UTREDNING AV FLYTEBRU OVER BJØRNAFJORDEN … NOT-MO-003 – METHOD STATEMENT, NAVIGATION CHANNEL IN...

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K:\03 PROJECTS\0880-0001 COWI Design Bjornafjorden\02 Project Folder\Engineering\Fabrication and Installation\Marine operations\Bridge Main bridge South\Delivered report\Method statement

South_maindoc.docx

ADRESSE COWI AS

Grensev. 88

Postboks 6412 Etterstad

0605 Oslo

TLF +47 02694

WWW cowi.no

OPPDRAGSNR. A058266

DOKUMENTNR. NOT – MO- 003

VERSJON 1.0

UTGIVELSESDATO 15.02.2016

UTARBEIDET Rolf Åge Vågen

KONTROLLERT Karl C. Strømsem

GODKJENT Sverre Wiborg

UTREDNING AV FLYTEBRU OVER BJØRNAFJORDEN

NOT-MO-003 - METHOD STATEMENT, BRIDGE WITH

NAVIGATION CHANNEL IN SOUTH

NOT-MO-003 – METHOD STATEMENT, NAVIGATION CHANNEL IN SOUTH


South_maindoc.docx

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INNHOLD

1 Summary 4

2 Introduction 5

3 Assumptions for base case method 6

4 Pontoons 7

4.1 Pontoon dimensions 7

4.2 Construction site for pontoons 7

4.3 Construction of pontoons 9

4.4 Towing of pontoons 12

4.5 Storage of pontoons 14

5 Abutment at Flua 15

5.1 Layout 16

5.2 Temporary quay 16

5.3 Towing 18

5.4 Installation 21

6 Bridge girder 23

6.1 General 23

7 Assembly of floating bridge 25

7.1 Assembly location 25

7.2 Assembly method floating bridge 26

7.3 Temporary mooring system at storage location 28

8 Building of stayed cable bridge 37

9 Establishing bridge girder at Flua 47

9.1 Method 47

9.2 Ballasting during installation of Floating bridge 49

10 Towing of floating bridge 51

10.1 Design requirements 51

10.2 Holding capacity 52

10.3 Maneuvering in narrow waters 54

10.4 Adequate speed 55

11 Installation of floating bridge 57

11.1 Operation description 57

11.2 Installation and towing weather criteria and durations 64

11.3 Straight bridge installation 66



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12 Installation of permanent mooring system (Straight bridge) 67

13 Progress plan 71

13.1 Overall project 71

13.2 Critical activities: 71

13.3 Non-critical activities: 72

13.4 Detailed estimation of critical activity duration: 72

14 References 75

Appendix A – Vessel and equipment specification 76

Appendix B – Required vessels and equipment – quantities 77

Appendix C – Brief stability check for pontoons 78


K:\03 PROJECTS\0880-0001 COWI Design Bjornafjorden\02 Project Folder\Engineering\Fabrication and Installation\Marine operations\Bridge Main bridge South\Delivered report\Method statement South_maindoc.docx

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1 Summary

At this stage in the project no showstoppers are identified for the construction and installation of the two floating bridge alternatives. However, more detailing is required at later stages in order to confirm and optimize the presented methods. The bridge design has been developed continuously throughout the project phase. The construction and installation methods are developed in parallel with the bridge design, but there may be cases where the method is not entirely representing the latest design. The presented methods are considered applicable nevertheless. As a base case, the bridge girders will be pre-fabricated in 20 m lengths and transported to a specified quay in Norway. There the bridge girders is welded together to longer sections before the final section is connected to the pontoons. A 20 m element weighs 200 t (each road part is taken a separate element of the cross section) for the curved bridge and 300 t for the straight bridge. The reason for choosing 20 m elements is that these weights can be handled using standard cranes and equipment at the assembly and construction sites. The pontoons are proposed constructed in a dry dock. On request from the Client, Hanøytangen is currently used as a base case. This is an existing facility with the required dimensions. Due to the size of the pontoons it is necessary to have 10 construction cycles to complete all pontoons in addition to the abutment at Flua. There are however, several possible solutions that could lower the construction time, and give more flexibility to the project as well as reduce construction time and cost, e.g. building on submersible barges and larger production sites outside of Norway. To minimize the dry dock time it is proposed to complete the pontoons in a floating modus. The abutment at Flua will be started in the in the dry dock, and completed floating. The depth of the abutment (40 m) makes it difficult to perform all work inside a dock. With the current base case, the dock capacity is critical. It is therefore beneficial to float out the abutment as early as reasonable practical to free up capacity for the construction of the pontoons. For previous projects for the offshore industry, a deep-water quay has been established at Hanøytangen. The same quay is proposed established for the floating construction phase of the abutment. The abutment will be built early in the project to avoid risk of delay to the installation of the bridge. The major part of the floating bridge length will be assembled by skidding the bridge girders directly onto the pontoons. This will be done from a floating quay established using standard North Sea barges. These barges could either be bought second hand, or rented for the duration of the assembly period. For the transition section of the bridge (between the lower part and the stay cable bridge) a Heavy Lift Vessel will be required to carry out four (4) lifts. The stay cable bridge tower will be constructed using standard slip forming. For the parts of the stay cable bridge that are suspended above the water (North of the tower) the cantilever building method will be applied. A framework will temporarily support the parts that are above land until the stay cables are connected. The floating part of the bridge will for both alternatives be installed as one section. The towing operation and positioning of the bridge will be carried out using anchor handling vessels and tugs. A guiding system will together with winches control the motions of the bridge ends during installation. When in position, the floating bridge will temporary be secured to Flua and the stay cable bridge by bolted connections. The bolted connections will keep the bridge parts together until the permanent connection (welding) is established. For the straight bridge it is possible to use the pre-installed mooring lines during installation to provide additional guidance and support. Estimates of expected delay are calculated by computer simulation of the weather sensitive operations. The following operations are investigated: Towing of pontoons, towing of the abutment for Flua, installation of the abutment, assembly using HLV (Heavy Lift Vessel) and installation of the complete floating bridge. The simulations show that some delay may be expected, however due to the relatively short duration of the operations it is possible to get a weather window for most operations throughout the whole year. The basis for these simulations is time series of wind received from the Client.



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2 Introduction

This report covers the methods for construction and installation of the bridge over Bjørnafjorden. Both the

curved bridge and the straight bridge are included in the report. However, as a basis the method is

explained using the curved bridge, as this alternative is seen as most challenging in the installation

phases due to its size and layout. Any special considerations for the straight bridge are mentioned

throughout the report if deemed necessary.



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3 Assumptions for base case method

Main assumptions for the method statement are as follows;

- Permissions for proposed locations are in place, and the facilities have the required capacity.

Most of the vessels are taken from the spot market. There are however operations that requires

that vessels are reserved in due time before the operations. This is particularly relevant for parts

of the assembly operation using Heavy Lift Vessels (HLV) and the towing and installation

operations (large number of towing vessels required).

- Building of pontoons and abutment at Flua is carried out at Hanøytangen Askøy, Norway.

- Assembly of floating bridge is carried out in Eikelandsfjorden. In this fjord, a storage location and

an assembly quay will be established.

- The bridge girder is ordered in 20 m lengths, and delivered to assembly quays and to the stay

cable bridge building location as required. I.e. no storage location for steelwork is planned for at

this stage.

- Pontoons are stored in a fjord close to Eikelandsfjorden between construction and assembly.

Figure 3-1 illustrates the different locations specified above.

Figure 3-1: Overview of construction and assembly locations.



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4 Pontoons

4.1 Pontoon dimensions

The pontoons for the floating part of the bridge will be made of concrete. The pontoons for the straight

bridge and curved bridge are identical. There are 19 pontoons on the curved bridge and 18 pontoons on

the straight bridge.

An illustration of the pontoons together with the main dimensions are shown in Figure 4-1 below.

The mass of each pontoons is approximately 18 000 t.

Figure 4-1: Pontoons with main dimensions

4.2 Construction site for pontoons

At this stage it is planned to build the pontoons in Norway. However, at a later stage, it could be that it is

reasonable to build the pontoons outside of Norway (e.g. Denmark, UK, France, Portugal, and Croatia) as

there are dry docks in these countries with larger capacities. In that way it could be possible to lower the

construction time significantly compared to the alternative presented in this report. A longer tow or

transportation on heavy lift vessels, and the risk of waiting on weather during the towing operation must

be accounted for in the progress plan. It all comes down to a cost-benefit evaluation. Approximately 20

days of towing must be accounted for from Lisbon in Portugal to Bergen Norway (with 3 knots speed).

Building of pontoons and steelwork are probably both on the critical path, and must be seen in relation to

each other in the planning phase.

It is not many alternatives when it comes to existing facilities in Norway. The only dry dock that is large

enough for several pontoons is Hanøytangen outside of Bergen (there are dry docks that can facilitate

one pontoon, but these are disregarded in this report). The dimensions of the dry dock is 125 m x 125 m,

with a depth of 17 m. Throughout this report Hanøytangen is used as a base case, but some alternative

constructions facilities are discussed below.



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Lutelandet is a possible location, with an area that is already included in a zoning plan. The industrial site

3-4 hours north of Bergen has future plans for a dock with the dimensions 362 m x 132 m, and with a

depth of 21 m. As per now, no definite plans for building of the dock is in place. Figure 4-2 illustrates the

future plans for the Lutelandet industrial area.

Figure 4-2: Lutelandet industrial site (future plans). Photo: www.lutelandet.no/

Another alternative is to build the pontoons on a semisubmersible barge. With the current dimensions of

the pontoons (and especially the breadth of 38 m) there are a limited number of barges that are large

enough to facilitate the pontoons. In Figure 4-3 an example of a semisubmersible barge from BOA with a

width of 38 m is shown. This barge would be able to facilitate two pontoons in one construction cycle.

Using a barge could be a good complementary solution if the building time of the pontoons shows to be

important.

Figure 4-3: BOABARGE 37, semisubmersible barge. Photo: http://www.boa.no/Default.aspx?ID=303

http://www.lutelandet.no/

http://www.boa.no/Default.aspx?ID=303



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There are areas that historically have been used for construction of large concrete Gravity Based

Structures (GBS) for the offshore industry. An example of such an area is Åndalsnes, which was used to

build two GBS platforms in the 1970s. This location is basically a shallow area that are enclosed from the

sea using a filling, and further drained. A challenge with the Bjørnafjord project compared to the GBS

projects is that the construction cycle off the pontoons will be repeated many times, due to the number of

pontoons. It is therefore beneficial to have a relatively standardized system, which make the filling and

discharging time as short as possible. The alternative of using a shallow non-established area with a

filling is therefore disregarded in this report.

Figure 4-4: Construction of GBS platform Frigg in Åndalsnes. Photo: Norsk Oljemuseum.

4.3 Construction of pontoons

A layout of the pontoons in Hanøytangen is illustrated in Figure 4-5. With 19 pontoons for the curved

bridge, 10 construction cycles is required to complete the pontoons. The straight bridge requires 9

construction cycles. A mean duration of the cycles is expected to be around 5 months with 3 months is

inside the dock.

Bridge alternative

Construction cycles

Construction time all pontoons

Dry dock total duration.

Curved bridge 10 (Including Flua abutment)

10 x 5 months = 50 months 10 x 3 months = 30 months

Straight bridge 9 (Excluding Flua abutment)

9 x 5 months = 45 months 9 x 3 months = 27 months



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Figure 4-5: Overview of construction cycles for the curved bridge.

