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Über dieses Buch

This book presents a selection of the best papers from the HEaRT 2015 conference, held in Lisbon, Portugal, which provided a valuable forum for engineers and architects, researchers and educators to exchange views and findings concerning the technological history, construction features and seismic behavior of historical timber-framed walls in the Mediterranean countries. The topics covered are wide ranging and include historical aspects and examples of the use of timber-framed construction systems in response to earthquakes, such as the gaiola system in Portugal and the Bourbon system in southern Italy; interpretation of the response of timber-framed walls to seismic actions based on calculations and experimental tests; assessment of the effectiveness of repair and strengthening techniques, e.g., using aramid fiber wires or sheets; and modelling analyses. In addition, on the basis of case studies, a methodology is presented that is applicable to diagnosis, strengthening and improvement of seismic performance and is compatible with modern theoretical principles and conservation criteria. It is hoped that, by contributing to the knowledge of this construction technique, the book will help to promote conservation of this important component of Europe’s architectural heritage.

Inhaltsverzeichnis

Frontmatter

Historical and Constructive Aspects

Frontmatter

Cooperating Timber and Stone Antiseismic Frames in Historic Structures of Greece

On the Kefalonia Island a Historical Building, dated to 1670, is located. The structure withstood successfully three catastrophic earthquakes in the past, until the severe earthquakes of 2014, during which it partially collapsed. Apart from the building’s historic value, it actually constitutes a rare example of double load bearing structure. The main concept behind this double anti seismic system is the following: Masonry walls transfer the loads of the wooden structure of the floor and the roof, which was also simultaneously supported by a row of wooden posts placed in parallel position and close to the masonry, by means of a wooden beam which was based on them. When, during earthquakes, parts of the masonry fail to function properly, then it is this second parallel system of wooden skeleton frame which takes over the load transfer, until masonry walls are repaired. Moreover, this system demonstrates very advanced and detailed connections of the wooden load bearing structures, which have pre-scheduled absorption capacity of the dynamic energy released by the earthquake. Therefore, this enables the structure to absorb the seismic energy during the severe earthquakes in the region of the Ionian Islands, avoiding in this way the building’s failure.

Panos Touliatos

The Role of a Post-Byzantine Timber Roof Structure in the Seismic Behavior of a Masonry Building—The Case of a Unique Type of Timber-Roofed Basilicas in Cyprus (15th–19th Century)

In the Troodos area of Cyprus there is a distinctive type of wooden roofed basilicas, dated from the mid-15th to the late-19th century AD, whose unique constructional feature is the existence of two separate but cooperating parts of the roof, the Inner Roof and the Outer Roof. The Inner Roof forms a wooden rigid triangular prism, with horizontal tie-beams and dense inclined rafters, from which the Outer Roof is literary suspended. The two pairs of tie-beams at the western and eastern end of the church are forming, along with the two composite beams on the northern and southern walls, a full timber circumferential binding. This roof type fully adopts the principle of a uniform distribution of loads on multiple paths, and obtains its overall stiffness through numerous partially semi-rigid joints. To achieve this goal, this particular roof structure was developed through years into a unique and cleverly designed bearing system, retaining a high level of simplicity in all construction details. As far as the overall structure is concerned, the timber-roofed churches of Cyprus present a unique system of co-operation between the rigid roof and the stone masonry, achieving in this way the absolutely necessary stiffness for both.

Marios Pelekanos

Historic Earthquake-Resistant Constructive Techniques Reinforced by Wooden Logs in Algeria

The seismicity of northern Algeria is light to moderate and thus a moderate-seismic hazard country. Except the Orléansville 1954, El Asnam 1980 and Boumerdes 2003 earthquakes which happened during the twentieth century, the Algerian country has experienced in the past several moderate seismic events that caused loss of human lives and damage to property in different regions. The historical earthquakes known since ancient time Rusucurru (42) (Central region), Lambaesis (262) (Eastern region), Mostaganem (345) (Western region) and during recent time Algiers (1365, 1716), Cherchell (1732), Dellys (1731), Oran (1780), Blida (1825, 1857), Jijell (1856), Constantine (1858) and Biskra (1869), greatly increases the probabilities of an earthquake occurring and damage in the future. Based on this information, fundamental questions of interest for the architects and engineers are: how did the local population build their houses resisting earthquake loads? What structural techniques did the local population use for building their houses to protect themselves against earthquakes? This paper present the timber-frame earthquake resistant techniques developed such a local seismic culture in northern Algeria cities observed in the Casbah of Algiers and Miliana (Central Algeria), Mostaganem (Western region) and in Batna Highlands region (Eastern Algeria).

Amina Abdessemed-Foufa

A Comparative Evaluation of the Results of Two Earthquakes: Istanbul and Lisbon Earthquake in 18th Century

Earthquakes affect both urban texture and social structure of cities in history. It can be seen that in two scales such as urban scale and building scale. In this context, two earthquake examples such as the 1755 Lisbon Earthquake and the 1766 Istanbul Earthquake will be analyzed in different scales. This paper is giving introduction to the main urban texture in 1700s consisting of timber housing structures and damages of these earthquakes. Construction system of Istanbul and Lisbon will be analyzed. In the methodology of this study a comparative evaluation of the 1755 Lisbon Earthquake and the 1766 İstanbul Earthquake will be presented. By looking at the archive records, the development of urban structure after earthquakes has different tendencies in Lisbon and Istanbul. The first inclination is to remove the old city and re-build completely the new city as in Lisbon. By doing this renovation the new regulations are settled down. The second inclination is reproduction of the old housing construction system in Istanbul. It could be seen from both the local archive documents and European travelers’ records. The aim would be a comparative approach in order to develop and preserve the historic urban areas and historical buildings that has a potential to make an evaluation by the reflection of past to the present.

