Aerostatic instability mode analysis of three-tower suspension bridges via strain energy and dynamic characteristics

Wen-ming Zhang,Kai-rui Qian,Li Wang,Yao-jun Ge 한국풍공학회 2019 Wind and Structures, An International Journal (WAS Vol.29 No.3

Multispan suspension bridges make a good alternative to single-span ones if the crossed strait or river width exceeds 2-3 km. However, multispan three-tower suspension bridges are found to be very sensitive to the wind load due to the lack of effective longitudinal constraint at their central tower. Moreover, at certain critical wind speed values, the aerostatic instability with sharply deteriorating dynamic characteristics may occur with catastrophic consequences. An attempt of an in-depth study on the aerostatic stability mode and damage mechanism of three-tower suspension bridges is made in this paper based on the assessment of strain energy and dynamic characteristics of three particular three-tower suspension bridges in China under different wind speeds and their further integration into the aerostatic stability analysis. The results obtained on the three bridges under study strongly suggest that their aerostatic instability mode is controlled by the coupled action of the anti-symmetric torsion and vertical bending of the two main-spans’ deck, together with the longitudinal bending of the towers, which can be regarded as the first-order torsion vibration mode coupled with the first-order vertical bending vibration mode. The growth rates of the torsional and vertical bending strain energy of the deck after the aerostatic instability are higher than those of the lateral bending. The bending and torsion frequencies decrease rapidly when the wind speed approaches the critical value, while the frequencies of the anti-symmetric vibration modes drop more sharply than those of the symmetric ones. The obtained dependences between the critical wind speed, strain energy, and dynamic characteristics of the bridge components under the aerostatic instability modes are considered instrumental in strength and integrity calculation of three-tower suspension bridges.

A method for nonlinear aerostatic stability analysis of long-span suspension bridges under yaw wind

Zhang, Wen-Ming,Ge, Yao-Jun,Levitan, Marc L. Techno-Press 2013 Wind and Structures, An International Journal (WAS Vol.17 No.5

By using the nonlinear aerostatic stability theory together with the method of mean wind decomposition, a method for nonlinear aerostatic stability analysis is proposed for long-span suspension bridges under yaw wind. A corresponding program is developed considering static wind load nonlinearity and structural nonlinearity. Taking a suspension bridge with three towers and double main spans as an example, the full range aerostatic instability is analyzed under wind at different attack angles and yaw angles. The results indicate that the lowest critical wind speed of aerostatic instability is gained when the initial yaw angle is greater than $0^{\circ}$, which suggests that perhaps yaw wind poses a disadvantage to the aerostatic stability of a long span suspension bridge. The results also show that the main span in upstream goes into instability first, and the reason for this phenomenon is discussed.

<i>Haloactinopolyspora alkaliphila</i> sp. nov., and emended description of the genus <i>Haloactinopolyspora</i>

Zhang, Yong-Guang,Liu, Qing,Wang, Hong-Fei,Zhang, Dao-Feng,Zhang, Yuan-Ming,Park, Dong-Jin,Kim, Chang-Jin,Li, Wen-Jun International Union of Microbiological Societies 2014 International journal of systematic and evolutiona Vol.64 No.6

<P>A facultatively alkaliphilic actinomycete strain, designated EGI 80088<SUP>T</SUP>, was isolated from a saline-alkali soil sample from Xinjiang province, north-west China, and subjected to a polyphasic taxonomic characterization. Strain EGI 80088<SUP>T</SUP> formed fragmented aerial hyphae and short spore chains, and rod-like spores aggregated at maturity. Whole-cell hydrolysates of the isolate contained <SMALL>ll</SMALL>-diaminopimelic acid as the diagnostic diamino acid, and glucosamine, mannose, galactose, glucose and rhamnose as the marker sugars. The major fatty acids identified (>5 %) were anteiso-C<SUB>15 : 0</SUB>, iso-C<SUB>15 : 0</SUB>, summed feature 4 (iso-C<SUB>17 : 1</SUB>I/anteiso-C<SUB>17 : 1</SUB>B), iso-C<SUB>16 : 0</SUB> and anteiso-C<SUB>17 : 0</SUB>. The predominant menaquinone was MK-9(H<SUB>4</SUB>). The G+C content of the genomic DNA of strain EGI 80088<SUP>T</SUP> was 70.6 mol%. EGI 80088<SUP>T</SUP> showed the highest 16S rRNA gene sequence similarity to its closest phylogenetic neighbour <I>Haloactinopolyspora alba</I> YIM 93246<SUP>T</SUP> (98.5 %). The DNA–DNA relatedness value of the strain EGI 80088<SUP>T</SUP> and <I>H. alba</I> YIM 93246<SUP>T</SUP> was 59.3±5.2 %. On the basis of morphological, chemotaxonomic and phylogenetic characteristics and DNA–DNA hybridization data, strain EGI 80088<SUP>T</SUP> represents a novel species of the genus <I>Haloactinopolyspora</I>, for which the name <I>Haloactinopolyspora alkaliphila</I> sp. nov. (type strain EGI 80088<SUP>T</SUP> = BCRC 16946<SUP>T</SUP> = JCM 19128<SUP>T</SUP>) is proposed. The description of the genus <I>Haloactinopolyspora</I> has also been emended.</P>

