| Π shaped section is a common section form of main beam.This section form can reduce the height of main beam,increase the clearance under the bridge,increase the rigidity of the bridge,make the overall force transmission path of the bridge structure more clear,the main beam stress is clear,so it is widely used in large-span bridges.However,the π-section is a typical bridge section,which has poor aerodynamic performance.In practical application,there are often significant wind-induced vibration problems,especially vortex vibration.At present,most of the researches on the vortex vibration of π section are focused on the mechanism of vortex vibration based on the response of vortex vibration and the effective aerodynamic measures to suppress the vortex vibration,but the researches on the mechanism of vortex vibration of π section from the perspective of vortex excitation force are few.However,the research on the vortex excitation force has not been able to establish a vortex excitation force model which can well describe the vortex vibration law of π-shaped section.In this paper,based on the synchronous vibration and pressure measurement test of π section,the variation law of the response of π section to vortex vibration and its characteristics of vortex excitation force are summarized.Finally,a new model of vortex excitation force is established based on the characteristics of the vortex excitation force of π section and its good applicability to π section is verified.Around this topic,the main work of this paper is as follows:(1)Firstly,based on the wind tunnel test of synchronous measurement of vibration and pressure of π section,the curve of vortex response changing with wind speed and the distribution curve of surface pressure mean value and pulsation value of π section are obtained,and the law of vortex response changing with respect to wind speed is summarized.Based on the characteristics of flow around,the cause of vortex vibration of π section is analyzed.Then,the surface pressure integral method is used to obtain the vortex excitation force of π-shaped cross-section vortex vibration,and the relevant characteristics of the vortex excitation force of π-shaped beam are studied and summarized.(2)Then,the empirical linear model and the empirical nonlinear model are identified based on the time history of the displacement response of the vortex vibration measured by the synchronous vibration and pressure test of the Π shaped section,and the variation law of the aerodynamic parameters in the empirical linear model and the nonlinear model with the dimensionless frequency is summarized.At the same time,based on the characteristics of the vortex excitation force of the Π shaped section,the empirical linear model and the empirical nonlinear model are discussed It is considered that the empirical linear model and the nonlinear model are not suitable for describing the vortex excitation force of the π-shaped section.(3)Finally,through the analysis of Scanlan’s empirical nonlinear model,the reason why Scanlan’s empirical nonlinear model is not suitable for π-shaped cross section is obtained,and based on this,a new vortex exciting force model suitable for Π-shaped cross section is proposed.LM algorithm is used to identify the parameters of the new model,and the fitting characteristics of the new model are studied based on the characteristics of the vortex excitation force of the π section,which proves that the new model has good applicability to the π section. |
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