Şevket Erşan

Some Examples of Turkish Houses with Wooden Frame in the Seismic Zone Anatolia

Wooden frame Turkish houses in the area encompassed by the Ottoman Empire have their own special characteristics from the point of view of the order of the rooms, the design plan and the construction system. The earliest examples of these houses have been dated to the 17th century Today, there are few remaining examples of the first Turkish houses with an open hall “hayat”, wooden frame construction system, adobe fill, double rows of windows and mostly directed towards their own courtyard. In Turkish houses that passed through various developmental stages, the open hall was brought into a more protected arrangement and beside the types of open hall plan, the plan with inner hall “sofa”, corner hall and central hall were created; however, the use of the wooden frame construction system continued. The wooden frame construction system was preferred because it was the continuation of a tradition and because it suited the geography of Anatolia, located in an earthquake zone and rich in forested areas. In the wooden frame method; the assembly details were basic and the house could be put together like a tent, generally the frame was filled stones, adobes and bricks and sometimes wood and sometimes there would be no fill at all. The importance of the wooden frame houses did not receive much attention and were preferred to concrete apartment buildings until the 1970s, but their importance was noticed in our day even as old, important examples were torn down. So, using existing examples, the purpose of this study is to examine, document and make wooden frame Turkish houses known according to historical development.

Ayten Erdem, Uzay Yergün

Traditional Timber Housing Structure in Zeyrek

Zeyrek, as a World Heritage Site and one of the important residential areas of the old city of Istanbul, has a significant number of historical timber houses belonging to late 19th–early 20th century. Due to its topographical, climatic, social, economic and cultural features as well as its nearby wooded environment, local materials and traditional technology, Zeyrek has reflected a precious architectural pattern consisting of many of timber-framed buildings for a long time. This paper examines traditional architecture, presents and promotes the experience with timber housing restoration in Zeyrek, Istanbul, aiming to analyze the existing wooden housing pattern in the area and to investigate the restitution and restoration project of a traditional timber house in detail. The conservation and restoration process in the traditional structure of wood extracted positive lessons of history. In this context, the classification of physical characteristics commonly found in these timber housing settlement has been done considering the method of construction, the façade proportions of the elements, plan schemes, articulation of different forms, the conservation and restoration projects in the site. The present study follows methodological principles of historical research about Zeyrek. A case study about traditional timber house structure consists of field surveys and documentation. According to observation and analysis of the traditional housing settlement, the main classifications were obtained, along with photographical survey showing the current situation of the timber housing characteristics of the site. The paper focuses on this transformation by putting forward integrated conservation approach.

Aylin Akcabozan

Possible Precursors of Pombalino Cage

Pre-Pombalino buildings in Lisbon nowadays represent a rare alive witness to a major historic European earthquake event: the 1755 Lisbon earthquake with tsunami followed by a great fire. More substantial interest is however shown by researchers in the so-called Pombalino cage [1, 2], a structural typology created after the 1755 earthquake to rebuild the city, and considered by many authors, as a first engineered solution designed specifically to be resilient to earthquakes. The Pombalino cage is a composite timber-framed masonry construction with a wide use of St Andrews crosses and specific connections. In comparison very modest attention has been paid to clearly identify in history possible precursors of this technological solution, despite the many examples of vernacular masonry infilled timber framed buildings, which are common to many Mediterranean regions exposed to seismic hazard. An additional difficulty in tracing with certainty the historic development of the Pombalino cage is the lack of original drawings for this construction typology. This paper attempts to determine the conditions at the time, in terms of existing technical know-how and current construction methods that would have made the development of the Pombalino cage, possible. The work carried out in this research encompasses in situ surveys of 18th century buildings, documentation from several archival libraries, analysis of ancient treatises, and previous research by the authors. This manuscript presents first a review of: (i) traditional timber-framed construction systems belonging to earthquake-prone regions; (ii) then connects these to influential contemporary knowledge on the 1755 Lisbon earthquake; (iii) evidence from Portuguese legislation, regulations, and notices published after the earthquake; (iv) and finally the academic education and training of Portuguese military civil engineers and architects (before and after the earthquake) who developed the Pombalino Cage; (v) the paper concludes with a discussion of whether these elements can be identified as the necessary precursors of the Pombalino cage.

Alice Tavares, Aníbal Costa, Dina D’Ayala

Local Seismic Cultures: The Use of Timber Frame Structures in the South of Portugal

The well-known timber frame Pombalino construction system was devised after the 1755 Lisbon earthquake by the Portuguese government and its use was mandatory for the complex reconstruction process carried out in the city. It can be considered as the first technical regulation regarding seismic resistance. However, its use was not limited to Lisbon and the system was also embraced by local communities, which adopted it as a model of earthquake resistant construction. Its use thus spread around the country and eventually took root in the vernacular way of building of the country, becoming part of the Portuguese Local Seismic Culture. Nowadays, frontal walls can be identified in many vernacular constructions scattered across the country. This paper studies the use of frontal walls in vernacular buildings in the South of Portugal, which is the area with highest seismic activity within the country, focusing on the city of Vila Real de Santo António, which was chosen as the main case study. The paper also discusses the possible negative effects of the abandonment of this distinctive technique resulting from the Portuguese Seismic Culture on the overall vulnerability of vernacular constructions.

Javier Ortega, Graça Vasconcelos, Hugo Rodrigues, Mariana Correia

The Use of Wood with an Anti-seismic Function in the Architecture of Palermo During the 18th Century

The study analyzes the interventions in the historical buildings after the earthquakes that struck Palermo in 1726 and 1751, with a particular attention to the anti-seismic reinforcements. The research, based primarily on archival documents, focuses on a series of interventions in the architectural heritage, in which the use of wood for structural elements, was able to guarantee for an “antiseismic” reconstruction. Although wood was not commonly used as other materials (iron, for instance) in the post-earthquake reconstruction process of Palermo it was certified its use as an anti-seismic system in the reinforcements of the damaged buildings. It is documented, for instance, the insertion of wooden beams, used similarly to iron chains, both in monumental buildings, and also in the less valuable ones, useful to provide a better cohesion for the masonries, or the introduction of wooden and lightweight partition walls; or, even, the substitution of stone vaults with vaulted wooden structures or ceilings and the realization of staircases using wood for the entire main structure.

