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Aerodynamic damping is a decisive parameter influencing the dynamic response of overhead transmission line conductors. Methods of how to account for the effects of aerodynamic damping differ significantly and so might do the results. In this work, the source of aerodynamic damping being the result of the relative velocity between the structure and wind flow will be revised. Based on wind tunnel tests and validated by simulations, the differences of linear movement compared to a pendulum movement of a sagging cable are shown. The reasons for that Deviation are the large deflections, resulting in a movement non-parallel to the acting wind flow. For analysis in frequency domain, it is not possible to incorporate aerodynamic damping implicitly by fluid structure interaction. If the dynamic movement can be linearized at a working point of the mean deflection, a modification to the linear approach is suggested. This approach is validated by simulation with a finite element model of an existing overhead transmission line, calibrated with full scale measurements. Aerodynamic damping is incorporated in time step analysis by Rayleigh damping and modal damping. The differences between both approaches are emphasized and modal damping is shown to be the most adequate.
Bridge retrofitting of a section of the Berlin subway which is designed as railway on steel viaduct is presented. Fatigue damage in the superstructure of the over 70-years-old viaduct made an investigation of the damage causes necessary prior to the planning of retrofitting measures. The damage specifically occurred at the inverted arched steel plates of the ballast support elements. Those plates were provided for carrying the track ballast as well as the traffic load. For the retrofitting, the inverted arched plates were unloaded. The superstructure was redesigned into a fixed track system, which is able to transfer the traffic load directly into the substructure. The new rail fastening system made it necessary to verify the structural integrity of single elements as well as of the main system of the existing viaduct. The verification was based on several experimental investigations at BAM laboratory and on-site. Based on the evaluation of all test results the operation license could be issued.