Historic Timber Research Articles

Diagnosis and assessment of a historic timber structure in La Casa del Corregidor, using non-destructive techniques

This paper presents the assessment of the timber structure of “La Casa del Corregidor” building, a singular historic building in Cuenca (World Heritage City). The building is scheduled for restoration in the near future. The study made use of both non-destructive (NDT) and semi-destructive (SDT) techniques.A thorough experimental campaign and inspection were conducted on all the old wood elements across the eight floors of the building. More than 1200 elements of Pinus sylvestris L. wood were inspected. The data collected in this campaign allowed a mechanical evaluation of the timber elements.The following NDT and SDT were used: visual inspection, microphotography, moisture meter, stress-wave measurements, and resistance drilling. These techniques made facilitated the identification of the wood species, detection of natural defects and decayed areas, and estimation of the physical and mechanical properties of the timber elements. The experimental results were statistically analysed using a multidisciplinary approach to determine the scope of the intervention on the structure to meet the new use and its structural requirements. The final report produced at the end of the inspection was made of colour plans describing the singularities, natural defects, timber decays and damages of each single member.The results obtained will orient the building's conservation work. These findings support a minimal intervention, since more than 95 % of the structural elements were found to be in good condition.

Reconstructing the oaks’ growth patterns in Greece with the use of historical timber: Case studies from Western Peloponnese

Southern Greece is a region where available oak reference chronologies are still missing, making dendroarchaeology and dating of historical buildings rather challenging, if not impossible. In the current study we performed wood identification and dendroarchaeological analysis on timber from three historical buildings: the castles of Androusa and Koroni and the Church of Agios Dimitrios, in Western Peloponnese. The three monuments represent buildings of different uses covering different periods, but also sharing a common characteristic: oak was the only timber used in their construction, while the number of preserved timber elements is very limited. A dendroarchaeological examination of these three historical buildings, together with radiocarbon and wiggle-matching analysis, provided valuable chronological information for the local archaeologists, historians, and other scientists. Application of dendrochronological techniques has helped place the three buildings under study into the Ottoman period. Our results also show that timber was acquired most probably from local non-managed forests, which suggests that oak forests were present in the broader area at least from the late 15th to the first half of the 18th centuries. The discordance between dendrochronological and radiocarbon dates in one of the three cases highlights the need for further exploration of the study area through a combined implementation of both dendrochronological and radiocarbon dating analyses in order to develop well-replicated local oak chronologies. Our study also shows that dendroarchaeology can contribute significantly to the cultural and landscape history of Western Peloponnese even with an examination of limited number of preserved timber elements from historical buildings.

Saving a 15th-century nave roof from structural collapse at the Abbey Church of St Mary and St Melor, Amesbury, Wiltshire

This paper looks at the technical and practical challenges faced during the conservation repair of a large 15th-century trussed roof structure of a Grade I listed church building. Urgent repairs were required after a section of ceiling plaster fell, after years of water ingress, resulting in tight programme and budget constraints, with the added pressure of a global pandemic. The paper describes the early stages of the contract, with surprising discoveries such as a hive of over 40,000 honeybees, bat roosts, a secondary roof structure, concrete and extensive deathwatch beetle decay. The engineer’s economic solutions to complex structural problems are explained, as well as architect designed details to address ongoing causes of decay, such as new ventilated eaves and ridge details. This paper sets out to describe how technical challenges were overcome, but also explains how opportunities were taken to introduce new oak carvings and lead details, to leave a legacy and add to the historic narrative of the building. This paper will be of particular interest to anyone working on ecclesiastical or listed building structures, where there has been a history of poor maintenance or previous repairs. It should offer technical information relating to a wide range of traditional building trades, but particularly structural repairs of historic timber structures.

The deterioration state and degradation mechanism of historical timber structures from the Yunnan Military Academy

ABSTRACT Wood structural timbers at three locations (eave, beam frame, and column) were exploited to elucidate the deterioration state and mechanism of historical timber structures from the Yunnan Military Academy (Kunming, Yunnan Province). The morphological structures, physical and mechanical characteristics, and chemical components were measured to illustrate the deterioration state and elucidate the degradation mechanism. The results demonstrated that the deterioration of structural timbers was closely dependent on their locations in the architecture. The outside eave was in the worst deterioration state, which was caused by natural factors (ultraviolet rays, rain, and fungi), resulting in severe distortion of wood structures and a significant reduction in basic density and compressive strength. Significant carbohydrate losses that occurred in the eave and beam frame were mainly contributed by the brown rot fungi, predominantly due to the frequently wet condition and humid environment. Moreover, column structures were mainly attacked by insects (weevils) due to their location near the ground, accordingly in an obvious decline in mechanical properties. Collectively, structural timbers exhibited different deterioration states contributed by the degradation mechanism, predominantly influenced by their locations in architecture.