Tiziana Campisi, Federica Scibilia

Urban Planning and Building Reconstruction of Southern Italy after the 1783 Earthquake: The Case of Mileto

The seismic period, that started in 1783 and lasted three years in the southern Calabria (South of Italy), caused massive damages: over 35,000 victims and relevant upheavals in the hydrogeological asset of the site. The Borbone government immediately dealt with the reconstruction of backward provinces, attempting to reorganize the economic and administrative systems by innovative criteria and by the construction with anti-seismic techniques. In this paper a preliminary reviewing of the historical sources is analysed to frame the reconstruction, highlighting the differences compared with the initial models. By the regional to the urban scale, it was assumed as case study the historical centre of Mileto, one of the five cities entirely rebuilt on another site after the earthquake. Mileto preserves the scheme of the urban planning conceived in the end of the Eighteenth century. Also in Mileto, there is the Episcopal Palace, characterized by several architectural and construction features to increase the seismic response. Despite the advanced state of deterioration, the original structure is still perfectly recognizable and allows to deepen the knowledge regarding the technology, that is unquestionably a cultural heritage to preserve, enhance and possibly to be reused. Accordingly, the authors prefigure the importance of carrying out a census of still standing buildings characterized by the Borbone anti-seismic system by suggesting possible research methodologies.

Stefania Stellacci, Francesca Geremia, Enrico Pagano, Nicola Ruggieri, Ginevra Salerno, Michele Zampilli

The Masonry Timber Framed Load Bearing Structure of the Palazzo Vescovile in Mileto (Italy)

The Palazzo Vescovile in Mileto (Southern Italy), erected shortly after the catastrophic earthquake that struck the Calabria region, emblematically represents the application of principles and technical indications recommended in the Borbone seismic code Istruzioni and included in treatises of Eighteenth century seismic engineering. The building, characterised by various constructive events that caused a construction completion delay, presents devices aimed at consciously mitigating its seismic vulnerability, including the building geometry (i.e. in plan bi-axial symmetry, a front elevation regular development and a height limited to only one storey) as well as constructive solutions regarding the nature and the organisation of materials and resistant elements forming the load bearing structure. The vertical structural system is represented by masonry reinforced with timber frames whose main function is to bond the building intersecting walls with the aim of obtaining a box behaviour of the Palazzo Vescovile under earthquake excitations. On that purpose the particular arrangement and morphology of the members nodes, often with the addition of metallic devices, contributes to transfer stresses to a three-dimensional system of orthogonal walls. In addition to the vertical load bearing system the inter-storey floor also has a key role in influencing the building seismic response. In fact, the presence of notches strengthening the node beam to the wooden ring, improves, together with the latter, the resistance to out-of-plan actions. Furthermore, the floor is characterized by a moderate deformability, thanks to the narrow spacing and geometric features of the beams, useful for redistributing horizontal forces to the shear walls. The roof structure, constituted by king post trusses ensuring the absence of outward thrusts, benefits from the presence of saint Andrew’s crosses arranged orthogonally to the structural unit with the purpose of preventing the trusses from stacking under horizontal loads and, generally speaking, of ensuring a roof longitudinal stiffness. Moreover, the document devotes its attention to the behaviour of the Palazzo Vescovile in Mileto under gravitational actions, analysing the wooden frame contribution to the compression resistance of the entire constructive system.

Nicola Ruggieri, Francesca Geremia, Enrico Pagano, Ginevra Salerno, Stefania Stellacci, Michele Zampilli

A Multidisciplinary Approach to the Analysis of the Traditional Lefkada Houses

In the pre-modern age, the concept of preservation was mainly related to the possibility of achieving profits; the decision about restoring derived from the willing of people to keep living their houses and any configuration change was done only if unavoidable. In addition, within a context marked by strong and frequent destructive events, it is interesting to note how conservation may give the way to empirical attempts to improve the construction system. In the present work, the problem is discussed with reference to the particular case of the Lefkada Greek island which, being characterized by a high seismic hazard with a short return period in the context of a poor economy, has experienced a number of different foreign governments in history. Despite a long sequence of critical events, inhabitants decided to stay, developing an empirical resilient structural system able to control simultaneously several criticalities. The main purpose of this paper is to characterize, through a multidisciplinary analysis, this traditional construction system, the only one still surviving in the Ionian Islands. The preservation of this particular situation is a difficult issue, which can not be planned without the assumption of the transformation process which unavoidably affects both things and local people.

Sandra Tonna, Claudio Chesi

Numerical Analysis

Frontmatter

The “Gothic House” in Arquata Scrivia (Italy): Constructive Details and Seismic Assessment of a Timber Framed Masonry Structure

The paper presents the analysis of the structural and constructive system together with that of the seismic response of the “Gothic house” in ArquataScrivia, that constitutes a rare example of timber framed masonry structure in Piedmont (Italy). Besides a certain diffusion around Europe, which is documented in the 19th century chronicles, in Italy there are only a few timber-framed buildings left. The timber frame system of the “Gothic house” presents some analogies with the French and German one (area in which it is more widespread than Italy) although it is characterized exclusively by the presence of horizontal and vertical timber elements. In the paper, the analysis of the building has been supported by an extensive investigation campaign that included the execution of several non-destructive tests on both masonry and timber elements. Preliminary step for setting-up the investigation plan was a sensitivity analysis carried out on an equivalent frame model of the building by performing nonlinear static analyses. Aims of such sensitivity analysis were, firstly, to address the as-built information phase and, then, to improve the reliability of the final model to be adopted for the seismic assessment.

S. Cattari, S. Lagomarsino, R. Vecchiattini, G. Stagno

Seismic Assessment of Pombalino Buildings

Portuguese Pombalino masonry buildings were built mainly in Lisbon after the 1755s Lisbon Earthquake. These buildings are characterized by a mixed timber-masonry structure, known as the gaiola pombalina (cage), and were built aiming to withstand the horizontal seismic loads. The cage is composed of timber floors and improved mixed timber-masonry shear walls (“frontal” walls). It was arguably the first case in history of an entire town built with the purpose of providing seismic resistance to its buildings. In this paper, a description of the Pombalino buildings is presented, GIS mapping tool was developed to identify the main features of Pombalino buildings in Lisbon downtown area and the results of the seismic assessment of existing building are briefly discussed. A three-dimensional model was developed in Tremuri program based on the equivalent frame model approach. The building was modelled using non-linear beams for masonry panels. The “frontal” walls were modelled by a macro-element model developed and calibrated according to an experimental campaign. The seismic assessment of the global response of the building was determined through non-linear static (pushover) analyses. Due to the fact that building does not fulfil the safety requirements for the ultimate limit state, a strengthening solution was proposed in order to improve the seismic behavior of the building.

