Abstract:This paper discussed the bearing mechanism of ancient wooden structure from the aspects of damage and degradation of material, column foot joints, gaps and performance of mortise-tenon joints, performances of Dou-gong and wooden frame. A time-varying model of the wood component was proposed based on the macroscopic and microscopic analysis of the wood properties.Then the mechanical model and the fine analysis method of the wooden column with rocking-uplift behavior were established.Also, the probability distribution model of gaps of mortise-tenon joint was established, the model and analysis method of mortise-tenon joints were constructed.And the mechanical properties of single Dou-gong and the synergistic effect of Dou-gong layer were analyzed.Finally, the comprehensive seismic mechanism including the friction energy dissipation of the joints, gravitational potential energy storage of the heavy roof and the energy release of the frame by long period rocking were summarized through the experiment and theoretical analysis of the rocking wooden frame.

Abstract:Ancient timber structures on sloped lands are an important part of the ancient Chinese architecture. Due to the unequal height constraint at the bottom of columns, they are different from the ancient timber structures on flat lands in the aspects of architecture layout, structure characteristics and seismic performance. In recent years, the investigations on seismic damage of ancient buildings show that the damage degree of ancient timber structures on sloped lands is generally more serious than that on flat lands. To protect ancient timber structures on sloped lands much better, the basic concept of ancient timber structures on sloped lands is expounded and the architecture characteristics,structure forms and structure characteristics of ancient timber structures on sloped lands are summarized. According to the results of many investigations on seismic damage of ancient buildings, the typical earthquake damage characteristics and causes of ancient timber structures on sloped lands are analyzed, such as foundation failure, column foot slip, mortise-tenon failure, column frame torsion, roof failure and frame collapse.The similarities and differences between seismic damage of the ancient timber structures on flat lands and those on sloped lands are pointed out.The key scientific problems of seismic research on ancient timber structures on sloped lands are illustrated from the aspects of dynamic characteristics, analysis model, seismic mechanism, failure mode and reinforcement method and the thinking and direction for the subsequent seismic performance research are pointed out.

Abstract:In order to study the effect of stylobate on the seismic responses of Yingxian Wooden Tower, the models of octagonal stylobate, the upper timber frame and the overall structure are built by ANSYS finite element software. The modal analysis method is used to obtain the natural frequencies and periods of the model. The direction of the weak horizontal stiffness of the upper timber structure is obtained, and seismic wave excitation is input to the upper wooden structure and the overall structure model respectively. Then the seismic responses of the two models are compared and analyzed. Results show that the octagonal stylobate has a higher natural frequency and all frequencies are relatively close. And when the high-order frequency of the upper timber structure is close to that of the stylobate, the stylobate obviously affects the dynamic properties of the upper timber structure. The east-west direction of the wooden tower is the direction of weak horizontal stiffness.Compared with other seismic wave excitations, the acceleration and displacement responses of the upper timber structure and the overall structure model are greater when the long-period Tianjin wave is input. As the peak acceleration of the inputting excitation increases, the dynamic coefficients only considering the structure decrease.Under the excitation of the same type of seismic wave with the same peak acceleration, the acceleration and displacement response of the overall structure are greater than those of the upper timber structure.

Abstract:In response to the needs of seismic reinforcement and performance improvement of the mortise-tenon joints in wood structure buildings, this paper proposed the use of embedded dampers to enhance the performance of the mortise-tenon joints and made five groups of scaled mortise-tenon joint models including unreinforced, single-layer reinforced and double-layer reinforced embedded dampers. Through the test research of seismic performance, the seismic performance of the mortise-tenon joints with different thickness and number of layers was compared with that of the joints without reinforcement, and the seismic performance of embedded dampers with different parameters on the joints of mortise-tenon were analyzed. The results show that the embedded dampers have the characteristics of two-way energy dissipation, multi-point yielding and strong designability, which can greatly improve the seismic performance of the mortise-tenon joints and effectively suppress the tenon pulling phenomenon of joints; compared with the unreinforced joint, the embedded dampers-enhanced joints has a small increase in bearing capacity, the energy consumption capacity has been greatly improved and the initial stiffness has been greatly improved by more than 50 times; the steel plate thickness and the number of layers of the embedded dampers are the main factors affecting the seismic performance of the mortise-tenon joints, and the thickness has the greatest impact on the mechanical properties of the mortise-tenon joints strengthened by the embedded dampers; the double-layer embedded dampers is more effective than the single-layer energy dissipater.

