Civil Engineering Reference
In-Depth Information
Figure 7.11
Pier of STAR Viaduct (Photo: Benaim)
deck reaction is transmitted to the foundation stratum as economically as possible
without bending moments, Figure 7.10 (a). Eccentric live load moments, or dead load
torque due to plan curvature of the deck, are also carried to the foundations in direct
compression.
However, the pier is also subjected to lateral forces applied at the bearing, both
longitudinally and transversally. These create bending moments that are zero at the top
of the pier, and a maximum at the base. There is thus logic in widening the columns
near the base. This is shown clearly on the piers of the East Moors Viaduct, whose
articulation is described in
7.15.5
and Figure 7.26.
Piers consisting of one column per bearing are not always possible, or desirable.
When it is necessary to carry the deck on a pier consisting of only a single column,
the loads must be gathered in from the bearings by a crosshead. At one limit, this
crosshead may consist of a gradually fl ared column, Figure 7.10 (b), while at the other
limit it may consist of twin cantilevers, Figure 7.10 (c). Alternatively, the crosshead
may be incorporated into the deck as a diaphragm, Figure 7.10 (d) (the arrangement