Figure 4-6: Illustration of pontoons in Hanøytangen dry dock.

The construction phases of the pontoons are illustrated in Figure 4-7. The first phase is to cast the bottom

plate. Then the inner and outer walls are made. These two phases are carried out inside the dock before

the dock is flooded and the pontoons moved outside.



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Outside of the dock, the pontoons will be moored to a quay and the top plate is cast. Hanøytangen has

two quays with depths of 17 m and 20m that can facilitate one pontoon each.

The last operation for the pontoons is to mount the columns. These are lifted in place by a shore-based

crane for lifts below 400 t.

For lifts that are above 400 t, a floating crane will be used. This only applies for the straight bridge.

Curved bridge (10 t/m) Straight bridge (14 t/m)

No. of columns Column weight No. of columns Column weight

28 75 t 13 105 t

2 115 t 1 161 t

2 195 t 1 273 t

2 275 t 1 385 t

2 345 t 1 483 t

2 400 t 1 560 t

Figure 4-7: Construction phases

A suggested layout for the mooring of the pontoon while along the quay side is shown in Figure 4-8.



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Figure 4-8: Mooring of pontoon along quay side.

4.4 Towing of pontoons

When the pontoons are completed at the Yard, they are towed to a storage location. This storage location

will be in vicinity to the location where the bridge girder and the pontoons will be assembled.

The towing resistance for towing of one pontoon can be obtained in a simplified way by calculating the

drag force on the submerged projected area;

𝐹𝐷 = 1

2∗ 𝐶𝐷 ∗ 𝐴 ∗ 𝜌 ∗ 𝑣2

Where;

𝐹𝐷 = 𝐷𝑟𝑎𝑔 𝑓𝑜𝑟𝑐𝑒 [𝑁]

𝐶𝐷 = 𝐷𝑟𝑎𝑔 𝑐𝑜𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡 [−]

𝐴 = 𝑃𝑟𝑜𝑗𝑒𝑐𝑡𝑒𝑑 𝑎𝑟𝑒𝑎 [𝑚2]

𝑣 = 𝑇𝑜𝑤𝑖𝑛𝑔 𝑠𝑝𝑒𝑒𝑑 [𝑚

𝑠]

For a towing speed of 3 knots (1.5 m/s), and a drag factor of 1.6 the drag force of the pontoon will be

approximately 50 t. A large tug (bollard pull of approximately 100 t) will have sufficient capacity for towing.

In addition, a small harbor tug with a bollard pull of <50 t is required for assistance with the mooring and

unmooring operations.



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Figure 4-9: Towing route from construction site to storage/assembly location.

The towing distance from Hanøytangen is approximately 165 km for the towing route illustrated in Figure

4-9 (the inshore towing route presented for the abutment in section 5.3 is also relevant). A mean towing

velocity of 3 knots gives a duration of 30 hrs.

A weather criterion for the pontoon tow is showed in table below. At this stage, the weather criteria is

based on experience from comparable operations. For the actual tow, safe havens must specified prior to

towing commencement.

Operation Weather criteria Planned

operation

duration

Contingency

time

Weather

window

Offshore towing

operation

Wind: 20 m/s

Wave: 2.5 m Hs*

30 hrs. 15 hrs. 45 hrs.

*- Wave conditions estimated from Beaufort scale based on received wind data.

By using Global Maritimes marine operation simulation software GMOPSIM, the expected weather delay

for the operation is calculated and shown in the figure and table below (the presented value indicates the

expected duration for waiting on forecasted weather window). Wind conditions at Marstein is used as

input to these simulations, ref /4/. See Figure 4-10.



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Figure 4-10: Expected monthly delay for pontoon towing (hours) due to weather from GMOPSIM.

4.5 Storage of pontoons

The pontoons will be stored in a sheltered area close to the assembly site. It is not necessary with a lot of

preparations for the storage location. However a few bollards and anchors must be installed prior to

storage of pontoons. The pontoons are moored together, with Yokohama fenders between in order to

avoid damage to the pontoons. This is a normal procedure for storage of barges, as illustrated in Figure

4-11.



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Figure 4-11: Storage of barges close to land.

5 Abutment at Flua

The abutment at Flua will be built inside a dry dock and then floated out and completed when floating.

The reason for this is that there are no dry docks with sufficient depth for completing the abutment and

still be able to float it out. It is assumed that after 3 months production inside the dock, the abutment will

be floated out with a draft of approximately 10 m. The draft will increase to 18.5 m during the completion

(without top plate).

The abutment will be towed to Bjørnafjorden without the top plate, as the abutment will be permanently

ballasted after it is positioned on the shallow area Flua.

The top plate is cast including all of the connections that will make the connection between the bridge

girder and the abutment.



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5.1 Layout

Figure 5-1: The abutment at Flua (Curved bridge). Extract from drawing K92405.

5.2 Temporary quay

At Hanøytangen a temporary deep-water quay must be established in order to accommodate the

Abutment at Flua. This has previously been done, e.g. for the building of the Troll B platform, as shown in

Figure 5-2 and Figure 5-3.

The quay is established using barges that are fixed to bottom fixed tripods. The available depth at this

quay is 60-100 m, and the abutment will be connected to the barges using standard mooring equipment.

Another lay out than for the Troll platform will be used for building the abutment. This is used in order to

give access on all sides of the abutment during construction. A sketch of this layout is shown in Figure

5-4.



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Figure 5-2: Project based deep water quay at Hanøytangen.

Photo: http://www.bergen-group.no/page/6474/Deepwater_Facility

Figure 5-3: Project based deep water quay, Hanøytangen.

Photo: http://www.bergen-group.no/page/6474/Deepwater_Facility

http://www.bergen-group.no/page/6474/Deepwater_Facility

http://www.bergen-group.no/page/6474/Deepwater_Facility



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Figure 5-4: Temporary quay using three standard North Sea barges.

A suggested mooring layout during building along the temporary quay is shown in Figure 5-5.

Figure 5-5: Suggested mooring layout during building at temporary quay.

5.3 Towing

The abutment will be towed by using 3 x towing vessels from Hanøytangen to Bjørnafjorden. The base

case is to use 2x AHVs and one tug. See Figure 5-6.



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Figure 5-6: Towing configuration for abutment

From Hanøytangen there are two possible towing routes to Bjørnafjorden. The first alternative is to tow

the abutment on the west side of Sotra, while the other is an inshore tow under the Sotra Bridge and

through Vatlestraumen. The two alternative routes are shown in Figure 5-7.

Figure 5-7: Towing route alternatives from Hanøytangen to Bjørnafjorden.

The first alternative is an offshore tow that requires a sufficient weather window, while the inner towing

route is sheltered. However, the inner towing route has shallow and narrow areas with occasionally

significant current that could create difficulties for maneuvering. The base case route is therefore the

offshore alternative.



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A study of the expected weather induced delay is carried out. This study show that the operation can be

carried out all year around, but with some expected delay. The building of the abutment at Flua is planned

carried out early in the project, and waiting on weather is not seen as critical for the overall project

duration or for costs.

Same towing distance (165 km) and towing speed (3 knots) as for the pontoons are used to obtain

expected delay for the towing operation. However, the abutment at Flua has a stricter weather criteria.

See table below.


operation

duration

Contingency

time

Weather

window

Offshore towing

operation

Wind: 15 m/s

Wave: 1.5 m Hs*

30 hrs. 15 hrs. 45 hrs.

*- Wave conditions estimated from Beaufort scale based on received wind data.

By using GMOPSIM, the expected weather delay for the operation is obtained. Wind conditions at

Marstein is used for these simulations, ref /4/. See Figure 5-8.

Figure 5-8: Expected monthly delay for pontoon towing (hours) due to weather from GMOPSIM.



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5.4 Installation

The area where the abutment will be installed will have to be prepared prior to installation. For details of

the preparations, including leveling and ground works reference is made to ref. /1/. The installation of the

abutment at Flua is illustrated in Figure 5-9.

At this stage, the Flua abutment has been positioned at a location that is assumed to give as little ground

works as possible. At a later stage of the project, a study of the optimal position should be carried out.

Figure 5-9: The Flua area leveled and ready for installation of the abutment.

When the abutment is towed in position, it will be held in place by 4 vessels (same as towing vessels plus

an additional tug) before the lowering of the abutment is initiated. Seawater will be filled, using pre-

installed pumps in specified compartments to allow lowering the abutment in a controlled way. It could be

necessary to use guiding pins in order to position the abutment on the ground if the installation tolerances

are strict. The installation criteria must be decided at a later stage when more information of Flua is

available. The duration of this operation is estimated to be 12 hrs.

When the abutment is positioned within the tolerances on the ground, grouting using grouting pipes in the

abutment will be carried out.

Formwork is established and the top plate will be cast. A barge will be used to transport the concrete from

shore. The connections between the bridge girder and the abutment (shear studs) will be cast into the

abutment during the construction of the top plate.


operation

duration

Contingency

time

Weather

window

Installation of abutment

at Flua

Wind: 10 m/s

Wave: 0.5 m Hs*

12 hrs. 12 hrs. 24 hrs.

*- No wave conditions used in simulations (Beaufort scale is not valid inshore).

By using GMOPSIM, the expected weather delay for the operation is calculated and shown in the figure

and table overleaf. Wind conditions at Bjørnafjorden is used for these simulations, ref. /4/. See Figure

5-10.



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Figure 5-10: Expected monthly delay for Flua installation (hours) due to weather from GMOPSIM.



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6 Bridge girder

6.1 General

The production of the steel elements should be detailed out at a later stage in the project. In a building

phase, the steel production location is most likely subject to the entrepreneur’s decision. It is therefore

difficult to cover all alternatives in this report at the present stage. The aim in this report is to identify a

possible solution that does not restrict the choice of yard and to prove feasibility. The production location

will also decide the suitable pre-fabrication length for transportation. Delivery to installation / assembly

location should be included in the production cost regardless of building location.

At this stage, it is assumed that the bridge girder is ordered in pre-defined lengths and delivered to the

stay cable building location and the floating bridge assembly location. 20 m lengths are used as base

case, as these are seen as flexible regarding type of transportation. It is also a method that is feasible for

production locations all around the world. 20 m elements are possible to handle using standard

equipment after arrival to building and assembly locations. A production close to the bridge location will

allow for pre-fabrication of larger elements as the transportation will be less complex. The bridge girder

may for this alternative be transported directly on the pontoons.

Storage is an issue that must be looked upon in relation to the production location. If the bridge girder is

pre-fabricated in the vicinity of Bjørnafjorden, most of the storage issues can be disregarded. However, if

the steel is pre-fabricated e.g. in Asia a storage location should be established as a buffer in order to

lower the impact of delay during transportation.

The weight of the steel work varies for different positions along the bridge, in order to handle the local

forces e.g. above the columns. For a full overview of the variation, reference is made to ref /5/ and ref /6/.

The weight of the bridge girder will be lower in the installation phase than in the permanent phase as

tarmac and other final outfitting will be installed after the bridge is installed. In Table 6-1 some average

values are presented in the Table 6-1.

