Structural System Identification Based On Health Monitoring Testbed Of Tongde Plaza Yue Center

Structural health monitoring is to determine and track the structural integrity and evaluate the properties of structural damage.Identify the virgin structural state and monitor the structure for a long time is in order to evaluate the structural health state better.On the basis of automatic data acquisition,the structural monitoring system evaluates the working state by monitoring the environmental load and the whole deformation of the structure.By monitoring the structural response before and after the supernormal load,the change of structural characteristics can be obtained and the structural damage can be detected and evaluated.Structural degradation is detected by long-term monitoring.This thesis is based on constructing a structural health monitoring testbed-Tongde Plaza Yue Center in most active seismic area-Kunming,Yunnan province,China.Using the ambient vibration test data of monitoring project.Then simplify the structure into a uniform Timoshenko beam,calculate the structural characteristics and the wave propagation characteristics.Next get the finite element model of this structure,calculate the structural characteristics,seismic responses and so on.Simplify the structure into 1-layer and 5-layer Timoshenko beam,which is used to analyze the structural system identification.The main research contents and conclusions are as follows.Structural health monitoring system consists of four parts,which are monitoring system,data acquisition and transmission system,data processing system and structural health assessment system.Monitoring system is mainly used to record the acceleration,velocity and displacement data.Data acquisition and transmission system is mainly used to collect and save data.The two subsystem are responsible for the preliminary data signal acquisition.Data processing system and the structural health assessment system are mainly to evaluate the structural health state in later analysis.Monitoring system and data acquisition and transmission system are the fundamental system.We can only obtain the abundant monitoring data by a thorough monitoring testbed.By studying the existing health monitoring projects at domestic and abroad,we can know that domestic monitoring projects are usually in inactive seismic areas,which are lack of abundant seismic monitoring data.So we choose active seismic areas in China and install dense accelerometers,which aims to construct a new structural health monitoring testbed.Then start the structural health monitoring,structural system identification and earthquake damage monitoring.The site selection of testbed should be considered from the following two aspects:(a)a new built modern structure,which is helpful to track and monitor the structure from the virgin state;(b)the structure should be located in the active seismic area,which is helpful to obtain the seismic monitoring data in a relatively short period,and is good to start the following studies.Therefore,Tongde Plaza Yue Center in Kunming,Yunnan province is selected.This monitoring object is a new modern super high-rise building,which is convenient for obtaining the virgin structural characteristics.Meanwhile,the 50 strong earthquake monitoring stations are distributed in Kunming city,which can provide abundant seismic monitoring data.By analyzing the seismic situation around Tongde Plaza Yue Center,it can be seen that the seismic distribution density around Tongde Plaza Yue Center is relatively high.Then compare the recorded peak ground acceleration by earthquake monitoring stations with the predicted peak ground acceleration by regression model,and calculate the rate of exceedance of different levels of peak ground acceleration at Tongde Plaza Yue Center site.It can be seen that recording small accelerations over a period of just few years is quite likely,and is helpful to carry out the following studies.The selection of equipment and network system is introduced.The EQR120 sensor is the main component equipment,which is used to record seismic data of the structure and basement.Compared with other sensors,such as ETNA2 and GDQJ,this sensor has optimum cost and sufficiently low threshold of recording that is adequate for both seismic and microtremor excitations.CUSP-WEA is used to record climate data,CUSP-BOR is used to record seismic data near the pile bottom,and CUSP-Me is used to collect and summarize data.All equipments are synchronized through the PTP time synchronization system,which is provided by CUSP-Me.Compared with GPS,NTP and other time synchronization methods,the PTP time synchronization system is more accurate and has precision in the nanosecond range(higher than 1 μs and up to 1 ns),which can effectively ensure the synchronization of data.The layout of the sensors and the principle is introduced.The layout principle of the sensors is mainly considered from the data analysis requirements in the future,such as torsion,rocking,soil-structure interaction and so on.Therefore,the sensors are arranged at the refuge floors,the roof,the basement and near the pile foundation.The monitoring system consists of the following parts:(a)a structural array of 25 accelerometers installed at 10 levels aboveground;(b)a basement array of 14 accelerometers distributed in the first and fourth basements;(c)two borehole arrays installed close to the basement perimeter wall,each with one accelerometers at the surface and another one at 50-m depth,which is the depth reached by the piles.With such dense instrumentation of structure,basement,and pile foundation,this site will be the first permanently instrumented full-scale testbed to enable identification of a soil-foundation-basement-structure system and validation of many assumptions commonly made in the predication of the soil-structure interaction effects.In order to obtain the virgin dynamic characteristics and provide reference data for the future monitoring data.Two ambient vibration tests were conducted in 2018 and 2019 respectively.The ETNA2 strong earthquake monitoring instrument provided by Yunnan Earthquake Bureau was used and the monitoring points were arranged according to the sensor installation positions in the monitoring system.The Matlab software is used to analyze the recorded data.Firstly,we analyze the Fourier spectra of ambient vibration test data and get the frequencies ratio in EW,NS and torsion component of first ambient vibration test.The three component frequencies ratio are fi:f2:f3=1:2.94:5.24,1:4.08:8.64 and 1:3.31:6.44 respectively.The frequencies ratio of the three component are between the pure shear ratio(1:3:5)and pure bending ratio(1:6.27:17.5).Analyze the Fourier spectra of second ambient vibration