Traditional Timber Structures Research Articles

Spatial rotational behaviour of intact and damaged column foot joints: numerical modelling

Columns in traditional Chinese timber structures barely rest on stone bases, and the column foot joints are capable of resisting moment around any direction. This study numerically investigated the spatial rotational behaviour of intact and damaged columns based on experiments. Unidirectional cyclic loading tests were carried out on two intact and three damaged column foot joint specimens. A fibre element-based numerical model for the column foot joints was developed and validated by use of the unidirectional loading test results. Numerical analyses were performed based on the fibre element-based model to obtain the rotational behaviour of the intact and damaged column foot joints under spatial loading. The analyses indicated that the moment–rotation curve of an intact column foot joint under spatial loading was on an umbrella-shaped surface. The damage at the column foot not only unidirectionally decreased the moment-resisting capacity of a column foot joint but also resulted in a rotational performance degradation valley on the moment–rotation surface of the joint. The rotational behaviour of both the intact and damaged column foot joints under spatial loading was highly non-linear. This developed fibre element-based model can be further utilised to analyse the structural performance of traditional timber structures under three-dimensional excitations.

Effects of environmental humidity on the gap of mortise-tenon joints: Experimental and numerical investigations

Mortise-tenon (MT) joints play a vital role in the lateral deformability and seismic performance of traditional timber structures. However, moisture exposure can cause shrinkage-induced gaps and then affect the durability of MT joints. Limited knowledge exists on the humidity response of MT joints. To investigate the effect of environmental humidity on the gaps between mortise and tenon, multiple measurements of moisture content (MC) and shrinkage deformation were conducted on straight MT joints that were subjected to humidity variations. Different ambient conditions and exposure levels were taken into account. Three-dimensional numerical models were established to simulate the humidity response of MT joints. Model validation was then performed by comparing the simulation and experimental results in terms of moisture distribution and gaps. On this basis, quantitative analysis was made to reveal the development mechanism and main influence factors of moisture-induced gaps. Results show that straight MT joints are vulnerable to environmental humidity changes. The observed gap is estimated to cause a decrease of up to 23.1% in the initial elastic stiffness. Although only contributed by the shrinkage deformation of tenons, the vertical gap is theoretically larger than the horizontal one which is attributed to a combination of both mortise and tenon. A clear linear relationship is found between the vertical gaps and the MC decrease, with the product of the radial shrinkage coefficient and tenon height as the theoretical ratio. Controlling the moisture exposure is considered the most effective way to reduce moisture-induced gaps in MT joints.

Experimental and numerical studies on influences of wedge reinforcement on seismic performance of loose penetrated mortise-tenon joints

Wooden wedges significantly affect the rotational stiffness and load-bearing capacity of penetrated mortise-tenon joints (PMTJ). To clarify the role of wedges on the seismic performance of loose penetrated mortise-tenon joints, three types of full-scale PMTJs, including reference, loose, and wedge-reinforced joints, were tested under quasi-static loading. The deformation characteristics, hysteresis curves, rotational stiffness degradation behavior, and energy dissipation of PMTJs with wedge were analyzed. Three-dimensional nonlinear finite element models were established to simulate the wedge effects, and the stress states of joint were analyzed. The results indicated that the ultimate bending moment capacity of reference and loose joints was reached when the splitting failure of tenon occurred, while the wedge-reinforced joint reached such capacity when the transverse compression failure occurred at the wedges. The maximum bending moment of PMTJ with a 10 mm gap and a 25 mm gap were 18.3 % and 55.3 % lower than that of reference joint, while maximum bending moments of wedge-reinforced joint with a 10 mm gap and a 25 mm gap were 12.6 % and 17.03 % larger than that of reference joint, respectively. Numerical simulation showed that wooden wedge reduced stress concentration in the tenon and alleviated compression damage of the tenon. Higher load-bearing capacity and rotational stiffness were observed in joints when hardwood wedges were used, compared with that of soft wood. Wedge reinforcement could effectively improve the load-bearing capacity of loose PMTJ. These results yielded valuable data for the performance evaluation and retrofitting of penetrated mortise-tenon joints with wedges in traditional timber structures.

