A Reference-free Displacement Estimation Method And Verification Based On Cantilever Structure

Structural health monitoring(SHM)technology is becoming an increasingly important part of the construction industry because of the need for performance assessment of existing in-service structures and the fact that some of the in-service structures are gradually reaching service life.In the performance evaluation,displacement evaluation is extremely important,but many sites are difficult to set up traditional sensors for direct and accurate measurement.Therefore,many new sensing technologies(reference-free and non-contact)and other methods of displacement evaluation have very great requirements and are integrated into structural health monitoring systems to overcome the limitations of reference point based displacement sensors.The main contents of this paper are as follows:(1)This paper discusses a displacement estimation method without setting a reference point.There is reference-free displacement estimation method,which is mainly for the lateral total displacement of railway bridges.This reference-free displacement estimation method decomposes the total displacement into two parts:a high-frequency dynamic displacement component and a low-frequency pseudo-static displacement component.It uses contact accelerometers to collect two types of data,one is the acceleration data in the vibration direction,and then uses the finite impulse response(FIR)filter for dynamic displacement component estimation;the other type of data is the mutually perpendicular two-direction acceleration data used to calculate the tilt angle,and then the dynamic co1ponent in the tilt angle is eliminated using a simple dynamic average(SMA)filter,and the pseudo?static displacement component is estimated using a theoretical formula.Finally,the dynamic displacement component estimation curve and the pseudo-static displacement component estimation curve are superimposed to obtain a total displacement estimation curve.(2)This paper uses the shaking table experiment to verify the reference-free displacement estimation method.The shake table experiment is divided into two categories,one using a self-made low-cost efficient wireless integrated sensor 2(LEWIS2)that can measure three-axis accelerations,and the other using a Model 3711E1110G DC responsive accelerometer manufactured by PCB Piezotronics,which is a capacitive accelerometer.The results show that when the large amplitude displacement time history data is input into the shake table,the data measured by LEWIS2 which is used to estimate the pseudo-static displacement time history curve has a large deviation,which also has a relatively large impact on the final total estimated displacement time history curve.This effect is less pronounced in capacitive accelerometer experiments.The total displacement E2 error mainly reflects the fitting of the estimated displacement time history curve and the reference displacement time course curve.The E2 error in LEWIS2 experiment is about 30%.and it in the capacitive accelerometer experiment is less than 10%.It is shown that the reference-free displacement estimation method has certain practical significance,and the sensor equipment has a certain influence on the reference-free displacement estimation method.The estimated effect of the LEWIS2 experiment is not as good as that of the capacitive accelerometer experiment.It can be reflected in the pseudo-static displacement estimation.The error of LEWIS2 when measuring low-frequency data is larger than that of the capacitive accelerometer(3)In this paper,ANSYS finite element is used to simulate the shake table experiment.The comparison curve and the quantization error data are perfect,and the total displacement E2 error is below 2%.It is proved that the reference-free displacement estimation method is reasonable.The results show that the contrast curve and the quantization error data are perfect,the total displacement E2 error is below 2%,and the pseudo-static error values are almost zero.It is proved that the reference-free displacement estimation method is reasonable.Compared ANSYS finite element simulation with shake table experiment,the results show that the contrast curve of ANSYS finite element simulation is more perfect and the error data is smaller.The ANSYS finite element simulation total displacement E2 error is only 1/5 of the capacitive accelerometer experiment,which is only 1/15 of the LEWIS2 experiment.The quantitative error data and the comparison curve of the finite element simulation can show that the reference-free displacement estimation method is reasonable,and once again,the sensor equipment has a certain influence on the reference-free displacement estimation method.