Ma
aribyrnong
g River Bridges: Planning and
a Assesssing the Upgrade
e to a
P
Portal
Frame
1
B
Brwa Mohamed1
Accting Team Le
eader, VicRo
oads M80 Up
pgrade
Abstractt: This pape
er provides a general desscription of th
he backgroun
nd, planning and assessm
ment of the
Maribyrn
nong River Bridges (also known as E.
E J. Whitten Bridge) loca
ated over the
e Maribyrnon
ng River as
he corridor wide M80 Ring
g Road Upgrrade. The Ma
aribyrnong R
River Bridges are the seco
ond highest
part of th
road brid
dges in Victorria with lengths of 520 me
etres and heiights of 50 m
metres above the valley flo
oor.
dges were co
onstructed in
n the early 19
990s as partt of the origin
nal Western Ring Road
The existing twin brid
w
thro
ough the centre by way off a portal fram
me that will
Project; tthis included the provision for future widening
connect the existing ttwin parallel piers using a series of new substructture crossheads supporting the new
superstru
ucture eleme
ents.
er will addresss significantt features of the Maribyrn
nong River B
Bridges upgra
ade associatted with the
The pape
planning, assessmen
nt, and Contra
act Award off the Project. These features include
•
•
•
•
tthe challenge
es in planning
g and design
n conceptualization;
cconsideration
n and input frrom various d
disciplines an
nd stakeholders;
e
emphasis on a higher level of expecta
ations pertain
ning to safetyy, traffic, and community impact; and
g
greater consiideration for a Whole of L
Life approach
h.
ds: Planning
g, Portal Fram
me, Future Proof, Whole o
of Life, Box G
Girder.
Keyword
1.
IIntroductio
on
The M80
0 Ring Road Upgrade is a is a $2.25
5 billion Proje
ect to improvve the 38-kilo
ometre M80 Ring Road
which extends from
m the Prince
es Freewayy at Laverto
on North to the Green
nsborough H
Highway at
Greensborough. Due
e to the size
e and complexity of the M80 Ring Road Upgra
ade, deliveryy has been
divided in
nto eight secctions as iden
ntified in Figu
ure 1.
Figurre 1. M80 Riing Road Up
pgrade completed and rremaining se
ections
ect scope of the 3.1 kilom
metre section
n from Sunshine Avenue tto Calder Fre
eeway comprrises
The Proje
• w
widening to p
provide five la
anes includin
ng an auxiliarry lane in eacch direction;
• conversion of the northern Keilor Park Drive abutment from spill through type to retaining;
• implementation of Intelligent Transport System (ITS);
• landscape and architectural works; and
• widening and strengthening of the Maribyrnong River Bridges.
The Contract for this section was awarded to Fulton Hogan Construction Pty Ltd in August 2016. The
Design Joint Venture of SMEC, Arup, and Flint Neill was engaged to develop the design.
2.
The Existing Bridges
The Maribyrnong River Bridges, as photographed in Figure 2, are an integral part of the M80 Ring Road
and the greater Victorian road network servicing up to 165,000 vehicles per day.
The structure is the second highest road bridge in Victoria. The original design and construction took
place between 1992 and 1994 by Transfield and Hardcastle & Richards respectively.
Figure 2. Aerial view of the Maribyrnong River Bridges.
2.1 Design
The existing bridges are 520 metres in length across over the Maribyrnong Valley and up the 50 metres in
height over the Maribyrnong River. The bridges are also adjoined at the southern side to a 120 metre long
approach structure over a former tip. The bridge has 8 pier to pier spans 54 metres long and 2 abutment
to pier spans of 44 metres.
The superstructure element is a single cell prestressed concrete box girder trapezoidal in shape which is
3.8 metres deep, 5 metres at the soffit and 14.3 metres wide at the top, however, the Greensborough
bound structure girders are a further 3 metres wide to accommodate the Shared Use Path and railing.
The girders are supported by reinforced concrete piers on typically driven 350 mm piles. Each pair of the
pier pile caps are connected with two foundation steel tie beams beneath the earth surface with concrete
casing for durability.
