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Victoria Bridge Penrith - Structural Feasibility Study for the Attachment of a Shared Pathway DECEMBER 2010

Pub No: RTA/Pub. 10.376

ISBN No: 978-1-921766-89-3

December 2010

Victoria Bridge Structural Feasibility Study

TABLE OF CONTENTS 1.1 Purpose 6

1.2 Background 6

2 Bridge description 8

3 Structural feasibility studies 9

3.1 Constraints 9

3.2 Condition assessment and survey 9

3.3 Concept development of the proposed pathway 15

3.3.1 Penrith City Council suggestion 15

3.3.2 RTA investigations 16

3.3.3 Assumptions and limitations 18

4 Description of the RTA concept options 20

4.1 Underslung support frame 22

4.1.1 Attachment of a support frame to the cross girders 22

4.1.2 Attachment of the support frame to the bottom flanges of

the longitudinal box girders 24

4.2 Overslung support frame 27

4.3 Pathway decking option 31

4.4 Pathway structure in approach spans 1 to 3 and 8 to 10 31

5 Summary of the structural feasibility investigations 32

6 Strategic concept estimate 33

7 Conclusions 34

References: 35

APPENDIX A 36

APPENDIX B 43

APPENDIX C 44

Victoria Bridge Structural feasibility study for the attachment of a shared pathway

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Executive summary

Purpose of this study

This study investigates the structural feasibility of attaching a shared pathway onto the southern side of the road bridge over the Nepean River at Penrith, Victoria Bridge, on State Highway No5 – Great Western Highway. It is one of a number of studies that will be required to assist with the determination of a preferred option to provide a pathway crossing of the Nepean River at Penrith.

Penrith City Council proposed a structure be added to the bridge to provide connectivity for pedestrians and cyclists. This is shown in the figure below.

Other options being considered by Council include a clip on structure on the nearby railway bridge and a structure straddling the adjacent pipeline crossing of the Nepean River.

Following an approach by Penrith City Council, the RTA undertook an engineering investigation into the structural feasibility of this proposal. The RTA tested:

• A straight path option (preferred by cyclists and pedestrians) that requires a structure cantilevered some 7 metres off the existing bridge.

• A path that weaves around the sandstone piers with corbel detailing.


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Bridge description

The bridge was built in 1867, initially to carry railway traffic.

The bridge itself has ten spans. Spans 4 to 7 comprise the main spans over the river while spans 1 to 3 and 8 to 10 are approach spans over land.

The main spans, which originally supported a timber deck and railway track, consist of wrought iron longitudinal twin web plate girders and cross girders forming a U-frame. The approach spans (1 to 3 and 8 to 10) were initially constructed from timber piers and timber deck, but in 1907 changes were made:

• Railway traffic was diverted to a new bridge on the northern side of Victoria Bridge. • The timber deck in spans 4 to 7 was replaced with a concrete deck to carry road and

pedestrian traffic. • The timber piers and deck of the approach spans were replaced with concrete piers,

steel girder and concrete deck.

The existing pedestrian pathway on the bridge is the only means of pedestrian access across the river at this location. The pathway is approximately 1.4 metres wide. It is not separated from traffic by a traffic barrier; as such there is a potential risk to pedestrians. Cyclists are required to dismount and walk their bikes across the bridge.

Structural investigations

The available bridge plans do not provide sufficient structural details to carry out a capacity assessment for the addition of a pathway. For this study the RTA has therefore undertaken a condition assessment and survey at critical locations on the main longitudinal girder.

Section 5 of this report outlines the concept design options that were investigated in order to establish the feasibility of a clip on structure.

While a (shared) pathway width of 2.5 metres satisfies the 1992 Austroads Bridge Design Code, further assessments and discussions are required to ascertain if this meets current standards expected by users. The primary driver behind the RTA’s proposed alignment and width of the pathway has been to eliminate or minimise the need to strengthen the existing bridge structure.

The preliminary structural capacity assessment of the superstructure has shown that spans 4 to 7 may require localised strengthening at certain locations as a result of any additional loading. Any strengthening proposal involves significant construction occupational health and safety risks, and constructability issues, explained in Section 2.

This study investigates the removal of the existing walkway and widening of the existing carriageway by installing a new concrete deck. New traffic barriers are proposed to protect the main longitudinal girders from vehicle impact damage. The approach spans 1 to 3 and 8 to 10 are not capable of supporting the cantilevered pathway. Therefore an


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independent sub-structure for the approach spans has been proposed to support the new pathway.

This study assumes that the substructure of other spans has adequate capacity to support the addition of the pathway.

Of the two design options considered, a 2.5 metres wide cantilevered pathway attached to the southern longitudinal box girder, with an alignment profile that follows the curved profile of the sandstone piers and the sandstone facades above the piers is considered to be structurally feasible. A 2.5 metre wide pathway is considered to be the maximum pathway width that is feasible without significant structural upgrading of the existing structure.

The preliminary cost estimate of $30 to $35 million (2010 dollars) for a 2.5 metre wide pathway is included in Appendix C of this report. The costs include:

- New approach spans.

- Cantilevered pedestrian/cyclist bridge.

- Removal of the existing walkway on the bridge and replacing with a new concrete dock to increase the carriageway width.

- Installation of barriers to protect the existing structure from vehicle damage.


