Civil Engineering Reference
In-Depth Information
Figure 3.7
Typical highway tunnel below the water table
3.5.4 Alternative types of reinforcement
Corrosion of carbon steel reinforcement is the principal cause of deterioration of
reinforced and prestressed concrete. Consequently much research is carried out into
alternative materials.
The starting point should be to examine whether reinforcement may be omitted, either
from one face of a member, or altogether. The walls of the Byker Tunnel, Figure 17.6,
were unreinforced, while some columns and walls carrying only compression and
small bending moments may also be designed as plain concrete. Designers may draw
inspiration from the many classical and mediaeval structures where columns, slender
towers, arches and vaults were built of unreinforced concrete or masonry. It is also
debatable whether the compressed faces of slabs need reinforcement. However, as
always when stepping beyond conventional wisdom, the designer must make sure
that he has considered every eventuality, such as exceptional load conditions that may
induce tension into otherwise compressed members.
Stainless steel reinforcement is becoming more frequently specifi ed for concrete at
particular risk of corrosion, such as in the splash zone of marine bridge piers. Stainless
steel reinforcement is several times more expensive than conventional carbon steel,
but may well be justifi ed when considering the whole life cost of a structure. It may
also be used sparingly, to reduce the risk of a brittle failure due to hidden corrosion.
For instance, the precast parapets of the East Moors Viaduct, designed by the author
in 1982, are attached to the deck by a series of links. 20 per cent of the links in each
precast panel are stainless steel, so that if the conventional links were to corrode due
