In this thesis, we theoretically and experimentally investigate the linear and nonlinear
dynamic behavior of a frame structure, which frequently occurs in engineering applications.
The structure consists of three continuous steel beams that are connected by two brass
hinges. Experimental modal analysis indicates that the obtained natural frequencies are
highly sensitive to changes in the oscillation amplitude, even for small motions. Thus, the
amplitude range where linear responses can be expected is, in practice, very small. Instead,
a strong nonlinear behavior is exhibited by the experimentally obtained backbone curves
for small vibrations. Furthermore, the experimentally obtained frequency-response curves
exhibit jump phenomena.
We investigated experimentally whether the nonlinear dynamic characteristics of the
structure are the result of modal interactions, such as internal and combination resonances.
We were unable to activate any of these resonances. Next, we investigated whether these
characteristics are due to geometric, inertia, material, or damping nonlinearities. The
answer is again negative. Finally, we examined the nonideal dynamic characteristics of
the hinges. We found that stiffness degradation hysteretic damping in the hinges is the
best model that explains the observed nonlinear dynamic behavior. A multilinear stiffness
degradation model was used to describe the overall hysteretic load-displacement relation.
An approximate analytical approach was used to compute the steady-state response of the
structure to a harmonic excitation. A good qualitative agreement between the computations
and the experimental results was obtained.
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