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1 Purpose and background

1.1 Purpose

The purpose of this report is to investigate the structural feasibility of attaching a new separate shared pathway on the southern side of the road bridge over the Nepean River at Penrith (called Victoria Bridge).

1.2 Background

Victoria Bridge was completed in 1867 making it the oldest still existing crossing of the Hawkesbury-Nepean River. It is listed on the Penrith Council LEP and RTA's Section 170 Register where it has been assessed as state significant. It is not listed on the State Heritage Register. Based on its listing on the Section 170 register, notifications to and discussions with Heritage Council will be required regarding a proposal which impacts on the fabric of the bridge. Heritage Council approval is not required, however it would be necessary to resolve any concerns raised by Heritage Council/Heritage Branch. The bridge is located on the Great Western Highway and carries an average daily traffic of 25,000 vehicles per day (2009). The current footway adjoining the roadway is the only way for pedestrians to cross the river at this location. The pathway itself is 1.4 metres wide and does not have barrier protection. It therefore poses a potential risk to the safety of pedestrians.

The existing width between the main longitudinal girders, 7.77 metres (25’6”), is not sufficient to accommodate two lanes and a pathway under current Australian standards.

Penrith City Council has proposed a new pathway be attached to the bridge superstructure, which is separated from the roadway, the sandstone piers and corbel detailing. Council’s concept involves a 3.6 metre wide pathway with a straight alignment. The structural feasibility of this alignment has been investigated in this study.

This structural feasibility study required the development of feasible concept design options for the pathway. The criteria to guide the development of these options were:

• To minimise the measures to be taken to strengthen the existing bridge. The reasons for this are discussed in this report.

• To maximise the width of the cantilevered pathway, within the limits of what the existing structure can support.

• To align the pathway so as to comply, as closely as possible, to geometric standards. This is necessary to keep the footway clear of the projection of the sandstone profile at the top of the pier.

A major constraint on the achievable width and alignment of the new pathway is the structural capacity of the existing structure. The key driver in arriving at the proposed


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width of the pathway and its alignment has been to eliminate or minimise any need to strengthen the existing structure.

The longitudinal girders of the existing bridge are made up of wrought iron box-shaped girders with twin webs and boxed flanges at top and bottom. Both top and bottom flanges of the longitudinal girders are boxed in spans 5 to 7; only the top flange is boxed in span 4. The top and bottom cells are inaccessible, while only limited space is available to access the middle cell forming the web of the girder. The clear width of the middle cell between the stiffeners is only approximately 540 mm for spans 5 to 7, and 440 mm for span 4. These constraints pose a significant construction occupational health and safety risk and place significant limitations on prospective strengthening measures.

Two cantilevered pathway alignments have been considered in this study:

1. An alignment that closely follows the profile of the sandstone piers with their corbel detailing.

2. A straight alignment that requires an extended cantilever span to keep the pathway clear of the profiles of the sandstone piers and corbel detailing adjacent to the main longitudinal girders.

The choice of material for the pathway deck has a significant impact on the structural adequacy of the existing longitudinal box girder, which needs to support the pathway in addition to the co-existing traffic loads.

Appendix A presents the findings of the preliminary capacity assessment, carried out to ascertain whether the existing longitudinal box girder can adequately support the proposed cantilevered pathway in the various concept options under consideration. The sketches of the concept options examined in this study are in Appendix B. Appendix C provides a strategic estimate for the option identified as most feasible.

A monorail access under the superstructure has not been considered in this study. This could be examined as it may facilitate future maintenance of the bridge and provide access during pathway construction.


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2 Bridge description

Victoria Bridge at Penrith was designed to carry railway traffic and horse-drawn road traffic. The main spans are twin web wrought iron longitudinal box girders and plate cross girders at close spacing of 0.915metres (3 ft) c/c. These spans supported both the original timber deck and a railway track. The approach spans were made of timber. In 1907 the trains were diverted to a new truss bridge on the northern side and the deck was replaced with a concrete deck exclusively for road traffic. In the1930s the timber members of the approach spans, which had deteriorated, were replaced with steel girders and a concrete deck. In the 1950s there was a plan to attach a separate pathway but it was not implemented.

The bridge, which has ten spans, is approximately 275 metres in length. Based on the drawings and recent survey, the spans measure 8.16 metres, 7.82 metres, 7.58 metres, 42.1 metres, 60.85 metres, 60.37 metres, 60.81 metres, 10.07 metres, 8.03 metres and 8.05 metres sequentially (with span 1 on the Emu Plains side of the bridge). The width of the deck is about 7.77 metres, measured between the top flanges of the main longitudinal girders. The carriage width is 6.1 metres and there is an approximately 1.4 metres wide footway at the southern side of the deck. The bridge carries two traffic lanes, one in each direction.

The superstructure of approach spans 1 to 3 is comprised of steel girders and a concrete deck. These spans are simply supported and each span has five steel longitudinal carriageway girders and one footway girder supporting the concrete deck.

Span 4 is a simply supported span comprising two main longitudinal wrought iron twin web (box) plate girders with a series of wrought iron cross girders spaced at 0.915metre centre to centre. The deck is thus supported by a U-frame formed by longitudinal and transverse cross girders. These box girders are fabricated from angles and plates riveted together. The top flange consists of a double cell box section, while the middle section (which forms the web) is comprised of a single cell box section made up of twin webs. The bottom flange contains multiple layers of plates riveted together. The built-up T sections are used as web stiffeners and to splice the web plates. The dimensions of the longitudinal box girders of span 4 are 0.76metres (wide) x 3metres (high).