Curved bridge Straight bridge

Element

length

Weight Element

length

Weight

Bridge girder

elements floating

bridge

20 m 440 t (220 t if

cross section is

divided in two)

20 m 320 t

Stay cable bridge 20 m 400 t (200 if

cross section is

divided in two)

20 m 260 t

Table 6-1: Unit weights for bridge girder elements

Figure 6-1 sums up the process of combining 20 m elements into bridge sections, and the bridge sections

to the complete bridge length from the abutment in South to Flua.



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Figure 6-1: Flow chart for bridge girder elements



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7 Assembly of floating bridge

Assembly of the floating bridge is the operation where the pontoons and bridge girder are mounted

together. The floating bridge will in the assembly operations be assembled to one length of approximately

3600 m that is towed to Bjørnafjorden for installation.

7.1 Assembly location

For the assembly of the bridge, a sheltered location is required in order to lower the down time due to bad

weather during the assembly phase. At this stage, Eikelandsfjorden is chosen as location for the

assembly. Figure 7-1 illustrates the location of the assembly location together with the final bridge

location.

If more detailed environmental data is available at a later stage of the project, it could be that other

locations that are closer to the bridge location prove to be feasible for this purpose. This will shorten the

towing distance of the assembled bridge.

Figure 7-1: Assembly location and bridge location.



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Figure 7-2: Overview of Eikelandsfjorden during assembly

7.2 Assembly method floating bridge

For the assembly of the floating bridge two different methods will be used. One method for the lower part

and one method for the higher/transition part. For the lower part of the bridge the bridge sections will be

skidded directly onto the pontoons. Due to the increasing height it is difficult to use the same method on

the higher/transition part. The bridge girder for this part will be lifted in place using a heavy lift vessel.

These two methods are further described in the following. Figure 7-3 shows for which part the two

different methods apply.

Figure 7-3: Assembly of the bridge. Skidding method for the lower part, and lifting method for higher part.

The parts that are built using the skidding method will be assembled to bridge sections with lengths

varying from 600 m to 800 m at the assembly quay. Further, the bridge sections will be moved to the

storage location where they are assembled with the rest of the bridge. Figure 7-4 illustrates the different

bridge sections that will be transported and mounted together at the storage location. It should be noted

that bridge section 1 will not be transported as one element, but be put together by lifting 4 elements,

each with a length of 200 m. The method for mounting bridge section 1- 5 is described in chapter 7.3.1

and 7.3.2 .



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Figure 7-4: Illustration of bridge section numbering with corresponding assembly method.

Figure 7-5 show the sequence of the mounting operations at the storage location.

Figure 7-5: Main assembly steps in Eikelandsfjorden.



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7.3 Temporary mooring system at storage location

Prior to the assembly at the storage location, a mooring system will be pre-laid. This system will be a

combination of mooring lines to bollards at shore, and anchors at the seabed. The mooring system will

designed to withstand a 100-year condition due to the duration of the assembly operation. It is however

expected that standard mooring equipment can be used. This is equipment that can be rented from

several companies.

The mooring lines to the seabed will typically consist of;

- 15 t stevpris/stevshark anchors

- 76 mm mooring chain (to avoid that wire or fibre rope are damaged in contact with sea bed)

- Mooring wire / fibre rope

Shore mooring lines will consist of;

- Shore bollard

- 76 mm mooring chain (to avoid that wire or fibre rope are damaged in contact with sea bed)

- Mooring wire / fibre rope

The top termination of the mooring system on to the bridge must be determined after the mooring system

is designed and will be dependent on the required pre-tension in the mooring system. For lower pre-

tensions, it should be possible to tension the mooring lines only using the installation vessel. If a higher

pre-tension is required it might be necessary to use tension barges or hydraulic jacks etc. At this stage, it

is assumed that tensioning using towing vessels is feasible, as the stiffness requirement in this mooring

system is believed to be low.

A typical layout for the temporary mooring system is illustrated in Figure 7-6 and Figure 7-7.



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Figure 7-6: Example of temporary mooring system during assembly.

Figure 7-7: Mooring system overview.

7.3.1 Assembly method lower parts (Bridge section 2, 3, 4 & 5)

The operation described in this section is carried out on the assembly quay. This location is illustrated in

Figure 7-2.



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The quay that will be used for this part of the operation will be established using 4 standard North Sea

barges. It is important that a stiff connection is established between the barges. This will give a quay with

a size of approximately 120 x 90 m. The benefit of using barges is that the quay will follow the tidal

variation together with the pontoon the bridge girder is resting on. The quay will be kept in place using

piles and/or mooring lines to seabed.

The bridge girder elements will be transported to the assembly quay either on a barge or on a

transportation vessel. As a base case, the elements have a length of approximately 20 m. The size of the

elements makes it possible for a standard mobile crane with approximately 200 t and 400 t capacity (for

curved bridge and straight bridge respectively) to lift each of the bridge girder elements onto the quay.

The skidding will be performed using hydraulic jacks that pushes the bridge girder from the quay and onto

the pontoons.

This method does not require a large quay area, however it is necessary to get sufficient height to be able

to skid the bridge girder on to the pontoons. This height is obtained by setting up a framework on the

barges. The required height for the framework is approximately 7.5 m. This includes all grillages, skidding

beams etc., see Figure 7-8.

Figure 7-8: Framework on assembly quay to achieve correct height.

The elements will be lined up and welded together before they are skidded onto the pontoon. For the

curved bridge each of the bridge girder elements will be lifted separately. When the bridge girder is

skidded onto the pontoon, there will be available space on the quay and more elements are added. This

is illustrated in Figure 7-9.



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Figure 7-9: Top view of quay for assembly step 1 and 2.

This cycle is repeated until another pontoon is added to the assembly. The pontoon will be ballasted

down, and de-ballasted after it is positioned under the bridge girder. In order to keep control of the

cantilever during building, a mooring system will have to be pre-laid outside of the quay area and hooked

up to the bridge when the cantilever is getting longer. It is assumed that the mooring lines can be

tensioned without any special equipment. This is illustrated in step 4 in Figure 7-10.



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Figure 7-10: Assembly step 3 and 4. Cantilever supported by temporary moorings

When a length of approximately 600 m to 800 m is welded together and floated out onto the pontoons (3-

4 pontoons), the assembled section is towed to the storage location and hooked up to the pre-laid

mooring system. Any overhang on of the bridge girder is supported by a barge, until the bridge section is

connected with the rest of the bridge. One barge can be re-used for the three sections that require

additional support (bridge section 3, 4 & 5, see Figure 7-4).

Figure 7-11: Overhang on bridge section supported by a barge.



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7.3.2 Assembly method higher parts (Bridge section 1)

The method that is described herein, was used during building of the Sundsvall Bridge in Sweden. This is

shown in Figure 7-12 below. There are some differences between the method proposed here and the

method used for the Sundsvall Bridge. The major difference is that the Sundsvall Bridge has bottom fixed

columns/pylons. For the method we propose the crane vessel will stay stationary with the floating bridge

hanging from the hook while the pontoon is towed underneath the bridge girder. For the Sundsvall Bridge

the crane vessel had to move in position with the bridge hanging in the hook. .

Figure 7-12: Building of the Sundsvall Bridge. Photo: http://max-

boegl.de/fileadmin/content/ueber_max_boegl/01_geschichte/2013_10.jpg

Using our proposed method required that the bridge girder is assembled into 200 m lengths before it is

connected on to the pontoons. See Figure 7-13. This is done in order to minimize the number of HLV lifts.

In total 4 elements will be lifted by HLV, and these elements will be assembled from 20 m lengths to 200

m lengths on a quay, or ordered in 200 m lengths from the production yard.

One proposed location for the assembly of the 200 m elements is at Eldøyane/Stord. It is beneficial to

keep this operation, separate from the skidding quay in order to make the skidding as effective as

possible. The assembly to 200 m elements and lifting in place by HLV is given large flexibility timewise in

order to have a flexible schedule when entering the heavy lift market to be able to minimize costs.

The 200 m elements can be loaded onto the barge using multiwheelers/SPMTs. The multiwheelers are

frequently used in load-out operations in the offshore industry and can be assembled as required in order

to obtain the required lifting capacity.

http://max-boegl.de/fileadmin/content/ueber_max_boegl/01_geschichte/2013_10.jpg

http://max-boegl.de/fileadmin/content/ueber_max_boegl/01_geschichte/2013_10.jpg



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Figure 7-13: Assembly from 20 m to 200 m bridge elements.

The lifting of the 200 m bridge girder elements will be done using a Heavy lift vessel in one end, and

strand jacks / deck erection crane that are mounted on Bridge section 2 in the other.

The 200 m bridge girder element is transported to the storage location on a large barge. The bridge

girder, lifting vessel and deck erection crane is illustrated in Figure 7-14.

Figure 7-14: Lifting of 200 m bridge girder element.

To allow for mounting of the pontoon, the bridge girder will be lifted slightly above the “in-place height”. A

small tug will be used for the positioning of the pontoon. See Figure 7-15.

The bridge girder is further lowered onto the pontoon and the pontoon is being de-ballasted in order to

carry the weight of the bridge girder. Conical guide pins will make sure the bridge girder and the column is

positioned correctly during the mounting.



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Figure 7-15: Positioning of pontoon under bridge girder during assembly.

The four lifts that will be carried out for Bridge section 1 are shown below. The strand jacks will be moved

along the bridge preparing for the next lift. See Figure 7-16.

Figure 7-16: Heavy lifts during assembly.

In this report we illustrate the procedure using the crane vessel Rambiz 3000 (lifting capacity 3300 t, and

lifting height of 79 m). See Figure 7-17. There are several heavy lift vessels that could be used for these

lifts. Another alternative, if the HLV market is tight, is to use a lifting tower on a barge (This method was

also used during building parts of the Sundsvall Bridge). The lifting weight of the bridge girder elements is

approximately 4600 ton (23 t/m x 200m). The weight will be divided between the strand jacks on the

bridge and the crane vessel. A capacity between 2500 t and 3000 t is therefore required (including a

margin for skewness and dynamic amplification during lifting).

On the bridge side, number of strand jacks are chosen based on the lifting weight. The capacity for each

strand jack is approximately 650 t, which means that approximately 5 strand jacks are required for the lift.



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Figure 7-17: Crane vessel Rambiz used for lifting of bridge girder on the Vasco da Gama bridge. Photo: http://www.scaldis-

smc.com/en-GB/civil-construction-works/26/

If there is a limited availability of crane vessels/lifting towers the time of building, an alternative is to split

the lifted bridge girders into smaller parts and support the overhang by a temporary pontoon. Selecting

this solution will depend on the cost of the various options available at the time of construction.


operation

duration

Contingency

time

Weather

window

Heavy lift operation Wind: 12 m/s

Wave: 0.5 m Hs*

24 hrs. 24 hrs. 48 hrs.


Using GMOPSIM, the expected weather delay for the operation is calculated and shown in the table and

figure overleaf. Wind conditions at Bjørnafjorden is used for these simulations, ref. /4/.

http://www.scaldis-smc.com/en-GB/civil-construction-works/26/

http://www.scaldis-smc.com/en-GB/civil-construction-works/26/



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Figure 7-18: Expected monthly delay for heavy lift operations (hrs.) due to weather from GMOPSIM

8 Building of stayed cable bridge

The tower of the stay cable bridge is located on Svarvhellaholmen and the abutment is located on

Reksteren. The tower foundation will be made first and then the tower will be slip formed. In parallel the

abutment on land will be constructed. Figure 8-1 illustrates the abutment and the tower after completion.