Research on wind pressure characteristics of traditional timber buildings: a case study of the main hall of Shisi Temple

Traditional timber buildings are sensitive to wind action. Studying the wind pressure characteristics is the premise for the preventive conservation of traditional timber buildings. To investigate the computational fluid dynamics (CFD) numerical simulation method for wind pressure on traditional timber buildings, a typical traditional timber building, the main hall of Shisi Temple, is chosen as a case to carry out the study. A comparative analysis is conducted to examine the effects of curve simplification of the roof slope, as well as the Dougong (bracket sets) and roof tile components, on the numerical simulation results of wind pressure on the building surface. Additionally, simplification schemes of geometric modeling are provided for the efficient and accurate simulation. The results indicate that moderate simplification of the roof curve has a relatively minor impact on the overall calculation of wind pressure, and the difference between the drag coefficients of the simplified model and the accurate model is no more than 3%. However, excessive simplification can lead to distorted simulation results, and a three-segment curve simplification method is recommended for roof cornices. The influence of Dougong on the wind pressure calculation results is negligible (within 5%), whereas roof tiles significantly reduce the drag coefficient, with an impact of over 30% at various wind directions. The impact of roof tiles on wind pressure distribution in traditional timber buildings lies in their alteration of the building aerodynamic shape rather than an increase in roof thickness. The findings can provide a basis for assessing the wind resistance of traditional timber buildings and helpful insights for improving the efficiency of wind pressure analyses of traditional timber structures.

Experimental and Parametric Study on Rotational Performance of Through-Tenon Joints in Traditional Timber Structures

ABSTRACT The rotational capacity of mortise-tenon joints is crucial for stability in traditional timber structures. However, these joints are influenced by various factors such as environmental conditions and internal features, impacting their rotational performance over time. To assess these influences, four groups of through-tenon joints with different small and large tenon lengths were constructed and tested. Deformation characteristics, hysteresis, bearing capacity, stiffness, and energy consumption of the joints were investigated. Finite element models were created and verified through testing. An orthogonal design scheme analyzed the effects of parameters and their interactions on rotational performance. The results indicated that increasing the length of the smaller tenon improved tenon pull-out length and ductility, while simultaneously reducing bearing capacity, stiffness, and energy dissipation. Tenon dimensions and the ratio of small tenon length to total tenon length were found to significantly impact peak moment. Critical parameters affecting rotational performance included tenon length, elastic modulus perpendicular to the grain, and the gap between the tenon and mortise.

Experimental study on the seismic performance of a full-scale two-story traditional timber frame on sloped land

In traditional timber structures built on hilly areas, columns of varying lengths are utilized to accommodate sloped terrain. This structural feature renders these structures more susceptible to seismic damage than structures built on flat land. To investigate the seismic performance of traditional timber structures on sloped land, the quasi-static test was conducted on a full-scale two-story timber frame on sloped land (FSL), while an identical frame on flat land (FFL) was served as a comparative reference. This study analyzed the deformation characteristics, bearing capacity, and energy dissipation capacity of the frame on sloped land, as well as its weak positions and failure mechanisms. The test results indicate that the frame on the upper ground is the weak position compared to the frame on flat land. Short columns of the upper frame have greater inclination angles, leading to larger pull-out lengths of the mortise-tenon joints, and the column foot becomes more susceptible to slipping and lifting. Although the FSL has a greater bearing capacity than the FFL under the same horizontal displacement, it experiences a more significant deformation and is more prone to tenon failure and column foot sliding out of the foundation stone. With excessive deformation, gravity becomes a detrimental factor for structures on sloped land to resist horizontal overturning moments, which would accelerate the collapse of the structure.

