Study Of Mechanics Model And Seismic Strengthening Of Tenon-Mortise Joints In Chinese Ancient Timber Structure

Chinese ancient timber structure is world famous for its magnificence and unique structure. It has become a representative of the oriental building structures, and produced profound influence to the emergence and development of building structures in neighboring countries. The Wenchuan earthquake in2008had brought an unprecedented disaster to ancient cultural heritage in disaster areas. Many ancient buildings considered to have good seismic performance appeared different degree of damage. Damage of the tenon-mortise joint is one of characteristics of typical seismic damage. So study on mechanism of the tenon-mortise joint and the corresponding reinforcement measures have significant social value. In this paper, mechanical model of the straight tenon-mortise joint is studied, according to theoretical analysis, and reinforcing method for tenon-mortise joint with dampers are also discussed. The main contents and the achievements of this paper are summarized as follows:At first, mechanics of the straight tenon-mortise joints under a loading loop is analyzed in detail. The theoretical model of M-θ relationship of the straight tenon-mortise joints is proposed, considering the nonlinear compression property of wood and the pulling process of the tenon. The theoretical M-θ relationship curve is in good agreement with the experimental ones, illustrated by Matlab program. Top and bottom surfaces of the straight tenon-mortise joints contribute most to the bending stiffness. Each feature points of the theoretical M-θ relationship curve is deduced by mechanics analysis and mathematical solution, with which the theoretical model is simplified for the convenience of engineering application.Secondly, tenon-mortise joint is simplified as variable stiffness springs in6directions, and two finite element models including straight tenon-mortise structure model and swallow-tailed tenon-mortise structural model are established. Comparison shows that dynamic amplification factor of the straight tenon-mortise structural model is larger than the one of swallow-tailed tenon-mortise structural model in higher seismic acceleration. It means that stiffness of the straight tenon-mortise is larger than the other one.Thirdly, one non-reinforced and three reinforced tenon-mortise structural models are analyzed. The reinforced tenon-mortise structural models are strengthened with flat steel, carbon fiber reinforced polyer (CFRP) sheet, and dampers, respectively. Analysis results show that the four strengthened methods affecting dynamic amplification factor in a descending order as:strengthened with flat steel, strengthened with CFRP sheets, the non-reinforced model, and strengthened with damper. It means that strengthening a tenon-mortise joint with dampers will reduce dynamic response of the whole structure, compared to strengthened with flat steel or CFRP sheets. Study shows that there is a optimal damping value when a tenon-mortise joint is strengthened.At last, according to the theoretical model of M-G relationship of the straight tenon-mortise joints, time-history analysis of Huangdi temple element model proves that symmetrical stiffness which causes the torsion results in seismic damage of the temple. After that, two reinforced tenon-mortise structural models are compared, including a model created according to the actual situation strengthened with flat steel, and a virtual model strengthened with dampers. Analysis result shows that the internal force and dynamic response of tenon-mortise joints strengthened with flat steel is increased compared to those strengthened with dampers. It indicates that these tenon-mortise joints are easier to be damaged in the future earthquake.While, the internal force and dynamic response of the whole structure will be reduced with dampers.In summary, unique mechanical characteristics of the tenon-mortise should be protected when reinforced. Strengthening a tenon-mortise joint with dampers has advantages compared with traditional ways. These studies will take important part in seismic mechanism and seismic strengthening of ancient timber structure.