Caracterização experimental de alvenaria antiga: reforço e efeitos diferidos

Dissertação de mestrado em Engenharia CivilO trabalho aqui apresentado é essencialmente de cariz experimental, tendo sido desenvolvido no Laboratório de Engenharia Civil da Universidade do Minho, no qual foram executadas duas campanhas experimentais, abordando o tema da preservação, requalificação e reforço do Património construído. A primeira campanha experimental incidiu sobre o comportamento e reforço estrutural de paredes de alvenaria de pedra de três panos, sob compressão, enquanto que a segunda incidiu no estudo dos efeitos diferidos, em alvenaria de tijolo cerâmico e de alvenaria de adobe, sob elevadas cargas de compressão. Este trabalho surgiu da necessidade de aprofundar o conhecimento sobre o comportamento de paredes de alvenaria de três panos e sobretudo, da necessidade de se conhecerem os efeitos de técnicas de reforço aplicadas. Por outro lado, os recentes colapsos ocorridos em edifícios de alvenaria famosos e de grande valor patrimonial (como foi o caso da Torre Cívica de Pavia, em Itália), devido ao dano provocado por efeitos diferidos, sobretudo fenómenos de fluência sob cargas de compressão elevadas, revelam a necessidade de estudar este fenómeno em alvenaria antiga. Na campanha experimental das paredes de alvenaria de pedra de três panos, foram realizados ensaios de compressão uniaxial em paredes de alvenaria de pedra de três panos, representativas de estruturas de alvenaria antigas. Foram ensaiadas paredes não reforçadas e reforçadas com pregagens transversais, injecção de uma calda comercial à base de cal e com a combinação destas duas técnicas. Estes ensaios permitiram avaliar os mecanismos associados ao colapso, sob acções de compressão, e permitiram identificar as alterações introduzidas pelo reforço ao nível do comportamento mecânico. No caso da campanha da fluência, foram realizados ensaios de fluência acelerada e a longo prazo, em provetes representativos de estruturas antigas de alvenaria de tijolo e alvenaria de adobe. Estes ensaios permitiram, entre outros aspectos, discutir as limitações dos ensaios de fluência acelerada e observar a influência do nível de tensão no comportamento diferido da alvenaria em questão.The work presented here is essentially experimental and it was developed at the Civil Engineering Laboratory of University of Minho, where two experimental campaigns were carried out, addressing the theme of preservation, requalification and strengthening of the built Heritage. The first experimental campaign was focused in the behavior and strengthening of three-leaf stone masonry walls, under compression, while the second one was focused in the study of long-term effects, in clay brick and adobe masonry, under high sustained loads. This work comes up from the need to gain a deep knowledge about the behavior of three-leaf masonry walls and the effects of strengthening techniques applied to them. Moreover, recent collapses of famous and of great heritage value masonry buildings (as it was the case of the collapse of the Civic Tower of Pavia, in Italy), due to damage caused by long-term effects, especially creep phenomena under high sustained loads, shows the need to study this phenomenon in ancient masonry. In the three-leaf stone masonry walls experimental campaign, uniaxial compressive tests on newly built three-leaf masonry walls were performed, representative of ancient masonry structures. Unstrengthened and strengthened walls with transversal tying, injection of a commercial lime based grout and with combination of these two techniques were tested. These tests helped to evaluate the mechanisms associated to the collapse, under compressive load, and to identify the changes in their mechanical behavior caused by the strengthening. In the case of the creep campaign, short-term and long-term creep tests were performed on representative ancient structures of clay brick and adobe masonry. These tests allowed to discuss the limitations of short-term creep tests and to observe the influence of the stress level in the long-term behavior of the masonry, among other features.Fundação para a Ciência e a Tecnologia (FCT) - projecto POCI/ECM/58987/200

