Experimental Study on the Effect of Large Axial Tensile Force on the Natural Frequency of a Fixed-Fixed Steel Beam
Steel beams are one of the most commonly used structural elements in building and bridge design, and in aerospace and mechanical engineering. The dynamic response, which is characterized by modification of the eigenparameters, changes when damage occurs. The linear relationship between the square of natural frequency and axial force within linear elastic region is well known. However, less research has been done on the nonlinear relationship between the two within the tensile plastic region. In this paper, experimental studies were conducted to measure the first natural frequency of a fixed-fixed steel beam under different axial tensile loads within both the elastic and plastic regions. It was observed that the curve softened after entering the plastic region. However, when taking into account the effect of length change on natural frequency, it shows a softening behavior first, followed by a stiffening behavior possibly due to strain hardening of the material.
KeywordsDamage detection Experimental dynamics Natural frequency Nonlinear dynamic Vibration theory
The authors wish to thank Yiming Liu and Bill Kuykendall for his assistance in the laboratory, and University of Washington for the Instron Machine in the laboratory.