Keywords: dynamic analysis, fatigue analysis, structural dynamics, steel and composite highway bridges.

Steel and composite highway bridges are currently subjected to the dynamic actions of variable magnitude arising from vehicles crossing the rough pavement of the deck. These dynamic actions can generate the nucleation of fractures or even their propagation on the structure. In this way, the behaviour and reliability can be compromised and the bridge service life can be reduced.

In this investigation, the moving load is modelled by an infinite series of equal vehicles, regularly spaced, and running at constant velocity. Considering the distance between two successive vehicles and if these cars cross the bridge deck one by one, a time repeated movement variation governed by the crossing frequency is created and is associated with the vehicle movement on the bridge [1,2,3].

The stress cycles counting techniques and the cumulative damage rules application combined with S-N curves were studied [1,4]. Based on an extensive review of the literature related to techniques to define the service life of steel and composite bridges and a study of the theoretical aspects of fatigue in steel, as well as considering the recommended procedures used by the main design codes [5,6] of steel and composite structures, a composite highway bridge was investigated.

The composite bridge investigated has a roadway width of 12.50m and a concrete deck thickness of 0.23m, spanning 40.0m by 13.5m. The structural system is constituted by four longitudinal composite girders and a concrete deck. The computational model, developed for the composite bridge dynamic analysis, adopted the usual mesh refinement techniques implemented in the ANSYS program [7].

The beam web thickness was represented by shell finite elements. The beam top and bottom flange and the longitudinal and vertical stiffeners were simulated by three-dimensional beam elements, where flexural and torsion effects were considered. The bridge concrete slab was simulated by shell finite elements.

The main conclusions of this paper focused on alerting structural engineers to the possible distortions, associated with the service life of steel and composite bridges when subjected to vehicle dynamic actions.

1

F.N. Leitão, "Fatigue Analysis of Composite Highway Bridges", MSc Dissertation, Civil Engineering Post-graduate Programme, PGECIV, State University of Rio de Janeiro, UERJ, Rio de Janeiro, Brasil, 2009. (In Portuguese) doi:10.4203/ccp.96.44

2

F.N. Leitão, J.G.S. da Silva, S.A.L. de Andrade, P.C.G. da S. Vellasco, L.R.O. de Lima, "Composite (Steel-Concrete) Highway Bridge Fatigue Assessment", Journal of Constructional Steel Research, 67(1), 14-24, 2011. doi:10.1016/j.jcsr.2010.07.013

3

J.G.S. da Silva, "Dynamical Performance of Highway Bridge Decks with Irregular Pavement Surface", Computer & Structures, 82(11-12), 871-881, 2004. doi:10.1016/j.compstruc.2004.02.016

4

Z.M.C. Pravia, "Steel Bridge Structures with Crack Stability", DSc Thesis, COPPE/UFRJ, Rio de Janeiro, RJ, Brasil, 2003. (In Portuguese)

5

AASHTO, "LRFD Bridge Design specifications", American Association of State High-way and Transportation Officials, Washington, USA, 2005.

6

EUROCODE 3, "Design of Steel Structures", European Committee for Standardisation. Bruxelas, 2003.

7

ANSYS Swanson Analysis Systems, Houston, PA, USA.

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