Rita Bento, Ana Paula Falcão, Ricardo Catulo, Jelena Milosevic

Numerical Approaches for the Analysis of Timber Frame Walls

Timber frame structures constitute an important cultural heritage of many countries, since they represent a typical anti-seismic construction adopted worldwide and are worth preserving. Recent experimental results have shown that the seismic response of traditional timber frame walls varies greatly with the type of infill, the type of connection and wall geometry. Two simplified 2D numerical models were created and in-plane monotonic tests were simulated and calibrated using recent experimental results. Material non-linearity was considered for all materials. Considering the numerous advantages of the use of simplified models, parametric analyses were carried out in order to evaluate the influence of parameters such as type of infill, infill-frame connectivity, timber type, connection type. The greater influence on the behaviour of the walls is given by the quality of the joints as well as the connectivity between timber and masonry, behaviour that is in accordance with experimental results. Additionally, the geometry of the wall influences its stiffness and load capacity.

Elisa Poletti, Graça Vasconcelos, Paulo B. Lourenço, Maria Pia Ciocci

Seismic Vulnerability of Borbone Masonry Reinforced with Timber Frames

After the 1783 earthquake, under the Borbone kingdom, new building regulations were introduced in the Calabria region (Italy) with the main scope of reducing the seismic vulnerability of the building asset in these highly seismic areas. The Borbone system consisted of masonry walls reinforced with timber frames and prescribed a symmetrical development in plan and elevation as well as height limitations. These measures aimed at increasing the seismic resistance of buildings and hence, in general, at reducing the socio-economic impact of future seismic events. In order to maintain, repair or retrofit these buildings, it is indispensable not only to understand their qualitative performance under an earthquake loading, but also to gain quantitative information on stiffness, load bearing and energy dissipation capacity and failure modes. This paper presents first investigations on the seismic vulnerability of simple Borbone structures where modelling assumptions such regularity in plan and elevation hold and only one shear wall system was used. Re-built shear wall specimens mirroring as exactly as possible a wall of the Palazzo Vescovile in Mileto (Italy), built according to the Borbone Istruzioni after the 1783 earthquake, were tested under quasi-static cyclic in-plane loading. By means of these tests, lateral properties and damage patterns of Borbone shear walls under horizontal loading were assessed and, even if limited to a single panel, earthquake behaviour patterns were evaluated. The test results on the shear walls in terms of hysteretic loops were used to develop a non-linear dynamic lumped mass model of a case study Borbone building which was subjected to various earthquake accelerograms. The single earthquake’s peak ground acceleration (PGA) values were increased until a previously defined near-collapse state in terms of maximum interstorey drift of the modelled building was reached. The thus obtained ultimate values for the PGA represent the sustainable level of seismic action of the investigated Borbone structure and ranged from 0.25g (North American earthquake) up to 1.52g. The effectivity of Borbone building regulations could be shown.

Nicola Ruggieri, Carmen Sandhaas, Ario Ceccotti

The Masonry Timber Framed Load Bearing Structure of “Baraccato” System: A Numerical Model

In the modern scientific culture, the seismic vulnerability of the architectural heritage is estimated numerically and need mathematical models of the mechanical behaviour of masonry buildings. The constructive system of “baraccate” houses, whose spread andarchitectural and engineering values have been rediscovered recently, still needs mathematical models. In this piece of paper this first effort has been done for a wall from Palazzo Vescovile in Mileto. The comparison between the numerical results and some experimental tests encourages the research efforts to be continued.

Ginevra Salerno, Francesca Geremia, Enrico Pagano, Michele Zampilli, Nicola Ruggieri, Stefania Stellacci

Load-Bearing Capacity of Traditional Dovetail Carpentry Joints with and Without Dowels: Comparison of Experimental and Analytical Results

Post-disaster field studies widely suggest that historical timber structures are seismically resistant, and a growing number of experimental studies support this observation. The joints between structural members, which are the major energy dissipation mechanism within the structure, play a crucial role in the overall robustness and the way that a structure handles the seismic demand. Joints mostly fail when the timber members are still in the elastic range, therefore a thorough understanding of their behaviour under various loading schemes is of utmost importance to gain deeper insight about the overall structural performance of timber structures. This paper summarizes the findings from a series of testing carried out on dovetail joints, which is one of the most common traditional carpentry joints, during the 5th COST FP 1101 Training School, held in University of Minho, Portugal. Within this framework, a dovetail joint (with and without dowel) was tested under compression and tension. The experimentally obtained load-bearing capacity of the joints was then compared to the capacity values calculated using analytical models, and the failure modes were further discussed. The results showed that the experimentally obtained capacity values can be successfully reproduced by analytical models for dovetail joints without dowel. On the other hand, the capacity of a dovetail joint with dowel under compression or tension is always underestimated by analytical models.