Repair of earth constructions by means of grout injection

Tese de doutoramento em Engenharia Civil (Área do conhecimento estruturas)Nowadays, one fourth of the World’s population lives in a house made from earth. Consequently, there is a large built stock widely distributed around the World going much beyond simple dwellings. An important part of the earth built stock is found often affected by cracking, whose repair is fundamental for the reestablishment of the structural integrity. However, the successful cracking repair of earthen walls requires employing adequate intervention techniques. With this respect, the injection of mud grouts is being put forward in the recent years and has been showing good results in the few reported cases. This thesis aims at contributing to the development of the limited knowledge on the injection technique applied to earth constructions. The broad extension of this topic led to selecting the injection of unmodified mud grouts (without mineral binders) in rammed earth constructions as case study. This thesis also intends contributing for the characterization of the rammed earth construction from southern Portugal and for the numerical simulation of its behaviour. An experimental program was defined and included the execution of a composition study about the behaviour of unmodified mud grouts, involving several variables of their composition and the characterization of important properties governing the injection technique. The design of a mud grout has shown to require accounting for both the limitation of the clay content and the effect of the addition of a deflocculant. The experimental program continued with the suitability assessment of four soils from Alentejo (Portugal) for unstabilised rammed earth construction, and the selection of a representative soil used to manufacture medium- and large-scale rammed earth specimens. These specimens were used to assess the repair effectiveness of three different unmodified mud grouts. The results indicated that the injection of mud grouts is capable of attaining adequate repair effectiveness, providing that the same soil used in the construction is incorporated in the grout composition. Finally, the shear behaviour of rammed earth wallets tested under diagonal-compression was modelled resorting to the finite element method, where both the macro- and micro-modelling approaches were used. Both cases provided an adequate simulation of the non-linear shear behaviour, being highlighted the enhanced shear ductility of rammed earth.Atualmente estima-se que um quarto da população mundial viva numa casa construída em terra. Consequentemente, existe um extenso património construído espalhado pelo mundo e que vai muito além de simples habitações. Uma parte importante deste património é frequentemente afetado por fendilhação, cuja reparação é fundamental para restabelecer a integridade estrutural. Contudo, a reparação bem sucedida da fendilhação requer o emprego de soluções de intervenção adequadas. A este respeito, a injeção de caldas de terra tem-se evidenciado nos últimos anos e tem demonstrado bons resultados nos poucos casos documentados. A presente tese tem como objetivo contribuir para o desenvolvimento do conhecimento limitado sobre injeção de caldas em construções de terra. A grande diversidade deste tema levou a que fosse selecionada a injeção de caldas de terra não modificadas (sem adição de ligantes minerais) em taipa como caso de estudo. A presente tese também pretende contribuir para a caraterização da construção em taipa do Sul de Portugal e para a simulação numérica do seu comportamento. Definiu-se um programa experimental que incluiu a realização de um estudo de composição sobre o comportamento de caldas de terra não modificadas, envolvendo várias variáveis da sua composição e a caraterização de propriedades relevantes para a técnica da injeção. Mostrou-se que o dimensionamento de uma calda de terra requer considerar uma percentagem de argila limitada e o efeito da adição de um desfloculante. O programa experimental continuou com a avaliação da adequabilidade de quatro solos do Alentejo (Portugal) para a construção em taipa não estabilizada, e com a seleção de um solo representativo utilizado na construção de provetes de taipa de média e grande escala. Estes provetes foram utilizados na avaliação da eficiência da capacidade de reparação de três caldas de terra não modificadas. Os resultados indicaram que a injeção de caldas de terra é capaz de proporcionar uma eficiência de reparação adequada, caso o mesmo solo utilizado na construção seja incorporado na calda. Finalmente, simulou-se comportamento ao corte de paredes de taipa ensaiadas à compressão diagonal com recurso ao método dos elementos finitos, utilizando-se tanto a abordagem da macro- como da micro-modelação. Ambos os casos proporcionaram uma simulação adequada do comportamento não linear ao corte, tendo sido evidenciada uma ductilidade relativamente elevada da taipa ao corte.Portuguese Science and Technology Foundation (FCT) for the granted scholarship with reference SFRH/BD/39145/2007 and f or the funding provided through project FCOMP-01-0124-FEDER-028864 (FCT-PTD C/ECM-EST/2396/2012

Grouting as a mean for repairing earth constructions

A good condition of the structural elements of an earth construction is essential for a good global structural behaviour. Therefore, the absence of major cracks is essential. Repairing cracks by using traditional techniques, involving the partial or the total reconstructions of the structural elements, constitutes a very intrusive solution that must, necessarily, be avoided in the case of historical earth constructions. Grouting constitutes an alternative and more practical solution for solving this problem. However, the design of the grouts for earth constructions demands the implementation of a methodical process that accounts both for the structural and durability demands of the construction. Previous works showed that the injection of mud grouts is a reliable and feasible solution. However, the knowledge developed is still very limited, hindering the further development of a methodology for designing mud grouts for earth constructions. Therefore, in this paper an initial methodology proposal for the design of mud grouts is presented and discussed. This results from an ongoing research that aims at the development of suitable grouts for earth constructions.Fundação para a Ciência e a Tecnologia (FCT

