Historic Timber Structures Research Articles

Numerical simulation and safety assessment of fires in historic timber structures based on fire load investigation

Historic timber structures face substantial fire loads and complex fire risks. Subsequent renovations and utilization may influence their fire safety performance. Therefore, accurately predicting indoor fire development in historic buildings and assessing their fire safety performance is crucial. Numerical fire simulation is currently at the forefront of analyzing and assessing fire risks in historic buildings. However, there is a shortage of globally accessible historic building fire data. This paper proposes a method to determine fire scenarios, peak heat release rates, and development curves of indoor fires in wooden historic buildings through a fire load investigation. Using the Guangzhou ancestral hall as an example, PyroSim fire dynamics simulation software is employed to calculate fire development and assess the available safe evacuation time. The simulation results are subsequently input into the Pathfinder evacuation simulation software to ascertain the required safe evacuation time for indoor occupants. A comparative assessment is conducted to evaluate the fire safety performance before and after the renovation of historic buildings. The research findings indicate that installing closed glass curtain walls in the courtyards of ancestral hall buildings in Guangzhou accelerates the infiltration of smoke during fires, leading to rapid fire spread and long-distance ignition, significantly reducing the time available for safe evacuation. Therefore, when renovating and utilizing the ancestral hall buildings in Guangzhou, the installation of ventilation and smoke extraction systems should be prioritized to slow down fire development. Additionally, controlling the number of indoor occupants is an effective management measure to mitigate fire damage in historic buildings.

An Analysis of the Fire Performance of Small-Scale Canadian Heritage Hardwood and Softwood

A common consideration in the rehabilitation of historic timber structures is addressing the concerns for fire safety. Heritage structures can have softwoods but depending on the time they were built they may also have hardwoods present. Currently, there is a lack of knowledge on the char rate of heritage hardwood and softwood. This study presents initial findings into the charring of these historic materials as they would be encountered in practice through samples taken from pre-existing aged timber structures in Canada that are greater than 100 years old. The materials were tested in a cone calorimeter following a modified ASTM 1354 procedure. Hardwood samples typically exhibited a faster charring rate than the softwoods but the charring rates converged at 1.05 mm/min when exposed to higher fluxes of 50 kW/m2. As rehabilitation and readaptation may require performance-based approaches such as structural fire modelling, a provisional framework for a numerical model using LS DYNA for historic timber members is presented. The objective is to identify future research and testing areas to develop a higher certainty model. In the a-priori model presented, results showed conservative charring rate results with charring trends seen in the experiment generally being followed.

Comparative Study on Complete Characterisation of Elastic–Ductile Compressive Behaviour of Aged and New Norway Spruce Timber

ABSTRACT Material properties of historical timber structures may change over time due to decay, change of chemical composition of material, biological agents, climatic conditions, etc. Adequate bending performance requires stiffness and strength both in tension and compression, as well as sufficient ductility in compression. While the focus of most research is on the former quantities, the latter one is generally disregarded. This study gives a comparative analysis on complete characterization of compressive behaviour of recent and 60-years-old aged spruce timber (Picea abies). Parallel-to-grain compressive tests on small-sized specimens were conducted to obtain stress – strain diagrams and to determine failure modes. All material properties of stiffness, strength, and ductility were calculated for each specimen. It was concluded that elastic stiffness, elastic limit stress, and compression strength are virtually invariable after sixty years of service while the ductility decreased and the post-peak behaviour became more brittle. It is also found that end-rolling failure mode can yield the same elastic and stiffness properties as the standard kinkband failure. Climatic changes increase the risk of material deterioration prompting for more thorough monitoring and study of historical timber structures.

Holistic Methods of Assessing the Historical Wooden Structure on the Example of the Floor of the Polish Manor House in Tarnowiec

Sustainable development should take into account the conservation and preservation of architectural features characteristic of a given cultural area for future generations. Chemical, physical and mechanical properties of timber components are key to assessing the technical preservation of historical timber structures, defining proper restoration methodology and extending the durability of timber structures. Moreover, this evaluation will help to elaborate assessment criteria to decide between the restoration or replacement of a given antique structure. The article presents a method of assessing a historical wooden structure on the example of an antique decorative wooden floor from the beginning of the 19th century, preserved in the Tarnowiec Manor House. It determines tests and scientific analysis as a tool for a decision of possibilities of further usage of the historical floor structure. We performed tests and scientific analysis by calculating the functional properties of the parquet panels, performing a visual inspection, as well as resistance tests, tests of longitudinal curvature deviation and shape preservation, tests of fungi infestation and its impact on the state of preservation, as well as future perspectives for the use of parquet elements. The results of the evaluation verify that the proposed methodologies are reasonable and will help to elaborate assessment criteria to decide between the restoration or replacement of a given antique parquet.

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.

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.

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.

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.

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.

A review of Scandinavian research on medieval church roofs

The remarkable clusters of preserved high medieval church roofs in Scandinavia have been known since the early 20th century but surveys aimed at mapping and document these structures began first around 2000. The author reviews the State of Scandinavian research and presents recent and ongoing survey projects in Swedish dioceses. These cross-disciplinary projects have enhanced the value of historic timber structures as archaeological source material. A reading of craft techniques and tool marks provides insight into the work of the medieval carpenters. An example is presented of how a structured survey followed by moderate cleaning shaped a basis for maintenance and restoration in compliance with international principles.

