The periodic load on the arch

in general

only causes the symmetric in-plane vibration of the arch. However

under certain conditions

it can cause in-plane anti-symmetric vibration and out-of-plane symmetric vibration with large amplitude

which is so-called the instability problem of an arch structure due to the parametric resonance. Aimed at studying the out-of-plane dynamic stability problem of circular shallow arch

the experimental work is conducted trying to explore mechanism of the out-of-plane dynamic instability under concentrated periodic load. By applying APS series vibrator

the single point harmonic excitation at vault was simulated. The B&K modal testing system was used to gain the transverse vibration response of circular arch including its vibration mode shape and damping ratio. The boundaries of unstable domain were distinguished by way of constant frequency back-and-forth sweep. The experimental results were compared with those from theory analysis

and the results show that remarkable transverse parameter resonance of the structure appears when the frequency of external excitation is about twice of the structural frequencies.  The parameter resonance occurs only when the external excitation amplitude is greater than the critical excitation force.Tthe existence of the damping affects the value of the critical excitation force. The greater is the excitation

the easier does the parameter resonance phenomenon occur. The experimental work reported  verifies the accuracy of calculating the outofplane dynamic instability domain of the circular shallow arch

and presents that research has reference value for the design of dynamic stability of arch structure.