Experimental Study And Theoretical Analysis For Hysteretic Behaviors Of Full-scale And Single-span Traditional Timber Structure

Ancient timber structures imply abundant cultural,artistic and scientific values,however,natural disasters and man-made destructions have inflicted severe accumulated-damage during hundreds of years,which is essential to restore and reinforce rationally.It is an important base to understand structural behaviours of ancient timber structures,especially hysteresis behaviours.Numerous findings have been obtained on the hysteresis behaviours of Dougong and mortise-tenon joints.However,research is limited in terms of a basic unit composed of bracket sets,columns and beam.In this paper,hysteresis behaviours and influences subjected by roof weight and model scale were revealed by experiment,then contributions from swing column and mortise-tenon joints for the total restoring force were obtained by theoretical analysis.Main content,methodology,and results of the study were as follows:?1?A full-scale and single-span timber structure was selected in accordance with the seventh grade of material systems.By analyzing the hysteretic curves,envelope curves,stiffness degradation and energy dissipation during the horizontal and low-cycle reciprocating-loading experiments,it was found that the timber frame was a self-restoring structure with high ductility,which developed a flag-shaped hysteretic loop.The rotation of the columns was main rotational deformation,and thus caused vertical lift and restoration of the whole structure.A large portion of the energy produced is converted to gravitational potential energy in the horizontal lateral process,thus traditional timber sturcture exhibits low energy dissipation.When 1/152<?<1/50??:displacement angle?,obvious stiffness degradation was caused by the column swing and frictional sliding.Frictional sliding was also a major source of the initial energy dissipation.When1/50<?<1/31,the increase of constraining force on components reduced the growth rate of energy dissipation.The frictional sliding and plastic deformation both exert significant influences on the energy dissipation when 1/31<?<1/22.?2?After the seventh-grade model was loaded vertically with three stages,it experienced the same vertical unloading,so influences on hysteresis behaviours from roof weight and loading process was obtained.The results showed there was a linear relationship between the lateral force,elastic stiffness and vertical loads.The column rotation,frictional sliding,and constraining force on components reduced the amplitude of increased stiffness due to vertical loading;During the process of vertical loading and unloading,the plastic deformation increased,however,the lateral force,stiffness and hysteretic energy dissipation decreased,and decreased amplitude and influence area expanded with the increase of vertical load level.?3?The horizontal and low-cycle reciprocating-loading experiments were carried for the eighth-grade model.Compared with the seventh-grade model,it was found that the relationship of timber structure between the ratio of hysteretic characteristics and the model scale is significantly different from the size effect of Dougong and mortise-tenon joints.The eighth-grade model had a larger proportion of energy dissipation and friction slip.When?>0.01rad,the scale ratio did not affect the stiffness of timber structure.In addition,the relationship between the structural behaviour ratio and model scale for seventh and eighth-grade models provided references for size effect.?4?The M-?relationship of mortise-tenon joints was theoretically derived based on embedment behaviours and spring back effect,and the restoring force of columns was obtained from F₁/F₀-?₁/B coefficient curve.The theoretical results together with tests showed when the horizontal displacement was small,column restoring force wss the dominant part of the total restoring force.When the displacement was large,the total restoring force was provided by columns and mortise-tenon joints.