Ancient Timber Research Articles

Structural behaviour of stop-splayed scarf joint reinforced with timber pegs

In restoring ancient timber structures, employing traditional connections would be advisable with the aim of minimal modification of the overall structural behaviour. Moreover, instead of steel connectors or adhesive resins and rods, commonly used in interventions, employing timber pegs can be an efficient solution. Nevertheless, the lack of design rules for traditional timber joints or for timber pegged connections in European codes doesn’t encourage this more conservative approach. In this study, stop-splayed scarf joints behaviour before and after reinforcement with steel pins or timber pegs is experimentally investigated, in order to understand the role of the fastener inside this carpentry joint and check the reliability of existing design methods. The experimental program has two steps: in the first one, three samples of fir scarf joints without fasteners, with timber pegs and with steel pins have been tested, trying to define the forces distribution among the different resisting elements. In the second phase, two samples of simple shear plane joints, made with the same timber and fastened with both timber pegs and steel pins have been tested to improve the analysis of fastener role in reinforced scarf joint behaviour.

Bondline strength of glued-in threaded rods in new and ancient chestnut (Castanea sativa Mill.) wood

Glued-in rods (GIR) are being increasingly used in connections of new timber structures, complying with design rules mostly based on tests with new softwood specimens. However, the system also shows great potential for use in strengthening and rehabilitation of ancient timber structures, in which hardwoods were often used, namely in the Central and Southern European countries. Aiming at contributing to the scarce information available for these particular applications, an experimental program is carried out, consisting of the production and testing of both new and ancient chestnut timber specimens, the latter cut out from beams of demolished buildings. Given the limited number of specimens available, the bonding length was selected as the only variable parameter, although the hole diameter, the bond line thickness and others also play a relevant role on the behaviour of these connections. The relevant dimensions were set in order to preclude the steel yielding failure mode, desirable in actual applications, to favour the cohesive or adhesive failure modes at the wood-adhesive interface and the timber splitting failure mode, where most of the unanswered issues stand. All specimens were first tested with a pull-pull setup, and the unfailed sides were later tested in pull-push mode. The results were compared to the estimates provided by some of the existing design methods proposed in the literature.

Evaluation of Seismic Performance of Ancient Timber Structure Based on Incremental Dynamic Analysis

In order to study the seismic performance of ancient timber structures under different earthquake intensities, this paper uses the finite element software ABAQUS to establish a finite element model. Through the incremental dynamic analysis (IDA) of the model under the action of two-way horizontal earthquake, IDA curves of multiple ground motion records are obtained, and the IDA curves of 16%, 50%, and 84% ratio are calculated. Combined with the earthquake vulnerability theory, the earthquake vulnerability matrix is established to evaluate the seismic resistance of the ancient timber structures. It provides a reference for the future anti-seismic research of ancient buildings, and also provides an effective way for timber structure anti-seismic safety evaluation.

Screening for internal defects of timber members based on impact evaluation method

This paper proposes a screening method and quantitative criteria for screening the internal defects of ancient timber members. Based on the impact evaluation (IE) method, two parameters, i.e. time of impact (TI) and proportion of integral area (PIA), were used to assess the internal defects. Impact tests were also conducted to study the effects of different influencing factors on the parameters (TI and PIA). The results demonstrated the satisfactory screening ability of PIA when the optimal proportion for the boundary value (fb) in the frequency domain was set as 50%. TI had a strong correlation with both the length of internal defects (ld) and the surface hardness (R2 = 0.74 and 0.93); however, PIA only had a significant correlation with ld (R2 = 0.84). The validation test results revealed that the proposed method and quantitative criteria could be used to detect the internal defects of ancient timber when the distance between internal defects and the surface (ha) was less than 35 mm.

