Experimental Study On Dynamic Stability Of The Circular Single Arch

Dynamic instability failure of the structure can result in significant casualties and property losses. As one of the most commonly used type of arch in engineering, circular arch has been paid much attention on its dynamic stability. However, previous studies focused on theoretical research, exploration has seldom been made on experiment of dynamic stability.Therefore, the experimental research on dynamic stability of arch has important practical significance and scientific value. Based on the theory of dynamic instability of circular single arch, various models of circular arch with different rise-span ratios and different associated mass have been designed in this paper. Experiments are then carried out to study the out-of-plane and in-plane instability problem of circular arch. The experiment measures the vibration modes and modal damping ratio of the arch models. Boundaries of unstable regions are determined by sweeping load frequency, characteristics of nonlinear vibration are tested by vibrations at fixed load frequency. The influences of exciting force, rise-span ratio and associated mass on dynamic instability are finally summarized. The main work is listed as follows:(1)The correctness of unstable regions and nonlinear vibration characteristics is verified through ANSYS numerical analysis. The waveform analysis method is put forward to judge the in-plane and out-of-plane parametric resonance of circular arch. Studies show that the waveform analysis method has good applicability in judging parametric instability, and distinguishing forced vibration, forced resonance, parameter resonance and transient vibration.(2)The mechanism of in-plane and out-of-plane parametric resonance of circular arch is revealed through the vibration experiments. The correctness of the calculation results of dynamic unstable region is verified by frequency sweeping test. It's shown that under periodicconcentrated load at the crown, the in-plane or out-of-plane parametric resonance occurs when the load frequency is about two times the corresponding natural frequency of arch. The phenomenon of nonlinear "traction" is observed by the fixed frequency testing, and the measured nonlinear vibration state and amplitude are compared with the theoretical results,which proves the correctness of vibration theories of nonlinear steady state and non-stationary state.(3)Parametric analyses are performed to investigate the dynamic instability of the arch structure by experiments. According to the control variable method, change some design parameter when other factors are kept invariant, and then the contrasting experiments are conducted under the same conditions. The experiments prove that, with the variation of exciting force, rise-span ratio and associated mass, the natural frequencies of arch, the distribution and width of dynamic unstable regions, the amplitude and state of nonlinear vibration will change. The main conclusions are:1 Larger exciting force, larger vibration amplitude of the arch. Whether the load frequency falls in the area of instability region determining the parametric instability of the structure.2 Smaller rise-span ratio causing greater natural frequency, so the dynamic unstable region moves towards the direction with higher frequency, and the width of instability region becomes bigger. The out-of-plane or in-plane amplitude of nonlinear vibration decreases with the rise-span ratio.3 Greater mass, lower the natural frequency. Therefore, the dynamic unstable regions moves towards the direction with lower frequency, and the range of the instability region becomes narrow. The nonlinear amplitude of out-of-plane or in-plane vibration decreases with the increase of mass.