• Wind and Structures
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• v.37 no.1
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• pp.39-56
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• 2023

To ensure the wind stability of a long-span suspension bridge during deck erection under skew wind, based on the aerostatic and self-excited aerodynamic force models under skew wind, a computational approach of refined flutter analysis for long-span bridges under skew wind is firstly established, in which the effects of structural nonlinearity, the static wind action and full-mode coupling etc are fully considered, and the corresponding computational procedure is programmed. By taking the Runyang suspension bridge over the Yangtze River as example, the flutter stability of the bridge in completion under skew wind is then analyzed with the aerodynamic parameters of a similar bridge deck measured from the sectional model wind tunnel test under skew wind. Finally, through simulating the girder segments erected symmetrically from the midspan to towers, from the towers to midspan and simultaneously from the towers and midspan to the quarter points, respectively, the evolutions of flutter stability limits during the deck erection under skew wind are investigated numerically, the favorable aerodynamically deck erection sequence is proposed, and the influences of skew wind and static wind effect on the flutter stability of suspension bridge under construction are ascertained.

• Wind and Structures
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• v.7 no.6
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• pp.421-447
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• 2004

This paper presents a time domain approach for predicting buffeting response of long suspension bridges under skew winds. The buffeting forces on an oblique strip of the bridge deck in the mean wind direction are derived in terms of aerodynamic coefficients measured under skew winds and equivalent fluctuating wind velocities with aerodynamic impulse functions included. The time histories of equivalent fluctuating wind velocities and then buffeting forces along the bridge deck are simulated using the spectral representation method based on the Gaussian distribution assumption. The self-excited forces on an oblique strip of the bridge deck are represented by the convolution integrals involving aerodynamic impulse functions and structural motions. The aerodynamic impulse functions of self-excited forces are derived from experimentally measured flutter derivatives under skew winds using rational function approximations. The governing equation of motion of a long suspension bridge under skew winds is established using the finite element method and solved using the Newmark numerical method. The proposed time domain approach is finally applied to the Tsing Ma suspension bridge in Hong Kong. The computed buffeting responses of the bridge under skew winds during Typhoon Sam are compared with those obtained from the frequency domain approach and the field measurement. The comparisons are found satisfactory for the bridge response in the main span.

• Wind and Structures
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• v.38 no.1
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• pp.43-58
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• 2024

To ensure the flutter stability of three-tower suspension bridges under skew wind, by using the computational procedure of 3D refined flutter analysis of long-span bridges under skew wind, in which structural nonlinearity, the static wind action(also known as the aerostatic effect) and the full-mode coupling effect etc., are fully considered, the flutter stability of a three-tower suspension bridge-the Taizhou Bridge over the Yangtze River in completion and during the deck erection is numerically investigated under the constant uniform skew wind, and the influences of skew wind and aerostatic effects on the flutter stability of the bridge under the service and construction conditions are assessed. The results show that the flutter critical wind speeds of three-tower suspension bridge under service and construction conditions fluctuate with the increase of wind yaw angle instead of a monotonous cosine rule as the decomposition method proposed, and reach the minimum mostly in the case of skew wind. Both the skew wind and aerostatic effects significantly reduce the flutter stability of three-tower suspension bridge under the service and construction conditions, and the combined skew wind and aerostatic effects further deteriorate the flutter stability. Both the skew wind and aerostatic effects do not change the evolution of flutter stability of the bridge during the deck erection, and compared to the service condition, they lead to a greater decrease of flutter critical wind speed of the bridge during deck erection, and the influence of the combined skew wind and aerostatic effects is more prominent. Therefore, the skew wind and aerostatic effects must be considered accurately in the flutter analysis of three-tower suspension bridges.

• Wind and Structures
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• v.16 no.3
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• pp.279-300
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• 2013

This paper presents a new analysis framework for predicting the internal buffeting forces in bridge components under skew wind. A linear regressive model between the internal buffeting force and deformation under normal wind is derived based on mathematical statistical theory. Applying this regression model under normal wind and the time history of buffeting displacement under skew wind with different yaw angles in wind tunnel tests, internal buffeting forces in bridge components can be obtained directly, without using the complex theory of buffeting analysis under skew wind. A self-anchored suspension bridge with a main span of 260 m and a steel arch bridge with a main span of 450 m are selected as case studies to illustrate the application of this linear regressive framework. The results show that the regressive model between internal buffeting force and displacement may be of high significance and can also be applied in the skew wind case with proper regressands, and the most unfavorable internal buffeting forces often occur under yaw wind.

• Wind and Structures
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• v.6 no.3
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• pp.179-196
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• 2003

A long suspension bridge is often located within a unique wind environment, and strong winds at the site seldom attack the bridge at a right angle to its long axis. This paper thus investigates the buffeting response of long suspension bridges to skew winds. The conventional buffeting analysis in the frequency domain is first improved to take into account skew winds based on the quasi-steady theory and the oblique strip theory in conjunction with the finite element method and the pseudo-excitation method. The aerodynamic coefficients and flutter derivatives of the Tsing Ma suspension bridge deck under skew winds, which are required in the improved buffeting analysis, are then measured in a wind tunnel using specially designed test rigs. The field measurement data, which were recorded during Typhoon Sam in 1999 by the Wind And Structural Health Monitoring System (WASHMS) installed on the Tsing Ma Bridge, are analyzed to obtain both wind characteristics and buffeting responses. Finally, the field measured buffeting responses of the Tsing Ma Bridge are compared with those from the computer simulation using the improved method and the aerodynamic coefficients and flutter derivatives measured under skew winds. The comparison is found satisfactory in general.