The bridges were designed in accordance with the 1992 AustRoads Bridge Design Code, adopting the
elastic theory of analysis. The bridges were designed to T44 and L44 loadings over 4 design lanes in the
current construction, and to 6 design lanes for the future arrangement. HLP400 loading has also been
applied to structure under existing and future conditions, this been applied located centrally on the outer
box girders.
It is important to note that whilst a number of design loading conditions have been accounted and
incorporated into the design, the existing structure has not been designed to withstand earthquake
loading.
2.2 Construction
Constructed by Transfield, the Contractor used an incremental launch technique in which the substructure
was constructed first, followed by the superstructure being constructed, jacked, and launched onto the
supports thereafter. The initial Project was in a greenfields site thereby making the incremental launch an
advantageous technique.
Each bridge included 20 segments 27 metres in length. The typical week long sequence of the launch is
detailed in table 1 below.
Table 1. Weekly box girder launching cycle.
Day
1
2
3
4
5
Activity
Install the web formwork and cast the soffit and webs
Strip the web formwork and install the deck formwork
Install the deck reinforcement
Pour deck concrete
Stress the longitudinal tendons, lower the formwork and launch the bridge.
Raise the formwork in preparation to repeat steps from above.
It is noted that the outer two segments of each bridge contain special tendons and diaphragms; as such,
the process in the table above was extended by a week. The girders were cast with a slag-blend cement
allowing for higher early strengths enduring the launching process. Figure 3 below shows the final launch
of the Altona bound structure.
Figure 3. Final launch of the Altona bound bridge.
2.3 Future Proofing
VicRoads acknowledged the requirement of future widening and specified this requirement as part of the
original design and construction. Future widening each pair of piers to a portal frame is allowed for in the
original design; the upmost section of the piers is a single tapered hollow rectangular box section allowing
for connection by way of a supporting post tensioned crosshead. The widening itself was intended to be
achieved by adding a third box girder between the two existing, joining the separate structures into a
single 42 metre wide portal frame bridge. Refer to Figure 4.
3.
The Southern Approach Structure
The Southern approach structure is a 120 metre long prestressed, post tensioned flat slab supported by
driven piles up to 15 metres in depth, typically comprising 20 metre spans.
The tip that exists on the southern side of the Maribyrnong Valley was formerly a basalt quarry that was
exhausted and subsequently converted to a rubbish tip. As a result, the tip is not a standard regulated tip
with standard EPA regulatory controls.
The surface beneath and surrounding the southern approach structure is exhibiting significant settlement.
Instead of being founded on sand at the base of the quarry, piles may have been driven through major
obstructions within the tip fill, such as engine blocks, resulting in further settlement post installation.
During the original construction, minor methane gas presence was identified. The Contractor installed a
venting layer between the existing decks.
4.
Investigations
The Maribyrnong River Bridges were less than 25 years into their design life when planning and
investigations began as part of the M80 Upgrade in 2008.
4.1 Level 2 Inspection
The Level 2 Inspection of the Maribyrnong River Bridges was undertaken by (then) URS Corporation from
13-14 April 2010 with representatives of VicRoads in attendance. The inspection found that there was
cracking in the tip structure piles, cutting of the tip structure piles for testing, minor cracking of the
diaphragms, and flooding of spans 9 and 10 of the Greensborough bound structure.
As part of the Level 2 Inspection, the team also walked through the box girders to understand the
condition of the bridge and key elements to consider as part of the proposed Level 3 Inspection,
recommended as a result of the Level 2 Inspection.
The Level 2 Inspection included a number of recommendations for each structure.
4.2 Level 3 Inspection
The Level 3 Inspection of the Maribyrnong River Bridges was also undertaken by then URS Corporation
over a week starting 30 August 2010 which also included concrete core testing focused on components
such as the piers, tip structure piles, diaphragms, expansion joints and flooded spans mention in 4.2
above. Depending on the testing locations, the coring results in some cases exceeded the original design
expectations.
