We have developed a new test rig that can provide data for determination of the aerodynamic flutter derivatives in a fast and efficient manner. For instance, in connection with the design of flexible structures such as long-span bridges. 

With the method previously applied, we could provide a set of eight derivatives corresponding to a two degrees-of-freedom motion. With the new rig, we are able to provide the full set of eighteen derivatives that describe motion in three degrees-of-freedom. The aerodynamic flutter derivatives for a given bridge deck are the key parameters to the assessment of the bridge deck’s buffeting response and stability limit by numerical methods. 

Buffeting response is a structure’s response induced by the turbulence in the oncoming flow. The stability limit is the critical wind speed above which the structure is no longer aerodynamically stable. The aerodynamic flutter derivatives can be used for calculation of the bridge deck’s buffeting response and stability limit for varying dynamic characteristics of the same deck geometry, e.g., various steps of construction. 

Free vibration technique

We used the so-called free vibration technique and system identification to obtain the flutter derivatives. However, the test method applied was limited to two degrees-of freedom corresponding to vertical motion and rotation (torsional motion). Further, the free vibration technique used was not suited for testing in turbulent flows. Forced 3D vibration test rig Due to the increasing demand for aerodynamic flutter derivatives for various bridge projects, a more effective test method was sought.

Also, as the demand for flutter derivatives relating to three degrees-of-freedom was increasing, it was decided to establish a three degrees-of-freedom rig which can effectively provide data for the full set of eighteen derivatives - both in smooth and turbulent flows - by using the forced oscillations technique. The new rig has already been used for a series of elaborate testing for a long-span suspension bridge.

We will continue to work on the development of the rig and its analysis methods in the coming years. Results obtained with the new rig were published in a paper presented during the summer of 2011.