Dr. J. P. Castro Gomes, Centre of Materials and Building Technologies (C-MADE), University of Beira Interior for making feasible Mercury Intrusion measurements, as well as Dr. G. P. Souza for helpful guidance and advices related to this work

Cathedral of Porto, Portugal : conservation works 2003-2008

This paper presents selected works carried out at the Cathedral of Porto, Portugal, as a case study that challenges current recommendations for the conservation and restoration of architectural heritage. The historical information is briefly reviewed and the general conservation approach for the different works is addressed. Afterwards, the aspects regarding the strengthening of the towers, diagnosis of a chapel, strengthening of the transept and diagnosis of the main façade are addressed

Creep in reactive colloidal gels: A nanomechanical study of cement hydrates

From soft polymeric gels to hardened cement paste, amorphous solids under constant load exhibit a pronounced time-dependent deformation called creep. The microscopic mechanism of such a phenomenon is poorly understood in amorphous materials and constitutes an even greater challenge in densely packed and chemically reactive granular systems. Both features are prominently present in hydrating cement pastes composed of calcium silicate hydrate (C-S-H) nanoparticles, whose packing density increases as a function of time, while cement hydration is taking place. Performing nanoindentation tests and porosity measurements on a large collection of samples at various stages of hydration, we show that the creep response of hydrating cement paste is mainly controlled by the interparticle distance and results from slippage between (C-S-H) nanoparticles. Our findings provide a unique insight into the microscopic mechanism underpinning the creep response in aging granular materials, thus paving the way for the design of concrete with improved creep resistance

Combinatorial molecular optimization of cement hydrates

Despite its ubiquitous presence in the built environment, concrete’s molecular-level properties are only recently being explored using experimental and simulation studies. Increasing societal concerns about concrete’s environmental footprint have provided strong motivation to develop new concrete with greater specific stiffness or strength (for structures with less material). Herein, a combinatorial approach is described to optimize properties of cement hydrates. The method entails screening a computationally generated database of atomic structures of calcium-silicate-hydrate, the binding phase of concrete, against a set of three defect attributes: calcium-to-silicon ratio as compositional index and two correlation distances describing medium-range silicon-oxygen and calcium-oxygen environments. Although structural and mechanical properties correlate well with calcium-to-silicon ratio, the cross-correlation between all three defect attributes reveals an indentation modulus-to-hardness ratio extremum, analogous to identifying optimum network connectivity in glass rheology. We also comment on implications of the present findings for a novel route to optimize the nanoscale mechanical properties of cement hydrate.National Ready Mixed Concrete Association (Research sponsorship)Education Foundation (N.J.) (Research sponsorship)Portland Cement Association (Research sponsorship

Production of H2 by water radiolysis in cement paste under electron irradiation: A joint experimental and theoretical study

International audienceLong-term confinement of nuclear waste is one of the main challenges faced by the nuclear industry. Fission products such as 90 Sr and 137 Cs, both β − emitters known to induce serious health hazards, represent the largest fraction of nuclear waste. Cement is a good candidate to store them, provided it can resist the effects of irradiation over time. Here, we have investigated the effects of β − decay on cement by performing electron irradiation experiments on different samples. We show that H 2 production in cement, the main effect of water radiolysis, depends strongly on composition and relative humidity. First-principles calculations indicate that the water-rich interlayer regions with Ca 2+ ions act as electron traps that promote the formation of H 2. They also show that holes localize in water-rich regions in low Ca content samples and are then able to participate in H 2 production. This work provides new understanding of radiolysis effects in cements