Super Long Span Bridge Aerodynamics
Mission Statement/Objectives
To define a standard in validating the software for the computation of the bridge response to the turbulent wind.
For long span bridges, the response to the turbulent wind is one of the major problems affecting the bridge design. The resulting vibrations have to be carefully considered for fatigue problems and life-time evaluation. Moreover, the safe design of the bridge must account for well-known types of instability, like flutter. Presently, there is no well-assessed method for computing bridge response to the turbulent wind.
In other fields of engineering, certified methods are available to deal with design and/or verification problems, such as the following examples:
a. software for computing the response of High Voltage Transmission lines to vortex-induced vibrations and subspan oscillations; this software is validated through benchmarks between different programs and against field measurements.
b. software for computing train dynamics to support homologation; the European Standard defines the procedure to validate the software through comparison between analytical and experimental results.
c. software for computing pantograph-catenary interaction; a European Standard to certify the software using a reference computation is available.
The activity of the Task Group should be organised according to the following steps:
1. Analysis of the different methods developed by researchers and designers involved in bridge design
2. Definition of guidelines identifying a procedure to obtain the data necessary for the computation, for instance:
a. Aerodynamic and aeroelastic parameters of the bridge that are to be identified
b. Structural parameters: modes of vibration and natural frequencies
c. Wind structure in the bridge site: design wind speed, wind turbulence index, etc
3. Definition of the computation procedure for:
a. Frequency domain or time domain
b. Fundamental issues of the computation method
c. Output results
Scope & Limitation
The fatigue design of long-span bridges usually depends on the results of numerical simulations that predict the structure response to turbulent wind. The reduction of the uncertainties of these numerical models would result in a more efficient and safety design and maintenance activity with direct impact on costs and scheduling.
As far as buffeting response of long-span bridges is concerned, a real estimation of the uncertainties is not easily predictable because of the complexity of the fluid-structure interaction problem and the lack of reliable benchmark data.
The main goal of this Task Group is the validation of numerical codes:
- The first step of the benchmark will be a comparison of the outputs of numerical simulations performed with different numerical codes used by the members.
- The second step of the benchmark will be a Numerical-Experimental comparison of the outputs of numerical simulations against wind tunnel tests results.
- The third step of the benchmark will be a Numerical-Experimental comparison of the outputs of numerical simulations against full scale tests results, if available.
Expected Project Output
- Guidelines and SEI reports/papers:
- Numerical vs numerical benchmark
- Numerical vs wind tunnel benchmark
- Organization of special sessions and workshops
- Special SEI issues
- Productions of reports which could be considered for publication as SED
Start Date: November 2016
Target Date of Completion: November 2022
As reported in IABSE Newsletter July 2021:
TG 3.1: Super-Long Span Bridge Aerodynamics (video link)
Stoyan Stoyanoff, Vice Chair, from Bromont Québec, Canada speaks about his Task Group's projects and aims. If you or any of your colleagues wish to join these projects, discuss, or contribute to ongoing discussions with leading structural engineers worldwide, then write to us at bose@iasbe.org and we will connect you to the respective TG. In Stoyan Stoyanoff's words, 'The main objective of TG 3.1 is to define generic problems that we hope would become benchmarks for all interested in long-span bridge aerodynamics. For example, anyone who would like to predict the response of a long-span bridge to strong winds, or its critical flutter speed, and would like to verify their approach, could solve the benchmark as defined by our Task Group and be able to get a sense right away if they are, or not, on the right track. It may also serve as the starting point of new theoretical and experimental studies.
This task group stems from the initiative of prof. Giorgio Diana of Milano, Italy who saw a clear gap in our bridge aerodynamics practice. In a nutshell, there are almost as many tools to predict the response of a bridge to strong winds as they are experts in the field, but there isn’t an internationally approved tool to verify or quantify the error margins of one’s prediction against a benchmark. The objective of our task group is to fill this gap. Our first meeting took place at the IABSE Congress in Stockholm in September 2016. We were a small group then, composed of structural engineers, bridge aerodynamics consultants, university professors and graduate students, and software developers, about 15 people. Four years later, the group has grown, it has almost doubled now. Even though our work is nearing the end, we plan to submit our final report in November 2022, there is still time if you are interested in this topic, do join us and contribute.
In our work so far, the task group has defined a series of case problems, predicting the aerodynamic stability limit on a simplified example of a suspension bridge and its buffeting response under well-defined sets of structural properties, aerodynamic characteristics and turbulent wind. All members of the group were asked to solve the problem ‘blindly’, that is without knowing the ‘answer’, and the results of the simulations were compared. It was a very useful exercise; we’ve got some surprises, good and more difficult and we’ve learned a lot. The first part of the work was presented at the IABSE Congress in New York City, in 2019 and was published in Structural Engineering International journal (Paper 1, Paper 2).
The group is now focusing on developing more complete case studies to go to the next level where complex interaction between the dynamics of the structure and its aerodynamics need to be well captured. As expected, this step has been more challenging, where the group members still continue to submit their solutions. It is planned that these results will be presented at the IABSE Congress in Ghent this September 2021. Register for IABSE Ghent.