Abstract:In view of the poor seismic performance of the ancient pagoda wall, a new seismic strengthening technology, strengthening the ancient pagoda wall with shape memory alloy wire (SMA wire), was proposed. In order to study the reinforcement effect, the mechanical properties of SMA wire were tested, and the influence of strain amplitude on its energy consumption was analyzed. The SMA wires were trained by loading and unloading to maintain a stable fully superelastic state. Then, the pseudo-static tests of two ancient pagoda wall models (one intact wall and one damaged wall) strengthened with SMA wire and one unreinforced model were carried out. The effects of SMA wire reinforcement on the seismic performance such as failure mode, hysteretic performance, bearing capacity, deformability, stiffness degradation law, ductility and energy dissipation capacity of historical masonry tower wall were studied. Test results show that SMA wire reinforcement does not change the failure mode of the wall, but can improve the brittle failure to a certain extent, can significantly improve the bearing capacity and energy consumption capacity of the wall, effectively limit the shear deformation of the wall and delay the wall cracking and stiffness degradation. Compared with the unreinforced wall, the bearing capacity and ultimate displacement of the wall strengthened with SMA wire increase by 16.91% and 22.65%, respectively. The bearing capacity and deformation capacity of the damaged wall strengthened with SMA wire are even greater than that of the intact wall. However, the stiffness and bearing capacity of elastic section and cracked section are obviously lower than that of intact wall.

Abstract:The palace-style timber building in Tang Dynasty is the earliest wooden structure remains in China, which has extremely precious historical and scientific research value. In order to further study the horizontal resistance of this kind of timber frame, the refined finite element model of single-room timber frame with four columns verified by model test was established, and the influences of brackets complexes, column head and column foot,load and position of vertical load on the mechanical performances of the timber frame were studied. The results show that the palace-style timber frame in Tang Dynasty swayed and uplifted under the horizontal reversed cyclic load, and its horizontal displacement was mainly the horizontal displacement of column frame layer, and the S-shaped hysteretic curve of the structure is anti-symmetric with pinch effect, which two ends are relatively full. The initial lateral stiffness of timber frame is the largest, and its degradation is obvious with the increase of displacement.The brackets complexes layer is a structural layer with high rigidity, and there is a certain redundancy in the connection between its beams. Both the column head and column foot can enhance the hysteretic energy dissipation and lateral force resistance of the timber frame, but they play different roles in different stages. The larger the vertical load is, the greater the hysteretic energy dissipation and the greater the lateral resistance are. The displacement of the action position within a column diameter length has no obvious effect on the hysteretic energy consumption and lateral force resistance of the timber frame.

Abstract:To study performance of the Chinese ancient timber buildings of Jiangnan area in the Song & Yuan Dynasties in the progressive collapse resistance, the finite element models of a typical Chinese ancient timber building and a corresponding building without Pu-zuo were established by the three-dimensional scanning survey for further pushdown analysis, through which their main collapse mechanism and the effect of the Pu-zuo against the progressive collapse were studied. The results show that: For Chinese traditional timber buildings of the Jiangnan area in the Song and Yuan Dynasties, when a column suddenly fails, the lateral components around it can provide multi-directional linkages to delay or prevent the progressive collapse.The existence of Pu-zuo improves the progressive collapse resistance of the whole structure. A "truss-like" structure is formed among the Pu-zuo to transfer the extra load when the progressive collapse happens, which effectively enhance the linkage and strengthen the alternative load path in the structure. Thus, compared with the timber building without Pu-zuo, the bearing capacity of the typical Chinese ancient timber building with Pu-zuo significantly rises, with increasing by 30%~50%; Compared with the failure of the middle columns, the failure of the side columns tends to result in the progressive collapse of the building.

