2 harwood bridge _ section 5 to 7

8/8/2019 2 Harwood Bridge _ Section 5 to 7

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Wells Crossing to Iluka Road Upgrading t he Pacific HighwayConcept Design Report

Harwood Bridge Options

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5. Bridge Design and Construction Options

The following bridge design and construction options have been developed for the low and high

level crossings of the Clarence River. The designs and costing are preliminary and have been put

forward for discussion purposes and to assist the development process. Sketches of the bridge

options are provided in Appendix A.

5.1 Low level bridge

The low level bridge would be approximately 900 metres in length, including 400 metres in

approaches and 500 metres over water.

5.1.1 Opening span for low level bridge

The length of the opening span for the low level bascule bridge has been matched to the existing

bridge, with a span length of 38 metres (refer Section 1.1).

For this assessment, the opening span is assumed to be a steel box girder with an isotropic steel deck

in order to minimise the weight.

As noted, mechanical and electrical designers have not been involved at this stage. Should the low

level bridge be adopted as the preferred option they would be involved once the structural conceptfor the opening span and the parameters for the operation of the opening span have been established.

Similarly technologies to those proposed here have recently be used for the Port River Bridge in

Adelaide, South Australia

5.1.2 Superstructure for low level bridge

The superstructure for a low level bridge option is dictated by the spans of the existing bridge. The

three spans either side of the opening span are 43 metres each whilst the approach spans are 22

metres. The 43 metre span is too long for precast concrete T-girders, so the superstructure for this

span and width of bridge is likely to be a single cell box girder of around 2.4 metre depth. If this

section is to be used for the main spans, construction efficiency would dictate that the approach

spans are constructed using the same section with 44 metre spans to match every second pier on the

existing bridge.

The concept design for the low level bridge has nine 43.7 metre spans (393 metres) on the northern

approach to the opening span and ten 43.7 metre spans (437 metres) on the southern approach. The

likely methods of construction for the superstructure are launched or span by span precast segmental

construction.


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Wells Crossing to Iluka Road Upgrading t he Pacific HighwayConcept Design ReportHarwood Bridge Options

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Launched superstructure for low level bridgeFor a launched bridge the superstructure would be cast on the river banks and launched across the

river to the opening span in a similar manner to the bridges over the Karuah River on the Pacific

Highway and the bridges over the Murray River at Albury, Corowa and Robinvale.

Launching a bridge involves construction of a casting bed for the box girder section and a launching

pad to jack against to push the completed segments out to cast the next segment of the bridge. The

construction of the girder segments would be set up so that installation of the reinforcement and

formwork, casting, curing, stressing and launching of the segments can be undertaken on a regular

cycle. It is assumed that a 21 metre segment (half a span) could be cast on a two week cycle.

For a bridge of 700 metre length it would be preferable to set up a casting yard and launching pad on

one side of the river and launch the bridge across to the other bank. At the Harwood Bridge site, the

southern bank of the river is the preferred site for the casting yard and launch pad because it is out of

the village, and rock is reasonably close to the surface. The cost of construction of a temporary

platform for the casting and launching of the bridge would be in the order of $1 million. The

northern bank of the river has very deep alluvial deposits and the cost of setting up the launching pad

would be in the order of $2 million, due to the cost of the large deep piles to support the weight of

the casting bays and resist the lateral forces due to the jacking of the bridge during the launching

process.

The complication with the Harwood Bridge is the inclusion of the opening span in the centre of the

river, and the need to ensure that the river remains passable during construction. Accordingly, it may

be necessary to launch the bridge from both sides of the river. To launch from both sides would

entail additional costs for the set up of the casting yard and launch pads on both sides of the river. If

the two approaches to the opening span are launched simultaneously there would be an additional

cost of around $1 million for the second launching nose and launching equipment. This cost is likely

to be offset by the cost savings associated with the 3 to 4 month time saving by not having to wait for

the first approach to be completed before commencing on the second approach.

