Material And Structural Behavior Of Dougong Bracket Complex

Dougong bracket complex,a special group of connection components between column and beam,plays a pivotal role in both structural force transmission and decorative function.With its unique shape with overlapping cantilevers,the special structure functions as a ductile connection to dissipate energy between column and beam,especially under lateral forces in earthquakes.In the meantime,as the large dimension log keeps decreasing worldwide,this study is aimed at exploring structural behavior of Dougong made of sawn timber and Glulam as well as the utilization of Glulam in conservation and reconstruction of traditional timber structures.Taking the Dougong bracket complex on the column of Tianwang palace in Baosheng Temple,Ming Dynasty as the research object,experimental study was carried out on 3 groups of cyclic loading tests of the full-scale Dougong specimen made of China pine sawn timber and Hemlock Glulam.The cyclic displacement schedule was set according to ISO 16670.As approximated actual roof load was calculated as about 2.4t,the vertical load added in the test was set as three steps,increased from 0.8t(1/3 of the actual load),1.6t(2/3 of the actual load)to 2.4t,in which the maximum cyclic displacements of the specimen were controlled as ±1/100 rad within the structural initial stiffness under vertical load of 0.8t and 1.6t.After the completion of the experiment,the specimen was pulled in static loading up to about 1/15 rad.In the static test under vertical load of 2.4t,visible damage occurred at the connection between Ludou with the basement(column),where embedment destroy appeared both at the bottom surface of Ludou and the top surface of the basement(column).Based on the hysteresis curve and skeleton curve of forcedisplacement obtained in the experiment under different conditions,the energy-distribution of main components and transformation of the lateral structural rigidity of the whole specimen under different vertical load was studied,and major conclusions are as follows.The rotation of Ludou component plays an important role in the whole deformation of Dougong bracket complex,in which the elastic modulus and embedment strength perpendicular to the grain give much influence to the rotation rigidity and strength of Ludou.In contrast with Dougong specimen made of sawn timber,the other one made of Glulam has more stable working and energy dissipating conditions under lateral load,but when Glulam applied on the smaller components or tenon and mortise connections,the different adhesive strength and fiber directions will increase the instability of their performance.In addition,the skewing and gap at the connection of Huagong and Chaang component are easily leading to the unbalanced force condition and large deformation of Dougong bracket complex,as well as contributing to dissipate more energy.On the other hand,Structural rigidity analysis were carried out based on existing theories.On account of the “rigid floor assumption”,the Dou-gong specimen can be simplified as 1Dspring analogy for the actual analysis.After overlying rotation deformation caused by embedment of Dou to Gong and sliding deformation caused by dowel-mortise connections,the global lateral rigidity of Dou-Gong specimen was finally acquired which was in good agreement with the experiment results.