Abstract:In order to accurately describe the lateral behavior of semi-rigid mortise-tenon frame under horizontal load, a simplified analysis model with elastic rod-spring element is proposed, which can comprehensively consider the semi-rigid effect of mortise-tenon joint and rocking column effect. The global stiffness matrix and lateral stiffness expression of the frame are obtained by direct stiffness method and static condensation method respectively. The proposed model is verified by comparing the calculated values with the low cyclic loading test results. The wood elastic modulus, mortise-tenon stiffness, column height and vertical load were selected as analytical parameters. The parameter results show that the lateral stiffness of the frame with consideration of rocking column is significantly greater than that without consideration. The influence of elastic modulus on the lateral stiffness is very small; The influence of rocking column on the lateral stiffness is gradually reduced with the increase of joint stiffness; The higher the column height, the smaller the column lateral stiffness. The vertical load can significantly improve the lateral performance of the frame. According to the results of parameter analysis, a practical calculation method based on rigid rod-spring element is further proposed. The calculation error is stable at about 10%, which can meet the requirements of engineering accuracy.

Abstract:In order to study the moment-resisting performance and seismic behavior of the interior joints with wooden peg of Chuan-Dou type wooden frame, two full-scale interior beam-column joint specimens of transverse frame and two that of longitudinal frame were designed and fabricated. Monotonic loading and low cyclic loading tests were carried out on the two types of joints, respectively. The failure mode, moment-resisting capacity, flexural stiffness, ductility and energy dissipation of the two types of joints were obtained. The results showed that the failure mode of transverse interior joint was the embedment plastic deformation on the mortise and tenon contacting area as well as the bending-shear combined deformation of wooden peg, while longitudinal interior joint was broken off at the neck of tenon. The initial stiffness of the transverse interior joint was higher than that of the longitudinal interior joint. The moment-resisting capacity of transverse interior joint could reach two times of that of longitudinal interior joint. The hysteretic loops of the two types of joint exhibited obvious squeezing and slip. The energy dissipation of the transverse interior joint was higher than that of the longitudinal interior joint. Both the two types of joint exhibited good deformation capacity, the transverse interior joint exhibited good ductility, while the longitudinal interior joint exhibited poor ductility.The longitudinal interior joint in the frame is the weakest part and need to be noted on the safety maintenance of the Chuan-Dou type wooden frame structure.

Abstract:In order to study the effects of wedge on the seismic performance of loose joints, three full-scale penetrated mortise-tenon joint models are made, including a standard joint, a loose joint and a loose joint with wedge respectively. The deformation characteristics and failure characteristics of three joints were compared and analyzed through laboratory full-scale tests. Hysteresis curves, skeleton curve, stiffness degradation law, energy dissipation and ductility of three joints were analyzed by full scale quasi static test as well. Results show that the failure mode of standard and loose joint is wood fiber torn along the grain at variable cross-section.The failure mode of the joint with wedge is the extrusion failure of wedge.The slipping phenomenon and pinch effect of hysteresis curve decrease after adding the wedge. External load resistance capacity and energy dissipation capacity of loose joint are obviously lower than that of standard joint, and the above performances of joint have a rising trend after adding the wedge. The bending moment of the joint with wedge is about 30% higher than that of the loose joint.

Abstract:Local decay and insect infestation are common damage types in the flexural members of ancient buildings, such as beams and columns.It is of great significance to analyze its mechanical performance by numerical simulation. In the framework of continuum mechanics and damage mechanics, the elastic-plastic damage constitutive model of wood was established, and the corresponding constitutive subroutine was developed based on the user-defined material subroutine UMAT in ABAQUS. The correctness of the constitutive model was verified based on the three-point bending wood beam test in the existing literature. Through the artificial prefabrication of local square groove, the local decay and local insect infestation on the actual wood beams and columns were simulated equivalently. Based on the developed constitutive model, the corresponding finite element model was established, and the correctness of the model was verified by the existing tests of the research group. The results indicated that the elastic-plastic damage constitutive model of wood and the finite element model of timber beam and column can better reflect the nonlinear stress and damage evolution behavior of damaged beam and column members in the stress process.

