CONSIDERING MUTUAL AERODYNAMIC INTERFERENCE OF BRIDGES IN IDENTIFICATION OF FLUTTER DERIVATIVES OF BRIDGES IN WIND TUNNEL

For two bridges in tandem which locate very closely in turbulent wind, strong aerodynamic interference may be incurred. Such kind of interference can not be correctly modeled when fixing one of the models in turbulent wind, or represented in any situation when testing in smooth flow. In this paper, such kind of aerodynamic interference will be treated as stochastic interference, and included into stochastic turbulent excitation. Based on the Stochastic Subspace Identification (SST), a method to extract flutter derivatives of bridges in tandem is developed and validated numerically with the Theodorsen thin plate. Section models of real bridges in tandem are suspended independently in wind tunnel as to represent the aerodynamic interference. Model responses under turbulent wind are recorded in order to identify flutter derivatives of both windward and leeward bridge sections. The present results are compared with the flutter derivatives for a single deck in smooth or turbulent wind. It is found that the windward bridge shows some interference on flutter derivatives of the leeward bridge, while the leeward bridge presents insignificant influence on the windward bridge.