In order to save time and cost with the launching of the bridge, it may be feasible to consider

launching both approaches from the southern bank with the two ends of the box girders temporarily

anchored together with stress bars. After the bridge has been launched across to the northern

abutment, the stress bars would be released and the southern approach would be pulled back into its

final position. There are some challenges with this system and it would require launching structures

at both ends and an intermediate launching frame for the retrieval of the southern approach, but there

are potential cost and time savings that would be significant.


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The option to close the waterway to traffic and launch from one side only could also be investigatedduring the environmental assessment and detailed design, in consultation with NSW Maritime and

the local community.

Pre-cast segmental superstructure for low level bridge

The span by span pre-cast segmental construction involves placing trusses below or over the bridge

deck and opening a series of pre-cast segments into position and post tensioning them together to

form simply supported spans. Alternatively the segments can be installed using the balanced

cantilever construction method then joined with a cast in situ infill segment to form a continuous

superstructure. This system worked very successfully on the M7, as both balanced cantilever and

span by span construction, and on the Windsor Flood Evacuation route project, as span by span. It is

also currently being used in balanced cantilever construction on the Gateway project in Brisbane.

The use of pre-cast box girder segments is, however, reliant on having a sufficient volume of bridge

structures on the project to warrant setting up a box girder fabrication yard for the project. There are

some forty bridges on the project, so it may be viable to set up a plant if the contractor chooses to use

box girder segments for most of the other bridges.

5.1.3 Substructure for low level bridge

It is proposed that the bridge piers would consist of a cast in situ concrete blade column supported on

a cast in situ concrete pile cap with two rows of raked piles.

The piles would need to be in the order of 40 metres deep to found on rock or in the dense sand and

gravel layers. The piles would also need bending strength in the top section of the piles to avoid

buckling in the water and soft silt layers and to resist lateral loads such as a vessel impact. It is

proposed that the piles are composite sections either using the 550 octagonal pre-cast pre-tensioned

concrete piles with a 310UC steel H piles or steel tubes with the top section of the pile filled with

reinforced concrete.

5.1.4 Alternative designs for low level bridge

A number of alternatives were considered but have not been pursued at this stage as the additional

complexity and cost would likely make them unviable. These options include:

Extending the spans from 43/44 to 86/88 metres and using balanced cantilever construction with

concrete box girders or using steel arches or trusses to achieve the longer spans.

Using cable stays from the opening span towers to create 130 metre spans either side of the

tower. This would create an iconic structure and remove some piers from the river. Although

there are construction and design issues relating to the resolution of the forces in the towers due

to the dislocation caused by the opening span that would be difficult to overcome. Moreover,


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the creation of a cable stay bridge could have significant visual impacts on the village ofHarwood.

5.2 High level bridge options

The high level bridge would be approximately 1500 metres in length, including 1000 metres in

approaches and 500 metres over water.

5.2.1 Superstructure for high level bridge

As with the low level bridge options, the high level bridge design is dictated by the spacing of the

piers for the existing bridge. The main differences between the high level bridge and the low level

bridge are that; (1) the high level bridge is 40% longer than the low level bridge length, (2) there

could be a requirement for twin bridges at the outset in order to realise the benefits of the high level

bridge and (3) the cost of the substructure is higher than for the low level bridge due to the

significantly higher piers and the longer span lengths that may be required to address issues related

to aesthetics, and hence options that were discounted for the low level bridge become feasible for the

high level bridge, e.g. minimising the number of piers in the river.

The three construction options considered for the high level bridge use a concrete box girder section

similar to the low level bridge, with the depths varying to suit the spans.

Pre-cast segmental construction (44 metre spans) for high level bridge

The first option is to keep the piers at the same spacing as the existing bridge and to have 43 and

44 metre spans on the approaches and a 38 metre span coinciding with the opening span on the

existing bridge.

The construction could be similar to the span by span form of construction described above for the

low level bridge, using pre-cast segmental construction with a truss below the deck and opening a

series of pre-cast segments into position and post tensioning them together to form each span.