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Figure 8-1: Abutment in South and the tower at Svarvhellaholmen is established.

In order to build the section of the stay cable bridge that passes over land, a framework is set up. This

framework will mainly be standing on land, but some of the legs will be positioned in water between

Svarvhellaholmen and Reksteren. These legs will either be supported on piles or with an underwater

casting. The framework will support the bridge girder elements during assembly. An illustration of the

framework is shown in Figure 8-2.

Figure 8-2: Framework for stay cable bridge assembly



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Figure 8-3: Work platform / transverse skidding area on framework.

The bridge girder elements are lifted onto the framework using a crane vessel. An element length of 20 m

is seen as a reasonable size as it can easily be handled. An element length of 20 m, gives a lifting weight

is approximately 200 t for the curved bridge (lifting each of the bridge girder boxes for each road section

separately) and 300 t for the straight bridge. Relevant vessels to be used in this operation would be

sheerleg-lifting barges. A lifting weight of 300 t gives reasonable flexibility in selection of lifting vessel

which will keep the cost and availability under control. In this report, the Norwegian crane vessel “Uglen”

is used as an example. The lifting capacity diagram for “Uglen” is shown in Figure 8-4, as seen in the

diagram, the capacity is sufficient for the required lifting height of 55 m.



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Figure 8-4: Extract from Uglen specification. Ref: http://www.jjuc.no/files/UGLEN-brosjyre-rev-april-2015.pdf

The channel between Svarvhellaholmen and Reksteren is relatively narrow and shallow East of the

bridge, therefore in the base case we assume that lifting vessel can only approach and lifting bridge

girder elements from the West side of the bridge, as illustrated in Figure 8-5 and Figure 8-6 with skidding

of the element to the East side of the bridge.

If it is seen as beneficial for cost and schedule reasons to lift larger elements, lifts may be performed from

both sides. The decision of moving in between Svarvhellaholmen and Reksteren with the crane vessel

must be agreed upon by vessel owner and the contractor. Another alternative if is to use a larger sheerleg

crane that can lift larger elements from the western side.

http://www.jjuc.no/files/UGLEN-brosjyre-rev-april-2015.pdf



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Figure 8-5: Lifting of first bridge girder element by HLV Uglen

Figure 8-6: Element is skidded from the West to the East side of the bridge.

As the first element is lifted onto the framework and skidded over to the eastern side of the bridge, the

transverse beams and the second bridge girder elements are lifted onto the work platform and mounted

together. The elements are only partly welded together in order to lower the period where the crane

vessel is required. Figure 8-7 illustrate the lifting of the second bridge girder element.



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Figure 8-7: Lifting of second bridge girder element onto work platform.

After the elements are mounted together, they are skidded along the framework towards the abutment.

This is done with strand jacks that are mounted onto the abutment in South. Figure 8-8 Illustrates parts of

the bridge in place, and another element that are skidded towards the abutment.

Figure 8-8: First bridge girder elements are skidded in place, another element assembled and ready for skidding.

There will be an overhang towards the sea on the North side of the tower. This section will be skidded

using wires that are routed via the tower. See Figure 8-9.



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Figure 8-9: Skidding of element towards North

The last element that is lifted in place, is the element above the working platform. The complete bridge

girder supported by the framework is shown in Figure 8-10.

Figure 8-10: Bridge girder complete and ready

The next phase for the construction is to erect the bridge girder on the North side of the tower. For this

phase, deck erection cranes mounted onto the bridge will be used. Bridge girder elements are lifted

directly from a barge as shown in Figure 8-11. The element length is approximately 20 m. All lifted

elements will have a transverse beam connecting the two bridge girder elements together during the lift.



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Figure 8-11: Lifting of bridge girder elements using deck erection cranes

The building sequence is further illustrated below in Figure 8-12 to Figure 8-16. For each of the elements

that are lifted in place using the deck erection cranes, the stay cable are connected to both the lifted

element and the corresponding part of the stay cable bridge on the south side of the tower. The deck

erection crane is moved after each lift.

Figure 8-12: Stay cable bridge with bridge girder supported by framework.



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Figure 8-13: First bridge girder element North of the tower lifted in and corresponding stay cables connected.

Figure 8-14: Second bridge girder element North of the tower lifted in and corresponding stay cables connected.

Figure 8-15: Third bridge girder element North of the tower lifted in and corresponding stay cables connected.



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Figure 8-16: Complete stay cable bridge. Framework can be removed.



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9 Establishing bridge girder at Flua

9.1 Method

In order to establish the rigid connection on Flua, it is decided to install a shorter bridge element that will

be relatively easy to secure for a temporary phase. It is seen as difficult to handle the forces from the

complete bridge length and at the same time fix the bridge girder to Flua.

It is therefore decided to float in an element with a length of approximately 170 m. This length is chosen

of following reasons;

- Bending moments around the strong axis in design conditions are low at this position (see Figure

9-1). A temporary securing arrangement of the remaining complete floating bridge will therefore

be easier to handle.

- Bending moment about weak axis is as close to the in-place condition as possible (as the

connection is close to the first pontoon)

- Short overhang on the remaining floating bridge when it is installed (connection towards the

floating bridge will be close to the zero-moment position). Any overhang would have to be

supported by a barge, which again will increase the forces on the towed bridge.

Figure 9-1: Bending moments about strong axis at connection points (100 year condition), horizontal axis indicating axis

positions. Flua to the right and stay cable bridge to the left.



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This element will be floated onto the abutment on two barges. One of the barges will only be used in the

installation phase, while the other will remain and act as a temporary pontoon until the rest of the bridge is

installed.

Figure 9-2: Element floated onto abutment on Flua on two barges

During installation the two barges are ballasted down until the element is resting on Flua. It is also

possible to use the tidal variation in the installation phase, but a ballast system will still be required.

Figure 9-3: Element lowered onto the abutment at Flua

The element will be temporary secured on Flua, and the barge closest to Flua will be removed. The

remaining barge will be ballasted to account for tidal variation until the element is fixed on Flua. The tidal

variation is approximately +/- 1 m, which corresponds to a roughly 4000 m^3 ballast that need to be

filled/removed during a 12 hour period. This is not a critical amount of ballast to handle.



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Figure 9-4: One of the pontoons are removed, the other remains at temporary pontoon.

After the element is fixed, the element will sustain the tidal through bending of the weak axis. As

mentioned above, with the present length, this bending will for all practical purposes be similar to the in-

place condition.

9.2 Ballasting during installation of Floating bridge

When the floating bridge is towed to Bjørnafjorden and connected to the element at Flua, the ballast

system on the barge will be used. The element will be kept at mean level in order to avoid any weak axis

bending of the element during installation, as this could involve a rotation of the connection point.

Figure 9-5: Height difference if installing at a high tide situation.

If a high tide situation is experienced during installation, the floating bridge will be ballasted down until the

mean level is obtained. In order to avoid inclination on the installed bridge, at least 3 pontoons will be

ballasted down simultaneously. The ballast system will be able to keep this elevation during installation by

de-ballasting as the water level decreases. In order to ballast the pontoon 1 m, approximately 1700 m^3

of water is required.



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Figure 9-6: Ballasting of pontoons to compensate for high tide

The bridge parts will then be connected by using the temporary connection that is defined in chapter 11.1.

Any minor inclinations will be removed by tensioning these connection points.

The barge is removed, and the cross section is permanently welded together.



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10 Towing of floating bridge

This section describes the towing of the floating bridge from the assembly location in Eikelandsfjorden to

Bjørnafjorden. As a base case, the bridge will be towed in one length. This will be a spectacular tow, but

at this stage it is seen as feasible and also the most effective way of installing the bridge.

The towing route is illustrated in Figure 10-1. The total towing distance is approximately 23 km, or 12.5

nautical miles.

Figure 10-1: Towing route for floating bridge.

10.1 Design requirements

The minimum required towline pulling force shall according to ref /3/ be documented for;

- Holding capacity (stationary condition)

- Maneuvering in narrow waters

- Adequate speed

The different scenarios are presented below.



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10.2 Holding capacity

The holding capacity will ensure that the vessels used in the tow are capable of holding the towed bridge

in position in case deterioration in the weather situation occurs during tow. For holding capacity the

weather conditions presented in Table 10-1 is checked, ref 3, sect 3.6.2.2.

In this case the criteria for unrestricted towing and “all year” environmental data is used in the absence of

seasonal data. The operation will have a weather criteria, and will be planned carried out in the summer

season. For now however, “unrestricted towing criteria” is used due to the high uncertainty in the

operations at this stage. Using unrestricted criteria, we ensure that the bridge is safe in case the towing

and installation duration exceed a weather restricted operational time window.

Holding capacity design criteria

10 year RP wind condition 27.6 m/s (at 10 m height).

1 year RP wave condition Hs = 1.9 m, Tp = 5.6 s

1 year RP current condition + 0.5 m/s

speed over ground

0.5 m/s + 0.5 m/s

Table 10-1: Holding capacity design criteria

The wind forces are estimated from a modified Novaframe model, wave drift forces are estimated from

Orcaflex and forces from current are calculated from drag forces (drag factor of 1.6). In this report it is

assumed that all environmental forces act in the same direction. For wind and waves this is seen as a fair

assumption as the waves in the fjord for these conditions are wind generated.

Static environmental loads in holding condition

Environment \ Direction 0° 45° 90°

Wind 62 t 1219 t 1662 t

Wave 95 t 133 t 285 t

Current 1080 t 890 t 445 t

Sum (Fenv) 1237 t 2242 t 2392 t

Table 10-2: Overview of static environmental loads on the towed bridge.

Figure 10-2 show the orientation for values tabulated in Table 10-2.

Figure 10-2: Direction of environmental loads for towed bridge



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Based on the results above, the most reasonable heading for the bridge in a storm is 0 degrees against

the environmental loads as this will minimize the wind forces. This is illustrated in Figure 10-3. Another

alternative is to tow northwards to get shelter. However at this stage, there are not available detailed

environmental data for the different areas, and a worst-case condition is therefore used to prove the

feasibility of the concept.

Figure 10-3: Heading and positions in a storm situation.

A suggested layout of the towing vessels is sketched in Figure 10-4.

Figure 10-4: Towing vessel layout

This layout uses 14 vessels for towing and station keeping. The heading of the vessels are 45 degrees

against the weather if a bridge heading of 0° towards the environmental forces are used.

𝐹𝑣𝑒𝑠𝑠𝑒𝑙 = 𝐹𝑒𝑛𝑣

𝑛𝑣𝑒𝑠𝑠𝑒𝑙𝑠 ∙ cos 45°=

1237 𝑡

14 ∙ cos 45°= 125 𝑡



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This calculation show that a mean bollard pull requirement will be in the range of 125 t. For the actual tow

it is beneficial to have a variety of larger and smaller vessels. The smaller vessels can be used to control

the orientation of the bridge during tow, while the larger vessels are pulling the bridge. The smaller

vessels can also be to connect directly to the pontoons.

10.3 Maneuvering in narrow waters

The vessel capacity for maneuvering in narrow waters is covered by the design criteria presented in

chapter 10.1.

Figure 10-5 and Figure 10-6 illustrates the bridge at different positions along the towing route together

with the clearances to shore while towing.

Figure 10-5: Towing of bridge from Eikelandsfjorden to Bjørnafjorden



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Figure 10-6: Clearance between towing vessels and shore when passing Fusa.