The superstructure in spans 5 to 7 is continuous, consisting of U-frame arrangements similar to those in span 4. The longitudinal wrought iron box girders of spans 5 to 7 measure 0.915metres (wide) x 4metres (high). The top and bottom flanges consist of double cell box sections fabricated from plates and angle sections riveted together. Like span 4, the web in the middle section is a box section comprised of web plates spliced with T sections.

The substructures for the approach spans 1 to 3 and 8 to 10 are comprised of concrete piers and abutments. The piers are framed structures with a headstock supported on four columns. Pier 3 consists of a pair of cast-iron cylindrical piers. Piers 4 to 7 are sandstone wall piers. Limited available information indicates that the approach span piers are founded on piles whereas the main span piers rest on rock.


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3 Structural feasibility studies

3.1 Constraints

A number of constraints exist, primarily as a result of the type of construction, material and condition of the bridge that affect the selection of feasible concepts for the attachment of a pathway to the existing structure. These are:

• The available bridge drawings are of poor quality. Consequently it was not possible to obtain accurate structural dimensions and member sizes to carry out the structural assessment. Therefore, it was necessary to undertake a condition assessment and survey, and to confirm measurements of the member sizes.

• It is not possible to get accurate structural dimensions and member sizes to carry out the structural assessment. Therefore, it was necessary to undertake a condition assessment and survey, and to confirm measurements of the member sizes.

• The level of information on the substructure of the bridge is lacking. It has been necessary to make assumptions about the substructure’s ability to support the addition of the pathway.

• If it becomes necessary to implement strengthening measures to the existing structure, the inaccessible spaces inside the girders can pose significant construction occupational health and safety risks.

• The structure comprises old wrought iron built up using angles, multiple plates and rivets. This structure imposes severe limitations on the types and details of connections and attachments that can be employed, as inappropriate choices could potentially compromise both the durability and strength of the existing structure.

3.2 Condition assessment and survey

The condition assessment and survey was carried out by Sinclair X-Ray Inspection Services Pty Ltd (September 2010). Access to the longitudinal box girders and cross girders of the bridge was provided using a barge. The investigations and the measurement of the member/element sizes were carried out using ultrasound equipment. This technique, however, could not be used at all locations, especially where multiple layers of plates were present. The varying layers of plates are shown in Figures 1 and 2.


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Figure1: Photo showing number of layers of plates in the bottom flanges

Figure 2: Photo showing number of layers of plates in top flanges


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Certain constraints were placed upon the condition assessment by a lack of access to the inside of the top and bottom cells of the main longitudinal box girders on spans 4 to 7. The thickness measurements of the plates with exposed edges had to be carried out by physical measurement using a tape measure, resulting in lower precision and a larger margin of error. The web thicknesses had to be measured using ultrasound equipment. Because of the limited scope of this study, the survey was carried out at a restricted number of locations. Figures 3, 4 and 5 illustrate typical examples of these locations.

Figure 3: Sketch showing typical locations for condition assessment and survey


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Figure 4: Sketch showing the plate thickness measurement locations for spans 5, 6 and 7 girders

Figure 5: Sketch showing plate thickness measurement locations for span 4 girder


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Existing inspection hatches in the web of the central cell facilitated visual inspection using the snake eye camera. The photos, shown in Figures 6 and 7, illustrate the limited access available to carry out construction activity, as described in Sections 1.2 and 3.1.

Figure 6: Photo inside the central cell of longitudinal box girder of span 5

Figure 7: Photo inside the central cell of longitudinal box girder of span 5


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Figure 8: Photo showing condition of bottom flange at certain locations

Information was not available on existing deck thickness and composition. Because this information is essential to carrying out an assessment of the available remaining reserve capacity of the existing girders, a pavement investigation was undertaken in March 2010. The investigation indicated that the deck is comprised of asphalt, tar-coated macadam and concrete. Based on the test core samples, the approximate maximum thicknesses of each of these layers in spans 4 to 7 is as follows.

• Asphalt – 70 mm

• Tar-coated macadam – 205 mm

• Concrete – 275 mm

The RTA structural assessment has been based on the above information.

The survey included measurement of the dimensions of the sandstone profile at the top of the pier projecting beyond the webs of the main longitudinal girder in order to determine the alignment of the proposed pathway.


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3.3 Concept development of the proposed pathway

3.3.1 Penrith City Council suggestion

From the three options being considered by Penrith City Council a concept for a new cantilevered pathway on Victoria Bridge was provided to the RTA.

There is limited available space on the northern side of the bridge and Council proposed the new pathway on the southern side.

Figure 9 shows Council’s concept for a 3.6 metre wide pathway on a straight alignment next to the bridge.

Figure 9: Penrith City Council concept sketch

Due to limited available width on the bridge deck, the proposed pathway is a cantilevered structure, supported off the main longitudinal box girders of spans 4 to 7.


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3.3.2 RTA investigations

Design standards

Table 1 provides the minimum required widths of a shared pathway according to the 1992 Austroads Bridge Design Code and the current AS 5100.1-2004 Bridge Design Code, that includes cyclists.

It is noted that RTA current design practice examines opportunities for shared pathways of 3 metres or wider. However the structural capacity of the existing longitudinal girders to support both the traffic and the new pathway, limited the width of the pathway to 2.5 metres. A width greater than 2.5 metres would increase the requirement to strengthen the existing girders and potentially exacerbate dynamic vibration problems.