Grouting as a repair/strengthening solution for earth constructions

Earth, as a building material, has been used since ancient times, and is still being used with that purpose. It was used for building shelters, houses, temples and even military constructions, like fortresses. As a consequence, currently, there is a great architectural heritage stock on this kind of constructions. Nevertheless, earthen materials are very sensitive when compared with modern materials, since they are more vulnerable to external aggressive agents, revealing most of the times a faster degradation rate. From a structural perspective they present a very low tensile strength, a low compressive strength and a fragile behaviour, making the earthen structures strongly vulnerable to earthquakes. The structural damage in this kind of structures manifests, in general, in the form of cracks or voids. Repairing these cracks is fundamental in order to obtain an improved structural behaviour, especially if the earth construction was built in a seismic zone. Injecting mud grouts may constitute a feasible and reliable solution for repair this kind of damage. Although, mud grouts experience many problems that hinder their application and the knowledge about them is still very limited. This requires that deep studies have to be carried out in order to solve their problems and to make this solution reliable. In this paper it is discussed the methodology that should be established for the design of mud grouts suitable for earth constructions. But first a summarized explanation about earth constructions and their problems is presented. This results from an ongoing PhD research that still is in an initial phase, and it aims, precisely, the development of grouts specifically to be applied in earth constructions.Fundação para a Ciência e a Tecnologia (FCT

Strengthening of masonry and earthen structures by means of grouting: design of grouts

Grout injection is a technique commonly used in the repair and strengthening of masonry, due to the simplicity in its execution. However, to design a suitable grout, a proper methodology must be followed. The grout must accomplish requirements that depend mainly on mechanical behaviour and durability features of the struc-tures. Grouting can be also applied to earthen structures, for repairing cracks and filling voids. The same methodology can be used to design grouts, but the requirements must be adapted. Therefore, this paper pre-sents a discussion concerning the repair and strengthening of masonry and earth constructions through grout injection. To emphasize the differences in the requirements, first a short characterization of earth as a building material is given. Subsequently, the main decay phenomena are identified. Finally, attention goes to the effect of shrinkage and swelling behaviour of earth and the design of an appropriate grout for injection.Fundação para a Ciência e a Tecnologia (FCT

Seismic assessment of a vernacular rammed earth building

Rammed earth constructions represent a valuable cultural heritage of vernacular architecture, whose significance has acquired even more importance in the last years with the renovated interest for this sustainable building technique. The aim of this work is to develop a FEM model typologically representative of a Portuguese vernacular rammed earth construction in order to characterize numerically its seismic performance and raise awareness about the level of improvement introduced by two compatible strengthening techniques: textile reinforced mortar (TRM) and a ring beam applied at the top of the walls.This research work was partly financed by FEDER funds through the Competitivity Factors Operational Programme (COMPETE) and by Portuguese national funds through FCT(Foundation for Science and Technology) within the scope of projects POCI-01-0145-FEDER-007633 and POCI-01-0145-FEDER-016737 (PTDC/ECM-EST/2777/2014). The support from grant SFRH/BPD/97082/2013 is also gratefully acknowledged

Numerical modeling of the seismic out-of-plane response of a plain and TRM-strengthened rammed earth subassembly

The importance of raw earth is highlighted by the millions of persons living in earthen buildings around the World and by numerous historical monuments made of this material. Its widely availability led to the development of a variety of building techniques, including rammed earth, which is the main focus of this study. Similarly to unreinforced masonry structures, rammed earth buildings acceptably withstand gravity loads, but are significantly vulnerable to earthquakes. In this regard, great attention has been put on the proposal of efficient, compatible, affordable and reversible strengthening solutions. However, very limited studies address either the experimental testing or modeling of the seismic response of such buildings. The current study investigates the seismic out-of-plane performance of a plain and subsequently strengthened rammed earth sub-assembly (U-shape) using an advanced finite element modeling approach calibrated based on previously conducted small-scale experiments. Here, failure mechanisms, corresponding capacity and efficiency of the adopted strengthening solution (low-cost textile-reinforced mortar) are evaluated by means of pushover analyses. Then, the reliability of the pushover analyses is assessed by comparing its outcomes with that of the incremental dynamic analyses. In general, the failure was found to be governed by overturning of the web wall due to its detachment from the wing walls, while the strengthening was found to increase the capacity and delay the damage development.This work was financed by FEDER funds through the Competitively Factors Operational Programme - COMPETE and by national funds through FCT - Foundation for Science and Technology within the scope of projects POCI-01-0145-FEDER-016737 (PTDC/ECM-EST/2777/2014) and POCI-01-0145-FEDER-007633. The support from grant SFRH/BPD/97082/2013 is also acknowledged