Alternatively, a truss over two spans could be used to install the segments in a balanced cantilever

sequence to provide continuous spans.

For the span by span construction a 2.4 metre depth box section would be used. For the balanced

cantilever the section could be reduced to 2 metres. The balanced cantilever method would also use

integral connections between the piers and superstructure which would reduce future maintenance.

The cost of the piers for the high level section over the river makes this option less efficient than it

was for the low level bridge and the span lengths are too short for the pier lengths. On the basis of

cost, this is unlikely to be the preferred option for this bridge.


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Pre-cast segmental construction (86 metre Spans) for high level bridgeThe second option for a high level bridge is to position the piers to match every second pier on the

existing bridge and use the balanced cantilever pre-cast segmental system for these 86 metre

maximum spans. A similar form of construction was used on the approaches to the main spans on

the Bolte Bridge in Melbourne and is currently being used for the approaches to the Gateway Bridge

in Brisbane. Based on the designs for these bridges the concrete box girder section would need to be

around 4.1 metres deep for the 86 metre span.

The bridge would be designed using an integral cast in situ pier head, which is match cast with the

adjacent pre-cast segments in order to avoid bearings at the piers and the associated complications to

the balanced cantilever construction and future maintenance. Expansion joints would be placed at

the 1/5 point on every fourth span to minimise the thermal expansion and contraction effects.

The size of the truss required to open the girders into position is significant and, depending on the

timing of major bridge projects in Australia, may need to be imported into Australia for the project.

The viability of setting up a pre-cast yard for the box girder sections is also an issue. The cost of

setting up a pre-cast yard for the manufacture of pre-cast concrete box girder segments is in the order

of $5 million. To compete with T-Girders from an existing pre-cast yard, there needs to be a

significant area of bridges to cover the cost of setting up a pre-cast yard. The Ballina Bypass project

included around 30,000 m2 of bridge deck, which was not considered large enough to justify the use

of pre-cast box girder segments. By comparison, the duplication of the Harwood Bridge would

require approximately 20 500 m2 of bridge deck for the low level bridge and 34 500 m2 for the high

level bridge.

If twin bridges are constructed this option is likely to be viable. If only one bridge is to be

constructed the viability would depend on the market and what other projects are taking place in

Australia and South East Asia.

Cast In situbalanced cantilever construction for high level bridge

Cast in situ balanced cantilever construction is significantly slower than the pre-cast segmentalconstruction described above. It has lower set up costs, so if the bridge is not on the critical path for

the project and only one bridge is being constructed, it is likely to be the most viable solution.

The existing bridge has 43 metre spans on either side of the central 38 metre opening span. A single

span of 125 metres has been assumed for the new bridge to correspond to the three central spans of

the existing bridge. There is then an 85 metre span either side of the main span to match the next

two 43 metre spans, two 66 metre spans each side to match 6 of the 22 metre approach spans and an

end span of 44 metres.


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This 647 metre cast in situ balanced cantilever bridge would be used across the river. Theapproaches on either side of the river would then be constructed using 33 metre long precast concrete

T girder spans, as this should be the most cost effective form of bridge deck construction for the land

spans.

5.2.2 Substructure for high level bridge

It is proposed that the bridge piers would consist of a cast in situ concrete blade column supported on

a cast in situ concrete pile cap with two rows of raked piles. With the higher columns, longer spans

and integral connections to the superstructure the vertical loads and shear and bending forces would

be higher than the substructure for the low level bridge. The piles for piers in the river are likely to

be large diameter steel casings driven to rock, with reinforced concrete protecting the top section

projecting above the river bed. The concrete would provide bending strength and stiffness and

provide for corrosion protection of the upper section of the piers (i.e. that section most likely to be

exposed to the corrosive effects of the Clarence River.

