Study On The Flutter Stability Of Cross-sea Large-span Cable-stayed Bridge In Construction State

In a strait area, the topography and morphology change drastically and the windfields distribute in a very complex manner. It is explicitly required by item3.2.7inWind-resistant Design Specification for Highway Bridges that reliable measures betaken to determine the design basic wind velocity in a strait area. Related studies haveindicated that aerodynamic derivative, as an important parameter to describe theaerodynamic performance of the main beam section, plays an essential role in the flutteranalysis of large-span bridges. With the help of Xiamen-to-Zhangzhou Cross-sea Bridgewind-resistant test project, this paper presents such studies as strait wind environmentanalysis at the mouth of Jiulong River, aerodynamic derivative recognition theory,vibration test with wind tunnel, dynamic finite element simulation of2-DOF (degree offreedom) main beam section model using MSC.NASTRAN and bridge flutter windtunnel test under least favorable working conditions. From these studies, the followingconclusions are drawn:1. By using probability curve correlation coefficient method, it was obtained thatthe100-year-return-period wind velocity in the location of the bridge in question wasexpected to be35.8m/s, which was lower than the design basic wind velocity39.7m/sas given by Specification.2. An independent-developed wavelet threshold filtering program developed withMatlab proved to be effective in de-noising in that it effectively raised thesignal-to-noise ratio of the original testing signal, which was favorable to finding themodes buried in noise. After comparing the recognition results of three different modalrecognition methods, it was found that wavelet threshold filtering method was of highspeed and high accuracy, especially in terms of the accuracy of modal damping ratio.3. A moving least square method was established to recognize the aerodynamicderivatives. This method is able to recognize all the aerodynamic derivatives at one timewith only the bending moment coupling2-DOF damped free vibration signal of thebridge segment model. A simulated wind tunnel test with slab section model showedthis method was highly noise-resistant and of good convergence and stability innonlinear iteration process. It was used to recognize the aerodynamic derivatives invibration tests of four typical2-dimensional bridge segment models and thereby provedto be highly accurate in recognizing the flutter derivatives of streamlined sections. 4. The flutter critical wind velocities were obtained respectively by observing theflutter critical wind velocity of four typical2-dimensional bridge segment models inwind tunnel vibration test and by simulating the aerodynamics of those four modelswith MSC.NASTRAN. Result of the test and that of the simulation are accordant witheach other.5. A flutter wind tunnel test was conducted on the720m north branch bridge of theXiamen-to-Zhangzhou Cross-sea Bridge under two least favorable working conditionsand a nonlinear analysis with secant method solution was made on the flutter ofmulti-mode participated three-dimensional cable stayed bridge. The result of the test isaccordant with that of the analysis, which shows the nonlinear analytic method can beapplied to the flutter calculation of large-span cable stayed bridges. The test resultshows that the north branch bridge of the Xiamen-to-Zhangzhou Cross-sea Bridge hasgood flutter stability in construction when the wind velocity is no more than98m/s.6. Theoretical studies on the application of intelligent materials to the control ofcantilever beam flutter show that LQG control law design method can be applied topractical problems and it has significant control effect. Compared to the uncontrolledflutter critical wind velocity, the controlled one is10%higher and the control law isstable.