The Main Structural Damages And Damage Mechanism Analysis On Yingxian Wooden Tower

The 65.86-m tall "YingXian Wooden Tower", a cultural heritage under first-class state protection, is not only the tallest but the oldest existing wooden tower in china. The tower, an octagonal structure of five stories and a liao-dynasty structure, was completely made of wood without a single nail used. Compared with the renowned leaning tower of Pisa in Italy, the wooden tower is 117 years older and 9.86 meters taller.The tower is faced to being repaired and it is important guarantee to analyze its damage state. The major material, the wood in the tower, has been suffered physics and chemistry corrosion and external force for nearly a thousand years, which made load-capacity of the tower fade down. The tower structure is different of modern building, the weak wood performance and strong external force make its damage to reach threat the level of its safety. The present damage situation and environment change land artificial unfavourable factors have accelerated the speed of the tower continued damage. In this paper, the damage types and mechanism of the tower are systematic analysed, one new analysis method on ancient building structure is formed and the repairing method of the tower is considered.(1) Horizontally and vertical level deforms of each column and the tower whole are gotten. There are greater change position relatively and discrepancy between each two components, especially that of puzuo layer of second floor pingzuo. These have caused serious threat on the safety of the tower and should be first considered.(2) The damage types of each kind of component have been analysed. There are pillar surface crack and corrode, column foot rotten and split ,the ageing of column surface layer. The ends of beam and fang have crack, rotten, ring split, large deforms etc. Hua arch droop and break, loudou split etc. All these become the common damage type in each kind of component. The result of damage weaken component effective section of the tower and partial components lose bearing capacity and have reduced the reliability of the tower. These are the large quantities and very difficult problems in repairing projects.(3) On-site measurements were conducted on the tower. Frequency domain transfer function and the first four vibration modes of the tower in two mutually orthogonal horizontal directions are obtained. Based on the experimental results, the vibration shape orthogonality and mass of each layer, the layer rigidity of the tower is deduced and the greater difference of rigidity of adjacent two floors is discovered. This difference shows that the horizontal relative displacement under earthquake will concentrate on the less rigidity layer. This conclusion is consistent with the current deformed state of the tower.(4)Using the technology of transfer function, we have analyzed the elastic displacement response of layer of the tower under different seismic waves, and established the elastic analysis method of this kind of structure.The 4-line-nonlinear model was obtained by pseudodynamic testing of1/10-scaled model of yingxian wooden tower and by considering its material performance deterioration and structure damage state. Under different seismic waves, the horizontal elastic-plastic displacements of each storey were analyzed in terms of equivalent energy principle, and the dissipated energy in different damage states are discussed.(5) We have preliminarily classified the damage grade of old wooden building and marked corresponding parameters. Two-parameter seismic damage norm on ancient wooden building are proposed to perform the seismic appraisement of the wooden tower. The tower energy dissipation ability is lowered for the damaged parts and remained displacements, which make the tower seismic resistance ability weak.(6) The inner mechanism which have formed the tower deform and damage are as follow: There are notable horizontal veins pressing deformation and obvious plasticity. Along with time passing, the strength and density and tenacity of timber are reduced and brittleness strengthens and drawing out thing increased. The beams and fu and fang and dou and arch etc. are horizontal veins pressing components. There are different rigidity ratio between two adjacent two floors of the tower and each layer quality center is not consistent with rigidity center. The column friction force reduction and each puzuo layer stability decreasing and the supplementary components relax etc. have reduced stability of the tower ? The external mechanism which have formed the tower deform and damage are as follow. The strong outside force which act on the tower are bombard, gale and earthquake. What cause wooden tower fatigue damage are wind and people stream mainly. What cause timber material corrode are physics, chemistry and biota etc..