Karel Šobra, Coralie Avez, Yasemin D. Aktaş, Richard de Rijk, Isabela Burawska, Jorge M. Branco

Codes Analysis and Safety Assessment

Frontmatter

Reliability of Timber Framed Constructions in Seismic Prone Areas in the Practice Codes Issued from 18th to 19th Century

The analysis of a few significant events of the modern and contemporary history, carried out examining not only the characteristics of the catastrophes but the phases following the occurrence, concerns the earthquakes of Guatemala (1541), Lisbon (1755), Calabria (1783), Lefkas (1826), Casamicciola (1883) and others. Apart from the concern for the humanitarian assistance to injured people, the tax exemption for a certain period, the indications of sanitarian policy in an emergency situation etc., that is a common factor of reports, rules or codes, it is to be noticed that only in a very restricted number of cases technical indications or rules are given for the construction/reconstruction in order to prevent or at least reduce the risk and the amount of damage caused on the buildings by seismic activity. The survey and analysis of the construction practice “codes” presently known, generally issued in seismic prone areas shortly after important earthquakes from the 18th century on, or the reconstruction really put into practice allow to perceive the evolution of the research concerning the origin of the seismic phenomena, the filing, classification, evaluation, interpretation of the damage as well as the slow evolution of the strategies of damage prevention and failure repair. The use and the role, documented since prehistoric times, of the reinforcement of the masonry bearing walls with timber elements or frames is documented in all the seismic zones of the Mediterranean basin, in the widest meaning of the term, as well as all over the world without any apparent mutual influence; then the recommendations, common to some national codes, to make new constructions adopting this building system, is to be regarded as a reference to the traditional practice that had proved to be efficacious at least in preserving the constructions from total collapse and reducing the loss of human lives. The concern for the conservation of the historic buildings, conflicting with the supposed necessity of demolishing the buildings that had been severely damaged, and the rules for the correct repair intervention are only dealt with in the contemporary codes.

Nicola Ruggieri

Assessment and Safety Requirements for Existing Structures

Extending life of existing structures should be supported by guidelines or technical rules. In the case of historic buildings, besides the technical, economic and social aspects to be taken into account, the historic importance may determine the level of intervention to be performed. In spite of that, the integrity of the building itself and protection to people must be safeguarded and structural safety must reach a minimum level. However, safety requirements are not always established. Some European countries have national regulations and standards regarding assessment and retrofitting of existing structures. There is a need for harmonised European technical rules on this subject which can be broadly accepted. This paper refers the existing design codes and the work under way to extend them to existing structures and discusses their application and limitations regarding historic buildings. Based on LNEC experience, an approach is also proposed concerning the safety requirements applicable to heritage buildings, discussing the suitability of specifying different target reliability levels. Those levels should depend on the heritage value of the structure and the consequences of a possible failure of the structure, thus linked to its acceptable use.

J. M. Catarino, Teresa O. Santos, Ana S. Louro, Helena Cruz

Building Regulations and Existing Buildings: Setting the Requirements on Structural Safety in Portugal

This paper deals with the application of building regulations to the rehabilitation of existing buildings, taking a recent Government initiative to deregulate construction works in existing buildings as a case-study. To contextualize the analysis, the Portuguese housing stock is briefly described and the way building regulations apply to existing buildings in Portugal is reviewed. The deregulation initiative was presented by the Portuguese Government as a pragmatic policy measure to stimulate urban rehabilitation but sparkled wide opposition from a number of professional and scientific associations, who questioned both its strategic sense and its technical convenience. The structural safety professional and scientific community was particularly active in this debate. Focusing on them, the analysis of the process shows that: (i) the opposing positions were founded on two equally reasonable priorities (i.e., to stimulate the rehabilitation of existing building stock versus to improve structural safety), (ii) both parties were unable to support their positions with hard facts and argued mostly around their respective priorities and (iii) the debate ended in a deadlock. Main conclusions are that to overcome the deadlock more applied research is needed to bring forward appropriate solutions to rehabilitate existing buildings, along with a better dissemination of this practical knowledge in the building and real estate sectors. An informed and enlightened debate involving all relevant stakeholders, including the consumers’ associations and the public, should also be actively pursued. A final important conclusion is that increased attention should be given to sustainability and resilience when accessing social and economic efficiency in the process of designing and updating building regulations. Conducting these processes in the future will require a broader and more comprehensive approach and a more extended reference time frame that have often been adopted in the past.

João Branco Pedro, Vitor Campos

Seismic Assessment Procedures for Flexible Timber Diaphragms

A review of the available procedures and guidelines for the in-plane assessment of existing timber diaphragms in unreinforced masonry (URM) buildings is provided. Most of the provisions that concern flexible wood floors and that are valid for URM, can as a matter of fact be adopted for historic masonry buildings reinforced with timber frames. Recommendations from the most recent international standards like ASCE 41-13 and NZSEE 2015 were thoroughly analysed. Particular attention was given to producing a step-by-step practice-oriented guideline that provides background information which helps understand better the procedure frame work and also gives suggestions for alternative interpretations when multiple choices are possible.

Ivan Giongo, Gianni Schiro, Roberto Tomasi, Dmytro Dizhur, Jason Ingham

Diagnosis

Frontmatter

The Role of Terrestrial LiDAR for Mechanical and Safety Evaluation of Historic Timber Floors

The paper describes an activity conducted by a multi-disciplinary research group (architecture, civil engineering, technology, geomatics) for the mechanical evaluation of a timber floor belonging to a historic residential building located in the city center of Torino. The floor was made of beams of solid wood and wooden boards and presented a mid-span deflection. Since the floor structure was hidden by a suspended ceiling, the difficulty was to determine with precision all the geometrical characteristics of the main beam and its creep with the aim of verifying its mechanical resistance and stiffness. Through an accurate application of laser-scanner technique, it was possible to carry out the precise assessment of the structure.

Clara Bertolini-Cestari, Antonia Spanò, Stefano Invernizzi, Elisabetta Donadio, Tanja Marzi, Giulia Sammartano

Traditional Timber-Framed Infill Structure Experimentation with Four Scales Analysis (To Connection from a House Scale)

The aim of this paper is to contribute toward a better understanding of the seismic behavior of timber-framed infill structure. For this purpose, the results of a multi-scale experimental program are presented. The paper presents also the feasibility to use a DIC analyse on a full-scale of a house tested on a shake table.