Table 1: Required pedestrian pathway widths as per Australian Standards

Sandstone piers

Figure 10 shows the piers and the corbel detailing around the main longitudinal girders.

The piers are sandstone, and the pier capping adjacent to the longitudinal girders are an architectural feature.

The profile of the sandstone pier projects beyond the face of the longitudinal girder by as much as 2.75 metres.

Description 1992 Austroads Bridge Design Code Section 1 Cl. 1.4.4

AS 5100.1-2004 Bridge Design Code Table 9.13(A)

Bicycle on carriageway (one way cycling)

2.0 metres preferred

1.5m minimum

2.0 metres minimum

Separate cycleway (two-way cycling)


2.0 metres minimum

3.0 metres minimum

Dual use (two-way cycling and pedestrians)


2.5 metres minimum

3.0 metres minimum


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Figure 10: Sandstone piers and sandstone corbel detailing at the top of the piers

To accommodate the straight alignment proposed by Council the pathway has to be extended clear of the edges of the sandstone piers and their corbel detailing (that is, a cantilever of 7 metres).

RTA consideration of a structurally feasible option

The RTA developed a pathway concept constrained by the structural capacity of the existing longitudinal box girders, which are the key structural element. As mentioned above pathway widths between 2.5 and 3.6m were tested using static analysis methods. . A pathway width of 2.5metres was the widest pathway which could be supported by the existing structures without the need for significant upgrading of the existing structure.

With long cantilevers to achieve a straight alignment, the magnitude of cantilever deflection at the tip of the cantilevered pathway is a critical consideration. Although the preferred concept design attempts to minimise the static deflection at the tip of the pathway cantilever, the acceptable limit can only be confidently determined by carrying out a detailed dynamic analysis and assessing the dynamic response of the cantilevered pathway. The accuracy of the dynamic analysis depends on assigning appropriate masses and levels of flexibility to various structural elements. Since this is a structural feasibility study with limited preliminary analysis and design, the acceptability limit of the deflections cannot presently be defined. This requires a more detailed design of structural elements.

The RTA considered an independent substructure between spans 1 to 3 and 8 to 10 because it is not feasible to support the cantilevered pathway using the existing superstructure.


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The RTA options include the removal of the bridge’s existing pathway once the new pathway is constructed. This would increase the lane widths and provide other improvements to the existing carriageway. However, it should be noted that the structural feasibility of widening the carriageway in approach spans 1 to 3 and 8 to 10 though not investigated in this study is not anticipated to pose any significant problems.

The RTA options include safety barriers by the side of the main longitudinal girders to prevent damage due to accidental impacts from vehicular traffic.

These options are described in Section 5. The effects of each of these options on the existing longitudinal box girder are described in Appendix A.

3.3.3 Assumptions and limitations

The following assumptions have been used in this structural feasibility study.

• A limited field condition assessment and dimensional survey has been performed, sufficient for the purpose of this study.

• Plate and element sizes used in the analysis, for elements such as internal webs of top and bottom box girders (no access), are assumed to be within close range of actual sizes.

• The yield strength of the wrought iron material is considered to be 200 MPa.

• Special analysis, such as structural dynamics and fatigue assessment, has not been undertaken.

• Analysis of the adequacy of member connections has not been carried out. This includes identification of connections with cracked /fractured /missing rivets, if any, in the built up element.

• It is presumed that any strengthening at identified locations envisaged in the preliminary design is possible from an Occupational Health and Safety and constructability point of view.

• Strengthening of areas where there is significant section loss due to corrosion is envisaged.

• Assessment of bearings and other elements of the substructure has not been included in this study and it has been implicitly assumed that the proposed pathway is unlikely to affect their performance.

• A curved pathway alignment that follows the sandstone pier profile, if adopted, does not pose sight distance risks to pedestrians and cyclists while negotiating the alignment.

• Discussions with agencies about the heritage value of the bridge and the heritage impacts of any options have not taken place. It should be assumed that there would be strong heritage constraints to the development of a preferred project.


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• That it is possible to relocate any existing services which are affected, either temporarily or permanently, during construction of the pathway.

• Some traffic disruptions would result from construction of the pathway. This needs to be assessed based on the construction sequence.

Additionally, the following live loads and load combinations have been considered in the structural feasibility study.

a. Live load on the pathway: 4 kPa for special event loading, without roadway LL, based on the loaded area as defined in AS 5100.2-2004 Bridge Design Code.

b. Single or multiple ST42.5 vehicles in each lane: for multiple vehicles in same lane a minimum distance between vehicles of 17.0 metres has been adopted with multiple presence factors specified in Austroads guidelines (4 – ST42.5 trucks at unfavourable locations).

c. Single or multiple BD68 vehicles in each lane: similar to ‘b’ above (4 – BD68 trucks at unfavourable locations).

d. T44 and L44 loadings: as defined in Section 2 of 1992 Austroads Bridge Design Code.

e. ST42.5 vehicular loadings: as defined in ‘b’ and ‘c’ in combination with pedestrian live load of 2 kPa and ultimate load factor of 1.8 to satisfy current provisions defined in AS 51200.2-2004 Bridge Design Code.

f. BD68 loading in combination with ultimate pedestrian live load: as defined in ‘e’ above.

g. T44 / L44 loadings in combination with ultimate pedestrian live load: as defined in ‘e’ above.


