###### Abstract
The seismic performance of typical mortise-tenon joints in traditional wooden buildings in southern China and the semi-rigid mechanical properties of four typical mortise-tenon joints were obtained by [PERSON] [11]. Five joints of the historical building in Yangzhou as the prototype were studied by [PERSON] [12]. All of the test samples were created using traditional manufacturing methods and were taken straight from the original structure. However, the time of a century or even a thousand years led to a different degree of loosening, resulting in a gap at the mortise-tenon joint. The main causes of the gap between the tenon and mortise may be a processing mistake, dry shrinkage brought on by a change in moisture content or creep brought on by long-term load [13]. The mechanical properties of mortise-tenon joints with different degrees of damage and good penetration were studied by artificial simulation [14]. The rotation behaviour of mortise-tenon joints with different degradation types and degrees was studied by [PERSON] [15] and [PERSON] [16]. The effect of the degree of loosening on the mechanical properties of the dovetail mortise-tenon was studied by [PERSON] [17]. The rotational performance of traditional Nuki joints with gaps in Japan was studied by [PERSON] [18; 19]. Theoretical estimation of the mechanical performance of the traditional mortise-tenon joint involving a gap was researched by [PERSON] [20]. The above studies have revealed the mechanical properties and seismic performances of standard and damaged mortise-tenon joints. However, mechanical performances and working principles of the models are mostly based on the small-scale model test. The wood structure is a nonlinear flexible structure, which has multiple nonlinearities in contact friction, elastoplasticity of material and cross-sectional dimension. Small-scale models cannot completely reflect the seismic performances of joints in the actual structure, and the study of mortise-tenon joints rarely involves the construction asymmetry and loose conditions of joints. When the scaled model is used for the structural test, the correlation between the mechanical properties of the test model and the original structure should be considered. The model dimension can be scaled linearly, while the external loads cannot be scaled linearly. Additionally, the nonlinear effects of the scale on the mechanical properties of the structure are overlooked in the current experimental research. The relationship of the vertical load between the test model and the prototype structure is paid less attention. The full-scale model can best capture the mechanical performance of the structure and resolve the nonlinear correlation of loads. Meanwhile, there is a lack of field investigation and analysis on the damaged types of joints. In this paper, current damage situations of mortise-tenon joints based on the field investigation in the Feiyun Wood Pavilion are summarized and analyzed. Then, the deformation characteristics and failure mode of loose joints under different degrees of looseness are studied by a low-cycle cyclic test. Rotational stiffness, stiffness degradation law and energy dissipation capacity of loose joints are analyzed and compared. The limitation value of gap is given, and the three-parameter power function model with neighbouring gaps and the failure section for the restoring moment of loose penetrated mortise-tenon joints are proposed. The stress state of loose penetrated mortise-tenon joints with different loose conditions is discussed.