137 research outputs found

    Seismic performance of traditional half-timbered walls : experimental results

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    Half-timbered structures constitute an important cultural heritage of many countries, since they represent a typical anti-seismic construction adopted worldwide [1][2]; therefore, their preservation is of the utmost importance. Although recent earthquakes have pointed out the good seismic behaviour of this kind of structures, few experimental studies are available on the performance of traditional half-timbered walls and their retrofitting solutions and mainly only qualitative information is available of the seismic response of such structures. Due to this lack of information, an extensive experimental campaign was carried out, performing in-plane cyclic tests on real scale half-timbered and timber frame walls, adopting connections and dimensions encountered in real structures and considering different infill types (brick masonry and lath and plaster). Moreover, keeping in mind the great rehabilitation effort that has been carried out in recent years on such buildings, such in the case of the Portuguese Pombalino buildings in Lisbon, it is important to study the effect of strengthening on traditional timber-frame walls. To do this, retrofitting solutions have been applied to traditional walls and tested under cyclic loading. Both traditional and innovative techniques have been considered, namely bolts, steel plates and NSM steel flat bars. Results on the behaviour of both unreinforced and retrofitted walls are analysed and their seismic behaviour is discussed.Fundação para a Ciência e a Tecnologia (FCT

    Assessment of the seismic behaviour of unreinforced: traditional half-timbered walls

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    Half-timbered buildings represent an important historical heritage in many countries. They are diffused in various regions for different reasons, among which for being able to resist seismic actions. Despite the great popularity of this kind of structures, few studies are available on their global behaviour or on that of their single structural elements. The aim of this paper is to study the behaviour under cyclic loading of traditional half-timbered walls, with connections, materials and elements dimensions encountered in existing buildings. Cyclic tests have been performed in order to evaluate the performance of distinct traditional retrofitting techniques of the connections, namely: (1) increasing the number of nails at the connection; (2) use of steel bolts; (3) use of steel plates. The idea is to compare the performance in terms of hysteresis loops and the assessment of the improvements of the cyclic response in terms of ductility and energy dissipation

    Full-scale experimental testing of retrofitting techniques in Portuguese “Pombalino” traditional timber frame walls

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    Traditional timber frame walls are constructive elements representative of different timber frame buildings that are well known as one of the most efficient seismic resistant structures in the world. Timber frame walls were also used in the reconstruction of buildings of the old town of Lisbon after the earthquake of 1755 aiming at improving their seismic global behaviour. As it is important to preserve these structures, a better knowledge about their behaviour under seismic actions is important and can give some indications about possible retrofitting techniques to be used to improve the seismic performance. Due to the great rehabilitation effort currently carried out in many countries, a better understanding of retrofitting techniques is also needed. Therefore, this paper aims at providing a study on possible retrofitting techniques adopting traditional solutions such as bolts and steel plates. Static cyclic tests have been performed on retrofitted traditional timber frame walls in order to study their seismic performance. The experimental results showed the overall good seismic performance of steel plates and the more ductile behaviour of retrofitted timber frame walls with bolts.Fundação para a Ciência e a Tecnologia (FCT

    A viscoplastic SANICLAY model for natural soft soils

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    This paper focuses on constitutive and numerical modeling of strain-rate dependency in natural clays while also accounting for anisotropy and destructuration. For this purpose the SANICLAY model that accounts for the fabric anisotropy with the additional destructuration feature that accounts for sensitivity of natural clays, is considered as the reference model. An associated flow rule is adopted for simplicity. The model formulation is refined to also account for the important feature of strain-rate dependency using the Perzyna’s overstress theory. The model is then implicitly integrated in finite element program PLAXIS. Performance of the developed and implemented model is explored by comparing the simulation results of several element tests and a boundary value problem to the available experimental data. The element tests include the constant strain-rate under one-dimensional and triaxial conditions on different clays. The boundary value problem includes a test embankment, namely embankment D constructed at Saint Alban, Quebec. For comparison, the test embankment is also analyzed using the Modified Cam-Clay (MCC) model, the SANICLAY model, and the viscoplastic model but without destructuration. Results demonstrate the success of the developed and implemented viscoplastic SANICLAY in reproducing the strain-rate dependent behavior of natural soft soils.Support to conduct this study is provided by the University of Nottingham’s Dean of Engineering award, and the Natural Sciences and Engineering Research Council of Canada (NSERC)