10.4 Adequate speed

With the current setup, the towing spread towing capacity is approximately 1237 t in the longitudinal

direction of the bridge. Seeing the actual tow as a weather restricted operation with a strict wind and wave

criteria, the main resistance will be current and forward speed. The towing velocity can therefore be

approximated as follows;

𝑉𝑇𝑜𝑤𝑖𝑛𝑔 = √2 ∙ 𝐹𝑑,𝑡𝑜𝑡

𝐴 ∙ 𝐶𝐷 ∙ 𝜌− 𝑉𝑐𝑢𝑟𝑟𝑒𝑛𝑡 = 0.57

𝑚

𝑠= 1.1 𝑘𝑛𝑜𝑡𝑠

(Current velocity is taken as 0.5 m/s, projected area is the total submerged projected area for all pontoons

as illustrated in Figure 10-7, and a drag factor of 1.6 is used).

With a towing speed of 1.1 knots, the towing duration will be approximately 11.5 hours (towing distance

12.5 nautical miles).



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Figure 10-7: Towing direction for pontoons during tow in narrow waters.

10.4.1 Bending moments in the bridge girder during towing

The pontoons that are being towed, will experience a force from the towing vessels which corresponds to

approximately 250 t. The pontoon will at the same have a force in the opposite direction due to the

resistance. With the presented towing velocity the resistance will be approximately 65 t. This gives a net

force of 190 t in the towing direction. For the shortest columns this give a bending moment in the bridge

girder of approximately 21 MNm (11.5 m moment arm) while for the highest column this give a moment of

84 MNm (44 m moment arm). This is negligible moments as the in place condition will have much larger

moments.

Figure 10-8: Bending moment during towing



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11 Installation of floating bridge

The installation of the curved bridge and the straight bridge is at this stage in the project almost similar.

Some special considerations for the straight bridge is presented in chapter 11.3.

At the time of the installation, the stay cable bridge is already completed and the segment at Flua is

established, ref chapter 8 and 9 respectively.

Measurements and length control of the bridge is carried out throughout the assembly phase. The bridge

girder elements will also be test-mounted prior to transport from production yard. In this way the length of

the bridge is assumed correct, and it is therefore considered possible to install the bridge with relatively

small tolerances. The bridge length will however be dependent on the temperature the day of installation.

As this is an operation that is carried out in the summer it is most likely that the bridge is longer rather

than shorter. The mean temperature (where the bridge has zero imposed stress from temperature) is +5°.

If the temperature is +15° the day of the installation (which is a realistic mean temperature in the warmest

summer month in the Bjørnafjord area), this will give an elongation of approximately 40 cm. If an extreme

temperature of +32° degrees is experienced this will elongate the bridge with approximately 1.2 m. A

method for handling this length variation is explained in the following.

11.1 Operation description

The bridge will be towed to the bridge location as described in chapter 10. The bridge will be towed

between the stay cable bridge and the abutment at Flua and rotated for the installation. Figure 11-1 show

the different steps (from 1 to 6) as the bridge is moved in position for installation.

Figure 11-1: Towing and rotation of floating bridge before installation



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From step 6 in Figure 11-1 above, the bridge is towed towards Flua and the stay cable bridge where

winch wires are connected. This is illustrated in Figure 11-2.

Figure 11-2: Installation is done using winch wires connected to Flua and the stay cable bridge.

The best way of controlling the motion of the bridge after connection to the winches is that the installation

vessels are holding back the bridge while the winches pull on the bridge in a controlled way. The

installation vessels will in this phase apply constant tension (The vessels are omitted from the Figure 11-2

for clarity. Vessels are indicated in figures in the coming).

One of the ends (in this case indicated for the southern end) is further winched towards the stay cable

bridge, where the floating bridge is connected to the stay cable bridge using guide pin(s). The guides will

allow rotation of the bridge and make sure that the motions of the bridge is restrained as the northern end

is moved in to position. See Figure 11-3. It should be noted that the guides are not dimensioned at this

stage, but the solution is scalable and the guide pin principle is frequently used in the offshore industry.



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Figure 11-3: one end winched in towards the guide pins on the main bridge.

A proposed vessel configuration is shown in Figure 11-4. Note that the heading of the vessels will vary

throughout the installation to account for the environmental forces.

Figure 11-4: Vessel configuration during installation.



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Figure 11-5: Floating bridge ballasted down to activate guide pin.

The longitudinal motion of the bridge will initially be controlled by the installation vessels. The winches will

eventually get a better angle of attack and control the bridge onto the guide pin(s). Further, any

movements of the Northern part of the floating bridge will be damped through a bumper system. See

Figure 11-8.

The resulting moment from the opposite forces from installation vessels and winches will slightly bend the

bridge, resulting in a decreased bridge length. This bending will compensate for temperature induced

expansion and provide sufficient installation tolerances.

A hold back force of approximately 33 t on each of the AHVs will result in a deflection of approximately 7

m of the bridge arc, and shorten the bridge length with almost 3 m. The vessels have a bollard pull

capacity above this, so the vessels should have no problems delivering the necessary forces. The

resulting winch pull will be approximately 50 t. Figure 11-6 show the end deflection of the bridge with a

total applied force of 100 t vessel pull.



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Figure 11-6: Bending of bridge due to installation vessels, 1 MN = 100 t (deformation is scaled).

To obtain a controlled interaction between the floating bridge and Flua, a guiding and bumper system is

used, see Figure 11-8. The green structures will damp out the motions while the blue structures will act as

fine guiding and align the cross sections and secure them for permanent connection (welding). Figure

11-10 show the layout of the temporary connection.

Figure 11-7: Bridge in position.



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As the northern end is approaching its position a guiding and bumper system will make sure the end is

moved into the correct position. Fendering systems designed to absorb energy is common for ships,

offshore structures and quays. These systems can be utilized in the installation operation, and should be

mounted on the bumper system to absorb the kinetic energy of the bridge as it is winched in place.

Figure 11-8: Bumper system (green), installation winches and temporary securing (blue). Clearance between bridge ends is

scaled for clarity.

When the northern part of the floating bridge is rotated in place, the forces from the towing vessels can be

gradually released in order to extend the bridge longitudinal and into its position. To lower the potential

risk of uncontrolled release of energy in this operation it is advised that hydraulic jacks are used between

the installed bridge and the northern part to assist the off-loading operation. It will make the off-loading of

the bridge arc smoother and reduce the risk for the personnel working close to the connection. See

Figure 11-9.

Figure 11-9: Hydraulic jacks used to off-load the bridge arc during installation.



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When in place, the temporary connections are tightened in order to position the cross sections for

welding. A drawing of the temporary connection is shown in Figure 11-10.

Figure 11-10: Drawing of temporary securing. Top left show example of position at the end, while top right show example at

a horizontal position.



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11.2 Installation and towing weather criteria and durations

Weather window, weather criteria, duration and contingency time for the towing and installation operation

are presented in table below. Contingency time is decided according to ref. /2/.


operation

duration

Contingency

time

Weather

window

Towing operation Wind: 10 m/s

Wave: 0.5 m Hs*

48 hrs. 48 hrs. 96 hrs.

Installation operation Wind: 10 m/s

Wave: 0.5 m Hs*

48 hrs. 48 hrs. 96 hrs.


Using GMOPSIM, the expected weather delay for both the towing and installation operation is calculated

and the results are shown in the figure and table below. Wind conditions at Bjørnafjorden is used for

these simulations, ref. /4/.

Figure 11-11: Expected monthly delay for bridge installation (days) due to weather from GMOPSIM.



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Prior to towing and installation operation is initiated, an evaluation of the defined weather window will be

done. This will be carried out for the waypoints presented in Figure 11-12 below. In addition suggested

safe locations in case of deteriorating weather is also planned. The decision procedure is described in the

flowchart in Figure 11-13

Figure 11-12: Operation waypoints and safe locations during installation.



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Figure 11-13: Weather window flow chart for installation operation.

11.3 Straight bridge installation

This chapter summaries the straight bridge installation;

- The complete floating bridge will be installed in one section as for the curved bridge.

- A 170 m bridge section will be pre-installed and supported by a temporary pontoon at Flua as for

the curved bridge.

- Where the curved bridge has a fixed connection at Flua, the straight bridge has a sliding bearing.

The sliding bearing at Flua will be utilized in the installation phase to compensate for

temperature-induced expansion and give sufficient installation tolerances. Instead of bending the

bridge (as for the curved alternative), the bridge girder element at Flua is moved Northwards by

using hydraulic jacks. This will compensate for temperature induced expansion and provide

sufficient installation tolerances.

- The bridge will then be temporarily secured to the bridge girder element at Flua. The jacks are

released (controlled) and the bridge is moved towards the stay cable bridge. Once interaction to

the stay cable bridge is obtained, a temporary connection is established. The same guiding and

securing system will be used for the straight bridge as for the curved bridge.



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- The permanent mooring lines will be connected to the floating bridge during installation. These

will be connected before the floating bridge is in position and help positioning the bridge during

installation. Pre-installation and connection of the mooring system is covered in chapter 12.

- The permanent mooring lines give straight bridge alternative more flexibility in the installation

phase. If required, the bridge can be installed in shorter sections. The mooring lines can then be

used to keep the cantilever bridge girder in place in the temporary phase.

12 Installation of permanent mooring system (Straight bridge)

The installation of the mooring system will be carried out in a separate operation outside of the critical

path of the project. The equipment can be laid down on the seabed or buoyed off to surface depending on

how close to the bridge installation, the operation is carried out.

Figure 12-1: Overview of permanent mooring system.

At this stage, the knowledge of seabed conditions is quite limited and it is therefore difficult to decide the

best anchor types and positions. The bridge concept is however flexible regarding anchor types and

positions as the pre-tension values can easily be adjusted to obtain required horizontal stiffness at each

pontoon. Relevant anchor types are gravity anchors (combination of steel and rock ballast), suction

anchors (steel), Drag embedded vertical load anchors and piling anchors.

The operation is carried out in the following main steps;

- Seabed surveys of potential anchor positions.

- Groundworks including leveling of the anchor positions.

- Installation of anchors (including ballasting for gravity anchors using fall pipe vessel)

- Installation of bottom chains and mooring wires.



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- Buoying-off mooring lines for installation (optional)

If gravity anchors is used they will require a heavy lift vessel for installation. The total anchor weight of

these anchors, including ballast, is approximately 2200 t. The ballasting will be carried out after the

anchor is positioned on the seabed and a lifting weight of approximately 500 t is required at this stage.

The principle for the anchor installation is shown in Figure 12-2.

Figure 12-2: Installation of anchor by using HLV and anchor handling tug.

When the anchor is positioned correctly on the sea bed, the mooring line is lowered onto the ground and

either laid down with a ROV pick-up system (the case if the installation is carried out long before bridge

installation) or buoyed off to the surface using a pick-up pennant and a surface buoy. In case the mooring

lines are laid down on the bottom, these are picked up by some of the anchor handling vessels used for

towing of the bridge prior to installation operation. This is a standard operation that is carried out

frequently in the North Sea.



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Figure 12-3: Buoyed- off mooring line ready for bridge installation.

When the bridge arrives Bjørnafjorden, the vessels used for towing will pick up the mooring line using the

subsurface buoy and connect to the mooring line end on the bridge.

Figure 12-4: Connection of mooring system.