• Wind and Structures
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• v.22 no.1
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• pp.43-63
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• 2016

In conventional buffeting theory, it is assumed that the aerostatic coefficients along a bridge deck follow the strip assumption. The validity of this assumption is suspect for a cable-stayed bridge in the construction stages, due to the effect of significant aerodynamic interference from the pylon. This situation may be aggravated in skew winds. Therefore, the most adverse buffeting usually occurs when the wind is not normal to bridge axis, which indicates the invalidity of the traditional "cosine rule". In order to refine the studies of static wind load on the deck of cable-stayed bridge under skew wind during its most adverse construction stage, a full bridge 'aero-stiff' model technique was used to identify the aerostatic loads on each deck segment, in smooth oncoming flow, with various yaw angles. The results show that the shelter effect of the pylon may not be ignored, and can amplify the aerostatic loading on the bridge deck under skew winds ($10^{\circ}-30^{\circ}$) with certain wind attack angles, and consequently results in the "cosine rule" becoming invalid for the buffeting estimation of cable-stayed bridge during erection for these wind directions.

• Structural Engineering and Mechanics
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• v.78 no.3
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• pp.255-267
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• 2021

The analysis of simply supported single-cell skew-curved reinforced concrete (RC) box-girder bridges is carried out using a finite element based CsiBridge software. The behaviour of skew-curved box-girder bridges can not be anticipated simply by superimposing the individual effects of skewness and curvature, so it becomes important to examine the behaviour of such bridges considering the combined effects of skewness and curvature. A comprehensive parametric study is performed wherein the combined influence of the skew and curve angles is considered to determine the maximum bending moment, maximum shear force, maximum torsional moment and maximum vertical deflection of the bridge girders. The skew angle is varied from 0° to 60° at an interval of 10°, and the curve angle is varied from 0° to 60° at an interval of 12°. The scantly available literature on such bridges focuses mainly on the analysis of skew-curved bridges under dead and point loads. But, the effects of actual loadings may be different, thus, it is considered in the present study. It is found that the performance of these bridges having more curvature can be improved by introducing the skewness. Finally, several equations are deduced in the non-dimensional form for estimating the forces and deflection in the girders of simply supported skew-curved RC box-girder bridges, based upon the results of the straight one. The developed equations may be helpful to the designers in proportioning, analysing, and designing such bridges, as the correlation coefficient is about 0.99.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.1
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• pp.67-73
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• 2017

This study has addressed to evaluate the effects of radius of curvature and skew angle on the negative reaction in a plate girder bridge with LRB (Lead Rubber Bearing) supports. As analytical parameters, various radius of curvatures and skew angles were selected and two seismic loads of El-Centro and artificial earthquakes were applied to the bridge in the longitudinal and transverse directions. As results of 3D analysis, the possibility of negative reaction is shown at the part of acute angle and inner side of the curved bridge, and becomes increased when seismic load is applied in the transverse direction. In addition, the occurrence of negative reaction is found to be increased as both radius of curvature and skew angle decrease, which means that curved bridge has higher possibility of negative reaction than straight one. Conclusively, all of earthquake wave, gradient, radius of curvature and skew angle should be considered together to investigate the possibility of negative reaction at the bridge support subject to seismic load.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10a
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• pp.553-558
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• 1998

Since the mid of the 20th century in the world, it has been observed that the number of minor or moderate earthquake motions tend to be increased year by year. Owing to the topographical condition, moreover, large numbers of skew bridges have been constructed for the requirements of more than DB18 ton bridge in Korea. It has been also observed from foreign countries that lots of superstructures collapse in bridge were occurred in previous earthquakes, inclusive of 1995 Kobe earthquake. This is caused by a relative displacement between the upper and lower structure of bridge by the earthquake and the rotation with respect to the vertical axis of skew bridges, which were subjected to and earthquake motion. In this study, the probabilistic analysis of unseating failure of skew bridges under scenario earthquake has been carried out by evaluating the longitudinal displacement of skew bridges.

• Journal of the Korea Concrete Institute
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• v.11 no.3
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• pp.3-12
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• 1999

This study presents a suggestion of regulation of skewed slab bridge. In order to find the characteristic behavior of skew bridge, many cases of skew bridges were analyzed with changed angle of skew. The comparison of design methods for cantilever part in pier was also made. It was found that : (1) The lower the skew angle was, the higher the maximum support reaction forces at the end point were. (2) The higher the ratio of L/B was, the higher the maximum support reaction force at the point was. (3) The effect of skew may be neglected for skew angles of $70^{\circ}$or more. (4) If elastic springs are applied to the boundary conditions to simulate the rubber pad bearings, the results will be more reasonable. (5) The shear deformation effect must be considered in the analysis of cantilever part of substructure. (6) Using strut and tie model to design cantilever part of pier, it will be more simple than finite element method with same accuracy and more accurate than using frame element.