Abstract:The structural design and seismic performance of Chinese traditional multi-story pavilion-style timber pagoda persistently attract researchers' attention. In this paper, a modeling method of pavilion-style timber pagoda was proposed and verified by using the shaking tablet test results of a scaled seven-story Tang-style timber pagoda. Based on it, the influence of structural swing component and lateral shear component on the seismic performance of traditional multi-story timber pagoda was investigated.The results show that increasing the lateral shear component could improve the structural stiffness and decrease the displacement response under different earthquake intensities, and obtain larger acceleration amplification coefficients and inter-story shear force of the structure simultaneously;The increase of the rocking component will lead to higher nonlinear response under high intensity earthquake.With the increase of the excitation intensity, the inter-story drifts and shear forces of lower floors increase and the acceleration amplification coefficients of upper floors increases first and then decreases.

Abstract:Ancient timber buildings are precious treasure of Chinese nation.However, some of them have suffered different types and degrees of damage after hundreds of years of service, which reduces the safety performance of structures. In this paper, the Tongdao Hall in the Imperial Palace at Beijing is chosen as the research object. Through on-site investigation and damage analysis, the typical damage types, characteristics, influences, quantity and distribution law of structural column frame layer, Dougong layer and beam frame layer are obtained. The causes of its damage are summarized and the protection suggestions are proposed. The results show that the types of structural damage mainly include component cracking, decay, missing, inclination, separation, and pulling-out of tenon joint, etc. Especially, the damage at the column frame layer is the most complex and serious. The reasons for structural damage can be summarized as material degradation and timber defects, biological erosion and variation of natural environment, long-term complex loading effect and irrationality of repair. Establishing structural health monitoring system, strengthening biological disease prevention and control, and promoting the basic research onmechanical performance of timber structures are essential for protection and repair of ancient buildings.

Abstract:In order to study the seismic performance and value damage pattern of timber frame, which are used in ancient timber architecture and infilled with windows and wall, Kanchuang frame is selected as the study object. Kangchuang frames are widely used in Qing official architecture. The 1∶2 reduced-scale models were made for low cyclic loading test. The load-displacement hysteretic curves, skeleton curves, stiffness degradation law and energy dissipation capacity of models were analyzed. The research results show that the load-displacement hysteretic curves have obvious pinching effect, and this effect becomes more obvious with increase of loading displacement and loading cycle number. The walls of Kanchuang frame cracked at first, then the cracks increase with the load increase. The wood structure appears to tenon pulling, lattice splintering and other damage. Walls contribute great stiffness to the structure. Combined with the possible value points of sill window frame, a value-based damage evaluation standard for Kanchuang frame is proposed, which provides good reference for the repair, reinforcement, and value loss evaluation of ancient timber architecture.

Abstract:In order to investigate the impact of different reinforcement measures on the seismic performance of the mortise-tenon joints in timber structures, five groups of mortise-tenon joint specimens of three types: Tou mortise-tenon joints, Ban mortise-tenon joints, and dovetail mortise-tenon joints were made to carry out the quasi-static tests referring to the typical mortise-tenon joint of traditional timber structure in the southwest region of China. The four groups were reinforced with iron hook, steel plate, and wood strip(two groups). The seismic performance parameters of reinforced and non-reinforced joint specimens, such as failure forms, hysteretic and skeleton curves, amount of tenon pullout, and energy dissipation, were comparatively studied. The test results show that the main failure modes of the unreinforced mortise-tenon joints are cracking in squeeze of the mortise-tenon and pullout of the tenon.The reinforced joints are mainly damaged by iron hook breakage, steel plate bending-torsion yielding, and wood strip breaking. All the reinforcement measures can effectively improve the bearing capacity of the joint and reduce the pullout of tenon. The reduction ratio of the pullout amount of the reinforced joint is more than 5%. By comparison, the bearing capacity of the joints reinforced with wood strip is improved significantly. The negative bearing capacity of the Ban mortise-tenon joints and dovetail joints is increased by more than 10 times after reinforcement.At the same time, the energy dissipation of the Ban mortise-tenon joint reinforced with wood strips is increased by more than 260%, and the energy dissipation of the reinforced joint with iron hook and steel plate can also be significantly improved.