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After the bridge is installed at Bjørnafjorden, the mooring line system will stay passive. Some re-

tensioning will be required in relation to inspections and planned maintenance. Adjustment may also be

necessary in case the mooring lines are elongated over time due to the permanent pre-loading in the

mooring lines. Permanent winches on board the pontoons are not an alternative due to the required

inspection regime related to these. The main focus for the top termination is therefore to transfer the

loading from the bridge to the mooring lines in the most proper way, and with the possibility to do minor

adjustments during installation and for maintenance.

The most obvious alternative at this stage is to use fairlead stoppers on top of the pontoons. There are

different suppliers for this type of equipment, but in this study Scana Offshore’s fairlead stopper is used

as example. The chain stoppers are designed in order to lower the out of plane bending (that can be

experienced when the chain runs through a fairlead wheel) in order to extend the fatigue life. The fairlead

stoppers are equipped with load cells that gives continuous monitoring of the mooring line loads. The

mooring chain is tensioned to the pre-defined tension using a removable hydraulic jack that are moved

between the mooring lines as required. Number of chain jacks should be optimized to make the

installation operation as effective as possible. An illustration of the concept is shown in Figure 12-5 below.

The removable hydraulic jack is shown at the left-most chain stopper.

Figure 12-5: Fairlead stopper and removable hydraulic jack from Scana Offshore. Photo: Scana Offshore.



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13 Progress plan

13.1 Overall project

The project is in this study set to start at 20.06.2020 and is divided into following main activities:

- Steel work

- Production of pontoons and Flua

- Groundworks and installation of Flua

- Building of stay cable bridge

- Assembly of floating bridge

- Pre-installation of permanent mooring (straight bridge)

- Installation of floating bridge

- Finalization

Figure 13-1 shows a suggested progress plan for the overall project. Several of the activities have high

flexibility in start-up time and the presented plan only shows one iteration prior to cost/time optimization.

The overall duration of the project is in this report estimated to 41,6 months (roughly 3,5 years). However,

the progress plan is currently high level and a building time of approximately 4 years is probably more

realistic.

Figure 13-1: Suggested overall progress plan

13.2 Critical activities:

The following activities are critical for the overall project duration (the completion time of the following

activities directly impact the duration of the project:

Critical Activity Directly affects:

Duration of steel production Building of stay cable bridge, assembly

of floating bridge

Duration of pontoon production Building of stay cable bridge, assembly

of floating bridge

Assembly of floating bridge Installation of floating bridge



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Installation of floating bridge Finalization

Finalization Project completion

13.3 Non-critical activities:

The following activities are deemed less critical due to high amount of slack in the time table. Reasonable

delays in the following activities are not expected to govern start-up of critical subsequent activities and

impact on overall project duration.

Non-critical activity Basis for evaluation

Groundworks and installation of Flua Can be done as soon as production of Flua and

groundworks are completed. Not expected to

influence any subsequent operations due to

flexibility in start-up time and limited duration

Building of stay cable bridge Start-up only governed by completion of

required steelwork. Necessary time window for

building prior to installation of floating bridge

should easily be achieved through controlling,

and if necessary accelerating the production of

steelwork

Pre-installation of permanent mooring Flexibility in start-up time. Short duration

13.4 Detailed estimation of critical activity duration:

Steel work:

Steel for each of the 5 bridge sections (and stay cable bridge) is assumed to take 6 months each to

produce, see Figure 13-2. For flexibility it is suggested to produce the steel for stay cable bridge in

parallel with section 1-5, which gives an overall production time of 30 months. If required the start-up of

stay cable bridge could be moved forward by earlier production of the required steel. The preliminary

production start-up of stay cable steel is defined to reduce the time between the stay cable bridge

completion and the final installation, while still keeping a robust margin for delays.

Figure 13-2: Suggested progress for bridge girder pre-fabrication.



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Pontoon production:

The pontoons (and the concrete part of Flua) are partly built in parallel as it is possible to complete the

structures floating (casting of top plate), see Figure 13-3. Each production cycle is assumed to last 5

months (7 months for the batch where the concrete part of Flua is cast), all batches requires 3 months in

dock. This gives a total duration of 32 months. Flua is set to be built at the beginning of the production

cycles to allow for a maximum time window for groundworks and installation. This however, may change

when more detailed planning is carried on as it may be found that it is necessary to have pontoons

available earlier to start producing and skidding the final bridge elements on to the pontoons. However,

none of this will change the overall schedule.

Figure 13-3: Suggested progress for pontoon production.

Assembly of bridge

The assembly of the 5 bridge sections from 20m elements is divided between two quays. Quay 1 for

assembly through skidding of section 2-5, while section 1 (incline section of the bridge) is partly

assembled (to 200m lengths) at quay 2. A heavy lift vessel (HLV) is required for the final 4 lifts (4x 200m)

in the assembly of bridge section 1. These lifts can be done as soon as bridge section 2 (which is the

connection point of section 1) and the 4x 200 m lengths of bridge section 1 are ready. Each lift is

assumed to take 1 week, which includes preparations and temporary securing.

The overall duration of the assembly operation is estimated as 26 months, in which 1 month of HLV

services are required. The lifting operations are not on a critical path, and start-up of the operation can be

adjusted to the heavy lift market situation.



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Figure 13-4: Suggested progress for assembly operations.

Installation of Floating Bridge

Total duration of installation excluding weather-induced delay is estimated to 12 days. This is shown in

Figure 13-5. However strict weather criteria for towing and installation will result in expected delays, ref.

chapter 11.2.

Figure 13-5: Suggested progress plan for installation of floating bridge



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14 References

/1/ NOT-GEN-017 Anslagsnotat seilingsled syd, krum bru & NOT-GEN-019 Anslagsnotat

seilingsled syd, rett bru

/2/ DNV-OS-H101 - Marine Operations, General

/3/ DNV-OS-H202 – Sea transport operations (VMO standard – Part 2-2)

/4/ E-mail from the public road administration 01.12.15 – Historically wind data for

Marstein, Bjørnafjorden and Eikelandsfjorden.

/5/ NOT-KTEKA-020 Straight Bridge_South-Summary of analyses

/6/ NOT-KTEKA-021 Curved Bridge_South-Summary of analyses



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Appendix A – Vessel and equipment specification

Vessel and Equipment List Nomenclature DP – Dynamic Positioning

ASD - Azimuth Stern Drive Tug

ATD - Azimuth Tractor Drive

AHV – Anchor Handling Vessel

AHTS – Anchor Handling Tug Supply

H – Height

R – Radius (outreach)

LC – Lifting Capacity

HLV – Heavy Lift Vessel

MLBC – Minimum Load Bearing Capacity

MBL – Minimum Breaking Load

MBF – Maximum Breaking Force

DP FFPP – Dynamically Positioned (Flexible) Fall Pipe Vessel

Vessels Item Description Barges

UR 93

NS Barge - DW tonnes 9.000 - LxBxH 90x27x6 - Ballast Pumps: 2 x 600 m^3/h - Availability: > 25 in Norway (Ugland,

Boa)

BOABARGE 29/30

Large NS Barge - DW tonnes > 17.000 - LxBxH > 124x31x8 - Ballast Pumps > 2 x 3.000 m^3/h - Availability: 6 in Norway (Boa)

H-541/H-542 (Heerema)

Very Large NS Barge - DW tonnes > 20.000 - LxBxH > 165x42x10.7 - Ballast Pumps > 2 x 3.000 m^3/h - Availability: 2 in Europe (Heerema)

BOABARGE 37

Submersible barge - DW tonnes: 30.000 - LxBxH: 152x38x9.15 - Ballast Pumps: 2 x 6.000 m^3/h - Availability: 1 in Norway (Boa)

Tugs

Mega Mammut (ATD)

Small Tug - ca 50 t bollard pull - LxB ca. 30 x 10 m - Availability > 25 in Norway (Bukser og

Berging, Boa, Østensjø)

BB Worker (ASD)

Large Tug - 75 – 100+ t bollard pull - LxB ca. 40 x 15 m - Availability: 15 in Norway (Bukser og

Berging, Boa, Østensjø)

Anchor Handling Vessels (AHV)

Normand Borg (AHT)

Small Anchor Handler - 200 t bollard pull - LxB ca. 80 x 20 m - 10 t crane - Bow, Azimuth, Stern thrusters - AH winch 500 t - Availability > 10 in Norway (Siem

Offshore, Solstad Offshore, Island Offshore, Olympic, etc.)

-

Normand Prosper (AHTS)

Large Anchor Handler - <300 t bollard pull - LxB ca. 100 x 25 m - 2x55 t crane - 2xBow, 2xAzimuth, Stern thrusters - Winches (up to 600T) - ROV - DP 2 - Availability > 15 in Norway (Siem

Offshore, Solstad Offshore, etc.)

Heavy Lifting Vessels (HLV)

Uglen

Small HLV - Lifting Capacity: 800-1.500 t - Radius/Height: ca 20/70m - Availability: 26 in Europe

Uglen (example vessel)

- Lifting Capacity: 800 t

- Height/Radius: H:60m, R:20m - 2 x 400 t (two hooks) - Highlift1 (LC:440t, H:92m) - Highlift2 (LC:440t, H:92m) - LxB ca. 80 x 25 m

- (Ballast: 2x500 m^3/h)

Medium HLV - Lifting Capacity: 1.500-3.500 t - Radius/Height: ca 40/100m - Availability: 20 in Europe

Rambiz 3000 (example vessel)

- Lifting Capacity: 3.300 t - Maximum height: 79m - LxB ca. 85 x44 m

Rambiz 3000

Balder

Large HLV - Lifting Capacity: 3.500-7.000 t - Availability: 11 in Europe

Balder (example vessel)

- 6300 t Lifting Capacity (tandem) - H:98m,R:33m - Port side, LC: 2.700t, H: 116m, R:33m - Starboard side, LC: 3.600t, H: 98m, R:37m

- LxB ca. 150 x 105 m

Specialized Vessels

Baldock (CSL Americas)

Selfunloader (Panamax) - Cargo capacity: 75.000 m^3 - Discharge rate: 5.000 t/h - LxB 245 x 33 m - Bom length: 80m - Availability in Europe >5

Stornes (Van Oord)

Rock dumper (Fallpipe) - Subsea Rock Installation using fall pipe - Rock installation depth >1.500m - Loading capacity 26.000 t - Dumping capacity: 3.000 t/h - LxB 175 x 26 m - DP Class 2 - Availability in Europe >5

Boa Deep C

Subsea Construction Installations Vessel - Crane: 250t, 13m outreach - 2 x WROV hangars - LxB 120 x 27 m - DP 3 - Moon Pool 7.2mx7.2m

Trym II

Drilling Barge - For under water blasting - Down to 35m - Deck area: 250m^2

Ballast Pumps

ALE

Ballast Pump 1 - Max Capacity: 2.200m^3 - Max Height: 17m - Cap1: (1.100m^3/h, 17m) - Cap2: (2.100m^3/h, 9m)

ALE

Ballast Pump 2 - Max Capacity: 500m^3 - Max Height: 45m - Cap1: (125^3/h, 40m) - Cap2: (300m^3/h, 30m)

Other Equipment

ACE Winches Norge AS

Winch 1 - 200 t WLL - 76mm wire rope, 1830m cap - LxBxH: 7m x 4.6m x 4.6m - Gross Weight: 93 t - Hydraulic

Skidding System (Gripper Jack) - Push/Pull Capacity: 950 t - Can move loads up to 3.800 t

Hydraulic Power Unit - 200kW diesel engine - Hydraulic pump - 575 L/min - Operating Pressure: 250Bar - LxBxH: 3.5m x 2.0m x 2.1m - Gross Weight 6 t

Mobile Crane - 200t – 400t capacity - LxBxH: 15m x 8.3m x 3.8m -

Multi Wheeler - Capacity: Approximately 40t per axis. - Can be assembled by several modules

to take the required load.

