Mariapaola Riggio

Refurbishment of a Traditional Timber Floor with a Reversible Technique: Importance of the Investigation Campaign for Design and Control of the Intervention

The strengthening and stiffening of traditional timber floors with the addition of timber planks and the use of dry connections falls into the category of “traditional” repair methods. Nevertheless, a high degree of innovation and scientific/industrial research is implicit in some modern applications of this type of intervention. If newly developed systems are to be satisfactorily adopted to repair ancient structures, their effectiveness and reliability need to be adequately evaluated. The study highlights the importance of investigation actions for the design, calibration, and control of intervention in the restoration of heritage structures. On the occasion of the adoption of an innovative timber-to-timber strengthening technique for the rehabilitation of a traditional timber floor in a mediaeval castle in Italy, a thorough investigation was carried out. Tests were performed in situ on the structural elements, in both the original and the repaired condition, and the results were compared with those obtained in the laboratory on a dismantled member. Despite some differences between the experimental conditions on site and in the laboratory, the two testing campaigns showed a good agreement of results. In particular, an increase of more than four times the effective bending stiffness was achieved, in both cases, after repair.

Typological and Structural Authenticity in Reconstruction: The Timber Roofs of Church of the Pieve in Cavalese, Italy

In case of exceptional or accidental destructive events (e.g., earthquakes, floods, fire), the advisability of completely reconstructing a vanished artifact may be questionable. Among the possible approaches for reconstruction, the so-called philological method allows the complete reading of the whole building. Analogous to the study of literary texts, this method is based on the analysis of the “architectural language” of a building that is its form and its technical characteristics as well as its structural behavior. This case study concerns reconstruction of the timber roof of the Church of the Pieve in Cavalese (Italy), destroyed during a fire on March 29, 2003, for which the philological approach has been chosen. The design process consisted of two important phases: first the determination of the precise form of the original roof, by considering different kinds of evidence, then the introduction of necessary modifications, to meet the present-day structural standards. Such design choice, far from being a simplistic solution, involved the participation of different experts and a thorough multidisciplinary investigation.

Characterization and Monitoring of Surface Weathering on Exposed Timber Structures With a Multi-Sensor Approach

The goal of this work was to understand and model the combined effect of time, geographical location, and exposure on the physical–chemical mechanisms of wood weathering in structures. Series of wooden samples were exposed to natural weathering in seven locations varying in climatic conditions, including Italy and north Germany. The set of samples was exposed for 4 years, collecting representative samples each year. Four exposure directions (north, south, east, and west) were investigated. Measurements of samples included: photogrammetry, near and mid infrared spectroscopy, color, gloss, roughness, and elemental composition (x-ray fluorescence spectroscopy). Results showed that the surface degradation mechanisms caused by weathering were affected by the site of exposure. The wood samples weathered in the Italian sites, in Udine and Macerata, were most degraded. The most significant changes were observed in samples exposed to the south direction. The original algorithm for calculation of “the weathering indicator”, by merging the multi-sensor data and linking these to the surface performance indicators was developed. Finally, the subjective visual assessment by the expert person was compared with parameters obtained by measuring the weathered surfaces with various sensors. A good correspondence between weathering indicator Wind and subjective quality index was established.

Non Destructive Characterization of Wooden Members Using near Infrared Spectroscopy

On site characterization of wood members is a very challenging task, after considering all the variables affecting the whole structure itself and material used for construction. The up-to-data procedures are limited to few characterizations, and in general based on visual assessment supported by local drilling resistance analysis, stress-wave time of flight measurement and/or moisture content estimation. The goal of this work was to promote near infrared (NIR) spectroscopy as a supplementary tool providing additional information for the expert assessing timber structures. The paper presents several examples of successful NIR application in species recognition, physical properties prediction, evaluation of wood weathering and/or fungal degradation level. However, it must be stated that implementation of NIR in routine assessment protocols requires prior preparation of a dedicated databases of high precision reference values to build reliable, flexible and sufficiently generalized models.

Morphology-based macro-scale finite-element timber models

This paper presents a non-invasive technique that can extract an accurate geometrical description of growth layer surfaces in wood. The method has been validated for sawn spruce elements (Picea Abies Karst.). The aim is to implement a procedure to model domain geometry in the numerical analysis of wooden elements, taking into account the intrinsic variability of the material. The approach presented by the authors avoids internal imaging and achieves a digital 3D model of growth layers, using, as input data, images of the ring pattern, which represents the growth surface boundary curves, visible on all the cut faces of the wooden element.

Monitoring of Wood Decay by near Infrared Spectroscopy

Wood as a natural resource is subject to continuous degradation by means of different environmental agents, where fungal decay is one of the main factors affecting timber structure elements. The goal of this work was to monitor and model effects of fungal growth on the chemical-physical properties of Norway spruce (Picea abies L. Karst.). The spectra of wood samples were obtained with near infrared spectrometer and subjected to chemometric analysis. It was found that the white root fungi (Trametes versicolor) affected spectral bands related to lignin and also hemicelluloses. Brown root fungi (Postia placenta, Coniphora puteana, Gleophyllum trabeum) exhibit spectra deviations mostly in the regions related to carbohydrates. However, it was evident that the degradation efficiency of Coniphora puteana was the highest among all the investigated fungi. It was possible to classify the wood samples to clusters separating the investigated fungi. Accordingly, different effects on the strength loss of the wooden members can be identified. It was shown that near infrared spectroscopy has a great potential for in-field assessment of the fungal degradation of wood.