test data,the frequencies ratio of EW,NS and torsion component are f1:f2:f3=1:2.97:5.30,1:4.08:8.64,1:3.28:6.28 respectively,which are roughly equal to the first ambient vibration test frequencies ratio and are also between the pure shear ratio and pure bending ratio.So the structure is simplified into Timoshenko beam model,the bending and shear deformation of the structure is considered at the same time.By calculating the transfer function between two points,the impulse response function,the phase velocity and group velocity of the structure,we can know the structural characteristics further.The transfer function is helpful to understand the frequencies and ratio of the structure more precisely,then we can get the whole structural deformation.From the transfer function fitting curve,we can know the frequencies ratio of EW,NS and torsion component respectively,which are f1:f2;f3;f4=1:3.0:5.2:7.9,1:4.1:8.6:13.4 and 1:3.3:6.4:9.6.The results are close to the ratio of the pure shear beam model(1:3:5:7),suggesting the structure as a whole deforms laterally primarily in shear as opposed to bending and that the contribution of bending is more significant for NS response.An appropriate simple model for such behavior in the longer-period range is a Timoshenko beam.On the one hand,the impulse response function can verify the fitting effect of the transfer function,and on the other hand,the impulse response time and velocity of the structure can also be obtained.From the impulse response fitting curves of EW and NS component,the impulse response time of the two components are 0.565s and 0.527s respectively.The impulse response velocity is 420m/s and 45m/s respectively.The Phase velocity and group velocity are helpful to understand the structural dynamic characteristics and wave propagation characteristics.The phase velocity are calculated by the frequencies,then the phase velocity and group velocity of EW,NS and torsion component are calculated by the Timoshenko beam model.The results show that the phase velocity and group velocity of EW,NS component tend to the theoretical value,which are 392m/s and 531m/s respectively.The phase velocity and group velocity of EW component tend to be flat after the first frequency,while the phase velocity and group velocity of NS component tend to be flat after the fourth frequency,also suggesting the bending deformation is significant in NS component.The structural dynamic characteristics are obtained by the above ambient vibration tests.The structure has different characteristics in EW and NS component.The two components should be analyzed separately.ETABS finite element software is used for finite element model and analysis,which compares with the results of ambient vibration test.Verify the applicability of the layered Timoshenko beam model of this structure,so that the seismic data can be directly used by this method.ETABS2015 is used to carry out the finite element model of Tongde Plaza Yue Center.The first six mode shapes and the frequencies of the structure are obtained.By comparing the frequencies of the model with the above ambient vibration test,it can be seen that the frequency error of the structure in EW and NS component is less 6%,and the results are relatively close.In the time history analysis,earthquake acceleration time history data of M6.6 in Ludian district,Yunnan province that is recorded by the Long Toushan earthquake station.Through the time history analysis and export acceleration time history data of each node according to the position sensor layout of the monitoring system,then the structure is simplified into to 1-layer and 5-layer Timoshenko beam model in EW component.Transfer function,impulse response function,the phase velocity and group velocity are calculated.The first three frequencies of the transfer function of each layer model is fitting well in EW component,and the frequency error between the model and ambient vibration test is less 3%.From EW component of each layered Timoshenko beam model output,the fitting error of 1-layer Timoshenko beam model in EW component reduces from 62%to 39%,the fitting error of 5-layer Timoshenko beam model reduces from 46%to 7%,suggesting that 5-layer Timoshenko beam model can imply the structural characteristics in more details.Shear wave velocity,modulus ratio and longitudinal wave velocity can be obtained in EW component at the same time.5-layer Timoshenko beam model can imply structural characteristics in more details.The impulse response curves of layered Timoshenko beam model in EW component are calculated.The fitting results of each layered model are well,and the above small fitting errors are verified.The impulse response velocities of each layer are obtained,which is roughly close to the ambient vibration test value 420m/s.The analysis method in NS component is similar to the EW component,the transfer function and impulse response curves are fitting well too.It also proofs that 5-layer can imply the structural characteristics better.The fitting error of 1-layer Timoshenko beam model in NS component reduces from 48%to 40%,the fitting error of 5-layer Timoshenko beam model reduces from 56%to 10%.Shear wave velocity,modulus ratio and longitudinal wave velocity of layered model are obtained.The impulse response velocity of each layer is obtained by the fitting impulse response curve of Timoshenko beam model in NS component.The impulse response velocity of the 1-layer model in NS component is close to the ambient vibration test values 451m/s.Based on the analysis of previous seismic data and ground motion attenuation model,it can be seen that the monitoring system is likely to record effective seismic data in a short time.This monitoring system has 43 triaxial accelerometers(129 accelerometer channels)and 1 climate monitoring station.It will be the first health monitoring testbed with high dense accelerometers and located in the active seismic area and put into long-term use.It can be carried out long-term,real-time and high-precision comprehensive monitoring.According to the ambient vibration test,the laterally deformation of Tongde Plaza Yue Center is mainly shear deformation,and the bending deformation is more significant in the NS component.At the same time,an appropriate simple model for such behavior in the longer-period range is a Timoshenko beam.The structure has different dynamic characteristics in EW and NS component,provide reference data for the future long-term monitoring.The finite element model is used to analyze the structural characteristics.The results of dynamic time history analysis and layered Timoshenko beam model show that the layered Timoshenko beam model is suitable for this structure and can reflect the structural characteristics in more details.