5.2.3 Alternative designs for high level bridge

A number of alternatives were considered but have not been pursued at this stage because the

additional complexity and cost would likely make them unviable. These options include:

Constructing a series of 125 metre span concrete arches under the deck. Although they can bequite elegant, arches are better suited to single spans with good foundation material at each side

of the river as the resolution of the thrust forces from the arch into the foundations would be

difficult during construction and operation.

The use of cable stays to increase the spans. This was not pursued because there are no

functional reasons to increase the span beyond 125 metres and it was considered that the bridge

is high enough without adding to the height with stay towers. The cost of this option is also

likely to be quite high. The main cable stayed section of the Anzac Bridge cost $90 million or

$6 000 per square metre. The rates for a cable stayed bridge at the Clarence River are likely to

be in the order of $9 000 per square metre due to the increase in construction rates, thegeotechnical conditions on the northern side of the river and the distance of the site from the

specialist contractors required for a cable stayed bridge.

5.3 Interchange impacts

Associated with the new bridges, the Yamba Road Interchange would need to be upgraded. The

upgraded interchange would be able to use a similar layout to the existing, which would include

ramps constructed on low embankments. To facilitate the large movement of cane vehicles, a grade

separated crossing of the upgrade would be provided at Watts Lane, with the upgraded highway

passing over Watts Lane.


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The concept design process has seen comparable interchange arrangements adopted for bothinterchanges under both the low level and high level bridge options. This applies to both the Yamba

Road and Watts Lane Interchanges. Although the interchange detail would differ between the low

level and high level bridge options, the general arrangements and footprints of the interchanges

would be the same.


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6. Urban Design

An urban design analysis was undertaken to assess the relation of the high and low level bridges to

the existing bridge as well as the potential impacts on the amenity of the village of Harwood. The

analysis considered the following:

Characteristics of Harwood village and the surrounding area.

Loss of convenience or connectivity for residents.

Visual impact on the historic bridge and its setting in the landscape.

Visual intrusion within the village and quality of views from it. Extent and effects of shadowing.

6.1 Characteristics of Harwood village and the surrounding areas

The visual environment to the south of the proposed bridge is characterised primarily by wetland

vegetation, Maclean Hill, the Yamba Road interchange and other local roads. The visual

environment to the north of the bridge is characterised by the trees and buildings of Harwood Village

and the sugar mill. The existing bridge with its distinctive towers and the sugar mill are the

dominant elements in a very flat landscape (Figure 3)

6.2 Connectivity

The features of Harwood Village are illustrated on the Maclean LEP zoning map ( Figure 7) and on

an aerial photograph (Figure 8).

There are three main roads in Harwood:

River Street, which extends parallel to the bank (about one kilometre long within the village).

Harwood Mill Road.

The northsouth Morpeth Street (west of the existing highway).

The Harwood Mill complex at the eastern end of River Street is the main development in the village.

Morpeth Street starts at the riverbank in a small commercial area where a punt would have landed

prior to the construction of the bridge and is one of the oldest streets.

As can be seen from the various photos (Figure 8 to Figure 10), the Pacific Highway, including the

bridge, its approach roads and associated buffer zone cut through the centre of the village, passing to

the rear of the school. However, as is evident from the photograph taken along River Street and the

layout of the village streets, the Highway and bridge are neither functionally nor visually divisive.


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Figure 7 Harwood Village Zoning (from Maclean LEP)

Figure 8 Harwood Village, north side of Clarence River.

1(a) Rural Agricultural

Protection

1(t) Rural Tourist

1(w) Rural (Waterways)

2(a) Residential (Low

Density)

3(a) Business Zone

4(a) Industrial zone

5(a) Special Uses

Harwood Mill complex

River Street

Morpeth Street

Mill Road


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Figure 9 View of Harwood Bridge from River Street, Harwood

Figure 10 View of Harwood Bridge from River Street, Harwood


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6.3 Visual context

6.3.1 Low level bridge

The low level bridge would use a bascule lifting mechanism for operating the opening span. Figure

11 shows the operation of a two-leaf bascule bridge, although a single leaf bridge may ultimately be

preferred to reduce costs. The assessment of whether a one-leaf bascule or a two-leaf bascule bridge

would be preferred for an opening bridge would be determined as part of the detailed design process,

should the low level bridge emerge as the preferred design solution.

