At the locations where the mainline was widened or
narrowed like the location of toll plazas and at the
ramp precast portals were used. The portal beams
spanning up to 3 traffic lanes in each direction were
rigidly attached to the mainline columns and to an
intermediate column on the outside. As the flow
of traffic had to be maintained at all times during
construction an overhead truss was used composed of two main
components,
the launching
girder and the
erection girder
that were
connected by
a turntable.
After the
l a u n c h i n g
girder was
fixed on three
m a i n l i n e
columns the
erection girder
was turned 90
degrees to
erect the
portal beam segments delivered from the median
without disturbing the traffic below.