A Multi Sensor Approach for Prediction of Weathering Effects on Exposed Timber Structures

The goal of this work was an attempt to understand and model the combined effect of time, geographical location, exposition, and coating type on the physical-chemical mechanisms for wood weathering in structures. A series of wooden samples non coated and coated with top industrial coating has been exposed to natural weathering conditions in seven locations varying in climatic conditions, including whole Italy and southern part of Germany. The set of samples has been exposed for four years, collecting representative samples each year. Four exposition directions (North, South, East and West) were investigated. All the samples have been collected from the field site and stored in a dark and conditioned room including non-weathered reference samples. Measurements of the samples included: photogrammetry, near and mid infrared spectroscopy, color, gloss, roughness and elemental composition (X-Ray Fluorescence spectroscopy). Such a wide set of information collected has been used for investigation of the collective effect of the above mentioned variables on the surface properties of timber structures exposed to weathering. A dedicated algorithm has been tested for modeling the exposure time and service life prediction.

Novel Nail-Like Wood Connectors

In traditional timber structures, hardwood connectors such as a nails, wedges, dowels and pegs have been used as reinforcement of carpentry joints or to fix wooden ceiling matts or floor boards. In the study reported, the possibility to rely on enhanced mechanical and technological properties of densified wood, for the production of wooden nails to be used in the repair of traditional timber structures is discussed. The wood used for connectors were domestic wood species; ash, beech, black locust and poplar. Wooden blocks were exposed to densification procedure with the purpose of increasing the materials density, dimensional stability and possibly, improve durability and selected mechanical properties. The densification ratio varied between 50 and 67%. A dedicated research has been performed in order to determine the effect of densification on the compression behavior of wood in the form of nails. The progress of pushing force during insertion of the wooden nails into wood samples was also monitored and served for insertion process control. A preliminary series of push-out tests have been carried out on timber-to-timber joints assembled with the densified nails.The results obtained show potential for using the novel wooden nail connectors for substitution or integration repair works in traditional timber systems.

Comparison of In Situ and Laboratory Testing for the Characterization of Old Timber Beams before and after Intervention

In this paper an investigation campaign, carried out in occasion of the restoration of a timber floor in the Belasi Castle (Trentino, Italy), is reported. In order to validate a testing procedure for the calibration and control of an innovative wood-wood strengthening technique, results of tests performed in situ on the structural elements, in both the original and the repaired condition, have been compared with those obtained in laboratory on some dismantled beams. For the characterization of the material decay, both local mechanical and global vibrational testing have been carried out. For the mechanical characterization of the beams, before and after repair, direct static bending tests have been performed, with distributed loads, on site, and according to standard four-points loading schemes, in laboratory.

Assessment of Historical Timber Structures: Select Papers from the Second International Conference on Structural Health Assessment of Timber Structures (SHATIS13)

Stone is considered the “classical” material of architectural heritage, the material of cathedrals and castles, of ancient Greek temples and Asian mausoleums. Somehow the commonplace is that stone, and masonry in general, is more durable than timber and that timber structures have a more vernacular character than the monumental stone based architecture. In the past decades however, interest in conservation of the architectural timber heritage has steadily increased and contributed to a more balanced view of the importance of historic timber architecture. The successful conservation of timber structures requires the concerted effort of many different specialisms, from wood scientists, to structural engineers, craftsmen knowledgeable of traditional carpentry, architects and conservators, environmental scientists. It is necessary to examine the original and actual structural behavior and soundness of the timber structure, identifying the wood species, understanding and quantifying decay and ageing phenomena, assessing damage and deformations, and evaluating residual global and local structural capacity. By understanding nature, extent and causes of failures, damage and vulnerabilities, the best course of action for preservation, conservation or strengthening can be determined. A substantial body of knowledge has been developed since the ICOMOS International Wood Committee (IIWC) was first established in 1975. This knowledge has progressed alongside an ever-increasing interest in modern timber structures as a more sustainable option for the construction industry. The convergence between the rediscovery of traditional methods and the development of robust engineering approaches to the design of timber structures has created a unique environment for the development and dissemination of reliable and comprehensive approaches to the assessment and repair of exiting and historic timber structures. It is our pleasure to be the Guest Editors for this Special Issue of the International Journal of Architectural Heritage. Planning for the Issue began in Autumn 2013, with the aim of selecting high-quality articles focusing on the assessment of historical timber structures among the ones presented at the Second International Conference on Structural Health Assessment of Timber Structures (SHATIS13), which took place from September 4 to 6, 2013, in Trento, Italy. The conference was a great success, under the chairmanship of Professor Maurizio Piazza from the University of Trento, in collaboration with the Trees and Timber Institute of the National Research Council of Italy and the COST ACTION FP 1101 Assessment, Reinforcement and Monitoring of Timber Structures. This special issue provides a significant insight in the challenges and advances in the assessment of historical timber structures and indicates diverse procedures and tools that can assist the conservators and engineers in formulating reliable diagnosis about their current state of conservation, their safety and the need for intervention. The assessment of timber structures is based on a multi-stage, interdisciplinary approach that involves different levels of analysis, from the identification of the material of each timber member and connection to the analysis of the overall structural system. The selection of papers collected in this issue reflects the most important steps of this cognitive process: