Time domain buffeting analysis of large-span cable-stayed bridge

Tese de mestrado. Estruturas de Engenharia Civil. Faculdade de Engenharia. Universidade do Porto. 200

Aerodynamic Flutter and Buffeting of Long-span Bridges under Wind Load

With the continuous increase of span lengths, the aerodynamic characteristics of long-span bridges under external wind excitation have become much more complex and wind-induced vibration has always been a problem of great concern. The present research targets on the aerodynamic performance of long-span bridges under wind load with an emphasis on bridge flutter and buffeting. For the aerodynamic flutter analysis of long-span bridges, the present research investigated the effects of the wind turbulence on flutter stability. The characterizations of the self-excited forces are presented in both the frequency-domain and in the time-domain, and the flutter analysis is conducted under both uniform and turbulent flows. The effect of wind turbulence is directly modeled in time-domain to avoid the complicated random parametric excitation analysis of the equation of motion used in previous studies. It is found that turbulence has a stabilizing effect on bridge aerodynamic flutter. A probabilistic flutter analysis of long-span bridges involving random and uncertain variables is also conducted, which can provide more accurate and adequate information than the critical flutter velocity for wind resistance design of long-span bridges. For the buffeting analysis of long-span bridges, the stress-level buffeting analysis of the bridge under spatial distributed forces is conducted to investigate the effects of wind turbulence on the fatigue damage of long-span bridges. It is found that the increase of the turbulence intensity has a strengthening effect on the buffeting-induced fatigue damage of long-span bridges. For buffeting control, a lever-type TMD system is proposed for suppressing excessive buffeting responses of long-span bridges. The lever-type TMD with an adjustable frequency can overcome the drawback of excessive static stretch of the spring of traditional hanging-type TMD and be adaptive to the change of the environment and the structure itself. To effectively apply the lever-type TMD to future feedback control design, the control performance of the lever-type TMD for excessive buffeting responses of long-span bridges has been studied. The effects of wind velocity and attack angle and the stiffness reduction of bridge girder on the control efficiency have also been investigated to determine the adjustment strategy of the lever-type TMD. It is found that the control efficiency of the lever-type TMD varies greatly with the change of the location of the mass block. The lever-type TMD should be adjusted accordingly based on comprehensive consideration of the environment change and specific control objectives

Wind Action Phenomena Associated with Large-Span Bridges

In the past, the design of bridges over increasing distances was limited by construction techniques and, as always, by economics. As technological advances have turned possible cable-supported bridges of incredible spans, a new challenge has been added to the equation: that of withstanding the action of winds without developing undesirable dynamic responses. In this chapter, the several aerodynamic phenomena of relevance to long-span bridges are classified and discussed. This will interest both experts and non-experts in the field, thanks to the overview that is given. For certain cases, codes of practice recommend wind tunnel tests. The reader is introduced to these, as well as to numerical simulations, which are currently gaining increasing importance. Next, measures for attenuating susceptibility for undesirable dynamic responses are reviewed. The chapter ends with a discussion of the Vila Real Bridge deck section, based on wind tunnel tests and numerical simulations carried out by the authors: the aerodynamics was effectively improved with geometrically subtle modifications that were proposed and adopted still in the design phase

Safety Assessment of Road Vehicle in Crosswind Considering Driver Behavior

With expansion of the economy, more and more highway networks extend to coastal areas and mountain valley areas. Vehicles will be exposed to strong crosswinds when driven on these highway roads, especially in hurricane season and in winter in these two different topographic areas. Strong crosswinds threaten the safety of transportation infrastructure and passing vehicles in forms of vehicle accidents that usually result in traffic blockage and driver injury, posing negative effects on economic growth. This dissertation aimed to evaluate the vehicle safety when running through crosswinds in consideration of driver behaviors. Firstly, the aerodynamic characteristics of road vehicles were identified using computational fluid dynamic method. Aerodynamic coefficients of a high-side lorry running in crosswinds using both traditional resultant-wind velocity method and relative-motion approach were compared. In addition, the aerodynamic coefficients of multiple types of vehicles were investigated. The curves of aerodynamic coefficients for different vehicle types against wind yaw angles were obtained. Secondly, an experimental investigation on the vehicle performance and driver behavior was conducted by taking advantage of the LSU’s driving simulator. This study revealed the repeatability of driver behavior and the effect of crosswind speeds on the vehicle performance and drivers’ behavior through a statistical analysis. More scenarios were considered, such as driving in windy-rainy conditions. A regression model of the steering wheel angle turned by drivers was obtained. Finally, safety assessment of vehicles was performed based on an improved wind-vehicle-bridge coupled system and considering driver’s behavior using a series of driver behavior models. For different types of road vehicles, rigid frame vehicle model and flexible frame vehicle model were developed. Accident criteria of lateral side slip, rotational deviation, and rollover were considered. To investigate the influence of driver models, four driver models were considered in different integration methods. Results between cases from different driver models were compared

Aerostructural Optimization of Long Span Bridges: Current Advances and Challenges