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4 Description of the RTA concept options

In principle, two options for the pathway support frames for a cantilevered pathway were considered for the main spans 4 to 7.

1. An underslung cantilevered pathway support frame.

2. An overslung cantilevered pathway support frame.

The proposed pathway alignments considered for these options are as shown in Figure 11 and Figure 12 respectively.

Figure 11 shows the straight alignment of the pathway, which is similar to the original concept proposed by Penrith City Council. The cantilever span for a 2.5 metre wide pathway would be well over 5.5 metres in order to maintain the straight alignment and to keep the pathway well clear of the profiles of the sandstone pier.

Figure 11: Straight alignment of pathway


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Figure 12 shows the pathway alignment that locates the pathway closer to the existing longitudinal box girders, thus reducing the required cantilever length in the main spans. This alignment follows the profile of the sandstone section, at the top of the piers, for spans 4 to 7.

Figure 12: Curved alignment of pathway

The radius for the transition from the straight to curved alignment has been adopted from the RTA’s NSW Bicycle Guidelines as shown in Figure 13.

Figure 13: RTA NSW Bicycle Guidelines for curved paths


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These alignments are investigated for each of the above two options of support frames. Following is a brief description of the options considered in this feasibility study.

4.1 Underslung support frame

This option considers locating the pathway support frames below the deck. Two sub-options for the underslung support frame have been considered.

1. Attachment of support frames to the cross girders.

2. Attachment of support frames to the bottom flanges of the longitudinal box girders.

The options are described in the following sections.

4.1.1 Attachment of a support frame to the cross girders

The existing cross girders are fabricated from angles and plates riveted together. The pathway frame would need to be supported via a suspended connection since the cross girders are located on the top of the bottom flange of the main longitudinal box girder.

Due to the presence of rivets in the bottom flange, it is envisaged that the support frame would need to be connected through the web of the existing cross girders (see figures 14 and 15). The connection of the pathway frame to the bridge must be located close to the longitudinal girders, but this is complicated by the fact that the cross girders taper near the box girder connections. Because the web is critical at the cross girder support locations, it is anticipated that any additional connections to the web at these locations would require strengthening of the webs because the web is critical at the cross girder support locations.


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Figure: 14: View of cross girders

Figure 15: Typical cross girder connections to main longitudinal girders


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The capacity of the existing connections between the cross girders and longitudinal box girders has not been assessed at this stage. Because this connection is critical to the substructure’s ability to sustain the additional load of the pathway, further investigation is required before this option can be considered feasible. This connection is critical to the substructure’s ability to sustain the additional load of a pathway. This would include a fatigue assessment at the cross girder connection to the main longitudinal box girders, which is subjected to significant fatigue loading from vehicular traffic. Due to the complexities involved in the connections between the pathway support frames and the cross girders, this option is not explored further in this study.

Drawings have not been prepared for this option.

4.1.2 Attachment of the support frame to the bottom flanges of the longitudinal box girders

This option considers the attachment of a cantilevered truss frame to the bottom flanges of both longitudinal box girders to support the pathway.

The proposed support arrangement for this option is a U-frame clamp that goes around the cross girders and gets bolted through the webs of the existing longitudinal box girders. Typical arrangements for both straight and curved alignments are shown in Figure 16 and 17. The presence of rivets in the bottom flange can be seen in Figure 18.

Figure 16: Typical section of pathway for straight alighment


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Figure 17: Typical section for curved alignment profiled around the piers

Figure 18: Photo showing typical bottom flange of longitudinal box girders

With this option, the static deflections at the tip of the cantilevers would be within acceptable limits, subject to confirmation of the dynamic behaviour described in Section 3.3.2. Both the straight and curved alignments would satisfy the static deflection requirements. The optimum spacing of the pathway support frames along the span is considered to be a maximum of 2.8 metres.


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The preliminary analysis indicates that, for the curved alignment with a 2.5 metre wide pathway, the capacity of the existing longitudinal box girder is exceeded at certain locations in spans 4, 5 and 7. At these locations it would be necessary to strengthen the box girder. In this option the longitudinal box girder on the southern side of the pathway frame is subjected to the entire loading from the pathway, in addition to loading caused by the overhang action required to balance the uplift reaction at the northern longitudinal box girder.

Due to increased overhang span, the extension of the pathway well clear of the pier necessary to achieve the straight alignment would further increase the loads on the southern longitudinal box girder. For this reason, and in the interest of minimising any strengthening of the existing longitudinal box girders, a 2.5 metre wide pathway with curved alignment would be the only feasible option.

Advantages:

• The static deflections would be within acceptable limits.

• Lower visual impact - the support arrangements and attachment are on the underside and therefore not visible to pathway users.

• Little or no traffic closure anticipated during construction of the pathway.

Disadvantages:

• The presence of rivets in the bottom flanges imposes severe limitations in terms of type of connection (see Figure 18).

• There is no access within the bottom cell of the longitudinal box girders of spans 5 to 7. Therefore any direct connection would not be feasible.

• The entire construction would have to be carried out via barge access, using cranes for lifting and for the installation of pathway frames.

• The present vertical clearance under the bridge would be affected.

• Access would be difficult for future inspections of the underside of the deck and cross girders, and during maintenance of the pathway and existing bridge girders.

• Local strengthening of the webs of both the southern and northern longitudinal box girders may be required in the vicinity of the support frame connection.

