Experimental Study On Dynamic Parameter Instability Under Vertical Periodic Vibration Of Foundation Of Circular Arch

The stability of arch under dynamic load has been paid much attention for a long time.The dynamic stability of circular arcs under the periodic vibration is closely related to the actual engineering,which is an advanced topic in the field of dynamic stability of engineering structures.Many scholars have carried out the study on the in-plane dynamic stability of circular arches under harmonic loads,however,little research on the in-plane dynamic instability of arches under harmonic acceleration has been reported in the literatures.In this paper,the research is conducted on in-plane parameter instability under the simple harmonic excitation which is applied on the base of arch.The main research contents are as follows:(1)The waveform analysis method is proposed for judging the parametric resonance in the circular arch plane.It can effectively distinguish the forced vibration,forced resonance,parametric resonance,transient vibration and other vibration states.(2)Based on the circular arches with different rise-span ratio,the in-plane dynamic instability experiment is carried out.By using "hammer striking method”,the circular arch vibration modal,corresponding natural frequency and damping ratio are obtained.In order to predict the dynamic stability critical frequency,and the nonlinear amplitude curves of arch,the frequency sweep excitation method is used.,The variation of dynamic instability with the amplitude of excitation force and the rise-span ratio under the action of periodic excitation is obtained.(3)Through the excitation experiment,the mechanism of in-plane parametric resonance of arch is revealed.By the forward sweep frequency test,it is shown that when the frequency of load is two times of natural vibration frequency or arch,the parametric resonance occur;consequently,the response of the nonlinear vibration is predicted which are verified by FEM.(4)T The dynamic instability of the arch in the experiment is analyzed.Using the control variable method,taking a parameter as the control variable and other parameters as constants,the dynamic experiments are performed under the same conditions.It is shown that with the variation of vibration force,span ratio and weight,the vibration frequency,dynamic instability domain and of nonlinear vibration state and amplitude are varied accordingly as following:(1)The greater the excitation force is,the greater the amplitude of the arch is;the frequency of the excitation load directly affect he parametric resonance instability of the arch in the excitation region.(2)The smaller the rise-span ratio is,the greater the natural frequency of the arch is;the dynamic instability domain moves to the high frequency direction,at the same time,the width of the instability domain increases;the amplitude of nonlinear vibration increases with the decrease of the rise-span ratio.