Cyclic loading from interaction with the wind is regarded as an important source of fatigue damage in decks of long span bridges. In this paper a suspension bridge model with a steel deck is used as a case study for performing numerical simulations. The wind loading is considered as the main dynamic excitation and it is applied on the towers, the cables and the deck of the suspension bridge. The wind load, is simulated as a spatially correlated process and acts in the horizontal direction, transverse to the deck. The wind intensity is tuned at different levels and the multipurpose ANSYS finite element code is used as work frame.

Passive and semi-active control strategies are implemented on the suspension bridge model for the mitigation of the wind effects. The latter type of control system is implemented in a decentralized configuration and enjoys the same positive qualities of passive ones. From a structural point of view semi-active systems are able to modify the stiffness and damping characteristics of the bridge without introducing mechanical energy. This aspect ensures that the controlled system behaves in a stable manner during the response to a dynamic excitation.

The standard deviation of the internal forces in the bridge deck is a valuable parameter for assessing possible fatigue effects suffered quite frequently by suspension bridges as a result of vibrations induced by buffeting [1,2,3]. The proposed semi-active control strategy, in particular, is able to reduce significantly the values of such parameters both at mid-span and at the tower for gale wind intensities. For breeze wind intensities, its positive effect is confirmed at mid-span but an increase of the standard deviation is predicted at the tower. Influences on the fatigue damage, taking into consideration the different return periods associated with gale and breeze winds, need further studies depending on the specific site.

1

M. Gu, Y.L. Xu, L.Z. Chen, H.F. Xiang, "Fatigue life estimation of steel girder of Yangpu cable-stayed Bridge due to buffeting", Journal of Wind Engineering and Industrial Aerodynamics, 80, 383-400, 1999. doi:10.1016/S0167-6105(98)00209-8

2

M. Hosomi, H. Kobayashi, Y. Nitta, "Fatigue strength design for vortex-induced oscillation and buffeting of a bridge", Journal of Wind Engineering and Industrial Aerodynamics, 67-68, 227-237, 1997. doi:10.1016/S0167-6105(97)00075-5

3

S. Pourzeynali, T.K. Datta, "Reliability Analysis of Suspension Bridges against Fatigue Failure from the Gusting of Wind", Journal of Bridge Engineering, ASCE, 10, 262-271, 2005. doi:10.1061/(ASCE)1084-0702(2005)10:3(262)

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