Influence of component damage on the mechanical performance of bracket set joints in ancient timber structures

Ancient Chinese heritage buildings have high historical and artistic value. The bracket set in heritage buildings plays an important role in transferring and bearing load. However, over time, damage appears in these heritage buildings, which is especially serious in bracket sets. As damage seriously affects the safety and stability of the structure, studying the mechanical properties of the damaged bracket set and analyzing its influence on the entire structural system is vital for protecting ancient timber structures. This paper studies the influence of two kinds of damage on the mechanical properties of the bracket set. The model experiment results show that the force area reduction of the components in bracket sets has a distinct influence on the bearing and deformation capacities of the bracket set, with the impact on the stiffness of the bracket set being most significant. When damage occurs in the first layer of the Gong, the effect on the strength and the stiffness of the bracket set is the greatest. Numerical simulation shows that although the lateral displacement of the component will affect the seismic performance of the bracket set, the energy consumption ability remains good. The sidesway of the Cap Block has the greatest influence on the seismic behavior of the bracket set.

How the decayed straight mortise-tenon joints influence the seismic performance of ancient timber building? Evidence from experiment scenarios of the benchmark wood frames

This paper focuses on the effect of the decay damage of the ancient timber building (ATB) with the one-way straight mortise-tenon (OWSMT) joints on the seismic performance of the wood frame (WF). The artificial damage simulation method was used to consider the varying degrees of damage to OWSMT joints considering the damage depth and surface damage of the mortise. Three damaged WFs with three different joints damage and a non-damaged WF were made according to the Song Dynasty's Construction Formula. The scale of reduction was 1:3.52.Moreover, they have carried out low-cycle loading tests on the four WFs, compared and analyzed the strain variation characteristics at the edge of the OWSMT joints. Besides, the study discussed the hysteretic features, stiffness degradation, and energy dissipation capacity of the WF. The results show that the damage depth of mortise has a more significant impact on the seismic performance of the WF.

What tree rings can tell us Tree Story: The History of the World Written in Rings Valerie Trouet Johns Hopkins University Press, 2020. 256 pp.

From ancient timbers to mountaintop forests, trees hold important climate clues

Retrofitting ancient timber glulam mortise & tenon construction joints through computer-aided laser cutting

This study is aimed to rationalise and demonstrate the efficacy of utilising laser cutting technique in the fabrication of glulam mortise & tenon joints in timber frame. Trial-and-error experiments aided by laser cutter were conducted to produce 3D timber mortise & tenon joints models. The two main instruments used were 3D modelling software and the laser cutter TH 1390/6090. Plywood was chosen because it could produce smooth and accurate cut edges whereby the surface could remain crack-free, and it could increase stability due to its laminated nature. Google SketchUp was used for modelling and Laser CAD v7.52 was used to transfer the 3D models to the laser cutter because it is compatible with AI, BMP, PLT, DXF and DST templates. Four models were designed and fabricated in which the trial-and-error experiments proved laser cutting could speed up the manufacturing process with superb quality and high uniformity. Precision laser cutting supports easy automation, produces small heat-affected zone, minimises deformity, relatively quiet and produces low amount of waste. The LaserCAD could not process 3D images directly but needed 2D images to be transferred, so layering and unfolding works were therefore needed. This study revealed a significant potential of rapid manufacturability of mortise & tenon joints with high-quality and high-uniformity through computer-aided laser cutting technique for wide applications in the built environment.

Damage Detection Method of Ancient Timber Structure Based on BP Neural Network and Total Wavelet Energy Rate

In order to detect the damage of beams and mortise joints of ancient buildings under environmental excitation, a damage identification method combining wavelet transform with improved BP neural network is proposed. The acceleration signal of the structure under the environment excitation is extracted and the total energy change rate of wavelet is obtained by wavelet discrete reconstruction, which is taken as the damage index. A finite element model of a timber frame of Xi’an bell tower is established to verify the proposed method. When the damage extent is less than 50%, 96% of the test samples in the neural network output the desired value; This method provides a theoretical basis for the study of damage prediction of timber structures in ancient buildings under environmental incentives.

