Experimental study on possible vortex shedding in a suspension bridge. Part II – Results when under typhoon Babs and York

S.S. Law,Q.S. Yang,Y.L. Fang 한국풍공학회 2007 Wind and Structures, An International Journal (WAS Vol.10 No.6

Statistical analysis on the measured responses of a suspension bridge deck (Law, et al. 2007) show that vibration response at the first torsional mode of the structure has a significant increase at and beyond the critical wind speed for vortex shedding as noted in the wind tunnel tests on a sectional model. This paper further analyzes the measured responses of the structure when under typhoon conditions for any possible vortex shedding events. Parameters related to the lifting force in such a possible event and the vibration amplitudes are estimated with a single-degree-of-freedom model of the system. The spatial correlation of vortex shedding along the bridge span is also investigated. Possible vortex shedding events are found at both the first torsional and second vertical modes with the root-mean-square amplitudes comparable to those predicted from wind tunnel tests. Small negative stiffness due to wind effects is observed in isolated events that last for a short duration, but the aerodynamic damping exhibits either positive or negative values when the vertical angle of wind incidence is beyond 10o. Vibration of the bridge deck is highly correlated in the events at least in the middle one-third of the main span.

Experimental study on possible vortex shedding in a suspension bridge - Part II - Results when under typhoon Babs and York

Law, S.S.,Yang, Q.S.,Fang, Y.L. Techno-Press 2007 Wind and Structures, An International Journal (WAS Vol.10 No.6

Statistical analysis on the measured responses of a suspension bridge deck (Law, et al. 2007) show that vibration response at the first torsional mode of the structure has a significant increase at and beyond the critical wind speed for vortex shedding as noted in the wind tunnel tests on a sectional model. This paper further analyzes the measured responses of the structure when under typhoon conditions for any possible vortex shedding events. Parameters related to the lifting force in such a possible event and the vibration amplitudes are estimated with a single-degree-of-freedom model of the system. The spatial correlation of vortex shedding along the bridge span is also investigated. Possible vortex shedding events are found at both the first torsional and second vertical modes with the root-mean-square amplitudes comparable to those predicted from wind tunnel tests. Small negative stiffness due to wind effects is observed in isolated events that last for a short duration, but the aerodynamic damping exhibits either positive or negative values when the vertical angle of wind incidence is beyond ${\pm}10^{\circ}$. Vibration of the bridge deck is highly correlated in the events at least in the middle one-third of the main span.

Experimental studies on possible vortex shedding in a suspension bridge - Part I - Structural dynamic characteristics and analysis model

Law, S.S.,Yang, Q.S.,Fang, Y.L. Techno-Press 2007 Wind and Structures, An International Journal (WAS Vol.10 No.6

The suspension bridge is situated in an area of complex topography with both open sea and overland turbulence characteristics, and it is subject to frequent typhoon occurrences. This paper investigates experimentally the possible vortex shedding events of the structure under high wind and typhoon conditions. A single-degree-of-freedom model for the vibration of a unit bridge deck section is adopted to determine the amplitude of vibration and to estimate the parameters related to the lifting force in a vortex shedding event. The results of the studies are presented in a companion paper (Law, et al. 2007). In this paper, statistical analysis on the measured responses of the bridge deck shows that the vibration response at the first torsional mode of the structure has a significant increase at and beyond the critical wind speed for vortex shedding as noted in the wind tunnel tests on a section model of the structure.

Wind characteristics of Typhoon Dujuan as measured at a 50m guyed mast

Law, S.S.,Bu, J.Q.,Zhu, X.Q.,Chan, S.L. Techno-Press 2006 Wind and Structures, An International Journal (WAS Vol.9 No.5

This paper presents the wind characteristics of Typhoon Dujuan as measured at a 50 m guyed mast in Hong Kong. The basic wind speed, wind direction and turbulent intensity are studied at two measurement levels of the structure. The power spectral density of the typhoon is compared with the von Karman prediction, and the coherence between wind speeds at the two measurement levels is found to This paper presents the wind characteristics of Typhoon Dujuan as measured at a 50 m guyed mast in Hong Kong. The basic wind speed, wind direction and turbulent intensity are studied at two measurement levels of the structure. The power spectral density of the typhoon is compared with the von Karman prediction, and the coherence between wind speeds at the two measurement levels is found to compare with Davenport's prediction. The effect of typhoon Dujuan on the response of the structure will be discussed in a companion paper (Law, et al. 2006).with Davenport's prediction. The effect of typhoon Dujuan on the response of the structure will be discussed in a companion paper (Law, et al. 2006).

