Flutter stability of a long-span suspension bridge during erection

Investigation on aerodynamic stability of long-span suspension bridges under erection

Parameter sensitivity study on flutter stability of a long-span triple-tower suspension bridge

To investigate the full-range characteristic on nonlinear aerostatic of long span cable-stayed bridge. taking a cable-stayed bridge under construction for example, the realization process of inner and outer incremental double iteration method to solve the aerostatic stability and the full-range physical characteristics of instability are described in detail. Analysis result shows that the critical velocity and instability shape are relation with the corresponding three-component force coefficients of the initial attack angle and the slope of three-component force coefficient curve. Concretely, the iterative positive or negative changing direction of effective attack angle in full-range of aerostatic instability is ascertained by the positive or negative value of lifting moment coefficient in initial attack angle; in addition, which will influence the lifting force coefficient value and drag force coefficient value, the bigger the slope of lifting moment coefficient curve is, the smaller the critical velocity is; when the initial angle is located in the smallest of the positive and the biggest of the negative value of lifting moment coefficient curve, the critical velocity reach the maximum in different rotation direction separately, and with the increase of absolute value of lifting moment coefficient in effective attack angle, the critical velocity presents descending trend in those two different rotation directions.

Recently, the following rapid development of the national economy and the advancement of communication and transportation, the construction of Long-Span Suspension Bridges have been increasing gradually. Long-Span Suspension Bridges are greatly preferred by engineering designers rather than other bridges equipped with construction supporting systems, not only for economic reasons, but also Long-Span suspension bridges are in the possession of advanced construction techniques when we deal with long distances, for Long-Span suspension bridges acquire supporting constructions features rigged with main cables and ropes. Long-Span suspension bridges are bridge constructions included with cable systems and under strong nonlinear factor effects, which the more the suspension increases, the more the bridges construction lightens, and the more the flexibility grows. There is a lot differences shown in the cost of the Suspension bridges according to different opening. The effect of the deck material is like the effect of the openness. The cost of the suspension bridge in the world is to be discussed too, so the cost is to investigate the effect of opening the drawbridge. The cost of suspension bridges in the world is very controversial, so investigating the financial effect of openness and deck material on suspension bridges is required. In this study, a three-dimensional model of the main cable, suspension rope, deck and tower elements of suspension bridge system by using CSI Bridge Program was constructed and numerical analysis was carried out. The standards used in analysis and design are used the AASHTO LRFD standard, which is common in the world. Suspension bridges of 250, 500, 750, 1000, 1500, 2000 meters were analyzed and designed in different deck material and openings. The material and cost of the suspension bridges have been investigated. The costs according to the openness and deck material of Suspension bridges have been shown by the obtained results.

Structural robustness is defined by the international engineering community as the capabilities of structural systems that enable them to survive unforeseen or unusual circumstances. In order to highlight the unforeseen and unusual characteristics of wind hazards, this study introduces the concept of structural robustness into the wind-resistant design and evaluation of bridges and proposes the robustness evaluation of aerodynamic flutter and aerostatic torsional stability of long-span bridges. Furthermore, the return period of the design wind speed that a bridge can resist is used to represent wind-resistant robustness. Aiming at the problem of aerodynamic and aerostatic stability, the analysis methods of aerodynamic flutter stability robustness and aerostatic torsional stability robustness of long-span suspension bridges are respectively established. Based on the established methods of aerodynamic flutter stability and aerostatic torsional stability robustness evaluation, robustness analysis is carried out on eight completed long-span suspension bridges and two long-span suspension bridges to be built. The evaluation method proposed in this study makes it possible to measure the ability of bridge structures to resist multiple disasters using the same index.

This work presents some analytical and numerical results of a dynamic analysis of the dimensionless 2-D sheet flight equations. Two empirical models for aerodynamic forces and moments are used and compared. Results show that the initial condition of rest is always unstable, and for long times three distinct flight regimes are possible, depending on the initial angle of attack, the Tachikawa number, Ta (in fact, the parameter chosen was its inverse, <TEX>${\Omega}$</TEX>), and a mass ratio <TEX>${\Phi}$</TEX>. The final orbits in the velocity space and their maximum kinetic energy are compared with a theoretical asymptotic state of the motion equations, and some design considerations are proposed.

Analytical prediction of trajectories of ice pieces after release in an airstream

Due to the occurrence of whole-span and subspan vibration at the same time during the galloping of the iced bundle conductors, the distance between the subconductors changes, resulting in the variation of the aerodynamic parameters for the leeward subconductors. The existing conventional studies usually only consider the whole-span galloping, ignoring the relative motion and the electromagnetic force between the subconductors. Based on considering the above two factors at the same time, a new numerical simulation method to study the galloping behaviors of the iced conductors is presented. Then, the galloping behaviors of the iced twin bundle conductors’ transmission line with different current intensity, initial wind attack angle, and spacer layout are studied. The galloping oscillation behaviors include time histories of vibration displacements, mode, amplitude, frequency, motion traces, and the distance between two subconductors. The simulation results showed that the whole-span and subspan vibration appear at the same time during galloping oscillation and two subconductors may collide with each other when affected by the varying electromagnetic and aerodynamic forces. The effects of varying electromagnetic and aerodynamic forces on galloping behavior cannot be ignored. The new method presented in this work can contribute to the galloping study of the iced bundle conductors.