Feasibility Study on Hyperspectral LiDAR for Ancient Huizhou-Style Architecture Preservation

Huizhou-style ancient architecture was one of the most important genres of architectural heritage in China. The architecture employed bricks, woods, and stones as raw materials, and timber frames were significant structures. Due to the drawback that the timbers were vulnerable to moisture and atmospheric agents, ancient timber buildings needed frequent protective interventions to maintain its good condition. Such interventions unavoidably disrupted the consistency between the original timber components. Besides this, the modifications brought about difficulty in correctly analysing and judging the state of existing ancient buildings, which, in current preservation practices, mainly rely on the expertise of skilled craftsmen to classify wood species and to identify the building-age of the timber components. Therefore, the industry and the research community urgently need a technique to rapidly and accurately classify wood materials and to discriminate building-age. In the paper, we designed an eye-safe 81-channel hyperspectral LiDAR (HSL) to tackle these issues. The HSL used an acousto-optic tunable filter (AOTF) as a spectral bandpass filter, offering the HSL measurements with 5 nm spectral resolution. Based on the HSL measurements, we analysed the relationship between the surface and cross-section spectral profiles of timber components from different ancient architectures built in the early Qing dynasty (~300 years), late Qing dynasty (~100 years), and nowadays, and confirmed the feasibility of using surface spectra of timber components for classification purpose. We classified building-ages and wood species with multiple Naive Bayes (NB) and support vector machine (SVM) classifiers by the surface spectra of timber components; this also unveiled the possibility of classifying gnawed timber components from its spectra for the first time. The encouraging experimental results supported that the AOTF-HSL is feasible for historic timber building preservation.

Structural Health Monitoring System Based on FBG Sensing Technique for Chinese Ancient Timber Buildings.

Due to the long-term service, Chinese ancient timber buildings show varying degrees of wear. Thus, structural health monitoring (SHM) for these cultural and historical treasures is desperately needed to evaluate the service status. Although there are some FBG sensing-based SHM systems, they are not suitable for Chinese ancient timber buildings due to the differences in architectural types, structural loads, materials, and environment. Besides, a technical gap in Fiber Bragg grating (FBG) sensing-based column inclination monitoring exists. To overcome these weaknesses, this paper develops an FBG sensing-based structural health monitoring system for Chinese ancient Chuan-dou-type timber buildings that aims at monitoring structural deformation, i.e., beam deflection and column inclination, temperature, humidity, and fire around the building. An in-situ test and simulation analyses were conducted to verify the effectiveness of the developed SHM system. To validate the long-term-operation of the developed SHM system, monitoring data within 15 months were analyzed. The results show good agreement between the developed SHM system in this paper and other methods. In addition, the SHM system operated well in the first year after its deployment. This implies that the developed SHM system is applicable and effective in the health state monitoring of Chinese ancient Chuan-dou-type timber buildings, laying a foundation for damage prognosis of such types of timber buildings.

Experimental and Numerical Investigation on Seismic Performance of One-Way Straight Mortise–Tenon Joints Based on a Novel Method to Simulate Damage of Deteriorated Ancient Chinese Timber Buildings

AbstractBeing exposed to weather directly or indirectly for more than 100 years, ancient timber buildings have experienced different levels of mechanical degradation. Especially the mortise-tenon j...

Safety-state evaluation model based on structural entropy weight–matter element extension method for ancient timber architecture

This article investigates various factors that may influence the safety state of ancient timber architecture, to improve the accuracy of safety-state evaluation results for ancient timber architecture. During the process, a safety-state evaluation system for ancient timber architecture is developed. This safety-state evaluation system includes five parts: foundation, plinth, timber frame, enclosing wall, and roof. Based on the system, a safety-assessment model for ancient timber architecture based on structural entropy weight–matter element extension model is also introduced. In this model, the structural entropy weight method is applied to calculating the weight of each index and takes the influence of subjective and objective weights into consideration comprehensively. This model has the following three detailed steps. First, correlation function and correlation degree of extension set are used to quantify the relationship between the evaluation indexes of the components, joints, and evaluation interval of each safety state. Second, the safety states of units are determined according to the distribution of safety state of the components. Third, the safety degree of the entire structure is determined via the minimum safety state of units. This study also uses the Niaoqiangsanchu in Forbidden City as a study case and found that the evaluation results are consistent with the results of the practical damage survey and the actual situation of the architecture. The model thus minimizes the uncertainty of qualitative and quantitative factors in the process of evaluating the safety degree of ancient timber architecture, to finally obtain the objective evaluation results.