    Characterization of the seismic behaviour of traditional timber frame walls

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    Tese de doutoramento Engenharia Civil - EstruturasTimber frame structures constitute an important cultural heritage of many countries, since they represent a typical anti-seismic construction adopted worldwide. Therefore, the preservation of these structures is of the utmost importance. Although recent earthquakes have pointed out the good seismic behaviour of this kind of structures, few experimental studies are available on the performance of traditional half-timbered walls and their retrofitting solutions. Aiming at filling this research gap and at better understanding the behaviour of these historic elements under seismic loads, an extensive experimental campaign has been carried out, performing in-plane cyclic tests on real scale half-timbered and timber frame walls, adopting connections and dimensions found in real structures and considering different infill types (brick masonry and lath and plaster). Moreover, considering possible damages caused by earthquakes, after the unreinforced tests, the walls were retrofitted and re-tested to compare the efficiency of the retrofitting solutions in terms of maximum load, ductility, cyclic stiffness, energy dissipation and equivalent viscous damping. Both traditional and innovative retrofitting techniques were adopted, namely bolts, steel plates and near surface mounted steel flat bars. Moreover, since the behaviour of the walls was governed by their connections, in-plane cyclic and pull-out tests were performed on traditional connections used in the walls. Additional retrofitting techniques were adopted, such as self-tapping screws and glass fibre sheets, to overcome some limitations found during the in-plane tests on the walls. From the experimental results, an analytical hysteretic model was derived, based on the modification of existing models and calibrated on experimental results. This can be used in simplified numerical models to represent the hysteretic response of the walls. Finally, numerical analyses were performed on timber frame walls with and without infill. The models were calibrated on the experimental results. Parametric analyses were then performed taking into account different variables.Os edifícios com paredes de madeira tradicionais constituem um importante património cultural de muitos países, uma vez que representam uma construção anti-sísmica típica adoptada mundialmente. Portanto, a preservação dessas estruturas é de extrema importância. Embora os terremotos recentes tenham apontado o seu bom comportamento sísmico, relativamente poucos estudos experimentais estão disponíveis sobre o desempenho sísmico das paredes tradicionais. Tendo como objectivo alargar a investigação e de obter uma melhor compreensão do comportamento destes elementos construtivos (paredes de frontal em edifícios Pombalinos) sujeitos a cargas sísmicas, foi realizada uma extensa campanha experimental composta por um conjunto de ensaios cíclicos no plano em escala real de paredes de frontal. Foram consideradas paredes sem preenchimento, utilizando ligações e dimensões encontradas em estruturas reais e considerando os diferentes tipos de enchimento (alvenaria de tijolo e fasquio). Por outro lado, considerando os possíveis danos causados em caso de terremoto, após os ensaios, as paredes foram reforçadas e ensaiadas novamente para comparar a eficácia das soluções de reforço em termos de carga máxima, ductilidade, rigidez cíclica, dissipação de energia e de amortecimento viscoso. Foram adoptadas técnicas de reforço tradicionais e também inovadoras, nomeadamente parafusos, chapas de aço e barras de aço inseridas ao nível das ligações. Além disso, uma vez que o comportamento das paredes é controlado pelas suas ligações, foram realizados ensaios cíclicos no plano e ensaios de pull-out em ligações tradicionais utilizadas nas paredes. Foram adoptadas técnicas de reforço adicionais, tais como parafusos auto-perforantes e folhas de fibra de vidro, para superar algumas limitações encontradas durante os ensaios cíclicos das paredes. A partir dos resultados experimentais, foi derivado um modelo de histerese analítico, com base na modificação de modelos existentes e calibrado com base em resultados experimentais. Este modelo pode ser utilizado em modelos numéricos simplificados para representar a resposta de histerese das paredes. Finalmente, foram realizadas análises numéricas em paredes de frontal com e sem preenchimento. Os modelos foram calibrados com os resultados experimentais. Foram realizadas análises paramétricas tendo em conta diferentes variáveis

    Edifícios pombalinos: comportamento e reforço

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    A análise estrutural de edifícios existentes é um desafio complexo por muitas razões, incluindo o desconhecimento sobre o comportamento dos materiais e componentes estruturais. Os edifícios pombalinos representam uma tipologia valiosa do nosso edificado, pelo contexto cultural do sismo de 1755 em Lisboa e de criação de uma cidade nova, bem como pelos aspetos tecnológicos inovadores. O presente artigo apresenta, inicialmente, um breve estado do conhecimento dos edifícios alvenaria-madeira. Posteriormente, são apresentados resultados de ensaios cíclicos recentes na Universidade do Minho sobre esta tipologia de paredes, que permitem caracterizar o seu comportamento e avaliar diferentes soluções de reforço