Seismic performance of a historic timber structure on a slope

In southwest China, a seismically active zone, most of the historic timber buildings are built on slopes. To ensure the structural safety of these heritage buildings, this study aims to determine the dynamic characteristics of a typical historic timber building on a slope and investigate further its seismic performance using the multi-scale model based on the principle of equal work done. The in-situ dynamic test revealed that the first and fourth-order frequencies of the Erwang temple range from 3.079 Hz to 11.265 Hz, and the first and third-order mode shapes are translational along the perpendicular to the slope direction and along the slope direction, respectively. The time-history analysis of the Erwang multi-scale model indicates that the area of interaction between the tenon and mortise exhibits plastic behavior and that the irrecoverable deformation in the tenon is more severe, while the column and beam remain in the elasticity. The irregularity in the heights of the columns causes an abrupt change in the inter-storey drift angle in the third floor along the slope, and the base shear force value of the column foot in the upper embedding end is the largest. The maximum value of the inter-storey torsion angle of the Erwang temple is found at the upper embedding storey. Therefore, the upper storeys of the building is its weakest region and should be given priority in seismic strengthening.

Comparative Analysis of the Seismic Performance of a Full-Scale Historical Timber Structure by Numerical Simulation and Mechanical Test

ABSTRACT In order to accurately use numerical analysis results to evaluate seismic performance, a quantitative relationship between the parameters of the ideal finite element model (FEM) and full-scale test model (FTM) of historic timber structures must be established. In this study, a single-story full-scale timber structure with four columns and Dou-gongs that was common during the Song dynasty of China (A.D. 960–1279) was taken as the object, and pseudo-static test (or simulation) analysis was carried out on the FTM and the corresponding FEM. The numerical model was consistent with the test model in terms of the structural deformation pattern and stress characteristics of the key nodes. The key-point loads of the skeleton curves, stiffness ratio, ductility coefficient, and stiffness relationship were quantitatively established for the two models. Accordingly, approximate formulas for the above relationships were proposed.

Historic timber roofs, a knowledge-based approach to strengthening: the case study of a Renaissance palace in Ferrara

Knowledge is essential to preserve timber roof structures for their historical and architectural value, since it allows to fully understand their cultural significance and actual structural behavior, thus planning specific strengthening interventions. This paper presents the case study of Palazzo Costabili in Ferrara, Italy, to propose a method to plan architectural strengthening intervention on historical timber roof structures based on a detailed knowledge of the structures’ features and state. The palace object of this study is characterized by historical timber structures, an expression of traditional local building techniques, which were partially damaged in the 2012 earthquake. Therefore, an in-depth and careful study of the structure was carried out to identify specific parts that needed to be reinforced. A strengthening of the roof structure was thus designed considering the performances of the timber components and their historical-cultural value. More specifically, the timber roof was first assessed to identify the main wood species, the constructive types, and their related vulnerabilities. At the same time, the parts that showed consistent signs of structural stress were later evaluated by specialists using visual and instrumental analysis. Finally, data collected were critically analyzed to better plan the strengthening intervention, considering both the stress state of the single components and their specific weaknesses, in full compliance with preservation criteria and needs.

Reinforcement methodologies of timber elements in historic timber roofs

This paper aims to present a comprehensive review of the reinforcement of historic timber roofs, focusing on their main characteristics, advantages, and disadvantages, which would help professionals select and define the design of reinforcement solutions. Cultural heritage issues are taken into consideration. Reinforcement can be done via different methods – traditional and modern – using simple or sophisticated techniques. An overview of the main materials and the techniques used for selected case studies are presented, illustrating how various reinforcement methods are implemented in practice.

