Numerical simulation method of thermal analysis for bridges without using field measurements

Abstract: Bridge vortex induced vibration (VIV) is a resonance phenomenon caused by the periodic shedding of vortices generated by natural wind passing through bridges. Bridge VIVs will not only cause fatigue damage to the structures but also affect driving safety for the passing vehicles. With the popularization of structural health monitoring (SHM) systems, machine learning technology is widely used in the field of vortex induced vibration identification for long-span bridges, due to its intelligence, real-time performance, and sensitivity to data. However, although traditional machine learning algorithms can identify the VIV based on the response data history of long-span bridges collected by SHM systems, they are difficult to apply to bridges which do not have historical vortex induced vibration data. Therefore, this paper proposes an adaptive transfer learning method for identifying VIV in the main girder of long-span suspension bridges. The proposed method can identify VIV without VIV history data of the target bridge. Results show that it can well identify VIVs at the earlier stage based on the SHM datasets of two long-span suspension bridges, verifying its effectiveness and generalization ability.

Influence line (IL)–based damage indices for long-span bridges are investigated in this study. Their effectiveness is experimentally validated for the first time through the scaled physical model of the Tsing Ma Bridge (TMB). First, the IL mechanism for damage detection and its corresponding damage indices are briefly introduced. Subsequently, the scaled TMB model instrumented with different types of sensors, including displacement sensors, strain gauges, and accelerometers, is introduced. The IL characteristics of different bridge components are compared. Two different damage cases with single- and double-damage locations at the bottom chord were tested. In the single-damage case, different ILs extracted from the nearby components were used for damage identification. These ILs can successfully locate damage visually. The strain IL (SIL) is more sensitive to local damage than deflection IL, but its detection performance degrades rapidly with the increasing distance between sensor and force locations. In the double-damage case, the SIL extracted from a single sensor cannot identify both damage cases because of the limited detectable range of each SIL; therefore, using multiple sensor information becomes necessary. For comparison, the modal parameters were also employed for damage detection. These experimental results validated the merits of the IL–based methods proposed for long-span bridges, indicating that IL–based damage indices are good indicators of local damage detection in long-span bridges. This finding contributes to the development of real-time techniques for damage localization in long-span bridges equipped with a structural health monitoring system.

<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>

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.

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

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.

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.

Ride comfort evaluation of stochastic traffic flow crossing long-span suspension bridge experiencing vortex-induced vibration

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

Track-bridge deformation relation and interaction of long-span railway suspension bridges subject to strike-slip faulting

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

Accurate and timely identification of modal parameters of long-span bridges is important for bridge health monitoring and wind tunnel tests. Wavelet analysis is one of the most advantageous methods for identification because of its good localization characteristics in both time and frequency domain. In recent years, the wavelet method has been applied more frequently in parameter identification of linear and nonlinear systems. In this article, based on wavelet ridges and wavelet skeleton, the improved modal parameter identification method was studied. To find the appropriate time-frequency resolution, an optimal wavelet basis design principle based on minimum Shannon entropy was proposed. Aiming at endpoint effect in wavelet transform, a prediction continuation method based on support vector machine (SVM) was proposed, which can effectively suppress the endpoint effect of the extended samples. In view of the fact that the ridges of metric matrices obtained by the traditional crazy climber algorithm cannot fully reflect the distribution of ridges of modulus value matrices of wavelet coefficients, an improved high-precision crazy climber algorithm was put forward to accurately identify the position of the ridge of wavelet coefficients. Finally, taking a long-span cable-stayed bridge and a long-span suspension bridge as the engineering background, improved continuous wavelet transform (CWT) was applied to modal parameter identification of bridge under ambient excitation. The modal parameters such as modal frequency, damping ratio, and mode shape were obtained. Compared with the calculation value of the numerical simulation of long-span cable-stayed bridge and wind tunnel test of long-span suspension bridge, the reliability of CWT for modal parameter identification of long-span bridges under ambient excitation was verified.

In this work, thermal characteristics of a board-level chip-scale package, subjected to coupled power and thermal cycling test conditions defined by JEDEC, are investigated through the transient thermal analysis. Tabular boundary conditions are utilized to deal with time-varying thermal boundary conditions brought by thermal cycling. It is obvious from the analysis that the presence of power cycling leads to a significant deviation of the junction temperature from the thermal cycling profile. However, for components away from the die, the deviation is insignificant. Moreover, for low-power applications, temperature histories from coupled power and thermal cycling are approximately linear combinations of temperature histories from pure power cycling and the ones from pure thermal cycling.

The dynamic performance of railway bridges under high-speed trains draws the attention of bridge engineers. The vibration issue for long-span bridges under high-speed trains is still not well understood due to lack of validations through structural health monitoring (SHM) data. This paper investigates the correlation between bridge acceleration and train speed based on structural dynamics theory and SHM system from three foci. Firstly, the calculated formula of acceleration response under a series of moving load is deduced for the situation that train length is near the length of the bridge span, the correlation between train speed and acceleration amplitude is analyzed. Secondly, the correlation scatterplots of the speed–acceleration is presented and discussed based on the transverse and vertical acceleration response data of Dashengguan Yangtze River Bridge SHM system. Thirdly, the warning indexes of the bridge performance for correlation scatterplots of speed–acceleration are established. The main conclusions are: (1) The resonance between trains and the bridge is unlikely to happen for long-span bridge, but a multimodal correlation curve between train speed and acceleration amplitude exists after the resonance speed; (2) Based on SHM data, multimodal correlation scatterplots of speed–acceleration exist and they have similar trends with the calculated formula; (3) An envelope line of polylines can be used as early warning indicators of the changes of bridge performance due to the changes of slope of envelope line and peak speed of amplitude. This work also gives several suggestions which lay a foundation for the better design, maintenance and long-term monitoring of a long-span high-speed bridge.

During thermal shock, large thermal gradients exist within a molded plastic ball grid array (PBGA) package. The conventional assumption of uniform temperature distribution becomes invalid. In this paper, an integrated thermal-mechanical analysis was performed to evaluate the transient effect of thermal shock. For comparison, an isothermal analysis was also conducted. The computational fluid dynamics (CFD) method was used to obtain the thermal boundary conditions surrounding the package. The heat transfer coefficient obtained through CFD was compared to two analytical solutions. It was found that the analytical values were not acceptable in the time period of interest. Therefore, to obtain the actual maximum die stress, CFD solution has to be used instead of analytical solutions to derive the thermal boundary condition. This boundary condition was then applied to the package and a sequentially coupled heat transfer and thermal stress analysis was performed. The transient analysis has shown that high stresses occur in the die due to thermal shock, which can not be seen under the traditional isothermal assumption. The impact of PBGA package parameters on transient die stress was also studied, including mold thickness and substrate thickness. The results in this paper could be applied to either wire bond or flip-chip PBGA packages.