• Substantial increases in material and handling costs, due to the need to support the cantilevered pathway truss frame on both the longitudinal box girders.

• The additional load from the supporting arrangement in this option marginally increases the strengthening requirements of the existing longitudinal box girders.

This option, a 2.5 metres wide pathway with curved alignment, may therefore be considered structurally viable subject to strengthening at identified locations.

This option is shown in the drawing KA725CS03 as Option 3 in the Appendix B.


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4.2 Overslung support frame

In this option, the pathway support frame is directly supported on the southern longitudinal box girders of spans 4 to 7 through an inverted U-frame on the top flange and attached by a bolted connection to the web. This option would simplify construction and minimise the structural connection to the existing box girder. The entire pathway frame could be fabricated and then installed. The options considered are shown in Figure 19, 20 and 21 for the two alignments.

Figure 19 Typical cross-section for straight alignment – cantilever beam

Figure 21: Typical section for curved pathway alignment

Figure 20: Typical cross section for straight pathway alignment – truss frame


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Figure 22: Photo showing top flange of longitudinal box girders

Figure 21: typical section for curved pathway alignment – cantilever truss


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Two options have been explored:

1. A cantilever beam (figures 19 and 23).

2. A cantilever truss (figure 20, 21 and 24).

The deflection at the tip of the pathway cantilever is sensitive to the rotation of the top section of the box girder. This is because the box girder webs together with the cross girders acts like a U-frame and any rotation of the longitudinal box girders either inwards towards the traffic or outwards away from the traffic would accentuate deflections at the tip of cantilever. The static deflection at the tip of the cantilever was found to be very high in the range of span /100 for a cantilever span of 5.6 metres supporting a 2.5 metre pathway with a straight alignment. However, the limiting criterion for deflection would be dictated by the dynamic behaviour described in Section 3.3.2.

Depending on the decking material to be adopted for the pathway, it is envisaged that the optimum spacing of the U-frame brackets would be between 1.8 to 2.8 metres.

Figure 23: Exaggerated deflected shape for cantilevered pathway beam

Figure 24: Exaggerated deflected shape for cantilevered truss


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Within the limitations of this study it appears that, for the straight alignment option, excessive deflections are likely to cause dynamic instability as diagrammatically shown in Figure 23 and Figure 24. The cantilevered pathway in this option introduces significant shear and torsional stresses in the web. Similar load effects are reduced in magnitude for the curved alignment. The longer cantilever span would require significantly more strengthening to accommodate these additional shear and torsional stresses and is thus considered unsustainable. The straight alignment option with a pathway width over 2.5 metres is therefore considered to be impracticable.

The capacity assessment of the longitudinal box girder has therefore been carried out assuming a curved alignment and pathway width of 2.5 metres. The spacing of the pathway frames was likewise assumed to be closer than 1.8 metres in the vicinity of the pier, so as to accommodate the longer span length of the cantilever at these locations. At this stage, it has not been determined whether additional supports from the sandstone piers are required in the vicinity of piers 4 to 7.

Due to the direct load path and reduced load effects, this option is considered slightly more efficient than the underslung option at better utilising the limited capacity of the existing longitudinal box girder. From the results of the preliminary analysis it is apparent that the strengthening requirements of the existing box girder are at least minimised with the curved alignment option and a 2.5metre wide overslung pathway structure.

These options are shown in sketches KA725CS01(Option 1) and KA725CS02(Option 2) in Appendix B.

Advantages:

• Construction could be carried out from the existing bridge deck.

• All the connecting members are accessible and would therefore be easier to inspect and maintain.

• The strengthening requirements for the longitudinal box girder is reduced.

Disadvantages:

• The existing services located at the top flanges of the southern longitudinal box girders would require permanent relocation.

• Access to the inside of the central box, a confined space, would be required during construction.

• Some traffic closures would be required during construction (depending on the method used) if the work is carried out from the bridge deck.

• The deflections are sensitive to the rotation of the box girder because the support frame is located at the top of the box girder of the U-frame.

• Local strengthening of existing southern longitudinal box girder webs would be required in the vicinity of the support frame connection.

• The support frames would change the aesthetic appearance of the existing longitudinal box girders.


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4.3 Options for pathway decking

The preliminary analysis indicates that the dead load of the added pathway forms a significant proportion of the additional load on the existing structure. The decking initially proposed was comprised of a concrete deck, with a minimum 100 mm thickness, and longitudinal girders supported on cantilevered frames. This induced significant additional stresses to the existing main longitudinal girders. When considered in addition to the current vehicular traffic loading, the initial deck option would potentially increase the requirements for strengthening the bridge.

For the purposes of this study, the capacity assessment of the main longitudinal box girders was made assuming the use of timber decking with timber joists.

In any further work for this project one of the following options is recommended in order to minimise the dead load of the pathway decking:

• Timber deck with timber joists.

• Deck composed of fibre composite pultruded sections.

• Reactive powder concrete deck such as Ductal.

• Deck using aluminium sections.

One of the above methods could reduce the weight of the deck by over 50% relative to the conventional concrete option using steel girders. These options would need further evaluation in terms of their acceptability to cyclists, suitability of the material and maintenance costs. Decking options would need to be further developed in the detailed design stage.