Yannick Sieffert, Florent Vieux-Champagne, Stéphane Grange, Philippe Garnier, Jean-Charles Duccini, Laurent Daudeville

Characterization of Timber Masonry Walls with Dynamic Tests

Most of the Lisbon 18th century timber-framed masonry “Pombalino” buildings currently need seismic rehabilitation due to: (i) natural degradation with aging; (ii) need for adaptation to new serviceability requirements, generally involving higher loads and consequent structural changes; (iii) former interventions with elimination or damage of structural elements, affecting seismic resistance and (iv) noncompliance with the present seismic codes. The research presented in this paper aimed at experimentally evaluating the seismic vulnerability of the “Pombalino” buildings and at proposing a strengthening technique to reduce it by reinforcing their timber framed “Frontal” walls. The experimental program was based on extensive dynamic testing on prototype representative of the current characteristic of “Frontal” walls. The results of the dynamic tests carried out in the LNEC 3D shaking table are presented regarding the two types of tests performed: (a) seismic tests, in which the seismic action was applied with increasing amplitude in the direction of the walls; (b) dynamic identification tests, aiming at evaluating the decrease of the mechanical properties of the models. A comparison of the performance of the non-strengthened and strengthened tested prototypes is also presented.

Ana Gonçalves, Paulo Candeias, Luís Guerreiro, João Ferreira, Alfredo Costa

Assessment and Diagnosis of Two Collar Timber Trusses by Means of Visual Grading and Non-destructive Tests

The main objective of the present work is to evidence the importance of the inspection and diagnosis phase on the assessment of existing timber structures through visual grading and non-destructive testing (NDT) of its elements, especially for old structures with historical importance. To that aim, two collar timber trusses were inspected and assessed. These trusses were part of an old roof with over than one hundred years old that was decommissioned and then reassembled in laboratory conditions in the University of Minho (Portugal). The timber trusses were then tested on full scale at laboratory conditions until failure. The first part of this work presents the visual grading procedure complemented with NDT. During that part, all the elements of the trusses were visually inspected on each 40 cm segments with consideration of its geometric characteristics (exterior cross-section, wane and deformation), its defects (cracks, knots and decay) and critical sections. Non-destructive techniques, such as impact penetration, ultrasound and drilling resistance tests, were carried out in order to characterize the level of conservation of the elements at its present condition. The combination of the results of all NDTs allowed for a more substantiated grading of the segments and consequently of the elements. The results are presented through damage maps indicating the main pathologies of the structure and its residual cross-section, as well as correlations between different NDTs. In the second part of this work, a comparative analysis between the two trusses is made considering the prior results of the NDTs and the performance of the trusses on the full scale tests. To that aim the results of the visual grading and NDTs are correlated to the sections were failure of the segments was visible.

Isabel D. Gomes, Fotis Kondis, Hélder S. Sousa, Jorge M. Branco, Paulo B. Lourenço

Retrofitting Assessment and Numerical Models for the Historical Timber Roof Structures of the Towers of Valentino Castle in Turin

The paper analyses a reinforcement intervention conceived by one of the authors (C. Bertolini) and performed on the historical timber roof structure of the Valentino Castle in Torino (Italy) some thirty years ago. The timber roof of the towers, dating back to 17th century, is a three-dimensional frame structure with a height of about 12 m. In the transversal direction four main great trusses are present, and two small trusses are placed close to the transversal masonry walls. The pitch is strongly inclined. A ridge connects the structure in the longitudinal direction of the timber roof, in addition to five series of purlins and three orders of overlaid frames with stiffening functions. This structural complex is firmly secured to the covering planks that support the tiles of black stone. The intervention was carried out with timber elements anchored to the ancient masonry walls, in order to improve their seismic behaviour. This intervention proved to be particularly innovative, since at that time the regional area where the castle is located was not yet considered a seismic area by the national standards. Laser scanning surveying, non-destructive investigations and numerical simulations are adopted in the present study, in order to assess the efficiency of the intervention and the present condition of the joints.

Clara Bertolini-Cestari, Antonia Spanò, Stefano Invernizzi, Tanja Marzi

Repair/Reinforcement

Frontmatter

Development of Dissipation Panels for Seismic Retrofitting of Historic Buildings

In the reconstruction of Lisbon after the devastating earthquake of 1755, an innovative structural solution was implemented. The historic timber framed masonry walls represented then a structural key element regarding seismic action. As often as not the buildings that incorporated these seismic resistant walls require interventions in respect of their original structure, re-establishing or enhancing the seismic behaviour. Innovative Dissipation Panels for seismic retrofitting are under development. The design of the Dissipation Panels was based on the role of the historic timber framed masonry walls as well as on the incorporation of the quite recent seismic protection systems, which reduce damage and limit losses more effectively than the traditional approach. The new technology was designed to improve the energy dissipation capacity of the buildings associated with seismic actions whilst preserving and respecting their original structural concept and, therefore, their authenticity. Full scale prototypes of the developed Dissipation Panels were produced and tested in order to characterize its cyclic behaviour. Experimental characterization of the dynamic behaviour of the conceived prototypes show good energy dissipation capacity.

Raquel Paula, Vítor Cóias, Luís Guerreiro

Pombaline Buildings—Consequences of Some Rehabilitation Interventions

The Pombaline buildings of downtown Lisbon have undergone some forms of adulteration across time with a greater impact in recent years due to an increase in tourist activity. After the great earthquake of 1755, this area has been rebuilt according to an innovative, enlightened urban plan. The buildings have been built in a short period of time using a standardization and prefabrication system and also an innovative anti-seismic technique—the “Pombaline cage”—which was an unparalleled Portuguese contribution to construction technology and anti-seismic engineering. The recent conversion of historic buildings in hotels has led, in many cases, to total internal demolition while maintaining the facade in its original condition. This solution is not recommended in the case of historic centres because the maintenance of the internal structure and original materials of buildings is crucial to protect its authenticity. It may also undermine the performance of buildings throughout the quarter in the event of a major earthquake. This paper describes the original structure of a Pombaline building and the major alterations that these buildings have undergone as well as the implications on their overall performance in the event of an earthquake.

