Aerodynamic Admittance Research on Wide-body Flat Steel Box Girder
Abstract: Aerodynamic admittance is a key parameter affecting the analysis accuracy of the bridge buffeting response. However, few articles have covered the issue of the wide-body flat box girder with much smaller depth-width ratio (such as 1/12 studied in this paper). Therefore, to explore the real buffeting force of the wide-body flat box girder, experiments of the static force coefficients and aerodynamic admittance are carried out in wind tunnel. Wooden segmental model has a scale ratio of 1/60 to an actual 42 m wide suspension bridge girder. Using the high-frequency-force-balance (HFFB) equipment fixed with the segmental model under the conditions of different wind speeds and different wind attack angles, wind power spectrums of the buffeting force are measured and the variation of aerodynamic admittance parameters is analyzed. The results show that the aerodynamic admittance of the box girder measured in the experiment with this so much smaller depth-width ratio differs from the corresponding classical Sears expression. Some inspiration can be presented for the future study of the buffeting response for this kind of much wider bridge with the similar ratio in this paper.
Vehicle Effect on Vortex-induced Vibration of Flat Steel Box Girder
Vortex-induced vibration (VIV) occurs at low wind speed under normal condition, affected greatly by section type of bridge and its ancillary facilities. Few researches on VIV of vehicle-bridge system are conducted, and many researchers pointed that vehicle-bridge system should be paid attention to in wind tunnel test. In this paper, type of vehicle, number of vehicle and distance of traffic flow’s influence on VIV were studied with a flat steel box girder model. Results obtained from wind tunnel tests were displayed in order to prove the following rules: First of all, compared with conditions without vehicles, response of VIV is reduced severely when a vehicle is placed on the bridge. Secondly, response of VIV and range of VIV with three vehicles are greater than one vehicle on the bridge. At last, VIV is reduced when distance of traffic flow increases. Mechanism from fluid dynamic point view is given by simulating the working conditions with ANSYS 14.5.
The Invariance of the Vacuum is the Invariance of the World
The following theorem is demonstrated: If the vacuum is invariant under the group generated by the space integral of the time component of a local vector current, then the Hamiltonian is invariant also. A similar theorem holds for the group generated by the space integral of a space component of a local axial-vector current.