Wind characteristics of Typhoon Dujuan as measured at a 50m guyed mast

S.S. Law,J.Q. Bu,X.Q. Zhu,S.L. Chan 한국풍공학회 2006 Wind and Structures, An International Journal (WAS Vol.9 No.5

This paper presents the wind characteristics of Typhoon Dujuan as measured at a 50 m guyed mast in Hong Kong. The basic wind speed, wind direction and turbulent intensity are studied at two measurement levels of the structure. The power spectral density of the typhoon is compared with the von Karman prediction, and the coherence between wind speeds at the two measurement levels is found to compare with Davenport prediction. The effect of typhoon Dujuan on the response of the structure will be discussed in a companion paper (Law, et al. 2006).

Statistical damage classification method based on wavelet packet analysis

S.S. Law,X.Q. Zhu,Y.J. Tian,X.Y. Li,S.Q. Wu 국제구조공학회 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.46 No.4

A novel damage classification method based on wavelet packet transform and statistical analysis is developed in this study for structural health monitoring. The response signal of a structure under an impact load is normalized and then decomposed into wavelet packet components. Energies of these wavelet packet components are then calculated to obtain the energy distribution. Statistical similarity comparison based on an F-test is used to classify the structure from changes in the wavelet packet energy distribution. A statistical indicator is developed to describe the damage extent of the structure. This approach is applied to the test results from simply supported reinforced concrete beams in the laboratory. Cases with single and two damages are created from static loading, and accelerations of the structure from under impact loads are analyzed. Results show that the method can be used with no reference baseline measurement and model for the damage monitoring and assessment of the structure with alarms at a specified significance level.

Response prediction of a 50m guyed mast under typhoon conditions

S.S. Law,J.Q. Bu,X.Q. Zhu,S.L. Chan 한국풍공학회 2006 Wind and Structures, An International Journal (WAS Vol.9 No.5

This paper presents the wind excited acceleration responses of a 50 m guyed mast under the action of Typhoon Dujuan. The response of the structure is reconstructed from using a full finite element model and an equivalent beam-column model. The wind load is modelled based on the measured wind speed and recommendations for high-rise structures. The nonlinear time response analysis is conducted using the Newton Raphson iteration procedure. Comparative studies on the measured and computed frequencies and acceleration responses show that the torsional vibration of the structure is significant particularly in the higher vibration modes after the first few bending modes. The equivalent model, in general, gives less accurate amplitude predictions than the full model because of the omission of torsional stiffness of the mast in the vibration analysis, but the root-mean-square value is close to the measured value in general with an error of less than 10%.

Identification of Vehicle-Bridge Interaction Forces In Frequency Domain

S.S Law,Tommy H.T. Chan,Q.H. Zeng 한국소음진동공학회 1997 한국소음진동공학회 국제학술대회논문집 Vol.1997 No.1

Statistical damage classification method based on wavelet packet analysis

Law, S.S.,Zhu, X.Q.,Tian, Y.J.,Li, X.Y.,Wu, S.Q. Techno-Press 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.46 No.4

A novel damage classification method based on wavelet packet transform and statistical analysis is developed in this study for structural health monitoring. The response signal of a structure under an impact load is normalized and then decomposed into wavelet packet components. Energies of these wavelet packet components are then calculated to obtain the energy distribution. Statistical similarity comparison based on an F-test is used to classify the structure from changes in the wavelet packet energy distribution. A statistical indicator is developed to describe the damage extent of the structure. This approach is applied to the test results from simply supported reinforced concrete beams in the laboratory. Cases with single and two damages are created from static loading, and accelerations of the structure from under impact loads are analyzed. Results show that the method can be used with no reference baseline measurement and model for the damage monitoring and assessment of the structure with alarms at a specified significance level.

Response prediction of a 50 m guyed mast under typhoon conditions

Law, S.S.,Bu, J.Q.,Zhu, X.Q.,Chan, S.L. Techno-Press 2006 Wind and Structures, An International Journal (WAS Vol.9 No.5

This paper presents the wind excited acceleration responses of a 50 m guyed mast under the action of Typhoon Dujuan. The response of the structure is reconstructed from using a full finite element model and an equivalent beam-column model. The wind load is modelled based on the measured wind speed and recommendations for high-rise structures. The nonlinear time response analysis is conducted using the Newton Raphson iteration procedure. Comparative studies on the measured and computed frequencies and acceleration responses show that the torsional vibration of the structure is significant particularly in the higher vibration modes after the first few bending modes. The equivalent model, in general, gives less accurate amplitude predictions than the full model because of the omission of torsional stiffness of the mast in the vibration analysis, but the root-mean-square value is close to the measured value in general with an error of less than 10%.