Piotr Omenzetter

Identification of unusual events in multi-channel bridge monitoring data

Continuously operating instrumented structural health monitoring (SHM) systems are becoming a practical alternative to replace visual inspection for assessment of condition and soundness of civil infrastructure such as bridges. However, converting large amounts of data from an SHM system into usable information is a great challenge to which special signal processing techniques must be applied. This study is devoted to identification of abrupt, anomalous and potentially onerous events in the time histories of static, hourly sampled strains recorded by a multi-sensor SHM system installed in a major bridge structure and operating continuously for a long time. Such events may result, among other causes, from sudden settlement of foundation, ground movement, excessive traffic load or failure of post-tensioning cables. A method of outlier detection in multivariate data has been applied to the problem of finding and localising sudden events in the strain data. For sharp discrimination of abrupt strain changes from slowly varying ones wavelet transform has been used. The proposed method has been successfully tested using known events recorded during construction of the bridge, and later effectively used for detection of anomalous post-construction events.

Suppression of wind-induced instabilities of a long span bridge by a passive deck-flaps control system

Abstract A passive aerodynamic control method for suppression of the wind-induced instabilities of a very long-span bridge is presented. The control system consists of additional control flaps attached to the edges of the bridge deck. Rotational motion of the control flaps is governed by prestressed springs and additional cables connecting the flaps to an auxiliary transverse beam supported by the main cables of the bridge. The rotational movement of the flaps is used to modify the aerodynamic forces acting on the deck, as well as to provide aerodynamic forces on the flaps, used to stabilize the bridge. A time domain formulation of self-excited and buffeting forces is obtained through the rational function approximation of the generalized Theodorsen and Kusner functions, respectively. Performance indices assessing improvement in critical wind speed and degree of stability of the system are proposed to find the optimal configuration of the deck–flaps system. This paper lays the theoretical groundwork for the one that follows.

Sensitivity Analysis of the Eigenvalue Problem for General Dynamic Systems with Application to Bridge Deck Flutter

The mathematical models governing the dynamics of various engineering systems, such as airplane wings and bridge decks subjected to aerodynamic forces, mechanical and civil structures interacting with fluid or soil, or systems with time delays, yield transcendental eigenvalue problems. In this work, a general transcendental eigenvalue problem is first formulated and a biorthogonality relationship between eigenvectors is derived. Then, the sensitivities of eigenvalues and eigenvectors with respect to a system parameter are obtained. The method is employed to analyze in detail a transcendental eigenvalue problem arising in the analysis of a bridge deck subjected to aerodynamic forces. The sensitivities of eigenvalues and eigenvectors are successfully used to improve the performance of an iterative method used for solving the eigenvalue problem.

Time domain formulation of self-excited forces on bridge deck for wind tunnel experiment

Time domain formulation of the self-excited wind forces on bridge decks employs indicial functions. In bridge aeroelasticity, these functions are obtained by transforming the flutter derivative model to time domain. Studies have suggested, however, that the relative amplitude effect, i.e. the effect of structural oscillation amplitude relative to the amplitude of response to ambient wind, on flutter derivatives needs to be considered. This effect indicates the difference between the two cases, where the pulse response of an elastically supported body is smooth and where the motion is significantly affected by ambient wind forces. The non-linearity may affect the transformation of flutter derivative model to time domain. An alternative to obtaining the time domain formulation for the self-excited force is to treat the self-excited force as a separate dynamic system, so that the relative amplitude effect can be evaluated in more detail. In this paper, a self-excited force generation system coupled with the rigid bridge deck system is proposed to overcome the difficulties in the measurement and derivation of the time domain representation of self-excited force on bridge decks. This expression can be linked to a flutter derivative model, and a transform relationship between the two models is suggested.

Identification of unusual events in multichannel bridge monitoring data using wavelet transform and outlier analysis

Continuously operating instrumented structural health monitoring (SHM) systems are becoming a practical alternative to replace visual inspection for assessment of condition and soundness of civil infrastructure. However, converting large amount of data from an SHM system into usable information is a great challenge to which special signal processing techniques must be applied. This study is devoted to identification of abrupt, anomalous and potentially onerous events in the time histories of static, hourly sampled strains recorded by a multi-sensor SHM system installed in a major bridge structure in Singapore and operating continuously for a long time. Such events may result, among other causes, from sudden settlement of foundation, ground movement, excessive traffic load or failure of post-tensioning cables. A method of outlier detection in multivariate data has been applied to the problem of finding and localizing sudden events in the strain data. For sharp discrimination of abrupt strain changes from slowly varying ones wavelet transform has been used. The proposed method has been successfully tested using known events recorded during construction of the bridge, and later effectively used for detection of anomalous post-construction events.