URS concluded that the bridges appear to be in very good condition, with the observed cracking to be
minor hairline along the surface in general. Recommendations were made from the findings that have
been incorporated into the Contract specific requirements.
4.3 Southern Approach Structure
Geotechnical investigations undertaken by VicRoads Technical Services identified risks associated with
the southern approach structure foundations. Due to the conditions of the landfill, several issues were
found with the piles including damage due to driving through obstructions, further settlement, and some
reinforcement exposure due to the presence of leachate in the tip.
5.
Design Considerations
For the upgrade to a portal frame design, VicRoads had conceptualized a widening using a duplicate
concrete box girder, as intended by the original designers, supported by a concrete crosshead, to ensure
a consistent design and interface with the existing structures. The concept, designed in house by
VicRoads Technical Services Structures team, is shown in Figure 4 below.
Figure 4. M80 Ring Road Upgrade completed and remaining sections
Whilst the original and concept design for the widening was based on a concrete box girder, VicRoads did
not prescribe a specific material requirement so as to not stifle innovation. The Contract did not restrict
proponents to tender concrete material solutions only.
5.1 Widening
As shown in the figure above, the central widening is accommodated by removal of the fast lane barriers
and installation of new singular median barriers that separate the two carriageways. VicRoads set out
requirements that the widening proposals meet the performance requirements within the Contract sections
pertaining to Structures, Landscape, and Traffic Barriers.
VicRoads required the widening to be a central box girder of similar dimensions to the existing girders;
however, the Contractor is not limited to the design set out in the concept drawings. The design is
required to form a single integrally connected structure. The crosshead component is also required to be
designed such that it is also integrally connected to the piers and providing adequate working area and
clearances for bearing replacement and future maintenance and inspections.
The original design considered a final condition load casing which was cognisant of the twin bridges along
with the future widening and associated load cases as a result of a third concrete box girder and
crosshead. The crossheads may be post-tensioned through the existing ducts at the top of each pair of
pairs. The foundation tie beams beneath the surface are components that counteract the load application
of the widening components at each pier supports.
5.1.1 Stitch pour
One of the greatest challenges anticipated with the widening was detail of the interface between the old
and the existing structure. VicRoads recognises the creep and shrinkage behavior of the concrete since
first constructed and the intricacies with connecting to the new girders. To ensure a quality product, there
are stringent requirements with respect to the stitch pours i.e. vibration levels of an average Particle Peak
Velocity between 5-55mm/sec.
5.2 Strengthening
The existing and anticipated future sections had been designed to T44 loading as per the 1992
AustRoads Bridge Design Code. Since then, the AS5100 Bridge Design Code has been introduced to and
adopted by industry, bringing the existing structure to the current design introduced a level of complexity.
Some of the changes to the loads as a result of SM1600 superseding T44 included: changed traffic and
braking loading, inclusion of pedestrian loads (relevant to the Greensborough bound structure due to the
2.5 metre Shared Use Path) and altered and non-uniform lane reduction factors. VicRoads required the
existing structures to be strengthened to 75% SM1600, new components designed to SM1600, and
HLP400 loading to two design lanes (only one loading in each direction at any time).
5.2.1 Potential strengthening options
VicRoads identified a number of potential strengthening options based on the original design future load
casing and the conceptual design. With the inclusion of pedestrian loadings, a number of new barriers,
and redistribution of other loadings as per AS5100, it was anticipated strengthening of the deck may be
required; this was considered to be addressed by the provision of steel plates or Fibre Reinforced Polymer
(FRP) to the cantilever soffit. Diagonal struts from the bottom of the web to the deck soffit were another
option.
External post-tensioning was an optioned investigated by the team to counteract sagging, though this is
dependent on the widening design and material. A stiffer central girder system would also address this
potential issue; the Contract has allowed the Tenderers to explore other material options not just concrete.
There are a number of options to strengthen the substructure, should the requirement exist. The Project
considered addressing the substructure strengthening collectively by replacing some stiffer pier bearings
from fixed to roller, and strengthening the supports by thickening the pier and pile caps and further piling
around the existing.
