Naruhito Shiraishi

Rain-wind induced vibrations of cables stayed bridges

Abstract In the period of construction of a cable stayed bridge, large amplitude vibrations of cables were observed under rain and wind conditions for several times. The results of full scale measurement confirmed that the vibration is a new type of instability phenomenon which is caused by the combined influences of rain and wind. Based on the wind tunnel test with reproduced rain condition, it is shown that the rain influence is originated by a rain water rivulet formation along the upper windward surface of cable, and with this rivulet formation, an apparent cable cross section becomes aerodynamically unstable.

Aerodynamic behavior of inclined circular cylinders-cable aerodynamics

Abstract This study attempts to clarify of the mechanism of rain-wind induced vibration of the stay cables of a cable stayed bridge and to find an effective aerodynamic stabilization method. Through a series of wind tunnel tests the fundamental aerodynamic characteristics of a yawed and/or inclined circular cylinder with and without rain were investigated. An intense secondary axial flow was found to form in the early wake, playing a similar role to that of a splitter plate submerged in the wake. This axial flow resulted in an aerodynamic exciting force acting on the yawed and/or the inclined circular cylinder. The role of rain in the rain-wind induced vibration of the stay cable is shown to be that of an amplifier of the essential unstable aerodynamic exciting force acting on the yawed and/or the inclined circular cylinder. The role of rain the rain-wind induced vibration of the stay cable is shown to be that of an amplifier of the essential unstable aerodynamic characteristics of the yawed and/or the inclined circular cylinder. Aerodynamic stabilization should depend essentially on controlling this characteristic secondary flow.

Fuzzy importance in fault tree analysis

Abstract In fault tree analysis, system success or failure can be described by the state of the top event, which is usually defined by a so-called structure function. In this paper, we attempt to simplify the calculation process of the structure function and to newly define the state of the top event by the membership function, using fuzzy sets theory. Furthermore, it is shown that the importance of each basic event can be evaluated through fuzzy operations. The method proposed herein is demonstrated by some examples with respect to the failure analysis of structures.

On classification of vortex-induced oscillation and its application for bridge structures

Abstract A fundamental consideration is presented for mechanisms of generation of vortex-induced oscillations which are classified into three groups through wind tunnel tests. It is shown that the geometrical shape factor of the section, namely the slenderness ratio, takes an important role here and in addition to that the interrelation of the vortices formed at leading and trailing edges and the induced oscillations of sections is clarified.

On aerodynamic instabilities of tandem structures

Abstract The aerodynamic properties and the mechanisms of the aerodynamic behaviors on two-dimensional tandem bluff bodies were investigated by measurements of unsteady pressure distributions around the cylinders and the flow visualization technique. Two rectangular cylinders, two circular cylinders placed in series in a flow and a single circular cylinder with a fixed splitter plate submerged in a wake were tested in this paper. The torsional vortex-induced oscillation of two tandem rectangular cylinders mutually rigidly connected was very sensitive to the spacing ratio between two cylinders. Both the accelerated “gap flow” and the accelerated “outside flow” a round the downstream cylinder played important roles in the violent cross-wind oscillation of two tandem circular cylinders with a spacing ratio of L ∗ /D = 3 . The violent cross-wind oscillation of the single circular cylinder with a splitter plate had a similar mechnism to conventional galloping of a two-dimensional rectangular cylinder from the standpoint of being caused by the existence of an inner circulatory flow.

Knowledge-based expert system for damage assessment based on fuzzy reasoning

Abstract This paper attempts to develop a knowledge-based expert system for assessing damage states of bridge structure, where the focus is put on reinforced concrete bridge deck, because its failures have been occasionally reported. Similar to the usual expert systems, this system consists of a rule-base, working memory and interpreter. However, this system has such a remarkable feature that it includes a fuzzy set manipulation system which can treat fuzzy sets in the process of data handling, rule representation and inference procedure. Using this system, it is possible to deal with various kinds of uncertainties and ambiguities involved inherently in the data, rules and inference process in a unified and simple manner. An illustrative example is presented to demonstrate the applicability of the system developed herein.

On aerodynamic stability effects for bluff rectangular cylinders by their corner-cut

Abstract In this study, a slight modification of the geometrical shape of rectangular cross sections was tested as to its stabilizing effect on galloping oscillation. From each corner of the cross section a square was cut in the expectation that this would have a controlling effect on the separated shear layer generating from the leading edge. The relation between size of corner-cut and vibrational responses was investigated in a series of wind tunnel and water flume experiments. Such corner-cuts were also tested in a full scale model of the pylon members for the cable-stayed bridge which is now being constructed in Japan by Hanshin Expressway Public Corporation.

Mechanism of, and turbulence effect on vortex-induced oscillations for bridge box girders

Abstract This paper describes the hybrid characteristics of vortex-induced oscillation (VIO), which are caused by Karman vortex shedding and motion-induced vortices of bridge box girders and its response sensitivity to turbulence.

Reliability of bridge structures under wind loading: Consideration of uncertainties of wind load parameters

Abstract Reliability analyses of two types of long span bridges structures — i.e. a suspension and a cable stayed bridge — are performed. The results of the reliability analysis are utilized to identify the input parameters which mainly influence the structural failure probability estimates. It is shown that for both types of bridges the consideration of cyclonic winds has a significant influence on the results of a reliability analysis. Moreover, the parameter such a flutter amplitude growth ratio (bridge structure type No. 1) and nondimensional maximum amplitude of vortex induced vibrations (bridge structure type No. 2) significantly affect the reliability estimates.

Aerodynamic instabilities of twin circular cylinders

Abstract The aerodynamic, or more generally fluid-dynamic, instability of the downstream circular cylinder in the wake of a similar cylinder in subcritical flow is the focal point of this paper. These phenomena are known to cause fatigue problems and impair the serviceability and safety of structures in various engineering fields. The aim of this study is to clarify the mechanism of this phenomena, as well as to find the conditions under which vibrations occur. A series of wind tunnel experiments and corresponding flow visualization in a water flume were conducted to permit discussion of the unsteady pressure properties, the aerodynamic unsteady force characteristics including its nonlinearity, and their relationship to the flow patterns. The sudden decrease in pressure on the inward surface of the downstream cylinder when it approaches the upstream one, appears to play an important role in the vibration. Furthermore, an analogy between the unsteady aerodynamic force properties of the downstream cylinder and those of an isolated bluff body which undergoes both torsional and coupled flutter is postulated.