Use of polar coordinates for improving the measurement of resistant cross-sections of existing timber elements combining laser scanner and drilling resistance tests

Historic timber structures typically have elements with irregular cross-sections often with decayed segments, making of extreme importance to have proper methods to obtain the resistant cross-section. Knowing as accurately as possible the measurements of the resistant section of these beams is fundamental for the structural safety analysis. Small changes on the size and geometry of the resistant cross-section may be fundamental in an intervention decision process. In this work an algorithm was created that allows to obtain the geometry of the resistant section of existing timber beams by use of data obtained by laser scanning of the external apparent sections combined with drilling resistance tests. The algorithm is based on polar coordinates and proved to obtain more reliable resistant cross-sections than those obtained solely by common practice using drilling resistant tests. The developed algorithm was calibrated with a laboratory beam and subsequently applied and validated in a case study.

On-Site Risk Assessment Methodology of Historic Timber Structures: The Case Study of Santa Cruz Church

The conservation and repair of historic structures require significant resources. Therefore, it is important to conduct a complete assessment of the object. Specifically, historical timber frame structures are very common in the Spanish and Andalusian geographic area. This research proposes and develops a simplified approach to facilitate decision making when faced with this complex work. By the application of long-established non-destructive tests, such as organoleptic and measuring inspection, resistography, and electric moisture content test, combined with visual classification parameters, these data were used as boundary conditions into a simplified structural calculation method. This process, which is simpler than other calculation systems, allows compiling important information about the safety level of the structure and its critical points. Finally, it allows for a better approach to repair work while rationalizing resources. This method was applied to a historical structure, during an 18th century church repair project. The assessment methodology provided important information about the conservation state of the timber frame and its structural suitability.

Investigation of the Effects of Different Types of Traditional Timber Load-Bearing Systems Used in Turkey on Building Behaviour

Recently historic timber structures in Turkey are unfortunately not given the value they deserve. Although timber structures are unique symbols of our cultural heritage, they are forgotten for natural and human reasons. On the other hand, when traditional timber structures standing today to repairs and / or reinforcements and restorations are examined, it is seen that timber elements according to the knowledge and skill of construction foreman are constructed with different types of structural systems. This matter reveals that choosing the right timber structural system is very important. This study the effects of their behaviour of traditional timber structural systems of different types widely used in the construction of timber structures in Turkey were comparatively examined. With this purpose, teen different structural system models with the Sta-stell program of the timber-framed (with Çatkı) Safran mansion which is widely used in Turkey were created and the findings were compared with each other by carried out structural analyses. The findings obtained reveal that buttresses are important in meeting, distributing and transferring the loads acting on the structural system, especially earthquake loads, to the foundation and the displacement distributions in the storey levels of the buttressed building models are less. In addition, the findings obtained show that buttresses that increase the lateral rigidity of timber structures increase the performance of the structure in question and reduce the internal forces of the structural elements. Turkey's widely used timber structural systems (in accordance with the Safran mansion architecture, which received the best restored mansion award) were modelled and analysed. The results presented are aimed to design recommendations and better understanding of the behaviour of different timber structural systems in today’s architectural practice.

HBIM Application in Historic Timber Structures: A Systematic Review

ABSTRACT Despite the recent significant increase on the use of Building Information Modelling (BIM) in the cultural heritage field, its application on heritage timber structures aiming at their conservation and assessment has not yet been fully established. Comparing with other construction materials, timber presents singular features that must be addressed in order to carry out a proper condition assessment. For this reason, this review summarizes existing works on historical timber structures using Historical BIM (HBIM), focusing not only on various geometric surveying and 3D modelling methods, but also on nongeometric information included in the model which are especially related with conservation, testing, and monitoring. In addition, this work illustrates the effectiveness increase given by a structural analysis, as to assess structural heath, after being implemented within a HBIM-based framework. To that aim, a global framework is proposed where the development and implementation level of different analysis stages are described.

Apparent and resistant section parametric modelling of timber structures in HBIM

Historic timber structures are frequently composed by elements with irregular sections. Moreover, due to abiotic and biotic agent action, wood is especially vulnerable to decay, which can lead to destruction of external layers of the element. Due to this, a beam's resistant cross-section, which is the healthy section part that supports the structure, and the beam external apparent cross-section may not coincide. This can lead to an improper structural assessment regarding the load-capacity of that element. HBIM technology is currently being used for the representation and analysis of historic timber constructions' structural health. In this work, a methodology is proposed and applied that, based on the combination of LIDAR data with non-destructive tests, allows to obtain a single 3D HBIM model of decayed irregular wooden structures. This HBIM model contains both the apparent parametric model, that represents the structure external geometry and collects all necessary data for construction's conservation analysis, and also a parametric resistant model, that represents the beam's undamaged section, allowing to carry out a more accurate structural analysis. In this work, the methodology was first applied to an irregular and decayed beam at laboratory conditions for framework calibration, and then applied to a case study for validation. With respect to the storage space, the volume difference between the rendered models and the proposed parametric models was on average 3.2%, whereas the occupied memory space was 10 times lower in the parametric models. The case study was the Guimarães chamber roof (Portugal) which structure is made up of several truss systems composed by irregular beams, several of which with signs of past decay activity.