The Project team recognized the importance of the bridge to the Victorian network early in the planning
stage as part of a preliminary safety in design workshop. VicRoads made the decision to include
earthquake loading to the entire structure. Earthquake loading was to be design in accordance with
AS1170.04 and the AustRoads Technical Report AP-T200-12. The Project specified a Bridge
Classification type III, however, it was up to the Tenderers to develop their design and identify and justify
the Bridge Earthquake Design Category type.
5.3 Urban Design
The Urban Design Strategy was developed by VicRoads Landscape and Urban Design and Peter Elliott
Architecture and Urban Design for the entire M80 Corridor, including the Maribyrnong River Bridges.
The strategy considered issues and constraints with the existing structure, including compromises to the
form and aesthetics with respect to a central widening, particularly the future view of the underside from
the trail along the Maribyrnong River, sight distances and variance of barrier types.
The strategy offered design opportunities with respect to the above as identified in Figure 5. The urban
design considers architectural significance from the underside of the structure, where the bridge is most
noticeable. In response to the widening constraints, the urban design proposed a seamless design of the
widened section that integrates into the current form. The widening components would match the existing
alignments i.e. a perceivable continuous section from top of pier to top of crosshead thereby achieving a
seemingly integrated portal frame. The crosshead must have a chamfered soffit to the profile of the
adjoining piers. The urban design considered other features of the bridge- prescribing a tapered transition
from the high containment on-structure barriers to the medium containment off structure approach
barriers.
The Maribyrnong River Bridges cross a dark and deep valley where an element such as feature lighting is
most prominent; this has been prescribed at 15 metre intervals along the central median barriers and is
akin to the feature lighting of the Tullamarine Freeway City bound on-ramp to M80 Ring Road Altona
bound. The Bridge is considered a gateway to the western suburbs, as such; emphasis has been placed
on the gantry, which has been prescribed as an accessible truss type, over the southern section of the
bridge. The new Public Safety Barriers (PSB) is designed similarly to the barriers on the West Gate
Bridge; these barriers must also be integrated architecturally with the structure.
Figure 5 – Architectural Perspective View
5.4 Barriers
Risk assessments and road safety audits identified the need to increase the containment level of the
existing barriers. The existing level of containment of the on-structure barriers is Regular, and whilst the
bridge has a substantial horizontal curve, the Project team recognised the need to increase the
containment due to the height of the bridge and the impact of departure. The Project required High
containment level on-structure barriers as part of the upgrade.
At up to 50 metres high with pedestrian access, there exist significant pedestrian safety risks. Pedestrians
and cyclists on the Shared Use Path (SUP) are currently only separated from the Maribyrnong Valley by a
1.2 metre safety hand rail. The Project requires an upgrade to the safety barrier to Standard and, as
mentioned in section 5.3, provision of a PSB. The PSB will be 4 metres in height angled at 11° and made
of a climb resistant material that would deter the public from scaling the barrier. The PSB will be finished
with a smooth steel capping beam at angle deterring public from latching on.
5.5 Whole of life
As the impact of whole of life costs continues to be a challenge for VicRoads, the M80 Upgrade – S2C
Team looked to encourage the Tenderers to take a whole of life and maintenance in design approach in
their submissions. Some of the factors that have made asset maintenance more challenging include
allocation of maintenance budget, an increase in the extent of assets to maintain, and ageing assets
around the network. In delivery of the bridge widening, the Project intended to consider whole of life
aspects as part of the upgrade works.
As part of the Contract, there were requirements to upgrade portions of the existing asset and provide
means for making future inspections and maintenance an easier task. All bearings on the existing
Maribyrnong River Bridges are required to be replaced such that future replacements would be
undertaken for both the outer and central girders at the same time. Designs that are submitted must also
have safe access for purposes of inspection. The Contract required the provision of a maintenance
platform that provides safe access, designed for ease of access and operation, and designed for minimal
maintenance with minimal operational costs. A concept was not provided as the maintenance platform is
dependent and complementary to the widening design solution offered by the Tenderers.
6.
