Civil Engineering Reference
In-Depth Information
Figure 7.4
Concrete hinge
be used. The unreinforced hinge may carry horizontal loads up to one-quarter of the
co-existing vertical load.
Concrete hinges are not appropriate if the minimum load is too light, as they are
then vulnerable to displacement. As they rely on the tri-axial containment of the
concrete, the hinge must be suitably set back from all edges of the concrete. Finally, in
order to make it possible to inspect the hinge in service, the concrete above or below
(or both) should be gently chamfered.
The use of concrete hinges in the UK has been seriously inhibited by an ill-
considered, over-theoretical attempt at regulation [4]. This imposed drastic limits on
the rotation that the hinge could accept, and also required fussy details, insisting for
instance that the hinge and the zones immediately above and below it should be made
in small aggregate concrete, that there must not be a construction joint through the
hinge, which means it cannot be cast together with the parent bridge deck, and that
the throat should have a parabolic shape.
7.7 Design of foundations
7.7.1 General
It is not the intention of this topic to cover in detail either the geotechnical or the
structural aspects of the design of foundations. However, the choice of foundation
type affects fundamentally the articulation of the bridge. This section will discuss
bridge foundations in the context of the design of the articulation.
It is very surprising the number of times one comes across well-designed prestressed
concrete decks placed on over-designed foundations. It sometimes appears that bridge
designers are ready to delegate foundation design to soil specialists, as if it was some
incomprehensible black art. In particular, it is frequently not appreciated that the most
economical pile, recommended by the specialists, may not provide the most economical
foundation. The cost of the foundation usually includes a pile cap and generally a
substantial excavation in addition to the piles. Furthermore the elastic properties
of the foundation may affect the design of the piers and bearings and infl uence the
provision of expansion joints, and hence the overall cost and maintenance of the