In-plane seismic performance of plain and TRM-strengthened rammed earth components

Raw earth is one of the most widely used building materials and is employed in different techniques, among which adobe and rammed earth are the most common. The respective structural systems, like in masonry buildings, acceptably withstand against gravity loads, though they are significantly vulnerable to earthquakes. Moreover, a great percentage of the World’s population is still inhabited in such environments, which are endangered by future earthquakes. The current article investigates the seismic in-plane performance of an I-shaped rammed earth component by means of advanced nonlinear finite element modelling. In this regard, conventional pushover analyses were conducted to evaluate load/displacement capacities and to assess probable failure modes. It was observed that the component fails mainly due to detachment of the wing walls from the web wall and due to occurrence of diagonal shear cracks at the web. Subsequently, the application of Textile Reinforced Mortar (TRM) strengthening solution to the component was studied and shown to be able to maintain the integrity of the component for larger lateral load levels. Finally, the reliability of the pushover analyses to predict the seismic response was evaluated by comparison with outcomes from incremental nonlinear dynamic analysis.This work was financed by FEDER funds through the Competitively Factors Operational Programme – COMPETE and by national funds through FCT - Foundation for Science and Technology within the scope of projects POCI-01-0145-FEDER-007633 and POCI-01-0145-FEDER-016737 (PTDC/ECMEST/2777/2014). The support from grant SFRH/BPD/97082/2013 is also acknowledged

Repair of earth masonry by means of grouting: importance of clay in the rheology of a mud grout

Building with earth is one of the most ancient and traditional ways of building. Consequently, many historic and new-built earthen buildings can be found all over the world. However, the specific characteristics of earthen materials make the earth constructions very sensitive to external damaging agents. In particular, the weakness and fragility extensively recognized on earthen materials make this type of constructions very vulnerable from a structural perspective. In general, the structural damage on earth constructions occurs in the form of cracks, which debilitate the structural behaviour and compromise the durability. Injection of mud grouts can be seen as a reliable and economic solution for repairing earth constructions. The success of such intervention on a historical construction requires following an appropriated design methodology. However, the knowledge about mud grouts is still limited, and thus research efforts are needed in order to develop such methodology and to surpass many of the difficulties that the restorers of earth constructions are currently facing. Understanding the rheology of the mud grouts is one of the key issues of the all process. Hence, this paper explains an initial proposal of methodology for the design of mud grouts and an experimental campaign that aimed to understand the role of the clay fraction in the rheology of mud grouts.Fundação para a Ciência e a Tecnologia (FCT

An analytical approach for pull-out behavior of TRM-strengthened rammed earth elements

Rammed earth constructions, beyond being largely spread in the built heritage, are known for their high seismic vulnerability, which results from high self-weight, lack of box behavior and low mechanical properties of the material. Hence, to mitigate this seismic vulnerability, a compatible textile reinforced mortar (TRM) is here proposed as a strengthening solution, because of its reduced mass and high ductility. The few research about the structural behavior of TRM-strengthened rammed earth elements addresses the global behavior, overlooking the local behavior of the system. An analytical approach to infer the bond stress-slip relationship following the direct boundary problem is proposed. Based on a previous series of pull-out tests, an adhesion-friction constitutive law is portrayed considering also a damage model that considers the degradation of the reinforcing fibers due to friction.This work was partly financed by FEDER funds through the Operational Programme Competitiveness Factors (COMPETE 2020) and by national funds through the Foundation for Science and Technology (FCT) within the scope of project SafEarth - PTDC/ECM-EST/2777/2014 (POCI-01-0145-FEDER-016737). The support from grant SFRH/BD/131006/2017 is also acknowledged