The use of a dark grey finish on the concrete would reduce the visual impact of the bridge. Noise

walls near the end of the bridge and on its approaches may be required and have been assumed in

this preliminary visual assessment (refer to Section 6.4).

Figure 11 Low Level Bascule Bridge in Open Position

A low level bridge has a low profile that is aligned with the existing bridge and, as it would be at the

same level as the existing bridge, it would require minor embankments for its approaches. This

would minimise visual impacts on adjoining properties and the potential overshadowing that would

be created by a larger / taller structure.


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6.3.2 High level BridgeA photomontage for the high level bridge is provided in Figure 12. To achieve a 30 metre clearance

height in the centre, the bridge would have long approach spans which would impact on the views

from the surrounding properties. The use of a double cantilever structure for this bridge may be

more elegant, although this could entail more significant visual impacts, which would need to be

assessed prior to proceeding with this option.

Noise walls near the end of the bridge and on its approaches may be required and are assumed in this

preliminary visual assessment (refer to Section 6.4).

Figure 12 High Level Bridge with 44 metre Pier Spacing

.

6.4 Impacts of alternative bridge options

6.4.1 Visual

A low level bridge would have limited visual impact on the village, much of which could be

ameliorated through appropriate screening, e.g. trees, located particularly along the northern banks of

the Clarence River.


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The high level bridge would have a very strong visual presence on the river and there would bedifficulties in providing a form that was sympathetic to the existing bridge.

Embankments and approach structures to a high level bridge would be visible above cane fields and

out of scale with the surrounding streets and buildings.

While alternative design configurations could reduce the number of piers and spans needed to cross

the river, these changes would not alter the relationship of a high level bridge to the existing bridge,

the floodplain and the surrounding village area.

Within the village a high level bridge would be far more visually prominent than a low level bridge.The quality of views of the historic bridge from the village would be compromised by a high level

bridge.

6.4.2 Shadowing

A new low level bridge would increase the amount of shadow immediately adjacent to the existing

bridge. At approximately 25 metres above River Street, the shadow effects of a high level bridge, as

can be seen in Appendix D, are likely to be more widespread.

The new high bridge, located on the east side of the existing bridge, would only affect a few houses

and the church, on late winter afternoons.

6.4.3 Constraints on future growth

For both options an interchange is proposed for Watts Lane, thus the footprint required for each

option, north of Harwood, would be similar.


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6.4.4 Summary

The following table sets out and compares the potential impacts noted above.

Table 1 Comparison of Potential Impacts

Issue Option 1Low level bridge

Option 2High level bridge

Visual Impacton historicbridge & itssetting

Avoids visual conflict with existingtowers (see Figure 10).

Form would be sympathetic to thehistoric bridge.

Severe visual conflict with the formof the existing bridge (see Figure11).

Quality of views of historic bridgewould be compromised.

Visual impactin village & onviews from it

Limited visual impact on village and canpredominantly be ameliorated throughscreening.

Less visually prominent than high levelbridge.

Very strong visual presence on theriver.

Would be visible above cane fields.

Out of scale with surroundingstreets and buildings.

Shadow effects Would increase shadowing immediatelyadjacent to existing bridge.

At about 25m above River Street,shadow effects would be morewidespread (see Appendix D).

Would only affect a few houses, andon late winter afternoons, wouldaffect the church.

Constraint onfuture growth

Limited impacts. Limited impacts.