Shaking table tests on seismic behavior of ancient timber structure reinforced with CFRP sheet

This paper presents an experimental study on seismic behavior of ancient timber structure reinforced with Carbon Fiber Reinforced Polymers (CFRP) sheet. Based on a 1:2 scale one-bay and one-story ancient timber structure destroyed by the simulated earthquake, CFRP was used to reinforce the damaged ancient timber structure. Three seismic waves, including El Centro wave, Taft wave and Lanzhou wave, were input as the excitation wave. The displacement and acceleration response of the Column base, Column head, Pu-pai-fang, Bracket set and Eaves beam, the earthquake shear of structure and the internal force Sun-Mao node were analyzed quantitatively. Furthermore, the failure pattern of structure and dynamic property were analyzed qualitatively. The research shows that the friction and sliding of column base, rotation of semi-rigid tenon-mortise joint and sliding of Bracket set made the amplitude of seismic response of the structure greatly diminish with dynamic magnification factor about 1 which was much smaller than that of concrete structure about 2–4, and completely met the design requirements of Chinese code for seismic design of building. The distribution of the peak shear force of structure along the height appears at head or base of column, rather than must be the column base. The cumulative energy dissipation of three energy dissipation members reinforced with CFRP under different seismic conditions was calculated.

Probing Chemical Changes in Holocellulose and Lignin of Timbers in Ancient Buildings.

Wooden structures in China’s ancient buildings hold highly historical and cultural values. There is an urgent need to repair and replace the damaged wooden structures after hundreds and thousands of years of exposure to weather. Unfortunately, to date there is still a lack of insightful understanding on how the chemical structure, composition, and micro-morphology evolve over the long-term natural aging before artificial ancient timbers can be developed. This work aims to systematically examine the outer surface, middle layer, and inner surface of the same piece of Chinese fir (Cunninghamia lanceolate) collected from an ancient Chinese building. Based on qualitative and quantitative analysis, both cellulose and hemicellulose in aged woods are found to experience significant degrees of degradation. The crystalline regions of cellulose are also determined to undergo moderate degradation as compared to the control fresh wood. In comparison, the lignin basically remains unchanged and its content in the inner layer slightly increases, as evidenced by more free phenol groups determined. Relative to the outer and inner layer, the middle layer of the ancient wood shows the lowest degree of degradation close to that of the fresh wood. This work offers guidelines for fabricating artificial ancient woods to repair the destroyed ones in China’s ancient architectures.

Experimental Investigation on the Seismic Behavior of the Semi-Rigid One-Way Straight Mortise-Tenon Joint of a Historical Timber Building

ABSTRACT This article aims to disclose that the deformation and damages of the one-way straight mortise-tenon (OWSMT) joint, the key force transmission connection of traditional wood buildings, lead to a significant reduction in structural safety of ancient timber structure. For this purpose, the damage of mortise joint in practical engineering wassimulated by controlling the gap and width between mortise and tenon. A total of 23 groups of scaled 1:2 OWSMT joint specimens were fabricated and tested subjected to cyclic loadings, and the hysteretic curves of OWSMT joint with different damage degrees were obtained. Through skeleton curves, stiffness degradation curves, and equivalent viscous damping curves of the OWSMT joint, the seismic performance of damaged wood joints was quantitatively analyzed. The results show that, with the increase in the gap between the tenon and the mortise, the slip between them became increasingly obvious, the fullness and peak of the hysteresis curve gradually decreased, the gradient of the skeleton curve also dropped, and both the stiffness degradation curve and the equivalent viscous damping curve are gradually reduced. The research findings shed new light on the seismic assessment of aging timber buildings.

Nanomechanical and Topochemical Changes in Elm Wood from Ancient Timber Constructions in Relation to Natural Aging.

