Keywords: bridges, steel-concrete composite decks, shear lag, finite element, effective width.

Steel-concrete composite decks are used in many bridge typologies. In addition to the simple scheme of multi-span continuous beams, widely used in viaducts and flyovers, the composite decks are adopted also in combination with other elements in the bridges with complex static schemes such as arch bridges, bow-string bridges and cable stayed bridges

In these kinds of structures the usual assumption of bending theory, according to which the plane cross sections remain plane after loading, is not realistic and non-uniform stress distributions usually arise in the slab (shear-lag effect) reducing its effective width. In addition to the shear-lag effect, arising from vertical loads, other stress concentrations can arise in the slab from the application of longitudinal forces as in the case of anchorage of prestressing cables or stays, and in the case of differential non-mechanical deformations (e.g. shrinkage, thermal effects).

In these cases the method of the effective width proposed by the main codes of practice, for example [1], cannot be applied [2] and the stress concentration can be identified with refined finite element analyses by modeling the structure with shell or solid finite elements. Unfortunately, the results of such analyses are not synthetic and have to be post-processed in order to verify the structure. The authors proposed a beam finite element for the time dependent analysis of composite steel concrete decks taking into account the beam-slab partial interaction and the shear-lag effect on the slab [3]. This element, which will be called hereafter deck element, enables the concentration of the longitudinal normal stresses in the slab due to generic loads to be identified [4]. Treating the whole deck as a beam, the model gives the results in terms of stress resultants which are very useful for the structure verification. In the sequel the main problems encountered in the modeling of composite bridges with complex static schemes by using the deck element in combination with trusses and Euler-Bernoulli beams, are described.

1

prEN 1994-2, "EUROCODE 4: Design of composite steel and concrete structures - Part 2: Rules for bridges", European Committee for Standardization, 2003.

2

L. Dezi, F. Gara, G. Leoni, "Effective slab width in prestressed twin-girder composite decks", Journal of Structural Engineering, ASCE, 132(9), 1358-1370, 2006. doi:10.1061/(ASCE)0733-9445(2006)132:9(1358)

3

F. Gara, G. Leoni, L. Dezi, "A beam finite element including shear lag effect for the time-dependent analysis of steel-concrete composite decks", Engineering Structures, 31, 1888-1902, 2008. doi:10.1016/j.engstruct.2009.03.017

4

F. Gara, G. Ranzi, G. Leoni, "Analysis of the shear lag effect in composite bridges with complex static schemes by means of a deck finite element", International Journal of Steel Structures, 8, 249-260, 2008.

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