An iterative approach for time-domain flutter analysis of bridges based on restart technique

Wen-ming Zhang,Kai-rui Qian,Lian Xie,Lian Xie,Yao-jun Ge 한국풍공학회 2019 Wind and Structures, An International Journal (WAS Vol.28 No.3

This paper presents a restart iterative approach for time-domain flutter analysis of long-span bridges using the commercial FE package ANSYS. This approach utilizes the recursive formats of impulse-response-function expressions for bridge's aeroelastic forces. Nonlinear dynamic equilibrium equations are iteratively solved by using the restart technique in ANSYS, which enable the equilibrium state of system to get back to last moment absolutely during iterations. The condition for the onset of flutter instability becomes that, at a certain wind velocity, the amplitude of vibration is invariant with time. A long-span suspension bridge was taken as a numerical example to verify the applicability and accuracy of the proposed method by comparing calculated results with wind tunnel tests. The proposed method enables the bridge designers and engineering practitioners to carry out time-domain flutter analysis of bridges in commercial FE package ANSYS.

Frequency-based tension assessment of an inclined cable with complex boundary conditions using the PSO algorithm

Wen-ming Zhang,Zhi-wei Wang,Dan-dian Feng,Zhao Liu 국제구조공학회 2021 Structural Engineering and Mechanics, An Int'l Jou Vol.79 No.5

The frequency-based method is the most commonly used method for measuring cable tension. However, the calculation formulas for the conventional frequency-based method are generally based on the ideally hinged or fixed boundary conditions without a comprehensive consideration of the inclination angle, sag-extensibility, and flexural stiffness of cables, leading to a significant error in cable tension identification. This study aimed to propose a frequency-based method of cable tension identification considering the complex boundary conditions at the two ends of cables using the particle swarm optimization (PSO) algorithm. First, the refined stay cable model was established considering the inclination angle, flexural stiffness, and sag-extensibility, as well as the rotational constraint stiffness and lateral support stiffness for the unknown boundaries of cables. The vibration mode equation of the stay cable model was discretized and solved using the finite difference method. Then, a multiparameter identification method based on the PSO algorithm was proposed. This method was able to identify the tension, flexural stiffness, axial stiffness, boundary rotational constraint stiffness, and boundary lateral support stiffness according to the measured multiorder frequencies in a synchronous manner. The feasibility and accuracy of this method were validated through numerical cases. Finally, the proposed approach was applied to the tension identification of the anchor span strands of a suspension bridge (Jindong Bridge) in China. The results of cable tension identification using the proposed method and the existing methods discussed in previous studies were compared with the on-site pressure ring measurement results. The comparison showed that the proposed approach had a high accuracy in cable tension identification. Moreover, the synchronous identification of the flexural stiffness, axial stiffness, boundary rotational constraint stiffness, and boundary lateral support stiffness was highly beneficial in improving the results of cable tension identification.

Analytical study on free vertical and torsional vibrations of two- and threepylon suspension bridges via d’Alembert’s principle

Wen-Ming Zhang,Zhi-wei Wang,Hao-qing Zhang,Xiao-fan Lu,Zhao Liu 국제구조공학회 2020 Structural Engineering and Mechanics, An Int'l Jou Vol.76 No.3

This study derives the differential equations of free vertical bending and torsional vibrations for two- and three-pylon suspension bridges using d'Alembert's principle. The respective algorithms for natural vibration frequency and vibration mode are established through the separation of variables. In the case of the three-pylon suspension bridge, the effect of the along-bridge bending vibration of the middle pylon on the vertical bending vibration of the entire bridge is considered. The impact of torsional vibration of the middle pylon about the vertical axis on the torsional vibration of the entire bridge is also analyzed in detail. The feasibility of the proposed method is verified by two engineering examples. A comparative analysis of the results obtained via the proposed and more intricate finite element methods confirmed the former feasibility. Finally, the middle pylon stiffness effect on the vibration frequency of the three-pylon suspension bridge is discussed. It is found that the vibration frequencies of the first- and thirdorder vertical bending and torsional modes both increase with the middle pylon stiffness. However, the increase amplitudes of thirdorder bending and torsional modes are relatively small with the middle pylon stiffness increase. Moreover, the second-order bending and torsional frequencies do not change with the middle pylon stiffness.

