Vibrations of cable-stayed bridges caused by pedestrian interaction between bridge deck and cable

This contribution deals with vibrations of footbridges caused by pedestrians. European and German standards containing this theme are mentioned and the corresponding proofs are explained.

In case of simple beams the proofs are clear; the calculated values of natural frequencies and accelerations due to pedestrians match the measured ones. This is verified by measurements at several footbridges.

In case of cable stayed beams the interaction between cable and bridge deck vibrations has to be considered. If the ratio of natural bridge deck frequency to natural cable frequency is 2 : 1, special attention is necessary. Autoparametric resonance can occur and multiply the amplitudes of bridge deck vibration compared to the values without considering this phenomena.

To verify the autoparametric resonance by calculations a simplified dynamic model was conceived. This model of a cable stayed bridge is very simple, but it is suitable to study the principle interaction of the vibrations and to proof the software. By non linear transient calculations increased amplitudes and exchange of energy between the two local systems (bridge deck and cable) can be regarded.

The calculated values are compared with measured values of a cable stayed footbridge. At this bridge the effect of autoparametric resonance can be observed well.