e-mosty December 2018 e-mosty December 2018 | Page 38
Figure 4: Image of the intended future widening concept (Noonan, 1994)
The construction technique assumed was to cast in
situ the crosshead beam, and launch the concrete box
girder – similar to the original construction technique.
The original designer included key elements to facili-
tate the future widening, including:
When the widened structure is completed,
under transverse load distribution, the inner
cantilevers of the existing concrete box gird-
ers will be transformed from cantilever spans
to continuous sections.
.
This means the previous cantilever tip be-
comes an area of high sag moment. The origi-
nal design accounted for this change in the
behaviour of this element and provided suffi-
cient reinforcement in both the top and bot-
tom layers of bars to account for both the
original and future behaviours of this section.
Post Tensioning Ducts
12No. (laid out in two rows of six) 105mm di-
ameter ducts were provided across the top of
the piers to allow for a post tensioned con-
crete crosshead beam to be installed.
Foundations
The piers and foundations were designed for
the loads from the future widened structure,
namely a third concrete box girder under Aus-
troads 92 T44 / L44 traffic loading. The origi-
nal design also included a tie beam between
pile caps to assist with any lateral forces from
the portal frame action that would arise once
the new crosshead beam is installed. Aside
from the provision of a new crosshead beam,
new foundations or piers would only be re-
quired at the two bridge abutments for future
widening.
Deck Connection
The future concept anticipated an integral
deck connection so top and bottom rein-
forcement was provided in the cantilever tip.
4/2018
The detail at the end of the cantilever en-
sured the transverse reinforcement extended
beyond transverse tendon anchorages and
cantilever tip u-bars so a connection between
the new and existing reinforcement could be
made.
Articulation
Bearings were provided with removable guide
strips so the articulation could be changed in
the widened condition.
Main bridge abutments and expansion joints
were aligned so that the expansion joints in
the widened structure could be made con-
tinuous over the full width.