4.4 Pathway structure in approach spans 1 to 3 and 8 to 10

An independent sub-structure is proposed because a cantilevering arrangement is not feasible for the approach spans 1 to 3 and 8 to 10, an independent sub-structure is proposed. The structural capacity of the existing deck on the approach spans is not adequate to support a cantilevered pathway. The general concept of the pathway in these spans is shown in the attached sketches.

The focus of this structural feasibility report is the attachment of the new pathway to the existing main longitudinal girders of spans 4 to 7. The arrangement of the pathway in the other spans (approach spans) is only conceptual at this point and would be developed further during detailed design.


November 2010 32

5 Summary of the structural feasibility investigations

The RTA established the most realistic vehicular traffic loading on the bridge by collecting traffic load data and assessing the probability of multiple laden semi trailers (ST42.5) or B Double (BD68) trucks concurrently utilising the bridge at any given time. The preliminary analysis reveals that, under the current bridge loading (ie without an additional pathway), the existing longitudinal girder of span 4 is overstressed by about 10% for BD68 vehicular traffic.

The RTA considered the structural feasibility of two options for attaching a pathway, and pathway widths between 2.5 and 3.6 metres. The preliminary capacity assessment of the existing longitudinal girders for the attachment of the pathway, in combination with ST42.5 vehicles, notes:

• Span 4: the structural capacity is inadequate at 3 sections by up to 20% for an underslung support frame and up to 15% for an overslung support frame.

• Spans 5 and 7: the structural capacity is inadequate at 2 sections by up to 20% for an underslung support frame and up to 15% for an overslung support frame.

The results are shown in Appendix A.

As this stage, it is envisaged that the overstressed sections can be locally strengthened, provided the areas inside the central cell of box girders are accessible. This is a confined space and limits the size of the members that can be carried within the box girder. A constructability review carried out during the detailed design phase would be needed to resolve this question. It is considered that, any strengthening for sections that are more than 20% overstressed may be considered impracticable.

The structure is over 140 years old and would have sustained significant fatigue loading. In light of this, it can be assumed that a 2.5 metre pathway with a curved alignment and limited strengthening is structurally feasible, subject to the constructability of localised strengthening.

The strengthening requirement for the existing structure is not determined at this stage, since it would depend on several factors, including:

• The proposed new pathway decking.

• Thorough investigation of the critical locations described above, so as to confirm the pathway configuration that they can support. This is necessary because the survey undertaken for this feasibility study had severe accessibility and equipment limitations.

• Material properties, including the actual yield strength of the wrought iron used for the longitudinal girders.

The existing decking on the bridge is notably heavy. If the replacement of this decking is an option, it is possible to significantly reduce the dead load.


November 2010 33

6 Strategic concept estimate

The estimate is based on preliminary concept design of the option using an overslung support frame. Cost estimates have been prepared based on different construction methods;

• Construction by barge - Estimated cost $32 million (2010 dollars)

• Construction from existing roadway – Estimated cost $29 million (2010 dollars)

In addition to the construction of the pathway, the estimates have included provision for the relocation of identified services, the demolition of existing narrow footway and deck reinstatement to accommodate wider traffic lanes including approach spans, resurfacing the existing bridge deck with asphalt and providing new protection barriers to protect the girders from vehicle impacts.

In round terms the cost of attaching a pathway to the existing bridge is considered to be of the order of $30 to $35 million (2010 dollars).


November 2010 34

7 Conclusions

The scope of this study was limited to the structural feasibility of attaching a pathway to the southern side of the existing Victoria Bridge. The RTA considered two attachment options for a pathway for structural/engineering impacts on the existing bridge.

Of the two options considered (straight versus curved alignment), a maximum 2.5metre wide pathway with a curved alignment that follows the profile of the sandstone piers, is:

• Considered to be structurally feasible.

• Does not directly impact the existing bridge and avoids the sandstone piers and corbel detailing.

• Minimises the need to strengthen the bridge.

• Minimises construction occupational health and safety risk.

• Reduces other adverse structural impacts on the bridge.

• costs approximately $30 to $35 million in 2010 dollars.

These designs do not consider community needs, urban design, heritage, safety and environmental constraints. A comparison with other possible river crossing options is necessary to determine the optimum solution.

For the cycleway project the RTA recommends:

• looking at all strategic options to provide a 280 metre pathway crossing of the river; including the options identified by Penrith City Council and a freestanding option.

• including functionality, design, heritage, community and environmental considerations.

This study would be a working partnership between Council, the RTA and local stakeholders including Railcorp, utility authorities, Department of Planning (Heritage Office), DECCW, NSW Maritime, bicycle user groups and the community.


November 2010 35

References:

RTA Bridge Engineering Branch, May 2010, Bridge over Nepean River on SH5 at Penrith – Limited assessment and below deck inspection of spans 5 to 7.

Sinclair X-Ray Inspection Services Pty Ltd, September 2010, Ultrasonic and thickness survey of Victoria Bridge Penrith.

Australian Standards AS 5100 Bridge Design Code.

Austroads, 1992, Bridge Design Code

RTA, 2005, NSW Bicycle Guidelines

Bridge plans no. 0084 358RC0069.


