VIBRATION AND DAMPING BEHAVIOUR OF A CABLE- STAYED TIMBER DECK BRIDGE WITH ASPHALT PAVEMENT

摘要

The paper presents a study on the influence of a mastic asphalt pavement on the damping and resonance frequencies of a cable-stayed footbridge with timber deck having a total length of 19.2 m and a width of 1.6 m. Four bridge deck configurations were tested: two different timber deck systems (cross-laminated and stress-laminated plates) both with and without asphalt pavement. The bridge was subjected to stepped sine excitation, harmonic excitation with subsequent free vibration and random excitation at ambient temperatures. With asphalt pavement the damping ratios were five times higher than without pavement. The damping increased with increasing oscillation amplitude, whilst the timber decks with asphalt had nearly a constant damping ratio at higher amplitudes. The determined resonance frequencies were very similar for all excitation methods. The experiments showed that there is a considerable transfer of shear forces between asphalt pavement and timber deck although pavement and deck were not mechanically connected. This resulted in a noticeable increase of the stiffness of the deck and of the structure's damping. The beneficial effect of the asphalt pavement with regard to damping ratio should be made use of in timber bridge design and thus be included into design codes. However, it has to be studied to what extent this increase in damping can be accounted for in temperature ranges occurring in practice. Respective FE calculations and experimental tests are ongoing.