Knowledge of properties of building materials affected by aging is of great importance to conserve cultural heritages or replace their biopolymer components. The objective of the study was to investigate the chemical characterization change in the biopolymer components and identify whether these changes are correlated with alterations in the nanomechanical properties of the wood cell wall bio-composites in relation to natural aging. The effects of natural aging on the elm (Ulmus) wood component (dated from 1642 to 1681) of Chenghuang Temple, an ancient timber construction in China were investigated to understand the chemical and mechanical changes in the wood cell wall. Especially, confocal Raman microscopy and nanoindentation (NI) were used to track changes in the chemical structure and nanomechanical properties. The results showed that the morphological, chemical and physical properties of cell walls changed with aging. After aging, the cell structure showed evidential alternations, and the wood components, especially hemicellulose and lignin, were degraded, leading to deterioration of mechanical properties of aged wood compared with normal wood. Morphology deterioration and micromechanical changes only occurred on the surface with the depth of about 3.6 mm of the aged element. This study would be helpful to provide practical guidance for protecting the apparent performance of ancient timber structures.

Detection and Prediction of Internal Damage in the Ancient Timber Structure Based on Optimal Combined Model

It is currently known that using stress wave and drilling resistance to detect the internal damage in the ancient timber structure is not a highly precise process. To improve the detection precision of this process, a simulation test was used to detect the internal damage of poplar and elm in ancient buildings. In this empirical study, we compared the detection precision of these two detection methods. Based on the idea of variable weight, we introduced three combined forecasting models based on the IOWA operator, IOWGA operator, and IOWHA operator to predict the internal damage in the ancient timber structure. The results show that the combined forecasting model based on the IOWA operator is more effective in predicting compared to a single detection method and other combined forecasting models. To be more specific, the results show that the detection precision of the combined model is increased by 25.8% and 4.7%, respectively, compared to the precision of the stress wave and drilling resistance tests. The error indicators of the combined forecasting model based on the IOWA operator are better than those of the other combined forecasting models. In addition, the analysis results based upon cross‐validation theory show the combined forecasting model based on the IOWA operator has the best applicability, which provides a new practical method for evaluating internal damage of timber components in ancient buildings.

Seismic Performance of Damaged Dovetail Joints with Different Damaged Degrees in Timber Frames

The mortise and tenon joints are the main connection forms used in ancient timber buildings, and damaged joints have a critical effect on the safety of a timber structure. There are three main damaged cases of dovetail joints which are pulling, contraction, and mixing damages. In this study, using a theoretical analysis of the stress distribution in a mortise and tenon joint resulted from the pullout damage, a theoretical equation for the resisting moment of the joint was proposed. A finite element model was used to simulate the cyclic displacement loading of a frame with intact joints and with different levels of pulling and contraction damaged joints. The results show that the moment capacities both for the test and the simulation were in good agreement with each other. The simulation results also indicated that there are no changes in the capacity and energy dissipation of the pulling damaged joint compared to that of the intact joint, and good seismic performance still was provided when the pulling damage was less than 2/5 of the joint length. However, the capacity of the contraction damaged joint was significantly reduced, and its seismic performance was tolerably lost. The seismic performance of a mixing damaged tenon with the same degree of pulling damage was between that of the pulling damaged tenon and the contraction damaged tenon, and generally, it was controlled by the contraction damage. The friction between the tenon and the mortise is the main source of resisting moment and energy dissipation ability.

Safety State Evaluation Method Based on Attribute Recognition Model for Ancient Timber Buildings

To improve accuracy of safety state evaluation results for ancient timber buildings and to know the real state of the building, a safety grade evaluation model of ancient timber buildings is established based on attribute mathematic theory. From the perspective of macro, micro, qualitative, and quantitative, 22 factors may adversely affect the safety state of ancient timber building are considered in this model. First, evaluation system is established, and evaluation indexes are selected based on former study, seismic damage data, and Chinese current code about ancient timber buildings. In the evaluation system, whole building is divided into four parts, which are wood frame, enclosing wall, foundation, and plinth. Different parts contain different components. Every component has its own evaluation indexes. Second, based on the AHP and entropy method, the comprehensive empowering method is used to determine the weights of the indexes. Third, the attribute recognition model is established to identify the safety grade of components or units. Fourth, based on the evaluation results of components, safety grade of units is identified. Then, safety degree of the entire building is determined by the minimum safety grade of units. At last, the model is applied to the “Liben hall” in village Siping, Zhejiang province, China, and the assessment results are consistent with the results of damage identification.