November 2010 36

APPENDIX A

Preliminary Analysis Results – Check for Structural Adequacy of Existing Longitudinal Box Girder


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APPENDIX B

PRELIMINARY CONCEPT SKETCHES


November 2010 44

APPENDIX C

STRATEGIC CONCEPT ESTIMATE


November 2010 45

Project: VICTORIA BRIDGE PATHWAY

Prepared by: Mark Raven

CONCEPT DESIGN OPTION : CONSTRUCT FROM ROADWAY Rev:A Oct 2010 Project No: 06/065 Estimate Stage:Concept

Item Estimate 2010 $

Contingency

Estimate % of Total

Comments

(excluding % Amount Estimate contingency)

(including contingency)

1. Project Development 1 (a) Route/Concept/EIS or REF 541,961 35% $189,686 $731,648 1 (b) Project Management Services $40,647 35% $14,226 $54,874 1 (c) Client Representation $4,065 35% $1,423 $5,487 1 (d) Community Liaison $200,000 35% $70,000 $270,000 Sub total $786,673 35% $275,336 $1,062,009 3.7% 2. Investigation and Design 2 (a) Investigation and Design $1,082,305 45% $487,037 $1,569,342 2 (b) Project Management Services $81,173 45% $36,528 $117,701 2 (c) Client Representation $8,117 45% $3,653 $11,770 Sub total $1,171,595 45% $527,218 $1,698,813 5.9% 3. Property Acquisitions 3 (a) Acquire Property 60% $0 $0 N.A. 3 (b) Professional Services for Property 60% $0 $0 3 (c) Project Management Services 60% $0 $0 3 (d) Client Representation 60% $0 $0 Sub total $0 $0 $0 0.0% 4. Public Utility Adjustments

4 (a) Adjust Utilities 60% $0 $0 Included in Infrastructure

4 (b) Project Management Services 60% $0 $0 4 (c) Client Representation 30% $0 $0 Sub total $0 0% $0 $0 0.0% 5. Construction 5 (a) Infrastructure $16,177,951 45% $7,270,954 $23,448,905 5 (b) PAI Insurance $88,979 45% $39,990 $128,969 5 ( c) Primary Testing $177,957 45% $79,980 $257,938 5 (d) Project Management Services $1,213,346 45% $545,322 $1,758,668 5 (e) Client Representation $121,335 45% $54,532 $175,867 Sub total $17,779,568 45% $7,990,779 $25,770,347 89.5% 6. Handover 6 (a) Refurbish old route % $ $ 6 (b) Project data and performance 186046 30% $55,814 $241,860 6 (c) Project Management Services 13953 30% $4,186 $18,140 6 (d) Client Representation 1395 30% $419 $1,814 Sub total $201,395 30% $60,419 $261,814 0.9% TOTAL $19,939,232 44% $8,853,751 $28,792,983 100% Project Management $1,349,120 $600,262 $1,949,382 6.8% Client Representation $134,912 $60,026 $194,938 Reality checks: Document No: RTA-CSD-PMS-PR-P-95-A1 Issue 1.1 Page 1of 1


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Project: VICTORIA BRIDGE FOOTWAY

Prepared by: Mark Raven

CONCEPT DESIGN OPTION : CONSTRUCT USING BARGES

Rev:A Oct 2010

Project No: 06/065 Estimate Stage: Concept Item Estimate

(2010 $) Contingency

Estimate % of Total

Comments

(excluding % Amount Estimate contingency)

(including contingency)

1. Project Development

1 (a) Route/Concept/EIS or REF 541,533 35% $189,537 $731,069

1 (b) Project Management Services $40,615 35% $14,215 $54,830

1 (c) Client Representation $4,061 35% $1,422 $5,483

1 (d) Community Liason $80,000 35% $28,000 $108,000

Sub total $666,209 35% $233,173 $899,383 2.8%

2. Investigation and Design

2 (a) Investigation and Design $1,083,066 45% $487,380 $1,570,445

2 (b) Project Management Services $81,230 45% $36,553 $117,783

2 (c) Client Representation $8,123 45% $3,655 $11,778

Sub total $1,172,419 45% $527,588 $1,700,007 5.3%

3. Property Acquisitions

3 (a) Acquire Property 60% $0 $0 N.A. 3 (b) Professional Services for Property 60% $0 $0

3 (c) Project Management Services 60% $0 $0

3 (d) Client Representation 60% $0 $0

Sub total $0 $0 $0 0.0%

4. Public Utility Adjustments

4 (a) Adjust Utilities 60% $0 $0 Included in Infrastructure

4 (b) Project Management Services 60% $0 $0

4 (c) Client Representation 30% $0 $0

Sub total $0 0% $0 $0 0.0%

5. Construction

5 (a) Infrastructure $18,051,097 46% $8,346,616 $26,397,713

5 (b) PAI Insurance $99,281 46% $45,906 $145,187

5 ( c) Primary Testing $180,511 46% $83,466 $263,977

5 (d) Project Management Services $1,353,832 46% $625,996 $1,979,828


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5 (e) Client Representation $135,383 46% $62,600 $197,983

Sub total $19,820,104 46% $9,164,584 $28,984,689 91.0%

6. Handover

6 (a) Refurbish old route % $ $

6 (b) Project data and performance 180511 30% $54,153 $234,664

6 (c) Project Management Services 13538 30% $4,061 $17,600

6 (d) Client Representation 1354 30% $406 $1,760

Sub total $195,403 30% $58,621 $254,024 0.8%

TOTAL $21,854,136 46% $9,983,967 $31,838,103 100%

Project Management $1,489,215 $680,826 $2,170,042 6.8%

Client Representation $148,922 $68,083 $217,004

Reality checks: Document No: RTA-CSD-PMS-PR-P-95-A1 Issue 1.1 Page 1of 1

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