Jorge Mascarenhas, Lurdes Belgas, Fernando G. Branco

Experimental and Analytical Assessment of the Capacity of Traditional Single Notch Joints and Impact of Retrofitting by Self-tapping Screws

The joints are the most crucial parts of a timber building and determine the overall structural behaviour, load-bearing capacity and failure mechanisms. Therefore, keeping the joints fully functional is of utmost importance to ensure a desired structural performance of timber buildings under various actions. Since replacement of damaged parts of an existing structure is expensive and in many cases very difficult to perform in situ, retrofitting to avoid failure becomes an increasingly widespread strategy. In this paper, the capacity and failure mechanisms of single notch joints before and after a simple retrofitting intervention by means of self-tapping screws were investigated. To this end, a series of tests were carried out during the 5th COST FP 1101 Training School, held in University of Minho, Portugal. The joints were first tested under compression, and the load-bearing capacity values obtained at the end of tests were compared to the capacity values calculated using theoretical models proposed in a variety of national codes. Then, tested joints were retrofitted using self-tapping screws. The retrofitting strategy aimed to prevent failure mechanism that was shown to dominate joints’ behaviour in the unreinforced state, rather than to increase the load-bearing capacity or stiffness. The impact of retrofitting on the joints’ performance was discussed and the success of the proposed intervention was further debated.

Karel Šobra, Richard de Rijk, Yasemin D. Aktaş, Coralie Avez, Isabela Burawska, Jorge M. Branco

Repairing of a Timber Truss Through Two Different Techniques Using Timber Elements and Screwed Metal Plates

Structural reinforcement of timber buildings may be needed due to different reasons such as change of use, deterioration due to lack of maintenance, exceptional damaging incidents or loading, after changes in regulatory specifications, or interventions to increase structural resistance. In this work, two different techniques were considered for repairing a timber truss that was previously assessed on laboratory (test facilities of University of Minho) and taken up to failure during a load-carrying test. A collar beam truss, with more than one hundred years, was tested considering a vertical point load on each main rafter. Failure of the timber truss was located in the sections of the rafters near the loading positions by bending. Repairing techniques, based on the use of timber elements for one of the rafters and on screwed metal plates for the other rafter, were evaluated and compared to the original unstrengthened condition. The efficiency of the combined repairing techniques was evaluated taking into consideration the structural performance of the collar truss, namely its displacement and ultimate load capacity. In this paper, the results of the experimental tests are discussed attending to the analytical calculation of the contribution of the repairing techniques. Also, the different failure scenarios, for original and strengthened truss, were analyzed and compared.

Daniele Cibecchini, Niclas Bjorngrim, Hélder S. Sousa, Marco Jorge, Jorge M. Branco

Stiffness of Prosthetic Repairs for Historic Timber Beams

Glued connections are often used as reinforcements or repairs of decayed parts in historic timber frames. Those timber frames are most of the time statically indeterminate structures, meaning that the ratios of stiffness between different members and joints of the structure are related to distribution of stresses within the structure. Hence, a poor repair, i.e. a too stiff or at the contrary a too flexible intervention may change dangerously the distribution of stresses within the structure, induce cracks and damage the whole structure. However, there are still no guidelines on how to evaluate the stiffness of glued connections and therefore, on how to predict the impact of these interventions on the force distribution in the timber frame. This paper focuses on glued-in rods, and uses finite element models to predict and compare the stiffness of glued-in rods in different configurations of repairing connections. This study shows sensitively different axial stiffness between those configurations: they may indeed vary in the ratio of one to two for the same strength. This highlights the importance of predicting the stiffness of glued-in rod connections to be able to make recommendations for the configuration which best respects the original structure.

Coralie Avez, Thierry Descamps

Consolidation of a Collar Truss with a Steel Cable System

Post-tensioning techniques for strengthening existing timber elements have been used throughout history with excellent results. Former applications on wooden trusses have already shown some of the advantages of such a consolidating system, but very few tests were performed on the topic. During an experimental campaign, a full-scale historical timber truss was deeply analysed and tested in its original (unreinforced) condition, reaching a considerable level of damage. It was later repaired with a steel cable system, using prestresses to recover the structure bearing capacity, and tested again. The results show that the repair allowed a recovery of at least the 80 % of the ultimate load-carrying capacity. The complete failure was not achieved, but it is likely to be presumed that the structure could have regained the totality of its strength. The data acquired in both tests were later compared in order to understand in detail the behavior of the truss.

Giacomo Crivellari, Jorge M. Branco

A Timber Roof Structure for the Milreu Rural House Rehabilitation

Under the European Union (EU) support programs, the Portuguese heritage agency carried out several actions to develop archaeological sites with adequate infrastructures to be integrated into leisure routes. The archaeological site of the Milreu Roman ruins is located in the southernmost province of Portugal—the Algarve, near the small village of Estoi. This village is in the central Algarve region, 10 km north of the city of Faro and the coastline. Archaeological excavations conducted in the late XIX-th Century, by the archaeologist Estácio da Veiga showed the existence of both a roman Villa and a temple dedicated to the cult of water. Among other constructions on this site, a medieval rural house was built some centuries ago over the existing Roman ruins. In the 1950s, the German Archaeological Institute also excavated this location discovering unique Roman artifacts and archaeological structures (mosaic floors, masonry walls, water tanks, roman baths). In the mid-1960s, the Ministry of Public Works—Historical Monuments and Buildings Division (M.O.P.—D.G.E.M.N.) carried out a safeguard program to protect the XVI-th Century Rural House by installing a reinforced concrete (RC) roof system over the existing masonry walls. Several decades after the intervention, extensive deformations occurred followed by severe wall cracking. The proposed rehabilitation strategy for this rural building used traditional building techniques to provide an adequate rehabilitation standard. The RC roof was dismantled and removed, and it was replaced by a traditional timber roof, which resulted in a large decrease in the dead load (DL) mass, and reduced the seismic risk of this historical building.