Mechanical Behavior of a Novel Precast Concrete Beam–Column Joint Using the Mortise–Tenon Connection

The construction industry has been a significant contributor to global carbon emissions. Fortunately, it is well known that precast concrete structures possess the benefit of reducing carbon emission, of which the beam–column joint plays a crucial role in resisting severe loads. Nowadays, the cast-in-place joint is mostly adopted for beam–column joint The authors declare no conflict of interests of precast concrete structures, and the building industrialization degree is insufficient. In light of this, a novel precast concrete beam–column joint using the mortise–tenon (MT) connection is proposed inspired by traditional timber structures, and the contrastive analysis of mechanical behaviors of this joint and the same-sized cast-in-place joint is conducted by the finite element method. The results indicate that the proposed MT joint has a better mechanical behavior by comparing with the corresponding cast-in-place joint as the beam–column joint. Meanwhile, the MT connection mode has the characteristics of standardized construction, in line with the concept of sustainable development, which can greatly save the construction period. This research demonstrates the feasibility of MT joints in traditional timber structures as beam–column joints in precast concrete structures, and the application of MT joints may be promoted if the size and shape of that are further optimized. Furthermore, this in turn helps research and innovation of precast building construction technology and promotes the sustainable development of the construction industry in the direction of energy conservation and environmental protection.

Mechanical behavior of Dou-Gong brackets in Chinese traditional timber structures: An experimental study

This study investigated the mechanical behaviour of Dou-Gong brackets with different structural forms, including Jixinzao and Touxinzao. Scaled Dou-Gong models were designed and fabricated at a 1:3.4 geometrical ratio. Vertical load tests were conducted to determine the failure modes, load-displacement response, stiffness degradation, and deformation capacity of the Dou-Gong models. Under vertical load, the primary failure modes of the Dou-Gong models were observed at the Lu-Dou, Nidao-Gong, and Hua-Gong component. The specimens demonstrated excellent load-bearing capacity and high deformation resistance. The Jixinzao Dou-Gong model exhibited a 15.0% higher ultimate load-carrying capacity than the Touxinzao Dou-Gong due to the presence of transverse arches. The number of transverse arches in the Dou-Gong models positively correlated with the compression stiffness, while their presence had a negligible effect on stiffness degradation rates. The Touxinzao Dou-Gong model exhibited superior ductility, characterized by a ductility coefficient 8.57% higher than that of the Jixinzao Dou-Gong model. Although the regular layering of the Dou-Gong models was disrupted by Ang component, the models remained stable in both the vertical and horizontal directions. The bi-linear model can effectively simulate the deformation behaviour of the Dou-Gong model under vertical load.

Mechanical Model of Exposed-Dowel Half-Through Tenon Joints in Chinese Traditional Timber Structures Subjected to Bending

ABSTRACT The exposed-dowel half-through tenon (EHT) joint is a common and important connection configuration in southwest China. However, deformation and looseness in the EHT joint constitute the primary causes of failure in the joint connection performance. In this study, a mechanical model of the joints under bending was established and analyzed. The geometric, physical, and equilibrium equations were constructed, the bending moment-rotation relationship was obtained, and the bending moment-rotation envelope curve and the flexural capacity were calculated. A low cycle reciprocating experiment of the EHT joint was conducted to measure the moment-rotation hysteretic curve and envelope curve of the joints. A comparison of the envelope curves calculated using the model and test curves was conducted, and the results showed that the calculation curve was in good agreement with the test curve. The ultimate bending capacity errors of the joint in the forward loading stage and reverse loading stages were 11.2 and 5.8%, respectively. A parametric analysis of the joint using the established mechanical model showed that increasing the diameter of the wooden pillar and the width of the tenon greatly improved the flexural capacity of the joints while increasing the height of the small tenon and reducing that of the joints during the reverse loading stage. These research results provided a reference for the new construction and restoration of the Drum Towers in southwest China.