Abstract:Considering that traditional damage detection needs to install contact sensors, which is not conducive for protection of ancient timber structures, a non-contact damage identification method based on digital image correlation (DIC) by using painted patterns of ancient buildings itself was proposed. Firstly, the time series images of the painted wooden beam during vibration are captured by the digital camera. Then, use the integer and sub-pixel displacement search algorithm to calculate the displacement response time history of each point on the wooden beam as well as the Fourier transform to obtain the amplitude-frequency and phase-frequency curves. Finally, the operational mode of the wooden beam is extracted by the amplitude-frequency amplitude and phase-frequency phase angle.This study then adopts the rotation mode and the curvature mode as damage characteristic indicators for damage identification by the advantage of using the DIC method to obtain modal information of all pixels along the beam length. Results from simulation and experiment of painted simply supported beam show that the operational mode obtained by the DIC method can accurately identify the damage location and the relative damage degree of the wooden beam, which provides a new technique for preventive protection of ancient timber structures.

Abstract:Tibetan masonry is widely used in Tibetan building walls. Various forms of deterioration such as cracks, tilt and material damage have occurred under the influence of natural disasters, man-made damage and other environmental impacts. A reasonable assessment of the health of deteriorated Tibetan walls by using scientific methods has always been a difficult point for protection of ancient Tibetan masonry structures. This paper conducts a comprehensive study on several main damage forms that affect Tibetan masonry walls relied on the fuzzy evaluation method and the analytic hierarchy process. The weight coefficients of various influencing factors such as cracks, tilt and material damage are obtained through the parameter iterative process and verified by two brick masonry test models. A quantitative evaluation standard for performance of the masonry structure wall is given. It also gives the weight coefficient that objectively determine using fuzzy evaluation method.The research results can be used for the rapid comprehensive evaluation of the damage state of the dual-purpose Tibetan masonry structure, and provide a reference for daily inspection and safety assessment of Tibetan building walls.

Abstract:In this paper, the failure mode and damage of pagoda on Shanxi Jiwang Mountain under different earthquakes were calculated and analyzed by numerical method, which provides a basis for the seismic reinforcement of Jiwang pagoda. The plastic damage constitutive model was applied to describe the damage failure of masonry structures under earthquake. The displacement forms of the ancient pagoda under the action of seismic waves with different amplitude-modulation coefficients were given,the seismic responses values such as interlayer displacement and acceleration amplification factors were obtained, and the distribution rules of earthquake-induced damage were discussed. The results show that the overall stiffness distribution of the pagoda on Jiwang Mountain is uniform, and the acceleration amplification factor at the top pagoda is the greatest. Although the bottom wall of the pagoda is thicker than that on top, the tensile damage still initiated from the bottom under earthquake, and it expands upward with increase of seismic intensity. The stress contours show that the maximum principal tensile stress area at the bottom of the pagoda under earthquake expands obliquely, which easily leads to the formation of oblique cracks in the pagoda. The weak layers of the pagoda are the bottom three layers and the top layer.

Abstract:Structural modal parameter identification is generally the foundation and emphasis of structural health monitoring. It can evaluate the structural state and identify structural damage, which is of great significance to the subsequent maintenance of the structure, as well as the ancient building structure. Xi'an city wall belongs to the first batch of key cultural relic protection units in China, and its modal parameter identification needs more attention. Based on the monitoring system of velocity and acceleration dynamic characteristics of the wall at the Wengcheng of Xi'an urban wall, the vibration response data of the urban wall under the excitation of complex traffic environment were obtained through the field dynamic test. The structural modal parameters of the response data were identified by the combination of the three modal identification methods of the feature system realization algorithm (ERA), the random subspace method (SSI) and the peak value method (PP) to obtain the modal parameters of the urban wall in the region. Combined with the numerical finite element model, the modal parameters obtained by the three methods were compared to establish an effective structural dynamic model. The results show that these three methods can effectively identify the modal frequency of the structure under environmental excitation and finally obtain the vibration mode, which verifies the feasibility of the three modal identification methods for the modal parameter identification of the ancient city wall.

