Civil Engineering Reference
In-Depth Information
The design of bridge deck
components
9.1 General
The purpose of this chapter is to describe the logic that controls the dimensioning
of each component of a bridge deck. Clearly, this dimensioning will depend to some
degree on the code of practice to which the bridge is being designed. In particular, the
minimum thickness of members will depend on the current regulations on the cover
required to protect reinforcement from corrosion. For instance, in the 1960s, the top
slabs of precast Tee beam bridges (Chapter 10) on which the author worked in France
typically had a minimum thickness of 160 mm for a beam spacing of 1.87 m (Pont du
Saut du Loup) or 170 mm for a spacing of 3.35 m (Viaduc de la Porte de Versailles).
The greater cover requirements of the British code, together with heavier loading lead
Benaim to use a minimum thickness of 200 mm for the top slabs of precast Tee beam
and box section decks. Recent changes in the British code of practice have further
increased the required cover, and have led to another incremental increase in thickness
in the UK. In other countries, where the environmental conditions and the rules are
different, other minimum thicknesses will apply. The minimum thicknesses quoted in
this chapter correspond generally to a concrete cover of 35 mm for the components of
bridge decks in contact with the weather, and 30 mm for protected surfaces, such as
the inside faces of concrete boxes.
9.2 Side cantilevers
9.2.1 General
The side cantilevers of a bridge deck carry the highway, the footpath and the bridge
parapets, and they may act as storage for prestressing tendons. In addition they may
house the bridge deck drainage and other services, and have an important effect on the
appearance of the bridge.
9.2.2 Geometry of cantilevers
As explained in Chapter 8, one major design objective is to minimise the number of
webs in the bridge deck. This concern inevitably leads the designer to contemplate
long side cantilevers if the deck is wide. It is important for the economy of the deck
that these cantilevers should not be thicker than necessary.