Compressive behavior of damaged timber columns: Experimental tests, degradation model, and repair method

Local decay often appears in columns of traditional timber structures and negatively affects their compressive behavior. In this study, axial compression tests were conducted on four column specimens with different damage degrees, which were simulated by artificially removing local wood, and on three damaged column specimens that were reinforced by filling with different wooden blocks to investigate the degradation performance and repair ability of timber columns. The failure mode, load-axial displacement curves, load-lateral deflection curves, varied load-carrying capacity laws, and different stiffness of the locally damaged and repaired timber columns were obtained and analysed. The study results indicated buckling failure was observed on all column specimens. The compressive strength and stiffness decreased significantly with an increase in the damage degree for the locally damaged timber columns. Moreover, a theoretical degradation model was proposed to predict the compression strength of locally damaged timber columns, and a good agreement was obtained between the theoretical and experimental results. This degradation model can provide a theoretical basis for evaluating the compression behavior of damaged timber columns. For repairing timber columns, the local damage section can be filled with a wooden block; the larger the length and elastic modulus of the block, the better the repair effect. The compression behavior of the damaged timber columns repaired using the optimized wooden block could restore to that of the intact timber column.

Numerical Modelling of Traditional Timber Columns Resting on Stone Bases

ABSTRACT Columns in traditional timber structures are commonly seen resting on stone bases and are very important in resisting lateral loads. This paper numerically modeled the lateral resistance of the columns combined with experimental investigation. Different numerical models were developed, based on which sensitivity analyses were performed. A practical numerical modelling strategy was further proposed and verified. The analysis results indicated that instead of material properties and contact area, the columns’ lateral performance was much more sensitive to the variation of surface curvature at bottom surface. Without consideration of the surface curvature, the modeling error in the initial stiffness and peak load of a column was more than 607% and 8%, respectively. By best matching the load–displacement curves of tested column specimens, the optimal surface curvature was identified as 1/20306.5 mm−1. Then, a practical finite numerical model, characterized by the optimal curvature at the bottom surface, was proposed. This modelling method was validated by use of existing test results of traditional timber columns with different diameters and vertical compression loads. The modelling load–displacement curves agreed well with experimental curves both in terms of the initial lateral stiffness and peak load. Detailed simulation results based on the practical modelling strategy were presented and discussed.

Effects of seismic strain rates on the perpendicular-to-grain compression behaviour of Dahurian larch, Mongolian pine and Chinese poplar: tests and stress-strain model

Abstract Wood is mainly subjected to transverse compression in many critical parts of Chinese traditional timber structures, e.g. the mortise-tenon and Dou-Gong joints. Seismic is one of the dynamic actions faced by these structures and will cause wood to suffer higher loading speeds than quasi-static loads. The investigation of the seismic strain rates (SSRs) effects of wood under perpendicular-to-grain compression (PTGc) is important. One hundred and forty-four radial small clear wood specimens were prepared using Dahurian larch, Mongolian pine and Chinese poplar. Monotonic and cyclic compression tests were conducted under three SSRs (10−3 s−1, 10−2 s−1, and 10−1 s−1) and the quasi-static strain rate (10−4 s−1). Failure modes, stress-strain curves, yield strengths, elastic moduli and the unloading/reloading moduli were analyzed. Results indicated that the PTGc properties were highly sensitive to SSRs under both the monotonic and cyclic compression. Strengths showed higher sensitivity to SSRs than elastic moduli. The SSRs effects of wood under cyclic compression have greater variability than the monotonic counterparts. The unloading/reloading moduli shows little SSR effects statistically. Comparisons were made between the existing PTG and the parallel-to-grain test results and a fitted general expression was obtained. Furthermore, an SSR-dependent stress-strain model was proposed and verified by tests.

Theoretical Model for the Analysis of Rotational Behavior of Penetrated Mortise-Tenon Joints in Traditional Timber Structures

ABSTRACT Penetrated mortise-tenon joints (PMJs) are typical wood-to-wood connections commonly used in traditional Chinese timber structures. They play a crucial role in the structural behavior of timber constructions. This study derived a method of theoretical estimation for the rotational behavior of PMJs, which is unique and more comprehensive in that it takes both movement of the rotation center and bending deformation of the tenon into consideration. In addition, it experimentally and numerically validated the theoretical model, and quantitatively analyzed the position changes of the rotation center and the effect of the bending deformation. On this base, simplified calculation formulas are proposed for the prediction of equivalent elastic stiffness and peak moment of PMJs, and then applied for the calculation of the lateral stiffness of timber frames. As a result, the predicted lateral stiffness shows good agreement with test results, demonstrating the validity of the estimation method derived and its applicability to the structural analysis. The results of this study show that the rotation center of the tenon is not stationary, and its moving range in the horizontal direction is much larger than that in the vertical direction. Another pattern found is that the bending deformation of the smaller tenon counteracts more than 20% of the compressive deformation caused by the rigid-body motion, and therefore must be considered when analyzing the rotational behavior of PMJs.