Jorge N. Bastos

Design and Maintenance of a Long-Span Timber Roof

The historical Citadel of Almeida is located in the northeast part of Portugal, near the Spanish border and close to the town of Ciudad Rodrigo. This geographical location makes this region the natural entrance gate of invading armies to access the heart of Portugal and trying to reach the capital town of Lisbon. Therefore, the Portuguese border region has several military fortresses and, probably, the most unique one is twelve-point granite star of Almeida. Under a EU program to re-vitalize historical villages, the horse-riding school building (the manège) restoration project received the largest financing grant, in Phase 1, reaching 2.25 m Euro. Due to the lack of business investments, the hinterland Portuguese regions have shown during the past three decades a continuous population decrease and a migratory flux into the coastal regions, or even to other countries. The main purpose of this EU program is to help attracting new residents to these interior regions and to maintain the current residents in their locals with adequate business activities. The rehabilitation of several historical landmarks helps to provide a local sense of identity and improved living conditions by installing better infrastructures (electrical power, water supply and sewage treatment plants, telecommunication systems). Within these general program objectives, the leisure activities are one of the best “attractors” for tourism. The rehabilitation of the Almeida manège is integrated into the combination of three major guidelines: (a) historical heritage; (b) tourism and economy; and, (c) leisure activities. The designer rehabilitation criteria was: (1) to use a traditional timber solution, e.g., a scissor’s type truss; (2) to use improved joint connections, e.g., split rings; (3) to carefully detail steel supports and connections; and, (4) to innovate as required by the architectural functional program. After more than sixteen years under continuous use, the manège ensemble built in the Citadel of Almeida with extensive use of timber material can still be considered both an aesthetically sound, cultural enriching, and economically feasible rehabilitation solution to be enjoyed by all kinds of visitors.

Jorge N. Bastos

Timber Structures

Frontmatter

Assessment of the Mechanical Characteristics of Timber Floors Through Simple Dynamic Identification

The non-destructive in situ characterization of timber floors is difficult and may involve expensive procedures, such as loading tests. Alternatively, it is possible to estimate some mechanical properties by assessing the characteristics of timber beams through sonic or penetration tests (e.g. pilodyn and resistograph); however, the existing correlations are still not very reliable. Thus, this project aims assessing the characteristics of timber floors using dynamic identification procedures, a simple and low cost technique when compared to loading tests. In particular, and through the identification of the main frequencies, this research aims estimating the mechanical behaviour of timber floors, including the characteristics of the beams to walls connections.

José Coelho, João M. Guedes, Bruno Silva, Tiago Ilharco

Assessment of the Mechanical Behaviour of Tabique Walls Through Experimental Tests

The option for substituting timber structures by other materials when renovating old constructions often leads to more invasive solutions, less compatible with the existing structure, being often the cause for more damage. On the contrary, low invasive procedures, such as preservation actions, generates more sustained and respectful interventions, closer to the recommendations expressed in international charts and documents. However, such procedure simply having a good knowledge on the materials (properties and characteristics) and behaviour of the elements (mechanical, static, dynamic, long term, short term…). The present research aims contributing to this knowledge, by assessing, experimentally, the compression mechanical behaviour of a particular type of timber walls commonly found in old masonry constructions in Portugal and referred to tabique walls; the lack of data on the behaviour of this type of walls is probably the main reason why interventions quite often consider their full substitution by new elements. The work consisted on constructing 4 full scale specimens that were tested at the Laboratory of Earthquake and Structural Engineering of the Faculty of Engineering of Porto University to assess the compression strength and behaviour of these elements under no initial damage conditions. The results were also compared to numerical simulations using SAP2000 software.

Andreia Rebelo, João M. Guedes, Bruno Quelhas, Tiago Ilharco

Robustness Assessment of an Ancient Timber Roof Structure

During the last decades, it has become a usual practice to replace ancient timber roof structures by concrete or steel roof structures. Despite the durability of ancient timber, the lack of knowledge about how to reinforce or retrofit timber structures may have resulted in their disuse. However, the main reason may be attributed to the difficulty in assessing the real condition of timber frames while respecting the level of conservation. Within that scope, two timber collar trusses dating back to more than a hundred years were transferred from the Laboratório Chimico in Coimbra (Portugal) and tested up to failure in the structural laboratory of the University of Minho. According to the test results using non-destructive techniques, it was possible to develop different probabilistic analyses considering both exterior and residual cross-sectional dimensions. In this work, a robustness assessment is performed considering the spatial distribution of the strength of timber elements and also the variability of the stiffness of the connections. Permanent loads, snow load and wind load variability were considered for the structural safety analysis according to the provisions of the Joint Committee on Structural Safety. The robustness index was obtained based on the reliability indices of the intact and damaged roof structure, considering the geometric variation obtained for the exterior and residual cross sections respectively. Crude Monte-Carlo simulation method was used here to estimate the probabilities of failure of the structural system. The comparison between different imposed damage scenarios covering loss of bearing capacity of connections and timber frames is finally presented.

Leonardo G. Rodrigues, Chrysl A. Aranha, Hélder S. Sousa

FP1101 and RILEM TC 245 RTE Training School on Assessment and Reinforcement of Timber Elements and Structures: The Role of the Academic Community in Disseminating Knowledge

In the past decades, timber has been considered as a secondary construction material owing to the emergence of other materials such as concrete and steel, and as a consequence a large amount of knowledge on how to use timber has been forgotten or even lost. This has led to badly designed interventions on timber structures, which have misinterpreted the past structural solution and led to significant structural performance problems. However, the European research community has made a significant effort towards the dissemination of knowledge regarding the design and assessment of timber structures. Within that scope, COST FP1101 had the objective of increasing the acceptance of timber in both the design of new structures, as well as in the repair of old buildings by developing and disseminating methods to assess, reinforce and monitor them. To that aim, FP1101 and RILEM TC 245 RTE in collaboration with the University of Minho (Portugal) organized a Training School (TS) on the assessment and reinforcement of timber elements and structures during 11–14 May, 2015. The training school had the objective of disseminating knowledge to young researchers, as well as to others interested in wood and timber construction and the rehabilitation market. During the TS, several experts provided information on the assessment of existing timber structures, visual grading, interventions on heritage buildings and on analysis, repair and reinforcement of traditional and dowelled timber connections and structures. Also, full-scale tests on an old timber trusses and on connections were made examining both the original conditions and post failure reinforcement. This work presents the different areas of knowledge that were scope of that training school and its main achievements on the dissemination of knowledge to young researchers and other interested groups.

Jorge M. Branco, Hélder S. Sousa, Eleftheria Tsakanika, Marco Jorge, Paulo B. Lourenço
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