Abstract:The interface performance of rammed earth and timber beam of Fujian Tulou buildings determines the interaction of the two, and the bond slip relationship of rammed earth and wooden beam is a comprehensive reflection of the interfacial performance. In order to investigate the bond-slip performance of rammed earth-timber beam joints, eight pull-out tests of rammed earth-timber beam joint specimens were conducted. The test parameters included the vertical load, the timber beam penetration length, and surface roughness. The influences of these parameters on the maximum load and the composition of the bonding force were analyzed.The interface between timber beam and rammed earth was modeled and analyzed by finite element method, and the calculation method of bonding force was put forward. The results show that the interface failure modes of rammed earth and timber beam include pull-out failure of timber beam and cracking failure of rammed earth. The bond slip curve of such interfaces can be divided into three stages, including the linear ascending stage, the slip transition stage and the residual friction stage; the finite element simulation shows that the connector spring can well represent the interface performance of rammed earth-timber beam joints; the bonding force at the interface between timber beam and rammed earth includes the cementation force, the friction force between timber beam and the contact surface of rammed earth, and the matrix suction of soil. With continuous sliding, the cementation force keeps failing and approaches zero, and only the friction force and matrix suction exist in the friction residual section.

Abstract:The ruins soil of Qicheng is silty clay, typically linked with unfavorable characteristics such as loose structure, low strength, strong capillary action and poor hydraulic property. How to improve the performance of the soil in the restoration site is of great concern. In this study, glutinous rice slurry, quartz sand, alumina and calcium fluoride were added to the silty clay in Qicheng site for improvement. The imitation ruins soil was prepared by this method. The mechanical properties, microstructure and color difference of the imitation ruins soil modified with different glutinous rice slurry contents (of 0%, 1%, 3%, 5%, 7%, and 9% concentrations) were studied. The results show that with the increase of the glutinous rice slurry concentration, the strength and internal friction angle of soil samples increase first and then decrease, and the cohesion shows a linear increasing trend; Imitation ruins soil improved by 3% concentration of glutinous rice slurry had the largest shear strength, unconfined compressive strength and internal friction angle, and its microstructure is dense; The color difference analysis of the soil sample shows that the color difference between the imitation ruins soil, imitation ruins soil improved by 3% concentration of glutinous rice slurry and the ruins soil are all small; Furthermore, using glutinous rice slurry to improve the MICP technique, it is found that glutinous rice slurry can increase the activity of bacteria and promote the production of calcium carbonate. With increasing of maintenance days, the strength of modified MICP soil has an increasing tendency, and the biological mineralization time is longer.

Abstract:On the basis of field investigation and long-term monitoring results, the main factors that affect the mechanical performance of the Meridian Gate platform structure are studied by combining numerical simulation and experimental design method. This paper presents the results of the study in performance variation mechanism of the Meridian Gate platform structure through different aspects, i.e. freeze-thaw, partial water-saturation, differential vertical displacement at the bottom of platform, vertical load at the top of platform and coupled effect between the factors.The results show that the vertical load at the top, the uneven vertical deformation at the bottom and the partial water-saturation are main influential factors for the structural stress, and the number of freeze-thaw cycles, the coupled effect between the number of freeze-thaw cycles and the duration of partial water-saturation are also key factors for the maximum tensile stress in the area of arched doors; In the aspect of structural deformation of the Meridian Gate platform structure, the partial water-saturation, the differential vertical displacement at the bottom of platform and the vertical load are the significant factors. This study reveals the major factors and the influencing law of the mechanical performance of the platform structure and provides a scientific basis for the routine protection and preventative protection of similar heritage masonry structures.