A Mechanical Model Used for the Multifactor Analysis of Through-Tenon Joints in Traditional Chinese Timber Structures

ABSTRACT The through-tenon joint is one of the most widely used joints in traditional Chinese timber structures. The moment-rotation relationship of the joints was established using geometric, physical, and equilibrium conditions as well as full consideration of various influencing factors. Furthermore, three types of joints with different tenon lengths were manufactured and tested under quasi-static tests. The damage features and the moment-rotation relationship curves of these joints were obtained and used to verify the proposed mechanical model. Additionally, we compared the proposed model to the existing mechanical models using the experimental results of 16 groups from other scholars and conducted parameter analyses through the model. The results showed that the lengths of the tenon had a remarkable influence on the mechanical properties of the joints. The proposed mechanical model agreed well with the experimental results. The moment-rotation relationship can be divided into the slip and elastic stages as well as the yield at one side, and yield at both sides. The comparisons to the existing models indicate that the proposed model in this paper has broader applicability and can be used as a reference for the protection and reinforcement of mortise-tenon joints used in traditional timber structures.

Numerical analysis of traditional Chinese timber structure: Simplified finite element model and composite elements of joints

Mortise-tenon (M-T) joint, column foot joint, and Dou-Gong joint play a key role in the seismic behavior and energy dissipation of traditional timber structures. To simplify the modeling process and predict accurately the hysteretic behaviors of traditional timber joints as well as the global seismic responses of traditional timber structures, three types of composite elements, which were composed of varying non-linear one-dimensional spring elements available in the ANSYS finite element (FE) software, were proposed to characterize the hysteretic performance of the M-T joint, the column foot joint, and the Dou-Gong joint, respectively. The beam element was used for simulating the timber components with large size and not easily damaged. The parameters of the composite elements were identified from the simplified hysteretic model or test hysteretic curve of each type of joint. The simplified FE models of the M-T joint, M-T jointed timber frame, column foot joint, and Dou-Gong joint were developed, and verified using the cyclic loading tests of joints, respectively. Based on the validated composite elements and simplified FE models of varying joints, the three-dimensional simplified bar system FE model of a 1/3.52-scaled palace-style ancient timber structures was established using the ANSYS, and also validated using the shaking table tests, in terms of its dynamic characteristics and responses. Good agreements between the model predictions and test results were observed. Additionally, parametric analyses were performed, while revealing and quantifying the effects of performance degradation for the M-T joint, column foot joint, and Dou-Gong joint on the dynamic responses to the structure. It is found that the damage to the Dou-Gong joint had little effect on the maximum story drift of column frame layer, however, the damage to the M-T joint and column foot joint would significantly increase the maximum story drift of column frame layer. When the damage degree of the M-T joint, Dou-Gong joint, and column foot joint in the structure was up to 60%, the maximum story drift ratios of column frame layer were close to 1/48, 1/50, and 1/39, respectively, the maximum story drift ratios of Dou-Gong layer were approximately 1/164, 1/98, and 1/125, respectively.