Structures Congress 2020. 5-8 abril, 2020. St. Louis, Missouri[Abstract] This paper describes the evolution of deck shape of long span bridges since the Tacoma Narrows collapse trying to avoid undesirable aerodynamic behavior under wind flow and the trend in the last decades to increase the length of the main span of suspension and cable stayed bridges. The necessity to use advanced technologies to help the engineer to obtain the best possible design is highlighted and the advantages of applying optimization methodologies is encouraged. It is explained that this approach requires to use only numerical tools and hence to eliminate experimental studies, as wind tunnel tests using reduced models of full bridge of a segment of the deck, and their substitution by computational fluid dynamics (CFD) simulations. After doing so, the current capabilities of this approach are presented and, finally, the problems that need to be solved to have a fully operational methodology able to be implemented in real structures are outlined.This research has been funded by the Spanish Ministry of Economy and Competitiveness in the frame of the research project BIA2016-76656-R and the Galician regional government (including FEDER Funding) reference ED431C 2017/72. M. Cid Montoya has been funded by the Galician regional government (Xunta de Galicia) with reference ED481B 2018/053 and the Fulbright postdoctoral scholarship programXunta de Galicia; ED431C 2017/72Xunta de Galicia; ED481B 2018/05

Semi-Active Control Systems in Bridge Engineering: A Review of the Current State of Practice

In view of the grave socioeconomic consequences of earthquake damage to bridge structures, along with their critical role in modern and older road and rail networks, this article attempts to identify and summarise the current trends in the use of semi-active control technology in bridge engineering, as an enhanced seismic response control solution, combining increased adaptability and reliability, compared to passive and active schemes. In this context, representative analytical and experimental studies, as well as some full-scale applications of semi-active control devices are first reviewed and a brief description of relevant benchmark studies is subsequently presented, with a view to serving as a point of reference for further research and development. A framework of performance-based control principles aiming at the aforementioned objectives is finally set forth

Dynamic performance of bridges and vehicles under strong wind

The record of span length for flexible bridges has been broken with the development of modern materials and construction techniques. With the increase of bridge span, the dynamic response of the bridge becomes more significant under external wind action and traffic loads. The present research targets specifically on dynamic performance of bridges as well as the transportation under strong wind. The dissertation studied the coupled vibration features of bridges under strong wind. The current research proposed the modal coupling assessment technique for bridges. A closed-form spectral solution and a practical methodology are provided to predict coupled multimode vibration without actually solving the coupled equations. The modal coupling effect was then quantified using a so-called modal coupling factor (MCF). Based on the modal coupling analysis techniques, the mechanism of transition from multi-frequency type of buffeting to single-frequency type of flutter was numerically demonstrated. As a result, the transition phenomena observed from wind tunnel tests can be better understood and some confusing concepts in flutter vibrations are clarified. The framework of vehicle-bridge-wind interaction analysis model was then built. With the interaction model, the dynamic performance of vehicles and bridges under wind and road roughness input can be assessed for different vehicle numbers and different vehicle types. Based on interaction analysis results, the framework of vehicle accident analysis model was introduced. As a result, the safer vehicle transportation under wind can be expected and the service capabilities of those transportation infrastructures can be maximized. Such result is especially important for evacuation planning to potentially save lives during evacuation in hurricane-prone area. The dissertation finally studied how to improve the dynamic performance of bridges under wind. The special features of structural control with Tuned Mass Dampers (TMD) on the buffeting response under strong wind were studied. It was found that TMD can also be very efficient when wind speed is high through attenuating modal coupling effects among modes. A 3-row TMD control strategy and a moveable control strategy under hurricane conditions were then proposed to achieve better control performance

Buffeting performance of long-span suspension bridge based on measured wind data in a mountainous region

Long-span suspension bridge increases rapidly in size as a result of bridge construction in a mountainous region, in addition, more and more long-span suspension bridges are in process of preparation. The bridge stiffness decreases with the increase of bridge span length, and hence the buffeting performance of bridge is sensitive to external factors. In this paper, the Cuntan Yangze Bridge located in a mountainous region is taken as the background to study the effect of different power spectrums on the buffeting performance. A three-dimensional finite element model is set up on the ANSYS platform. The fitted power spectrum of extreme strong wind is recorded and taken as the sample to analyze the buffeting performance. The results are compared with the specified power spectrum in the time and frequency domains. Different from existing studies, buffeting performances with the fitted power spectrum are larger than those with the specified power spectrum on the whole. Two kinds of power spectrum are coincidental in the overall tendency in the frequency domain and are distinct in the low frequency region. Structure performance of long-span suspension bridge in the mountainous region should be the subject of specially paid attention

Reliability-based lifetime performance analysis of long-span bridges

2010 Fall.Includes bibliographical references.Long-span bridges generally serve as the significant hub in the transportation system for normal transportation and critical evacuation paths when any disaster happens. Thus, the safety and serviceability of long-span bridges are related to huge economic cost and safety of thousands of lives. The objective of this research is to establish a general framework to evaluate the lifetime performance of long-span bridges through taking account of more realistic load situations, such as traffic flow and wind environment. After some background information is introduced in Chapter 1, Chapter 2 covers the modeling of stochastic traffic flow for the bridge infrastructure system in a more realistic way by using the Cellular Automaton model. Based on the detailed information of individual vehicles of the stochastic traffic flow, the general framework to study Bridge/Traffic/Wind dynamic performance is developed in Chapter 3. Chapter 3 and Chapter 4 also report the results of the bridge's serviceability under normal and extreme loads events, respectively. In Chapter 5, the scenario-based fatigue model is further developed based on the dynamic framework developed in Chapter 3. Finally, the reliability-based analysis is conducted in Chapter 6 to study the fatigue damage caused by the coupling effects among bridge, traffic flow and wind throughout the bridge's service life