Identification of weak non-linearities in cables of cable-stayed footbridges

A time-frequency identification technique for the non-linear identification of a cable element was proposed in this paper. A polynomial form of non-parametric method was used. A long cable of a newly constructed cable-stayed footbridge was modelled in the ANSYS structural software. The model was reduced to a SDoF system, by applying a harmonic force in the first modal frequency and the first mode shape. A good match between the identified and numerical data was obtained. Some interesting non-linear phenomena were observed: only a cubic type of non-linearity was identified. Moreover, the values of the damping and cubic parameters stabilised at higher load amplitudes. However, parameter relevant to linear-frequency was increasing with the loading amplitude showing a typical hardening behaviour of cable structures. Superharmonics were present in the response at higher loading amplitudes. Therefore, the identification procedure was found to be effective at higher load amplitudes.