Analysis On Energy Dissipation Mechanism And Dynamic Characteristic For Chinese Ancient Timber Buildings

Chinese ancient timber buildings (CATB) system is a unique building system in the world ancient buildings with high historical, cultural relic, artistic and scientific value. The study of the structural properties and seismic performance of CATB is important for maintaining and protecting CATB. The palace timber structure was selected as a research object. The unique structural form and characteristics, load-transferring mechanism and seismic characteristics have been studied by theoretical analysis, model tests and numerical simulation.Through the low cyclic loading experiment of single Dougong, two Dougongs and four Dougongs, the degrading rule of lateral stiffness of Dougong have been studied. According that, the hysteresis curve and skeleton curve of force-displacement are researched and the formula of resilience model and mechanical model are established. From the experiment, we can see that slippage is the main deformation of Dougong. Energy dissipation because of frictional slippage is an important reason for the excellent seismic behavior of ancient wooden structure. Hysteretic loops of Dougong assume to be parallelogram-type. Experiment agrees with theoretic analysis, Plump area of hysteretic loop accounts for its excellent energy dissipation performance. The mechanic model of Dougong belongs to linear strengthen elastic-plastic model. Both the fitting equation of force-displacement and resilience model reflect the changes in stiffness of Dougong, and adapt to the research on static load delivery as well as dynamic structural analysis and calculation of similar wooden structure.The low-cyclic reversed loading tests were conducted on 9 wooden frame models, including 3 straight mortise-tenon structure models and 3 swallow-tailed mortise-tenon structure models made in accordance with the requirements of the Fabrication Methods of Song Dynasty (960-1270, A.D.),3 swallow-tailed mortise-tenon structure models strengthened with carbon fiber reinforced polymer (CFRP) sheets. Such behaviors as the failure characteristics, hysteretic curve and skeleton curve, degeneration of strength and rigidity, deformation and energy dissipation capacity are analyzed. Restoring force model is established based on this experiment, and that of prototype structure is obtained.An intermediate bay model of an ancient palace was made according to Fabrication Methods of Song dynasty, on which the shaking table test was carried out. The responses of the model and the data of the shaking table were measured under three waves: El Centro, Taft and LAN ZHOU waves. The failure mode, nature period, damping ratio, displacement, accelerations and hysteretic energy dissipation performance are analyzed. Those conclusions are achieved:The nature period and damping ratio of the model increase along with the increasing seismic power. The range of nature period T is 0.48-0.67s and the damping ratioξis 2.9%-4.6%. The dynamic magnification factorβ4 decreases under the seismic power. Dougong layer and column base dissipate seismic energy through the way of frictional slippage. The mortise-tenon joint of the frame has the strongest capability of energy dissipation. It plays an important part in shock absorption by energy dissipation.An ancient palace timber structure model was made according to the requirements of Fabrication Methods of Song Dynasty (960-1270, A.D.). All swallow-tailed mortise-tenon joints of frame were strengthened with carbon fiber reinforced polymer (CFRP) sheets after its collapse, then the shaking table test was carried out. The sensors were placed to measure the real-time responses of the model and the data of the shaking table itself under three waves:El Centro, Taft and LAN Zhou waves. The failure mode, dynamic behaviors and hysteretic energy dissipation performance are analyzed. Those conclusions are achieved:The nature period and damping ratio of the model increase along with the increasing seismic power. The range of nature period T is 0.53-0.67s and the damping ratioξis 2.8%-4.6%. The dynamic factorβdecreases under the increasing vibrational excitation. Dougong layer and column base dissipate seismic energy by means of frictional slippage. The joints strengthened with CFRP sheets have the strongest capability of energy dissipation and play an important part in shock absorption by energy dissipation.