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7. Traffic and Accessibility

7.1 Existing traffic and accessibility

In 2004, 10,000 vehicles per day, including 2,000 heavy vehicles (20%), crossed the Clarence River

at the Harwood Bridge. By 2021, the average daily volume will be almost 14,000 vehicles. The

peak hourly flow on an average day is approximately 7% of the daily volume, although the 30th

Highest Hourly Volume, which is more representative of busy holiday times, is closer to 10% of the

annual average daily traffic volume.

Based on information available for 2001 to 2007, the bridge is currently opened on average justunder thirteen times per month. Table 2 shows that whilst usage declines through the colder months

of the year, there is not an obvious pattern to the openings (also refer to Appendix E).

Table 2 Harwood Bridge Opening 2001 to 2007

Month 2001 2002 2003 2004 2005 2006 2007 2008

January Not avail 22 15 14 24 16 20 13

February Not avail 13 10 11 7 10 13 8

March Not avail 14 16 6 14 17 11 11

April Not avail 13 17 15 22 18 20 11

May 10 13 20 5 21 20 20 16June 8 6 17 10 14 12 16

July 13 11 13 6 15 8 12

August 17 10 15 7 10 15 8

September 18 7 8 7 14 11 16

October 18 9 6 10 9 15 13

November 12 12 14 14 8 13 9

December 15 8 10 8 7 12 13

Total 111 138 161 113 175 167 171 59

7.2 Low level bridgeA low level bridge would be at the same deck height as the existing bridge, and would therefore need

to have the capability to open to allow yachts and other vessels access to and from the river west of

the bridge. It is not expected that the frequency or duration of bridge openings would change due to

the presence of a second bridge.

The specifications for the Port River Bridge in Adelaide includes the following maximum times with

regards to the times to operate traffic control and safety equipment, open the road bridge and close

the road bridge:

Lower traffic gates: 7 seconds.


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Lower traffic barrier gate: 7 seconds.

Disengage span locks: 6 seconds.

Open movable bridge: 70 seconds, including time for ramping and seating.

Close movable bridge: 70 seconds, including time for ramping and seating.

Engage span locks: 6 seconds.

Raise traffic barrier gate: 7 seconds.

Raise traffic gates: 7 seconds.

This totals 90 seconds for each of the opening and closing cycles. It would be expected that similar

performance could be obtained from a new opening bridge at Harwood, although ultimately the

impact on traffic movement would be dictated by the volume of maritime traffic, and hence the

length of time for which the bridge was required to remain open. Although upgrading of the opening

mechanism of the existing bridge may marginally reduce opening times, this is unlikely to have a

significant influence on the overall efficiency of the opening/ closing cycle.

As outlined in Chapter 8, an opening time of 20 mins has been assumed in the economic analysis.

This is a conservation estimate, since an opening time of 10 minutes was recorded during a site

inspection undertaken on 30 October 2007.

7.3 High level bridge

In traffic terms, a high level bridge would not need to be opened to allow boat traffic to pass beneath

it, which provides advantages in terms of traffic efficiency. The bridge would, however, require

relatively steep grades for its approaches. A grade of 4.5% over a distance of 500 metres would be

required to reach the top of the bridge. Although the Austroads Guide to Traffic Engineering

Practice (Part 2 Roadway Capacity) indicates that a section of steep grade less than 800 metres in

length does not require specific analysis, the actual effect may be a reduction in capacity of as much

as 30%, taking into account the passenger car equivalencies suggested by Austroads for heavy

vehicles on longer sections of steep grade. While forecast volumes for the bridge are well within

even the reduced capacity, the high level bridge would have a lower capacity in comparison to the

low level option. Travel speeds, particularly for trucks, would be marginally lower for the high level

bridge option. However, the impact on overall travel times would be relatively small.

7.4 Local traffic

Local access arrangements would be expected to be comparable for the high and low level bridge

options. The current proposal is to provide an interchange at Watts Lane to provide access under

both the Class A and Class M scenarios. Whilst the ramp configurations may differ depending on

the bridge option, both bridge types would provide the same fundamental connections and levels of

accessibility for local traffic.

2 harwood bridge _ section 5 to 7

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