Three-dimensional nonlinear flutter analysis of long-span suspension bridges during erection.

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

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.

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.

The flutter stability of long-span suspension bridges during erection can be more problematic and more susceptible to be influenced by many factors than in the final state. As described in this paper, numerical flutter stability analyses were performed for the construction process of Zhongdu Bridge over Yangtze River using the commercial FE package ANSYS. The effect of the initial wind attack angle, the sequence of deck erection, the stiffness reduction of stiffening girders, the structural damping, and the cross cables are discussed in detail. It was found that the non-symmetrical sequence of deck erection was confirmed to be aerodynamically favourable for the deck erection of long-span suspension bridges and the best erection sequence should be investigated in the design phase. While the initial wind attack angle of -3o is advantageous for the aerodynamic stability, +3o is disadvantageous compared with the initial wind attack angle of 0o during the deck erection. The stiffness reduction of the stiffening girders has a slight effect on the flutter wind speed of the suspension bridge during erection, but structural damping has a great impact on it, especially for the early erection stages.

Stress-level buffeting analysis of a long-span cable-stayed bridge with a twin-box deck under distributed wind loads

Nonlinear seismic soil-structure interaction analysis of nuclear reactor building considering the effect of earthquake frequency content

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

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.

<p>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.</p>

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.

Seismic response analysis of long-span and asymmetrical suspension bridges subjected to near-fault ground motion

Parametric analysis on flutter performance of a long-span quadruple-tower suspension bridge

<p>A new method for improving the structural rigidity of a suspension bridge without dramatically increasing the weight of the structure is presented. The design introduces cable frames that are arranged in way to keep the distances of the cables. The frame provides an increase in the torsional stiffness. The aim of the frame is to maintain the position of the cables in such a way that they act together to provide the diaphragm effect. The new method is called a “2x4 Cables System”. It was first theoretically proven here that such a system improves the stiffness against torsional flutter. Then, vibration analysis for the torsional stiffness of the frame with four cables are shown and discussed. Vibration analyses were performed using SAP90 to check the structure’s aerodynamic rigidity and stability. Numerical results for the 2x4 models and basic model (model without the frame) were analyzed here. The natural frequencies of the different models were also discussed. Using the index created by Selberg that shows the stability of suspension bridges, the limiting wind velocity of flutter is shown to be controlled by both the bending and torsional vibration frequencies of the structure.</p><p>In conclusion, the 2x4 system is able to ensure about twice the torsional rigidity of suspended girder by the numbers of cable frames. And thus it will respond to the challenges in structural engineering to ensure more aerodynamic stability of the system and further examinations are being designed with the wind-tunnel test in mind. With the new method, it will become possible to control the stability and the weight of large suspension bridges and thus make these aesthetically pleasing structures feasible and economically viable.</p>

Numerical study of aeroelastic suppression using active control surfaces on a full-span suspension bridge

To explore the favorable structural system of cable-stayed bridges with ultra-kilometer main span, based on a fully self-anchored cable-stayed bridge with 1400 m main span, a partially earth-anchored cable-stayed bridge scheme with the same main span is designed. Numerical investigation on the dynamic characteristics, aerostatic and aerodynamic stability of both two bridge schemes is conducted, and the results are compared to those of a suspension bridge with similar main span, and considering from the aspect of wind stability, the feasibility of using partially earth-anchored cable-stayed bridge in super long-span bridges with ultra-kilometer main span is discussed. Moreover, the effects of structural design parameters including the length of earth-anchored girder, the number of auxiliary piers in side span, the height and width of girder, the tower height etc on the dynamic characteristics, aerostatic and aerodynamic stability of a partially earth-anchored cable-stayed bridge are analyzed, and their reasonable values are proposed. The results show that as compared to fully self-anchored cable-stayed bridge and suspension bridge with similar main span, the partially earth-anchored cable-stayed bridge has greater structural stiffness and better aerostatic and aerodynamic stability, and consequently becomes a favorable structural system for super long-span bridges with ultra-kilometer main span. The partially earth-anchored cable-stayed bridge can achieve greater stiffness and better wind stability under the cases of increasing the earth-anchored girder length, increasing the height and width of girder, setting several auxiliary piers in side span and increasing the tower height.