Learning from tradition: a case study of the diagnosis, dendrochronological dating, and intervention on a 16th-century timber roof structure in the western Italian Alps

The paper presents a significant case study: the Church of San Giovanni Battista in Salbertrand dates back to the 16th century and constitutes one of the most interesting examples of religious architecture in the Susa Valley of the western Italian Alps. Its historic timber roof structure was once at risk of demolition, but in 2000 finally became the object of necessary preservation and reinforcement works. Here, the interdisciplinary studies carried out for the diagnosis and assessment of the state of conservation are presented, starting with the identification of the wood species used, the geometrical survey, the visual and NDT diagnosis of the timber elements, and the structural evaluation. A special section is dedicated to the dendrochronological analysis, with a comparison of different case studies regarding larch roof structures of other historic architectures located in the northwest of Italy. The tree-ring sequences obtained from the buildings presented have also been used to define a larch chronology of the Susa Valley in Piedmont. Following the first assessment phase, a second phase involved defining the restoration and reinforcement interventions. The reinterpretation of historic craftsmanship rules and traditions, which already contemplated the use of steel devices, attempted to offer alternative design solutions. This reinterpretation constituted the basis of the reinforcement interventions carried out in Salbertrand in the early 2000s. This paper highlights the importance of learning from historical treatises, showing how, even in modern reinforcement interventions, the application of traditional carpentry rules can achieve the aims of preservation and structural efficiency with overall cost-effectiveness and durability, resulting in a favorable balance between tradition and innovation.

Remarkable historic timber roofs. Knowledge and conservation practice Part 2 - Investigation, analysis, and interventions

Remarkable historic timber roofs. Knowledge and conservation practice Part 2 - Investigation, analysis, and interventions

HBIM-Based Decision-Making Approach for Sustainable Diagnosis and Conservation of Historical Timber Structures

Historical timber roofs play a significant role in architectural heritage, as listed in the World Heritage List protected by UNESCO. Despite their complexity, they are frequently lacking in maintenance, with the consequence that only a few original examples have been preserved until today, contradicting the principle of minimum intervention. In the paper, a decision-making approach has been proposed for the best and most sustainable solution, in which tradition and innovation meet to achieve the maximum quality with minimum intervention. With an emphasis on sustainability (environmental, economic, technological, historic, and social), analyses have been carried out in order to compare various intervention alternatives, modeled in a Heritage-Building Information Modeling (HBIM) environment, assessed using the Analytical Hierarchy Process (AHP), and implemented with the multi-criteria Modelo Integrado de cuantificacion de Valor para Edificacion Sostenibles (MIVES) methodology. The case study is the roof of the Michelangelo Cloister in the Diocletian Baths in Rome, which is a significant example of historical timber roofs. The results are given in terms of a quantitative sustainability index SI, which takes into account different alternatives of intervention, including the task of diagnosis.

Probabilistic Models for Temperature-Dependent Compressive and Tensile Strengths of Timber

Reliable reduction factors for timber mechanical properties at elevated temperatures are needed to design timber structures for fire safety as well as to assess the safety of historic timber structures against fire hazards. In this paper, a compilation of the available data on the compressive and tensile strengths of timber at elevated temperatures is carried out. Then, a probabilistic modeling approach to predict the temperature-dependent reduction factors applicable to fire design is proposed. The collected data cover both solid and engineered timber at temperatures from 20°C to 300°C, with a variety of sample sizes, wood species, test protocols, and moisture content used in the experiments. The data revealed a large scatter in elevated temperature strengths, and a large conservativeness of the relationships of the current European standard, which is commonly used for the advanced design of timber structures under fire. To address this variability, multiple probability density functions were calibrated across the temperature range, quantifying the goodness of fit with statistical criteria. Two-parameter Weibull functions provided the best fit, and continuous temperature-dependent relationships were derived for the parameters of the distribution. The proposed probabilistic models can be implemented in a numerical code, facilitating their use in analytical and computational approaches, and can be applied to the probabilistic assessment of the structural performance and reliability of timber structures against fire.

A novel approach for modelling a historic timber roof

ABSTRACT Værnes church is one of the oldest mediaeval stone churches with the original wooden roof in Norway. The roof is made of several crossed layers of wooden boards connected with a large number of wooden dowels and has stood for centuries, but there are visible deformations in the lower parts of the structure. In this work, finite element models of the roof are presented in an attempt to characterise the behaviour of the wooden connections in the diaphragm. Two main scenarios are discussed: a first scenario that takes into consideration only the frame with line loads, considering the wooden boards merely as loads and a second scenario where the wooden boards are considered collaborating planks that influence the behaviour of the structure. As result of the work, it is possible to state that the wooden planks provide a stiffening effect, distributing the load on the gable walls. .