Delivery
The M80 Upgrade incorporated a number of requirements affecting safety, traffic, and community impact
in line with VicRoads Strategic Framework.
6.1 Safety
Safety is imperative on all VicRoads Projects. We have emphasized this on our Contract given the nature
and risk of the Maribyrnong River Bridges. Safety around road users and construction is heavily regulated
in the Contract. The Project team also considered the safety of pedestrians outside of working hours. The
Contract required Tenderers to provide a Temporary PSB, similar to the permanent design, to protect
pedestrians and cyclists along the SUP throughout the construction period also. The Contract also
required a Safety in Design workshop post award to ensure a quality outcome is collaboratively reached.
6.2 Traffic and Community Impact
The M80 Upgrade has stringent requirements with traffic management and the impact to the community.
Lane closures may only be implemented at specific times as prescribed in the Contract so as to not
impact the road user’s journey. The Contract did not allow for any full freeway closures, that is, closure of
both carriageways simultaneously, allowing only partial (single carriageway) closures. The Project team
investigated the viability of this requirement before specifying into the Contract, anticipating innovative
construction proposals from the Tenderers.
7.
Procurement
7.1 Tender
The Project is to be delivered as a Design and Construct Contract and assessment was subject to a
Project team developed Tender Evaluation Plan. Expressions of Interest were sought from the industry
before the shortlisting of three Tenderers. The Contract went out to an 11 week Tender process and the
Contract was awarded to Fulton Hogan Construction Pty Ltd. Due to the complexity of the Bridges and the
assessment model, detailed in section 6.1.1, a number of internal and external parties were invited to
participate in the assessment before the Project team made a Tender recommendation. The Contract
duration is 130 weeks.
7.1.1 Whole of life
In order to consider the whole of life implications of a Tendered design, VicRoads introduced a new
schedule into the Contract to be populated by the Tenderers. It was deemed that a Net Present Value of
the expected periodic maintenance and rehabilitation works of the EJ Whitten Bridge structures over the
100 years design life, in conjunction with the submitted Tender bid for the capital works of the whole
Project would provide the best whole of life cost of delivering the upgrade and a better understanding of
what the state would reasonably and indicatively expect in servicing and maintaining the upgraded asset.
The Project team entered into a workshop with the current asset owners to understand and develop a
model for evaluation. The Operation and Maintenance Costs, included as schedule 10 of the Contract and
shown in sample form in Figure 6, required the Tenderers to price each inspection and maintenance
activity in its entirety based on their Tendered design. The assessment team then performed a sensitivity
analysis based on 95% capital + 5% O&M costs to derive the lowest conforming Tendered price.
Figure 6 – Sample Operation and Maintenance Cost schedule for the bridge
8.
Conclusions
The Maribyrnong River Bridges were designed to be widened centrally; however, planning of the upgrade
has not come without its challenges. Since the provision for the widening, there have been a number of
changes to codes and standards that affected the upgrade.
The Project team investigated the implications of these changes and was able to cater for them in our
conceptualized design. The Project team also considered the possibility of innovative solutions that may
not have been considered as part of the initial design. The requirement of a concrete box girder solution
was removed thereby allowing the Tenderers to submit an innovative solution best fitted for the Bridges
that the Project may not have considered.
The allowance for an alternative widening type to the existing impacted the assessment process. The
Project team incorporated an assessment model that considered different material types but would also
cognisant of the whole of life implications of a Tendered solution. Considering the number of potentially
different designs, and the decreasing maintenance budget, the Project team included these two factors
into the Tender assessment model in order to wholly evaluate and recommend the best solution.
9.
Acknowledgement
The author wishes to acknowledge the contribution of past and current members of the Sunshine to
Calder Project team of the VicRoads M80 Upgrade in planning the Project, and VicRoads Network Design
and Asset Services for their ongoing support to the Project team.
10.
References
URS Australia Pty Ltd, “EJ Whitten Bridge Design Review Report”, 2010, Melbourne, Australia.
URS Australia Pty Ltd, “Level 3 Inspection of the EJ Whitten Bridge Report”, 2010, Melbourne,
Australia.