    Influence of infill on the cyclic behaviour of traditional half-timbered walls

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    Half-timbered buildings represent an important historical heritage in many countries. They are diffused in various regions for different reasons, such as availability of materials, to lighten a structure, low cost and the strength they offer, and as a construction element able to resist seismic actions. This latter issue is the research topic analysed here, as half-timbered buildings have been specifically used in reconstruction plans as earthquake-resistant buildings in many countries, such as Portugal, India, Greece, etc. The aim of this paper is to study the behaviour under cyclic loading of such half-timbered walls, with typical connections, materials and geometries encountered in existing buildings. Traditionally, different types of infill could be applied to half-timbered walls depending on the country, namely brick masonry, rubble masonry, hay, mud, etc. The focus of this paper is to study and compare the seismic behaviour of the walls considering two different infill typologies, as well as the possibility of having no infill, i.e. considering only the timber frame. Cyclic test were performed on traditional walls and their behaviour was studied in terms of ultimate capacity, deformability, energy dissipation and stiffness.Fundação para a Ciência e a Tecnologia (FCT

    An overview on the seismic behaviour of timber frame structures

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    Traditional timber frame walls are an important structural element of many buildings and are usually composed of vertical posts and horizontal beams with bracing diagonal elements. In Portugal the timber frame walls, known as frontal walls, are usually part of Pombalino buildings, which were introduced by the Marquis of Pombal, who was responsible for the reconstruction of Downtown Lisbon after the great earthquake of 1755, which partially destroyed the city. Given the increasing interest of the research community to this structural system, it is important to promote the discussion of the main findings that can contribute to the advance on the knowledge of the mechanical behaviour of timber frame buildings to seismic action. Therefore, this paper intends: (1) to give an overview of the different solution of timber frame structures in different countries with special focus on the frontal walls characteristic of Pombalino buildings; (2) provide some examples of the reasonable behaviour of timber frame buildings in past earthquakes; (3) to summarize the experimental research carried out in the recent years in analysis of the behaviour to in-plane cyclic loading

    Timber frames as an earthquake resisting system in Portugal

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    Timber frames are commonly adopted as a structural element in many countries with specific characteristics varying locally, in termsof geometry and materials.Their diffusion in Southern European countries is linked to their good seismic-resistant capacity, but only in the last decade interest has grown for this structural typology, and studies have been performed to better understand their behaviour. In this contribution, a brief state of the art on existing timber frame building typologies is presented, focusing on their seismic-resistant characteristics. Additionally, an overview of possible strengthening solutions, adopted both in practice, and tested experimentally are presented. Their performance when applied to walls and connections is also discussed.(undefined

    Application of near surface mounted (NSM) strengthening technique to traditional timber frame walls

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    Timber frame buildings are well known as an efficient seismic resistant structure popular all over the world not only due to their seismic performance, but also to their low cost and the strength they offer. These constructions still exist today and it is important to be able to preserve them, so a better knowledge on their behaviour is sought. Furthermore, historic technologies could be used even in modern constructions to build seismic resistant buildings using more natural materials with lesser costs. A great rehabilitation effort is being carried out on this type of buildings, as their neglect has led to decay or their change in use and alterations to the structure has led to the need to retrofit such buildings; only recently studies on their behaviour have become available and only a few of them address the issue of possible strengthening techniques for this kind of walls. In this scope, an innovative retrofitting technique (near surface mounted steel flat bars) is proposed and validated on traditional timber frame walls based on an extensive experimental program. The results of the static cyclic tests on distinct wall typologies retrofitted with the NSM technique are herein presented and discussed in detail. The main features on deformation, lateral stiffness, lateral resistance and seismic performance indexes are analysedThe authors would like to acknowledge Eng. Filipe Ferreira and A.O.F. (Augusto Oliveira Ferreira & C Lda.) for their expertise and collaboration in the construction of the wall specimens. The first author would also like to acknowledge the Portuguese Science and Technology Foundation (FCT) for its financial support through grant SFRH/BD/61908/2009. The authors would also like to acknowledge the project REABEPA (Structural rehabilitation of masonry walls in old buildings), founded through grant PTDC/ECM/100168/2008, to which part of this research is associated
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