Earthquake Response Analysis And Primary Study Of Structure Health Monitoring On YingXian Wooden Tower

"Yingxian Wooden Tower"is the existing tallest and oldest wooden tower in China. This tower situates at the"Shanxi Datong basin"earthquake belt, it has experienced many times of strong earthquake and artificial destruction during its one thousands years of life. There are many serious local damages in the tower body. The lumber which the tower is consisted of is becoming weak because of physical, chemical and biological influences."The Yingxian area"is an earthquake-prone region, so the first topic in this paper is the tower earthquake response analysis.Based on in situ measurement of modal parameters, earthquake response analysis was carried out by using modes decomposition method. Inputs with different amplitude, different spectrum were used .Analysis results show that the natural frequency and the damping ratio have the very tremendous influence on the structure earthquake resistance ability. The first natural frequency of the tower is lower (0.62Hz); the damping ratio is higher (8%). Northridge and El Centro earthquake records came from similar site condition as the tower; ratios of the response PGA to input PGA are 0.82 and 0.88 respectively; when the Mexico City record which came from soft site was used as input, the ratio of the response PGA to input PGA becomes 1.72. It is obvious that the predominant frequency of Mexico City record is close to the first modal frequency of the tower, and the predominant frequencies of Northridge record and EL Centro record are much higher than the first modal frequency of the tower. It can concluded that the tower hold a lot of potential to resist earthquakes as Northridge record or EL Centro record.An earthquake monitoring system was designed for"Yingxian Wooden Tower"The system will cover quake of free site, horizontal, vertical and torsional vibration of the tower body. The system consists of force balanced type of sensors and 16 bits of multi-channel of data recorder. Because of the large dynamic ranges, the system can measure both microtremor and earthquake.Because the tower is so important, a structural health monitoring system is designed for it. The system consists of BJQN-4 bridge deflection meters, SW-3 displacement sensors and high resolution of digital cameras. Local distortion, members damage and integral deformation will be monitoring.