e-mosty December 2018 e-mosty December 2018 | Page 43

Typically, access to many structures remains poor and
must be upgraded in advance of the main works. Pro-
vision for replacement of bearings and movement
joints also remains patchy, even in comparatively re-
cent structures.
For EJ Whitten, the restrictions on traffic closures
required all bearing replacements on the existing
girders to be done under full traffic load, but design
requirements for many newer structures (including
the new parts of this structure) do not typically con-
sider this. More focus must be placed on the ade-
quacy and practicality of any provision made.
Even if provision is made, it is often insufficient and
has an unnecessary impact on bridge operation. Take
the following examples: Movement joints need to be
replaced periodically during a structure's life, but they
are typically encased in concrete. This means major
works need to be undertaken to replace them. And
bearings are rarely replaceable under full live load, so
traffic reduction measures must be put in place, with
high cost and user dissatisfaction.
Operation and maintenance must be included as de-
sign inputs and the operation and maintenance man-
ual, at least at principles level, drafted prior to com-
pletion of the outline design. Basic provisions for
maintenance access are still often overlooked during
design, and yet basic provisions can improve the
safety of the structure over its lifetime.
As an example, the new steel girders for EJ Whitten
included multi-purpose drainage holes at regular in-
tervals, which could also function as hanging points
for scaffold or future maintenance platforms. Such
provisions are also likely to be used during construc-
tion, for bolting platforms or to ventilate the girder's
confined space.
Additional provision for the future is also rarely eco-
nomically feasible during strengthening, as each fur-
ther amount of reserve provided takes the structure
further beyond its original design.
While more sophisticated analysis means new struc-
tures can be designed with greater optimisation
(which itself will yield less future reserve) it can also
be onerous for existing structures where the advent
of computing power enables more exhaustive load
conditions to be examined.
This means that theoretical full utilisation of major
components is comparatively common in existing
structures, even before upgrade works commence,
and that the additional capacity yielded by upgrade is
limited by extent of the structure requiring work.
4/2018
3. Analysis and investigation
Analysis and investigative technologies can investigate
behaviour to a level which was often not possible at
the time of original design. This is due to increases in
the power of modern analytical software and the use
of instrumentation.
The structure itself provides the best analytical model
of behaviour and with the ever-increasing options for,
and decreasing cost of instrumentation, it is possible
to investigate the structure's behaviour in great
depth.
Instrumentation can often be used to mitigate the
extent of intervention required, and to manage the
problems predicted in service. The route can be in-
strumented for vehicle loading using weigh-in-motion
sensors, which can be used to inform a route or struc-
ture specific load model.
It is also apparent that the feedback loop from reality
back to codes and standards is inadequate. This feed-
back loop must be strengthened to ensure lessons
from the past are learned, and that mistakes or mis-
judgments are not repeated.
Design Construct contracts put increasing pressure on
performance to the letter of the design codes, rather
than permitting alternative approaches based on a
combination of first principle approaches, supplemen-
tary evidence and research, and reviewing the intent
and application of the original code provisions.
SUMMARY
Whilst it is clear that future provision is best made at
design stage, there is no standard guidance or ap-
proach. Asset owners or developers rarely see an
incentive to doing so, despite the long term cost to
society, including road closures.
Even today, engineers are rarely able to close a high-
way for any significant length of time due to the great
economic cost to a wide range of stakeholders. In the
future, we envisage that full, or even partial closures
might be inconceivable, and so it is up to engineers to
ensure provision is made at the start of any structural
design process.
ACKNOWLEDGEMENTS
We would like to acknowledge the other parties in the
project who, together with COWI, contributed to the
successful outcome of the widening to EJ Whitten
Bridge including co-designers, Arup and SMEC; the
constructor, Fulton Hogan; and client, VicRoads.