International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395 -0056
Volume: 04 Issue: 03 | Mar -2017
p-ISSN: 2395-0072
www.irjet.net
FREE VIBRATIONAL ANALYSIS OF CRACKED RC BEAM- A REVIEW Nimisha K P 1 , K Subha 2 1PG
Student , Dept . Of Civil Engineering , NSS College Of Engineering , Palakkad , India
2Professor
, Dept . Of Civil Engineering , NSS College Of Engineering , Palakkad , India
-------------------------------------------------------------------***-------------------------------------------------------------------Abstract - Identification of faults in dynamic structures and components are a significant aspect in judgment creating about their overhaul and retirement. Failure to identify the damages has various significances, and they change based on the use, and significance of the vibrating structures and elements. Premature identification of faults in engineering structure during their service period is the great challenge to the engineers. Though dynamic based fault diagnosis has been advanced for last three decades and there is large number of literatures, still there are so many problems avoid doing it from application. Cracks in vibrating system can lead to a sudden and total failure from which recovery is impossible. This results in change in the physical characteristics of a structure and thus the dynamic response also varies. Depth of the crack and its location from fixed are the main parameters for the vibration analysis. It becomes very important to know the changes in these parameters of the structure in order to access its reliability, performance and safety & to study the effect of the parameters on the natural frequency of beams. In this paper, the effect of crack parameters (relative crack location & crack depth, and crack inclination) on the modal parameters of a cracked fixed and simply supported RC beam are examined by finite element analysis using ANSYS 17. In future this analysis can be extended by considering different cross sections of the beam such as circular, trapezoidal etc. with different materials.
if it is not identified in early time. Modal parameters like modal frequencies, mode shapes are the functions of the structural properties like stiffness and mass of the structure. So, the variation of structural properties will cause the variation in the modal properties. The main objective of this paper is to study the variation in the modal parameters (natural frequency an mode shape) of an RC beam as the crack depth and crack inclination varies by conducting the free vibrational analysis in ANSYS 17.
2. THEORETICAL BACKGROUND The natural frequencies of a cracked system can easily be obtained through many of the structural testing methods. When any two natural frequencies of a cracked simply supported reinforced concrete beam are obtained from measurements, the location, inclination and the depth of the crack can then be determined.
2.1 Classification of vibration Vibration can be classified as:
Free and forced vibration: If a system, after an internal disturbance, is left to vibrate on its own, then the vibration is known as free vibration. Here no external force acts on the system. If the system is subjected to an external force, then the resulting vibration is known as forced vibration. If the frequency of the external force coincides with one of the natural frequencies of the system, resonance occurs and the system undergoes dangerously large oscillations.
Undamped and damped vibration: If no energy is dissipated in the friction or other resistance during oscillation, the vibration is called undamped vibration. If any energy is lost in this way, it is called the damped vibration. The consideration of damping becomes important in analysing the vibratory system near resonance.
Linear and nonlinear vibration: If all the basic components of vibratory system—the spring, the mass and the damper—behave linearly, the resulting vibration is known as linear vibration. If any of the basic components behave non-linearly, the vibration is called nonlinear vibration.
Key Words: Vibrational analysis, simply supported beam, fixed beam, crack, natural frequency ,mode shape
1.INTRODUCTION Vibrations are time dependent displacements of a particle or a system of particles with respect to an equilibrium position. One of the most important parameters associated with vibration of structure is the natural frequency. Each structure has its own natural frequency for a series of different modes which control its dynamic behaviour. All the structure which have some mass and elasticity is said to vibrate. When the amplitude of these vibrations exceeds the permissible limit, failure of the structure occurs. To avoid such failure, one must know the operating frequencies of the materials under various boundary conditions like simply supported, fixed or when in cantilever conditions. The presence of cracks in a structural member, such as an RC beam, causes variations in stiffness, the magnitude of which depends on the location, inclination and depth of the cracks. The monitoring of the changes in the response parameters of a structure has been used for the assessment of structural integrity, performance and safety. A crack in the dynamic structures can lead to untimely failure
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