Experiment :  VIBRATION CHARACTERISTICS OF RC BEAMS USING EMBEDDED PIEZO-ELECTRIC SENSORS

ABSTRACT

A simply supported RC beam was subjected to excitation with the help of a hammer. The response of the beam was sensed using accelerometer and PZT sensor. The signal from accelerometer was transferred to Oscilloscope through an amplifier and signal from PZT sensor directly to oscilloscope. The result obtained was in the form of Voltage v/s Time converted to the Voltage v/s Frequency graph using FFT in MATLAB. The results obtained from the accelerometer and PZT patch were compared with each other and the theoretical values.

OBJECTIVE

To study vibration characteristics of simply supported RC beam by using embedded piezoelectric sensor (PZT) and accelerometer and to compare the value obtained from embedded piezoelectric meter and accelerometer and theoretical values.

EXPERIMENTAL SETUP

The experimental set up consists of a simply supported RC beam embedded with a PZT in the centre of span and an accelerometer on the top surface of the beam.PZT patch is directly connected to the oscilloscope and accelerometer is connected to oscilloscope through the amplifier.

RESULTS

           

The natural frequency is calculated by:

Where, f_n= the natural frequency of the beam in the n^th order, n=1,2,3…,  

E= Modulus of Elasticity = 27386.127x10⁶ N/m²                              

I= Moment of Inertia about the axis of bending = 1857916.667 mm⁴.

ρ= density of the beam = 2500 kg/m³,  b=65mm, d=70mm, L=960mm. The damping ratio is calculated using the half power bandwidth method:

 f₁, f₂ = frequencies corresponding to 0.707 of the peak response,

 f_n = frequency corresponding to peak response (fundamental frequency).

For Accelerometer :  R_peak= 5.56   , 0.707 R_peak= 3.93  , => f₁= 80Hz , f₂= 107Hz , f_n= 93.5Hz

For PZT :                   R_peak= 27.5   , 0.707 R_peak= 19.44 , => f₁= 84Hz , f₂= 101.1Hz , f_n=100Hz

Table:

	Accelerometer	PZT sensor	Theoretical values
Natural frequency (Hz)	93.5	101.1	113.93
Damping ratio (%)	14 %	8.4 %	5-8 %

CONCLUSION:

1. As observed from Fig.(1) and Fig.(2),PZT patch records data more accurately and is also more receptive to minute vibrations as compared to the accelerometer as response measured by accelerometer consists majorly of the noise created by the AC supply to the oscilloscope. The value of natural frequency of PZT and accelerometer is coming less than the theoretical value.

2. In order to minimize the error in FFT due to noise from AC supply, only 150 values are considered.

REFERENCES:

1.                     Chopra, A. (2007), Dynamics of Structures, Prentice Hall of India limited, New Delhi.

2.                     Bhalla S., Manual of Experiment No. 5, Virtual Smart Structures and Dynamics Lab.

3.                     Lab Presentation Notes,CEP726, Dr. Suresh Bhalla, Civil Engineering Department, IIT Delhi.