Wind tunnel investigation on flutter and buffeting of a three-tower suspension bridge

Wen-ming Zhang,Yao-jun Ge 한국풍공학회 2017 Wind and Structures, An International Journal (WAS Vol.24 No.4

The Maanshan Bridge over Yangtze River in China is a new long-span suspension bridge with double main spans of 2×1080 m and a closed streamline cross-section of single box deck. The flutter and buffeting performances were investigated via wind tunnel tests of a full bridge aeroelastic model at a geometric scale of 1:211. The tests were conducted in both smooth wind and simulated boundary layer wind fields. Emphasis is placed on studying the interference effect of adjacent span via installing a wind deflector and a wind separating board to shelter one span of the bridge model from incoming flow. Issues related to effects of mid-tower stiffness and deck supporting conditions are also discussed. The testing results show that flutter critical wind velocities in smooth flow, with a wind deflector, are remarkably lower than those without. In turbulent wind, torsional and vertical standard deviations for the deck responses at midspan in testing cases without wind deflector are generally less than those at the midspan exposed to wind in testing cases with wind deflector, respectively. When double main spans are exposed to turbulent wind, the existence of either span is a mass damper to the other. Furthermore, both effects of mid-tower stiffness and deck supporting conditions at the middle tower on the flutter and buffeting performances of the Maanshan Bridge are unremarkable.

A method for nonlinear aerostatic stability analysis of long-span suspension bridges under yaw wind

Wen-Ming Zhang,Yao-Jun Ge,Marc L. Levitan 한국풍공학회 2013 Wind and Structures, An International Journal (WAS Vol.17 No.5

By using the nonlinear aerostatic stability theory together with the method of mean wind decomposition, a method for nonlinear aerostatic stability analysis is proposed for long-span suspension bridges under yaw wind. A corresponding program is developed considering static wind load nonlinearity and structural nonlinearity. Taking a suspension bridge with three towers and double main spans as an example, the full range aerostatic instability is analyzed under wind at different attack angles and yaw angles. The results indicate that the lowest critical wind speed of aerostatic instability is gained when the initial yaw angle is greater than 0°, which suggests that perhaps yaw wind poses a disadvantage to the aerostatic stability of a long span suspension bridge. The results also show that the main span in upstream goes into instability first, and the reason for this phenomenon is discussed.

Rapid assessment of suspension bridge deformation under concentrated live load considering main beam stiffness: An analytical method

Wen-ming Zhang,Jia-qi Chang,Xing-hang Shen,Xiao-fan Lu,Tian-cheng Liu 국제구조공학회 2023 Structural Engineering and Mechanics, An Int'l Jou Vol.88 No.1

With the gradual implementation of long-span suspension bridges into high-speed railway operations, the main beam’s bending stiffness contribution to the live load response permanently grows. Since another critical control parameter of railway suspension bridges is the beam-end rotation angle, it should not be ignored by treating the main beam deflection as the only deformation response. To this end, the current study refines the existing method of the main cable shape and simply supported beam bending moment analogy. The bending stiffness of the main beam is considered, and the main beam’s analytical expressions of deflection and rotation angle in the whole span are obtained using the cable-beam deformation coordination relationship. Taking a railway suspension bridge as an example, the effectiveness and accuracy of the proposed analytical method are verified by the finite element method (FEM). Comparison of the results by FEM and the analytical method ignoring the main beam stiffness revealed that the bending stiffness of the main beam strongly contributed to the live load response. Under the same live load, as the main beam stiffness increases, the overall deformation of the structure decreases, and the reduction is particularly noticeable at locations with original larger deformations. When the main beam stiffness is increased to a certain extent, the stiffening effect is no longer pronounced.

Wind tunnel investigation on flutter and buffeting of a three-tower suspension bridge

Zhang, Wen-ming,Ge, Yao-jun Techno-Press 2017 Wind and Structures, An International Journal (WAS Vol.24 No.4

The Maanshan Bridge over Yangtze River in China is a new long-span suspension bridge with double main spans of $2{\times}1080m$ and a closed streamline cross-section of single box deck. The flutter and buffeting performances were investigated via wind tunnel tests of a full bridge aeroelastic model at a geometric scale of 1:211. The tests were conducted in both smooth wind and simulated boundary layer wind fields. Emphasis is placed on studying the interference effect of adjacent span via installing a wind deflector and a wind separating board to shelter one span of the bridge model from incoming flow. Issues related to effects of mid-tower stiffness and deck supporting conditions are also discussed. The testing results show that flutter critical wind velocities in smooth flow, with a wind deflector, are remarkably lower than those without. In turbulent wind, torsional and vertical standard deviations for the deck responses at midspan in testing cases without wind deflector are generally less than those at the midspan exposed to wind in testing cases with wind deflector, respectively. When double main spans are exposed to turbulent wind, the existence of either span is a mass damper to the other. Furthermore, both effects of mid-tower stiffness and deck supporting conditions at the middle tower on the flutter and buffeting performances of the Maanshan Bridge are unremarkable.