The study reported in this paper investigates the dynamic behavior of a semi-definite nonlinear mechanical structure. It consists of a cantilever beam with uniform thickness subjected to a harmonic excitation at the base; two hinged rigid plates are attached at its free end. The plates can execute oscillations in the horizontal plane without restoring moments. The friction at the hinges is modeled as a Coulomb type with a nonlinear friction coefficient. The excitation parameters at which chaotic motion of the hinged plates is initiated are investigated experimentally as well as numerically. It is shown that the prediction of the dynamic response of this semi-definite system is not accurate in the resonance region. The prediction fails due to the existence of chaotic behavior in that region. The measurement of the dynamic response of the system is conducted using a He-Ne laser system. The numerical results are found to be in a good agreement with the experimental findings.