Research On Friction Energy Dissipation And Seismic Performance For The Joints Of Ancient Timber Structures

Affected by the earthquake, a certain amount of horizontal dislocation and friction in ancient timber structures is allowed to happen between the mortise-tenon joints, and it is just the friction and energy dissipation of mortise-tenon joints which make timber structure have a good anti-seismic performance. Therefore, the research on structure characteristics of ancient timber structure and its anti-seismic performance will be launched on the basis of the in-depth study about the characteristics of the mortise-tenon joints. In view of the principle of energy equivalence, this thesis deduces the equivalent damping coefficient from the energy dissipation of dry friction between mortise-tenon joints. And taking a single frame as an example, it launches a quantitative research on the friction energy dissipation and anti-seismic performance of the joints of timber structures. Based on the friction energy dissipation for the joints, a simplified model of the whole structure of Xi’an bell tower is established to explore the anti-seismic performance of timber structure. The main research work accomplished in this thesis is as follows,(1) Based on the principle of energy equivalence, this thesis establishes the equivalent friction damping system on the joints of timber structure and transforms the friction force between the contact surfaces of mortise-tenon into the equivalent damping to deduce the equivalence damping coefficient of mortise-tenon joints on energy dissipation from dry friction. Taking widely-used dovetail joints as example, the equivalent damping coefficient of the mortise-tenon of timber structure can be derived quantitatively.(2) Taking a single frame as an example, according to the equivalent damping coefficient of mortise-tenon joints on the energy dissipation of dry friction, this thesis launches the research comparatively on the relative displacement between the beams,capital and beam column under the earthquake action. In accordance with the analysis of hysteretic curve and accumulative energy dissipation curve of timber structure at all levels, introducing the damping coefficient b, the result shows that the friction sliding of mortise-tenon joints has a better damping effect under the earthquake and the damping effect will be more obvious along with the increase of seismic load, the energy dissipation of the pillar support connected by mortise-tenon accounts for the main part of total energy dissipation, and the friction sliding of mortise-tenon joints can also take a certain proportion of total energy dissipation.(3) To study the effect of energy dissipation dry friction quantitatively on the overall structure and take the Xi’an bell tower as the research object, according to the equivalent damping coefficient of friction energy dissipation of nodes and the modal analysis of the structure, the correctness of the model was verified, the displacement and acceleration response characteristics of the column base, first layer, second layer and roof under different earthquake excitation were studied, and the dynamic characteristics of structure and the displacement of roof deformation were compared and analyzed. The following conclusions are obtained.Each layer displacement damping coefficient of the timber structure is among 75%~80% in considering the friction damping, which quantitatively depicts the damping effect that friction energy dissipation of mortise-tenon joints effects on the overall structure,dynamic magnification coefficient on each layer gradually decreases from bottom to top, which indicates that ancient timber structures has better damping characteristics, sliding friction in ancient timber structures node can reduce lateral angle of wooden frame of the tower, which reflects the friction sliding of mortise-tenon joints between beam and column can ensure the overall deformation of ancient timber structures better.