Experimental study on the compression behavior of long timber column strengthened with the novel hybrid fiber sheets

Long timber columns are widely used in traditional timber structures worldwide; however, many of them possess bearing capacity issues and have to be strengthened. The current study aims to develop the novel Hybrid fiber reinforced polymers (HFRP) sheets suitable for long timber columns. In the first stage, six HFRP sheets were designed, and the evaluation of these sheets was carried out by the tensile tests and the Scanning electron microscopy (SEM) tests. Secondly, for the compression test, two sets of 36 timber columns were designed utilizing six types of HFRP sheets. Finally, the effects of different sheet types and strengthening methods on the compressive performance of timber columns were investigated. The findings reveal that bidirectional HFRP sheets have excellent compressive performance for timber columns. In the case of using one-layer interval reinforcement, the bearing capacity can be increased by 22.27%, which is 12.15–17.81% higher than that of the unidirectional HFRP sheets. Compared with one-layer reinforcement, the two-layer reinforcement increased from 0.91% to 5.35%. The current study's findings are intended to provide an essential scientific foundation for the advancement of fiber-reinforced timber column technology and the preservation of the heritage of timber structures.

ANALYSIS OF ROCKING COLUMN BEHAVIOR CONSIDERING STRESS DISTRIBUTION OF COLUMN USING FIBER ELEMENTS

In this paper, a numerical model considering the embedment reaction of column foot by the beam-column finite element method was proposed for evaluating the restoring force characteristics of the rocking column in traditional timber structures. Wood compression tests in contact with stones were conducted to investigate the characteristics of the embedment reaction and initial deformation generated at the end of the wood, and these characteristics were considered in the column foot numerical model. The validity and applicability of the numerical model were verified by analyzing several static loading tests of the rocking column.

Mechanical Behaviour and Failure Mode Analysis of Penetrated Mortise–Tenon Joint with Neighbouring Gaps Based on Full-Scale Experiments

The penetrated mortise–tenon joint (PMT) connecting column and beam in traditional timber structures often has neighbouring gaps between connected structural members due to initial manufacture errors and damage accumulated over years. Influences of the neighbouring gaps on the mechanical properties of the PMT joint have been analysed based on a full-scale experimental study. Four typical gap values are determined according to the probability analysis of on-site survey results of a Chinese traditional timber structure. Four full-scale models of PMT joints with varied gap values have been established. Failure modes and deformation characteristics have been studied by quasi-static tests. Results show that the failure modes are the tearing of wood fiber along the grain at variable cross-sections. The loose penetrated mortise–tenon (LPMT) joints all have high deformability. The slip distance of tenon grows as the gap value increases. Limit angles of the loose joints lag with the increasing degree of loosening. The bending bearing capacity and rotational stiffness of LPMT joints decrease as the gap value increases, and the limitation value of the gap is analysed. The resisting capacities of LJ-2, LJ-3 and LJ-4 are much lower than that of LJ-1. The changing ratios are 18.5%, 55.4% and 70.4%, respectively. A three-parameter power function model of the mortise–tenon joint with consideration of the neighboring gap is presented. Research results provide important references on the condition assessments of the existing traditional timber structures.

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.

Rotational Performance of Traditional Straight Mortise-Tenon Joints with Gap: Theoretical Model and Numerical Analyses

ABSTRACT Gaps are very common in the mortise-tenon (M-T) joints of traditional timber structures. To investigate the rotational behavior of straight M-T joints with gaps, the mechanical mechanism and contact states between the mortise and tenon for the straight M-T joints with gaps were analyzed. A moment-rotation theoretical model of straight M-T joint with gap, based on the embedded compressive and friction mechanisms of the contact surfaces, was proposed and verified by the cyclic loading tests of four 1/3.2-scaled straight M-T joint specimens with different gaps. To further predict the deformation modes and hysteretic behavior of the joint involving gap, nonlinear numerical analyses were performed using ABAQUS. Results indicated that the predictions of theoretical and numerical model were in good accordance with the experimental results. Then, the parametric analyses were carried out based on the validated finite element model, the effects on the rotational behavior of straight M-T joint of major parameters, such as the friction coefficient of wood, vertical gaps, and horizontal gaps, were analyzed. It is found that the initial rotational stiffness, yielding moment, peak moment, and ductility of the joint with gap increased with an increase in the friction coefficient. The initial rotational stiffness, yielding moment, and peak moment of the joint remarkably decreased with the increase of the vertical and horizontal gap. The ductility of joint significantly reduced with the increasing vertical gap, however, the joint slightly improved with an increase in the horizontal gap.