Prediction method for galloping features of transmission lines based on FEM and machine learning

We have developed a full-dimensional analytical abinitio potential energy surface (PES) for the Cl- + CH3I reaction using the Robosurfer program system. The energy points have been computed using a robust composite method defined as CCSD-F12b + BCCD(T) - BCCD with the aug-cc-pVTZ(-PP) basis set and have been fitted by the permutationally invariant polynomial approach. Quasi-classical trajectory simulations on the new PES reveal that two product channels are open in the collision energy (Ecoll) range of 1-80 kcal/mol, i.e., SN2 leading to I- + CH3Cl and iodine abstraction (above ∼45 kcal/mol) resulting in ICl- + CH3. Scattering angle, initial attack angle, product translational energy, and product internal energy distributions show that the SN2 reaction is indirect at low Ecoll and becomes direct-rebound-back-side (CH3-side) attack-type, as Ecoll increases. Iodine abstraction mainly proceeds with direct stripping mechanism with side-on/back-side attack preference. Comparison with crossed-beam experiments and previous direct dynamics simulations shows quantitative or qualitative agreement and also highlights possible theoretical and/or experimental issues motivating further research.

In this work, the aerodynamic stability of the Yichang Suspension Bridge over Yangtze River during erection was determined by three-dimensional nonlinear flutter analysis, in which the nonlinearities of structural dynamic characteristics and aeroelastic forces caused by large deformation are fully considered. An interesting result obtained was that the bridge was more stable when the stiffening girders were erected in a non-symmetrical manner as opposed to the traditional symmetrical erection schedule. It was also found that the severe decrease in the aerodynamic stability was due to the nonlinear effects. Therefore, the nonlinear factors should be considered accurately in aerodynamic stability analysis of long-span suspension bridges during erection.

In recent years several long-span bridges have been constructed and put into service in China's high-speed railway lines. These bridges usually cross the major rivers of China which serve as vital shipping channels. The long-span structure becomes the superior and sometimes even sole scheme to carry high-speed tracks over the rivers without impacting the water transportation at the bridge site. High-speed trains require stable and smooth geometries of the tracks on long-span bridges to achieve successful and safe passages. Nevertheless, the above mentioned track geometries can be threatened by multiple stressors, e.g., high-speed trains, wind, temperature, among others. Structural health monitoring (SHM) systems have been applied to the long-span bridges, aiming to collect real-time information about both the stressors and structure responses. This information can be used to investigate the performance of bridge structures, and eventually to ensure the running safety of high-speed trains. In this context, the present paper examines the acceleration responses of a long-span steel arch bridge, i.e., the Nanjing Dashengguan Yangtze River Bridge, under operating high-speed train loads. This unique long-span railway bridge and its SHM system are introduced. A coupled dynamic model of the high-speed vehicle and b ridge structure system is subsequently developed. Acceleration responses at the typical locations resulting from the coupled dynamic analysis are compared to the SHM data. It is found that at several specific velocity values the maximum accelerations of the bridge produce respective peaks through the parametric study on train speeds. This interesting phenomenon calls for more detailed investigation on the concerned topic in the future.

The present paper combined the natural environment excitation technology (NExT) with the eigen system realization algorithm (ERA) to identify the modal parameters of a suspension bridge. Firstly, the critical parameters in NExt–ERA, such as record length, window length, and ranks of the Hankel matrix, and their influence on identification accuracy have been discussed. Subsequently, based on the acceleration series obtained from the Xihoumen Bridge Health Monitoring System, 3015 sets of modal frequencies and modal damping ratios of the Xihoumen Bridge were identified under 7 sets of wind speeds by the NExt–ERA. Finally, the probability distribution and confidence interval of the structural modal damping ratios were analyzed. Besides, the dependence of identified frequencies damping ratios on wind speed was also discussed. The results show that at the same wind speed, the mean value, and variance of the torsional and lateral mode damping ratios are larger than those of the vertical mode, but this difference gradually decreases with the increment of wind speed. The modal damping ratios along three directions under different wind speeds all follow the generalized extreme value distribution, but wind speed affects the tailing properties of probability distribution of the vertical and torsional mode damping ratios. The estimated damping ratios could provide references for structural design and vibration control of similar long-span bridges.

&lt;p&gt;Infrastructure is a vital component for the development of countries, where bridges in particular are a segment of infrastructure that are vital for the society. As bridges age they could show signs of deterioration that can be caused by continuously being subjected to traffic loads and environmental effects. Structural Health Monitoring (SHM) is a modern technology to monitor the structural performance through the continuous collection of data. The method enables engineers to monitor the health of the structure during its operation, in order to plan for maintenance when any signs of failure are observed from the very beginning. This paper covers a detailed overview of the state of the art of various types of SHM systems implemented on long-span cable-stayed bridges and suspension bridges all around the world. A variety of cases, sensors, and methods of obtaining and studying the data to monitor the structural health of bridges are evaluated, showing the importance of installing SHM systems in long-span bridges.&lt;/p&gt;

The traffic load has grown significantly in recent years, which could pose a threat to the service safety of existing bridges. Thus, evaluating the actual traffic load effects on bridges using actual traffic data is an urgent task. This study presents a framework for extrapolating maximum dynamic traffic load effects on long-span bridges using site-specific traffic monitoring data. The framework involves traffic-bridge interaction analysis and probabilistic modeling of extreme values. The weigh-in-motion measurements of a heavy-duty highway were utilized to simulate stochastic traffic loads. Case studies of two long-span cable-supported bridges based on weigh-in-motion measurements were undertaken to demonstrate the effectiveness of the proposed framework. It was concluded that Rice’s level-crossing approach can capture both the dynamic and probabilistic characteristics of traffic load effects, and thus provides a reasonable extrapolation. The amplification factors for the cable-stayed bridge and the suspension bridge are 5.9% and 3.6%, respectively. For a longer-span bridge, the dynamic effect for extrapolation is weaker, but the effect of traffic volume growth seems more significant.