Enerpac

Strand Jack 1 - Capacity: 300t - No. of strands: 19 - Strands diameter: 18mm - Weight: 2t - Lifting speed: 7-11 m/h - Motor size: 15-37kW

Enerpac

Strand Jack 2 - Capacity: 650t - No. of strands: 43 - Strands diameter: 18mm - Weight: 4t - Lifting speed: 8-15 m/h - Motor size: 30-55kW

Illustration from Sutong cable stayed bridge

Deck Erection Gantry 1 - For lifting of 20m bridge elements (high

bridge) - For lifting of stay cable bridge

(cantilever method). - Assumed must be built - Assumed one Strand Jack 1 per crane - Capacity per crane: 300t

Illustration from Sutong cable stayed bridge

Deck Erection Gantry 2 - For lifting of 200m bridge span (sec 1)

together with HLV - Assumed must be built - Assumed two Strand Jack 2 per crane - Capacity per crane: 1.300t

Mooring Systems

Mooring System 1 - 1.5 – 30 t Stevpris anchor - 76 mm mooring chain, 200m - Mooring wire, 300m

Mooring System 2 - Bollard at land - 76 mm mooring line, 200m - Mooring wire, 300m

Mooring Lines

Mooring rope - Used for mooring of pontoons and

abutment along quay. - 76-90 mm diameter.

Ramnäs Bruk/Vicinay Cadena (Deep Sea Mooring)

Mooring Chain - 76/84mm diameter - Subm. Weight: 123 kg/m - MLBC: 7.2 MN

Anchors

Stevpris Mk6 Anchor - Weight: 1.5 – 30 ton - Adjustable fluke/shank angle to suit

different soil types

Chain/Fairlead Stoppers

BarLatch (Bardex)

Chain Stopper - Purpose built for permanent mooring

system. - Specs not yet acquired

Chain Jacks

Linear Chain Jack (Bardex)

Chain Jack - For tensioning of permanent mooring

system. - Stall Load: 500 t - MBL: 1.100 t

Mooring Rope/Wires

Bishop Lifting Products

Mooring Wire 1 - Up to 75 mm - 24 kg/m (75mm) - MBL: 360 t - Grade: 165kg/mm^2

KTL Offshore

Mooring Wire 2 - Up to 152 mm - 97 kg/m (152mm) - MBL: 1.300 t - Grade: 1508 kN/mm^2

Lankhorst Rope (GAMA98 w/dyneema)

Mooring Rope 1 - Diameter: 62 - 194 mm - MBL: 200 – 2.000 t - Subm. Weight: 0.03-0.28 kg/m

Lankhorst Rope (GAMA98)

Mooring Rope 2 - Diameter: 125 - 290 mm - MBL: 450 – 2.500 t - Subm. Weight: 2.8-15.2 kg/m



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Appendix B – Required vessels and equipment – quantities

For details regarding the

differnet items, reference is

made to Appendix A

B91.1 Marine Operasjoner (Høybru)

Item Total hire days

North Sea Barge 213

Small Tug 213

Large Tug 213

Small HLV 22


North Sea Barge 3 020

Very Large North Sea Barge 38

Small Tug 128

Large Tug 748

Small AHV 67

Medium HLV 36

Ballast Pump 1 2 046

Winch 1 32

Skidding System 598

Hydraulic Power Unit 598

Small Mobile Crane 598

Multi Wheeler 208

Strand Jack 2 144

Deck Erection Crane 2 72

Mooring System 1 27 372

Mooring System 2 27 372

Mooring Rope 6 840

Temporary Steel 1 300 mT


North Sea Barge 578

Small Tug 34

Large Tug 97

Large AHV 10

Self ‐ unloader 8

Ballast Pump 1 38

Ballast Pump 2 38

Mooring Rope 2 100

Temporary Steel 100 mT


North Sea Barge 18

Small Tug 18

Large AHV 18

Small HLV 18

Rock dumper (fall pipe) 6

B91.4 Marine Operasjoner (Forankring rett bru)

B91.2 Marine Operasjoner (Flytebru)

B91.3 Marine Operasjoner (Flua)

Assumptions

Temp storage of 20m bridge elements not included

Temp storage of 4 bridge spans not included

Personnel of vessels assumed included in dayrate

Item Amount Sequence Days Total days Total hire days Purpose mT

B91.3 Marine Operasjoner (Flua)

Preparations Flua abutment

North Sea Barge 3 1 150 150 450 Temporary quay for completion of abutment

Mooring Rope 14 1 150 150 2 100 Mooring abutment/quay during building

Temporary Steel 1 Assumed 50 t steel for tripods. 50

Ballast Pump 2 2 1 3 3 6 Ballasting of abutment at fabrication yard

Small Tug 2 1 1 1 2 Moving abutment out of dock

Towing of abutment

Large AHV 2 1 3 3 6 Main towing vessels

Large Tug 1 1 3 3 3 Assisting towing vessel

Installation Flua

Large AHV 2 1 2 2 4 Stationkeeping of abutment

Large Tug 2 1 2 2 4 Stationkeeping of abutment

Ballast Pump 2 6 1 2 2 12 Ballasting of abutment for installation

Self ‐ unloader 1 2 4 8 8 Filling Permanent ballast

Ballast Pump 2 2 1 10 10 20 For filling of water to compensate for hydrostatic pressure

North Sea Barge 1 1 45 45 45 Transport of concrete (top plate)

Large Tug 1 1 45 45 45 Transport of concrete (top plate)

North Sea Barge 1 1 45 45 45 Transport of equipment (reinforcement, etc.)

Large Tug 1 1 45 45 45 Transport of equipment (reinforcement, etc.)

Installation of bridge girder on Flua

Small Tug 4 1 8 8 32 Installation of segment at Flua

North Sea Barge 1 1 8 8 8 Only installation

North Sea Barge 1 1 30 30 30 Temporary pontoon and installation

Ballast Pump 1 1 1 8 8 8 Ballasting of installation barge

Ballast Pump 1 1 1 30 30 30 Ballasting of temporary barge

Temporary Steel Assumed 50 t. (temporary connection) 50

B91.1 Marine Operasjoner (Høybru)

Small HLV 1 11 2 22 22 Lifting bridge elements (20m), HLV

North Sea Barge 1 12 2 24 24 Deliver bridge elements (20m), HLV lift

Large Tug 1 12 2 24 24 Deliver bridge elements (20m), HLV lift

Small Tug 1 12 2 24 24 Deliver bridge elements (20m), HLV lift

North Sea Barge 1 21 9 189 189 Deliver bridge elements (20m), Strand Jacks lift

Large Tug 1 21 9 189 189 Deliver bridge elements (20m), Strand Jacks lift

Small Tug 1 21 9 189 189 Deliver bridge elements (20m), Strand Jacks lift

B91.2 Marine Operasjoner (Flytebru)

Building of pontoons outside dock

Small Tug 2 10 1 10 20 Moving pontoons out of dock

Mooring rope 6 19 60 1140 6 840 Mooring during final building of pontoons

Towing of pontoons from building yard

Large Tug 1 19 2 38 38 Towing of pontoons (tour, detour)

Small Tug 1 19 2 38 38 Towing of pontoons (tour, detour)

Storage of pontoons

Small AHV 1 6 3 18 18 Installation of mooring, storage location (all bridge sections)

Mooring System 1 38 1 500 500 19 000 Mooring of pontoons before and after assembly of bridge sections

Mooring System 2 38 1 500 500 19 000 Mooring of pontoons before and after assembly of bridge sections

Towing of 20m bridge elements

Large Tug 1 1 568 568 568 Towing of bridge girder elements, 20m (tour, detour)

North Sea Barge 1 1 568 568 568 Towing of bridge girder elements, 20m (tour, detour)

Delivery of bridge spans for section 1

Large Tug 1 1 38 38 38 Towing and stationkeeping of bridge spans for sec 1

Small Tug 1 1 38 38 38 Towing and stationkeeping of bridge spans for sec 1

Very Large North Sea Barge 1 1 38 38 38 Towing and stationkeeping of bridge spans for sec 1

Temporary Steel 1 400 t grillage for transport (10% of weight) 400

Establishment of assembly quay

North Sea Barge 4 1 598 598 2 392 Establish temporary quay

Small AHV 1 1 3 3 3 Installation of mooring, assembly quay

Small AHV 1 2 3 6 6 Installation of mooring, assembly site (for skidded part)

Mooring System 1 6 1 598 598 3 588 Mooring of assembly quay

Mooring System 2 6 1 598 598 3 588 Mooring of assembly quay

Mooring System 1 8 1 598 598 4 784 Mooring of pontoons during assembly

Mooring System 2 8 1 598 598 4 784 Mooring of pontoons during assembly

Small Mobile Crane 1 1 598 598 598 Lifting of birdge girder elements, 20m (xx tonnes)

Skidding System 1 1 598 598 598 Skidding at assembly quay

Temporary Steel 1 Assumed 500 t for assembly period 500

Hydraulic Power Unit 1 1 598 598 598 Power supply to skidding system

Ballast Pump 1 3 1 598 598 1 794 Ballasting pontoons, assembly quay

Towing to storage location

North Sea Barge 1 3 20 60 60 Temporary support of assembled bridge sections

Ballast Pump 1 3 3 20 60 180 Ballasting pontoons after tow, section 3‐5

Large Tug 3 4 4 16 48 Towing of bridge sectios to storage location

Small Tug 2 4 4 16 32 Towing of bridge sectios to storage location

Assembly of bridge spans for Section 1

Multi Wheeler 1 1 208 208 208 Joining 20 m elements to 200 m

Assembly of Section 1

Medium HLV 1 4 9 36 36 Lifting of bridge spans for bridge section 1, HLV

Ballast Pump 1 2 4 9 36 72 Ballasting pontoons during lifting

Strand Jack 2 4 4 9 36 144 Lifting of bridge spans for bridge section 1, Crane

Deck Erection Crane 2 2 4 9 36 72 Lifting of bridge spans for bridge section 1, Crane

Temporary Steel Assumed 200 t. (50 t on each connection) 200

Installation Floating Bridge

Small AHV 7 1 4 4 28 Towing of floating bridge

Large Tug 7 1 4 4 28 Towing of floating bridge

Small AHV 3 1 4 4 12 Installation process, pos mid on floating bridge

Large Tug 7 1 4 4 28 Installation process, pos end on floating bridge

Winch 1 4 1 8 8 32 Installation winches 2 on each side

Temporary Steel 1 Assumed 200 t. (100 t each side) 200

B91.4 Marine Operasjoner (Forankring rett bru)

Straight bridge ‐Installation of mooring system at Bjørnafjorden

Large AHV 1 6 3 18 18 Assist during installation (with mooring line)

Small HLV 1 6 3 18 18 Lifting anchor to sea bed

North Sea Barge 1 6 3 18 18 Transport of anchors for installation

Small Tug 1 6 3 18 18 Transport of anchors for installation

Rock dumper (fall pipe) 1 2 3 6 6 Ballasting anchor after installation



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Appendix C – Brief stability check for pontoons

Brief stability calculations are carried out for the pontoons to ensure that the stability is

sufficient in the temporary phases. No complete stability calculations are presented in

this report. For more details of the pontoon design criteria, reference is made to HYDA-

reports for the straight and curved bridge.