Modal parameter identification and seismic assessment of historical timber structures under near-fault and far-fault ground motions

Timber, one of the oldest structural materials, is an essential material in the construction of traditional structures due to its undeniable advantages. However, wood is sensitive to environmental effects, and hence, historical timber structures experience various degradations and destructions during their service life. This highlights the necessity of investigating the structural responses of such structures using experimental techniques and calibrated finite element models. This paper presents vibration-based system identification of two historical timber structures and an in-depth comparison of the effects of near-fault and far-fault ground motions on seismic responses. Ambient vibration tests were carried out using the operational modal analysis method. Enhanced Frequency Domain Decomposition and Stochastic Subspace Identification methods were used for experimental modal parameters estimation. Also, the initial finite element models were calibrated considering the ambient vibration test results to correctly assess the seismic responses of the selected structures under near-fault and far-fault ground motions. The distributions of maximum amplitudes (displacements, internal forces, and absolute accelerations) under earthquake records with near-fault and far-fault are comparatively presented. All numerical results indicated that both near-fault ground motions and their far-fault counterparts played major roles in terms of the seismic responses of selected historical timber structures. In addition, these results illustrate that both had the potential to increase displacements and, internal forces at load-bearing elements, and leading to notable structural responses and destructive effects.

Seismic performance of timber through-tenon joints with shrinkage flaw in tenon

In several Chinese historic timber buildings, widening flaws in tenon of joints are usually a consequence of weathering and shrinkage. To investigate the impact of flaws on the seismic performance of through-tenon joints (TTJ), cyclic loading tests on four specimens were conducted. The hysteresis, skeleton, energy dissipation and stiffness experimental curves were so obtained. A finite element (FE) model to describe the behavior of such experimental specimens has been then established calibrating the mechanical properties by means of coupon tests. By comparing the numerical simulation results with the experimental results, it is concluded that this kind of damage has less impact on the mechanical performance of TTJs under negative load, while it has a greater impact under positive load. The impact was more noticeable as the length of large head of through tenon increased. The rotation capacity, stiffness and energy dissipation capacity of the damaged joints were significantly lower than the intact ones. The bearing capacity of TTJs with the damage decreased by about 32.4%–38.5%, the energy dissipation coefficient decreased by about 17%–38%, and the cumulative energy consumption decreased by 33.3%–60%.

Mechanical behaviors of Tou-Kung in historic timber structures subjected to vertical load

This paper investigates the mechanical behaviors of Tou-Kung under the action of vertical loads. A 1/3.52 scaled model of intact Tou-Kung fabricated according to the Building Standards of the Qing Dynasty was carried out on vertical loading test. The failure modes, vertical load–displacement curves, and vertical stiffness analysis are analyzed. The results show that the main failure modes of Tou-Kung are the compressive splitting of Da-Tou and plastic compressive deformation of Qiao’s middle part along the radial direction. The vertical load–displacement curves of intact Tou-Kung can be divided into three stages: elastic, plastic, and hardening. In general, the vertical load and displacement of Tou-Kung increases as the loading progresses. And the vertical stiffness increases first, then decreases, and finally increases. On this basis, numerical simulation is used to investigate the effect of overall tilting on Tou-Kung’s mechanical behaviors. It can be found that the tilting of Tou-Kung significantly changes the load transferring path in Tou-Kung, and the stress distribution of Da-Tou and Qiao gradually changes from symmetry to asymmetry as the tilting angle increases. Furthermore, the stress in the embedded area between the Da-Tou and Qiao is the highest, which is consistent with the test results. The vertical load–displacement curves of all damaged FEMs show the same change trend. However, with the increase of tilting angle, the initial stiffness, ultimate load and ultimate stiffness decrease.

