e-mosty December 2018 e-mosty December 2018 | Page 41

Figure 9: Blue gantry crane used to lift steel girders into place Figure 10: Complete Bridge Widening
In the case of the pier crosshead beam, the problem
was resolved by using the pre-stress to eliminate ten-
sion at the connection. maintained either above deck, or removed for off-site
maintenance.
For the deck stitch, the solution was confined to only
using existing reinforcement bars, and making them
work optimally, which resulted in having to achieve a
high fatigue classification for the welded connection
between the stitch reinforcement and the existing
cantilever bars.
For the abutments, a shear only connection was suffi-
cient, however the problem of differential settlement
between the existing and new abutments had to be
catered for. Where differential settlement was pre-
dicted to be significant, dowelled bars in ducts were
used, which were grouted when the full permanent
load was reached.
The integral nature of the final configuration meant
that the original articulation would no longer suffice,
as there would be two bearings with transverse re-
straint on the same pier axis. VicRoads also took the
opportunity to specify the replacement of the existing
20-year-old bearings as part of the contract.
In addition, transverse seismic restraint blocks needed
to be installed at each pier. The solution was to
change the transverse restraint to occur at one of the
new steel box girder bearings, while the longitudinal
restraint remained at the three tall piers in the middle
of the viaduct.
Future maintenance access and durability were im-
portant considerations in the design of the new struc-
ture and upgrades. Efforts were made to ensure that
new steel elements, such as the PSB, could largely be
Although the new steel box girders are shielded by
the concrete boxes either side and so are in a rela-
tively benign environment, provision for future main-
tenance was made by providing four access hanging
points per section, at 2m intervals along the length of
the structure.
As this option caters for a variety of access platform
formats and functions, including local and whole
bridge maintenance, it was considered a better option
for the future than designing a bespoke maintenance
platform that would itself require maintenance and
refurbishment in time.
FORM OF CONTRACT
Contract forms such as Alliance, Early Constructor
Involvement, or Design Construct, all permit the De-
signer to work with the Contractor from the early
concept design stage to incorporate preferred con-
struction methodology.
This is highly advantageous, particularly when working
with existing structures.
For this project, the Design Construct contract created
many challenges, such as the need to accurately de-
termine strengthening requirements at tender stage.
Several parts of the existing structure were approach-
ing the limit where strengthening would be required.
There is a large cost difference between strengthen-
ing and not strengthening, which required the tender
stage analysis to be extremely precise.
4/2018