Part 1 of this appendix includes calculations of the metacentric height for different weight

scenarios for the final pontoon design. The different weight scenarios is as follows;

- Only the pontoon

- Pontoon with columns (calculated for axis 3 for curved bridge)

- Pontoon with columns and weight from 200 m bridge girder.

Part 2 include calculations performed for a previous study where the main bridge was

positioned in the center of Bjørnafjorden. The pontoons had different dimensions, but

indicates the stability performance of the pontoon design.

Appendix C - Part 1 – Metacentric height calculations for final pontoon design

Straight bridge stability check for temporary phasesGeneral input:

ρw 1025kg

m3

Density seawater

ρa 1.02kg

m3

Density air

Input pontoon:

Δ 18300 103

kg Displacement pontoon

VpΔ

ρw1.785 10

4 m

3 Volume displacement pontoon

Lp 40 m Length side of pontoon

Bp 28m Breadth of pontoon

Dp 10.5m Draft of pontoon

Hp 14.5m Height of pontoon

VCGp Dp 4.2m 6.3m Vertical center of gravity for pontoon

Input columns:

Hc 43 m Height columns

wc 19000kg

m Unit weight columns

VCGc Hp

Hc

2 36 m Vertical centre of gravity for column

Input bridge girder:

Lb 200m Effective bridge girder length

Hb 6.5m Height bridge girder

Cdb 0.867 Wind drag coeffiicent bridge girder.(Taken from HYDA report).

wb 28000kg

m Representative weight of bridge girder

Wind input:

Vw 39.3m

s 100 year return period wind speed

at 50 m height

Pontoon drawing:

Water plane stiffness for pontoon

Water plane stiffness in roll;

I44

Bp Lp3

122 0.110

Bp

2

4π

4Bp

2 1

2

Lp

2

4

3π

Bp

2

2

5.722 105

m4

Water plane stiffness in pitch;

I55

Lp Bp3

12

π Bp4

64 1.033 10

5 m

4

Definition of axis and hence motions (roll / pitch) is decided based on the bridgecoordinate system.

Metacentric height for pontoon in pitch;

Only pontoons (without columns and bridge girder):

KBDp

25.25 m

KGpontoon VCGp 6.3m

BM55

I55

Vp5.788 m

GMTpontoon KB BM55 KGpontoon 4.738 m

For pontoon with 1 columns of 43 m height (Axis 3):

KGcolumns

Δ VCGp wc Hc VCGc

Δ wc Hc 7.569 m

GMTcolumns KB BM55 KGcolumns 3.469 m

Stability in "pitch" including the bridge girder weight is not applicable as the pontoon will besupported by adjacent pontoons in this direction if the bridge girder is installed.

Metacentric height for pontoon with columns and bridge girder in the"roll" direction of pontoon:

BM44

I44

Vp32.048 m

The stability in the longitudinal direction of pontoon (roll) is only checked with the weightof the bridge girder. The included weight represent 200 m of bridge girder.

VCGbridge Hp HcHb

2 60.75 m

KGbridge

Δ VCGp wc Hc VCGc wb Lb VCGbridge

Δ wc Hc wb Lb 19.618 m

GMLbridge KB BM44 KGbridge 17.68 m

Stability for pontoon with bridge girder, wind force and towing force:

One pontoon with bridge girder checked individually.

C44 ρw g Vp KB KGbridge ρw g I44 3.173 109

N m Rotational stiffness inroll for pontoon, columnand bridge

Fw1

2ρa Cdb Hb Lb Vw

2 8.878 10

5 N Wind force on bridge girder

aw VCGbridge KGbridge 41.132 m Moment arm for wind

Mw Fw aw 3.652 107

N m Moment from wind

Towing force. Assumed150 t.Ft 150 10

3 kg g 1.471 10

6 N

at KGbridge Dp 9.118 m Towing force moment arm.Assumed connected inwater line.

Moment from towing line about center of gravityMt Ft at 1.341 10

7 N m

Rotation of pontoon(degrees) from wind andtowing force

α44

Mw Mt

C44

180

π 0.902

The pontoon will have limited rotation from wind even when moment from towing line is included.

Appendix C - Part 2 – GZ curves for pontoons for design with main bridge in south

NOT-MO-002 MARINE OPERATIONS - METHOD STATEMENT

https://projects.cowiportal.com/ps/A058266/Documents/03 Prosjektdokumenter/03.6 Masterfiler/Marine operasjoner/NOT-MO-002 Marine operations - Method statement.docx

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Further, the two towers will be mounted together to the complete high bridge

section. This section will be towed to Bjørnafjorden from the assembly location.

This is illustrated in Figure 25

Figure 25: High bridge section

6.6 Stability during assembly of high bridge

The stability of the high bridge pontoons 70t and 50t shown in chapter 5.2 during

transport and installation of the bridge have been studied.

The objective of the study is to ensure that the bridge installation is accomplished

with a safe and positive stability.

For the main 70t pontoon three different stages including transport and bridge

assembly have been studied in addition to a damage case. These stages and

damage case are described in Figure 26 and Table 5.

Figure 26: Bridge-installation stages studied in stability analysis



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Table 5: Description of bridge-installation stages

Stage Objective

1 Transport of main pontoon 70t

2 Assembly of column between main pontoon 70t and bridge girder

+ assembly of tower

3 Assembly of high bridge with two supporting barges

Damage

case

Loss of one bridge element on one side

The stability of the main pontoon 70t alone is sufficient during both stage 1 and 2.

The righting arm (GZ) curves for stages 1-3 and damage case can be found in

Appendix A.

In order to maintain a constant freeboard of 3m during stage 1 and 2 the main

pontoon 70t must be ballasted to a draft of 20m by pumping in water ballast in

addition to the permanent rock ballast.

It is to be noted that the reserve buoyancy will be limited by the freeboard

requirement of 3m. Therefore in a later phase of the study damages to

compartments of the main pontoon 70t during the different stages and during

damage of bridge element should be investigated.

The free surface moment of the ballast water in the main pontoon 70t have been

included in all calculations assuming that all compartments are slack (i.e. not

empty, and not full). This is a conservative assumption.

In order to obtain sufficient stability during stage 3 it is found that two barges must

be connected to the main pontoon 70t. Two standard North Sea barges

[L*B*D=91.44m*27.4m*6.1m] have been used in this study, and they will be

connected to the main pontoon 70t with an overlaying beam.

The stability analyses have been performed with the barges positioned with 1m

clearance between the barge and the pontoon. If larger clearance between the

barges and the pontoon is required this will increase the stability.

During stage 3 the water ballast of the main pontoon 70t is pumped out to maintain

a constant freeboard of 3m. The barges will be ballasted to a draft of 3.1m in order

to maintain a similar freeboard as the main pontoon 70t.

The worst damage case is assumed to be loss of the outermost bridge element on

one side of the bridge. Since this element has the largest distance to the bridge

centre this will generate largest heeling moment compared to other damage cases.



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The loss of the outermost bridge on one side of the bridge results in an equilibrium

condition where the main pontoon 70t and barges are heeling 1.39 degrees

towards the undamaged side of the bridge when wind is included. (Dynamics are

not checked at this stage).

An overview of the weights, corresponding centres of gravity (COG )and

hydrostatic particulars used in the stability analyses for stages 1-3 and damage

case is shown in Appendix A. The ballast plan for the barges during assembly of

the bridge elements in stage 3 are shown in Appendix A. The main dimensions for

the barges are also shown in Appendix A.

A preliminary overview of the different bridge weights and COG used in the stability

analysis for main pontoon 70t are shown in Table 6 when all bridge girder elements

on each side of the tower are installed.

Table 6: Bridge weights and centres of gravity used in stability analysis

Bridge elements at stage 3 Density [t/m] Length

[m]

Weight

[t]

VCG

[m]

Column between pontoon

and bridge girder

36.9 43 1586.7 44.5

Bridge girder with 3.5m high

cross section

27 330 8910 67.75

Bridge girder with 6.5m high

cross section

30 120 3600 69.25

Tower above bridge girder –

lower part

10.99 77 1692.46 111

Tower above bridge road –

higher part

8.42 26 437.84 162.5

Stay cables 0.06 3150 378 124

Total - - 16605 74.04

Margin - - 19794 -

A simplified wind model have been created with Global Maritime’s in-house

software Hydwind, ref /9/. This model have been tuned to match the wind moments

provided by COWI, ref /7/ and is shown in Appendix A. The wind moments are

shown in Table 7. These wind moments are included in the calculation of the

righting arm in stage 3 and during the damage case.



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Table 7: Wind heeling moments provided by COWI, ref /7/

Direction* Wind moment [t*m]

Longitudinal 43323

Transverse 16004

*Direction relative to main pontoon 70t

A stability analysis for the main pontoon 50t have also been performed. The

stability is sufficient for the pontoon before and after assembly of the column

between the pontoon and the bridge road. These two conditions are shown in

Figure 27.

Figure 27: Main pontoon 50t before and after column-assembly

The main pontoon 50t shall maintain a constant freeboard of 3m before and during

assembly of the column. This requires the pontoon to be ballasted to a draft of

24m.

It is to be noted that the reserve buoyancy will be limited by the freeboard

requirement of 3m. Therefore in a later phase of the study damages to

compartments of the main pontoon 50t before and after assembly of the column

should be investigated.

The righting arm curves for the main pontoon 50t before and after assembly of the

column can be found in Appendix A.

An overview of the weights, corresponding centres of gravity and hydrostatic

particulars used in the stability analysis for main pontoon 50t before and after

assembly of column is shown in Appendix A. The main dimensions used in the

stability analysis for the main pontoon 50t are shown in Section 5.2.

For the stability analysis, simple hydrostatic models of the main pontoons 70t, 50t

and barges have been created with Global Maritime’s in house software HydroGM

ref /8/. These models are shown in Appendix A.

BILAG A – PRELIMINARY CALCULATIONS FOR TEMPORARY PHASES MARINE OPERATIONS – METHOD STATEMENT . 19/34

4 Stability

4.1 Stability calculations and GZ-curves stage 1-3 and damage case


4.2 Stability calculations and GZ curves main pontoon 50t


4.3 Hydrostatic models of main pontoons 70t and 50t

Below is the hydrostatic model used in the calculations for main pontoon 70t with and without barges.


Below is the hydrostatic model used for the main pontoon 50t.


4.4 Simplified wind model of main pontoon 70t and bridge

The wind model is shown in the figure below seen from the side.


The simplified wind model is shown in the figure below seen from the front.


4.5 Main dimensions of barges and barge ballast plan

In the figure below the main dimensions for the standard North sea barges are shown.

Barge Port side Starboard side

Length [m] 91.4 91.4

Breadth [m] 27.4 27.4

Depth [m] 6.1 6.1

Draft [m] 3.1 3.1

In the figure below the ballast calculations for the barges are shown.


In the figure below the ballast plan for the barges are shown.

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