Experimental study on compressive behavior of intermediate slender timber columns with local damage and the retrofitting techniques for the damaged columns

The existing historic timber constructions are often affected by local damage such as decay, and their mechanical properties are significantly reduced. In order to explore the influence of local decay on the compression behavior of timber columns, this work conducted experimental investigations of 10 intermediate slender columns with different damaged conditions under axial compression. Damaged areas, damaged positions and damaged forms of the columns were considered. Based on the failure mechanism of damaged timber columns, the retrofitting technique for locally damaged columns using the combination of wood block, profile and carbon fiber reinforced polymer (CFRP) wrap was proposed, compared with the traditional methods of using wood block only, and both wood block and CFRP wrap. Experimental investigations of 10 retrofitted columns with 4 retrofitting techniques were also conducted. The compressive performances and effect among these retrofitting techniques had been compared based on the failure modes and ultimate load-carrying capacity stiffness and ductility. The results indicated that the compressive performance of the damaged columns was significantly reduced which magnified with the increase of damaged area, and the loss of the load-carrying capacity was much larger than the loss of the cross-section area. The load-carrying capacity and stiffness of the damaged columns were appreciably restored by these retrofitting techniques. The load-carrying capacity of the bilaterally damaged column retrofitted by the combination of wood block, GFRP profile and CFRP wrap was the highest, reaching 98.30% of the intact column.

Combining conventional tree-ring measurements with wood anatomy and strontium isotope analyses enables dendroprovenancing at the local scale

Dendroprovenancing provides critical information regarding the origin of wood, allowing further insights into economic exploitation strategies and source regions of timber products. Traditionally, dendroprovenancing relies on pattern-matching of tree rings, but its spatial resolution is limited by the geographical coverage of species-specific chronologies available for crossdating and, in the case of short-distance trades, by scarce environmental variability. Here, we present an approach to provenance timber with high spatial resolution from forested areas that have been exploited intensively throughout history, with the aim to understand the sustainability of the various woodland management practices used to supply timber products. To this end, we combined tree-ring width (TRW), wood anatomical and geochemical analyses in addition to multivariate statistical validation procedures to trace the origin of living oak trees (Quercus robur) sampled in four stands located within a 30-km radius around the city of Limoges (Haute-Vienne, France). We demonstrate that TRW and wood anatomical variables (and in particular cell density) robustly discriminate the eastern from the western site, while failing to trace the origin of trees from the northern and southern sites. Here, strontium isotopic ratios (87Sr/86Sr) and Ca concentrations identify clusters of trees which could not be identified with TRW or wood anatomy. Ultimately, our study demonstrates that the coupling of wood anatomy with geochemical signatures allows to correctly pinpoint the origin of trees. Given the small geographic scale of our study and the limited differences in elevation and climate between study sites, our results are particularly promising for future dendroprovenancing studies. We thus conclude that the combination of multiple approaches will not only increase the accuracy of dendroprovenancing studies at local scales, but could also be implemented at much larger scales to identify trends in historic timber supply throughout Europe.

Seismic safety assessments of historical timber buildings using updated finite element models: Case study of Yingxian wooden pagoda, China

Historical timber buildings are important for the global architectural heritage. However, establishing accurate models for seismic performance evaluations to assess the safety of historical buildings remains challenging. Therefore, simplified simulation methods—the dougong (DG) and mortise-tenon joints (MTJs) based on shear and bending plastic hinges—were developed. Moreover, a model updating method based on multiple degrees of freedom considering the initial inclination was improved to obtain accurate finite element (FE) models. Using the FE model of the Yingxian wooden pagoda in China as an example, the proposed methods were validated against field monitoring measurements. A time history seismic analysis was also conducted on the updated pagoda FE model. The results revealed that the simplified simulation method could accurately and efficiently simulate the plastic behaviors of the DG and MTJs. Furthermore, the model updating procedure reduced the maximum period difference from 9.77% to 2.98%. The maximum story drift ratio reached 1.590% under an earthquake, with a peak ground acceleration of 310 gal; this indicated that the pagoda model described moderate damage; certain components were in a plastic state with a maximum rotation of 0.0427. Notably, this study provides a useful method and a basis for establishing and evaluating models and assessing the seismic safety of historical timber buildings.

Historic timber roofs in Belgium: overview of materials and structures (1150-1960)

Belgium has a remarkable heritage of historic timber roofs that can be traced back to the 12th century. This contribution provides a review of 60 years of research on Belgian timber roofs and outlines their developments from 1150 to 1960. The focus is firstly put on wood resources, a crucial parameter for roof construction in a scarcely forested landscape. Then, the evolution of structural concepts over 800 years is discussed based on illustrations of remarkable roofs. Moreover, this broad overview raises several questions that open up new prospects for future investigations.