The Bjørnafjorden crossingFloating bridge – Concept development and selection process

Øyvind Kongsvik Nedrebø Anette Fjeld Svein Erik Jacobsen

E39 Stavanger – BergenNew highway

Stavanger

Bergen

Bjørnafjorden

Floating bridge, rev.: 2012

Subsea rock, Flua: -32 m

2016:

2016: NOT OK!

17.03.2017

1: Moved bridge east at north end (away from Flua)

Old, 2016

New, 2017

2: Changed from concrete to steel for pontoons

2017: New floating bridge design

K7

K8

End-anchored floating bridge

Side-anchored floating bridge

How to reach the required and convincing level clarity regarding which bridge candidate should be taken forward to FEED phase? Run additional conceptual design phase based onthe following:

a) Two teams work in parallel on four alternatives (K11…K14).

b) The two teams to be separated. No exchange of information between the teams are allowed.

c) The results reported to be based on extensive analysis work. The design documentation produced shall cover all major aspectsgoverning for the design.

d) Independant verification work to be carried out by DNV GL in parallel.

A challenging assignment! However, NPRA expectation:The two teams will be capable of reaching the same conclusionregarding which bridge alternative to select for FEED.

28.10.2019

Four alternatives nominated: K11, K12, K13, K14subject to assessment in new concept study phase (Nov. 2018 – Aug. 2019)

K7 →

Alternative K11: Arch-shaped floating bridge supported

only at each end, i.e. equivalent to K7.

Alternative K12: Arch-shaped floating bridge supported at

each end similar to K11, but in addition equipped with a mooring system.

Alternative K13: Straight side-anchored bridge similar to K8.

Alternative K14: Side-anchored bridge similar to K8.

However, straight part of bridge limited to the cable-stayed bridge. Floating bridge part to have curved geometry.

K8 →

1. The project setup of both teams

2. Proposed base cases from both teams

3. The different selection methods for both teams

4. Insight to one technical challenge; parametric exitation

5. Concluding remarks to our recommendation of K12

CONSULTANTS PART OF THE PRESENTATION

WORK COLLABORATIONNORCONSULT – OLAV OLSEN

HEYERDAHL ARKITEKTER AS

PROJECT ORGANISATION

COST AND UNCERTAINTY ANALYSES

K12

K13

K14

K11

PMCOMP. REPR.

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CAD/BIM

OTHER PLANNING

DISCIPLINES

SUPPORT

BASE CASES

K11: End-anchored K12: End-anchored with mooring

K13: Side-anchored K14: Side-anchored without

expansion joint

Base cases

QUANTITATIVE CONCEPT RANKING

COST ROBUSTNESS SUSTAINABILITY

+ AESTETHICS: Weighted value of monumental buildingadditional cost (1 billion)

CONCEPT DEVELOPMENT AND SELECTIONCOST MODEL

> Cost model connected to the concept definition model

> Bottom-up cost estimatecovering approx. 90% ofconstruction cost

> Consistant across thedifferent concepts

> Tool for working with themost important costelements

> Shows if proposed conceptalterations actually reducescosts and/or uncertainty

CONCEPT DEVELOPMENT AND SELECTIONROBUSTNESS CRITERION

> Over 100 events og risk elements were identified through workshops, interviews and a questionnaire. 21 of these where classified as concept specific and significant.

> Probability and consequence was estimated in a separate risk workshop (2 rounds) and the expected value of the risk element is calculated.

> Other risk elements (project general) was not evaluated and will be an addition to all concepts.

CONCEPT DEVELOPMENT AND SELECTIONRISK WORKSHOP INFLUENCE

12%

6%

Ship impact

Consequence cost distribution workshop 1:

Consequence cost distribution workshop 2:

Ship impact

VISUAL IMPACT

QUALITATIVE CONCEPT RANKING

K11 K12

Pros: - Known technology, built before (in a smaller scale)

- Simple system, easy to calculate response from loads, ductile behavior

- Known eigenperiods which are difficult to move

- Larger capacity for unknown overloading due to stronger bridge girder

- Installation of complete assembled floating bridge, less work in Bjørnafjorden

- Less maintenance, few “wearing parts”

- Redundant system with double horizontal load-carrying system.

- Largest potential for- and flexibility in designing a robust solution.

- Mooring reduces the response and increases design life compared to K11. Possible to increase design life further with small amount of

additional steel. - Fibre rope mooring gives favorable interaction

with bridge girder. - Linear behavior of mooring without risk of

successive mooring line failure for known load cases

- Installation of complete assembled floating bridge, less work in Bjørnafjorden, simple mooring hook-up

- Few and manageable anchor locations - No joints and bearings

Cons: - Lack of redundancy - Uncertain wind load as turbulence

spectra are normally not applied to structures with long eigenperiods

- Large, concentrated forces at landfalls

- Requires larger clearance between tower legs

- Mooring needs replacement within design life. Complexity and costs related to this operation not sufficiently reflected.

- Challenging soil conditions, risk of underwater slides

- Limited experience with taut mooring on these water depths

Rank: 2 1

Reason: Most simple Most robust

K13 K14

Pros: - Redundancy in mooring - Fibre rope mooring gives favorable

interaction with bridge girder. - Linear behavior of mooring without risk

of successive mooring line failure for known load cases.

- Simplest production. - Potential for moving landfall north onto

the bank outside Gulholmane and obtaining a shorter bridge.

- Redundancy in mooring - Fibre rope mooring gives favorable interaction with

bridge girder. - Linear behavior of mooring without risk of

successive mooring line failure for known load cases.

- No joints and bearings

Cons: - Mooring, part of main load-carrying system, needs replacement within design life. Complexity and costs related not sufficiently reflected.

- Challenging soil conditions, risk of underwater slides

- Many and some unfavorable anchor positions.

- Limited experience with taut mooring on these water depths

- Great number of work operations performed on the fjord.

- Monotonic driving experience - Maintenance of joints and bearings - Noise from joints

- Mooring, part of main load-carrying system, needs replacement within design life. Complexity and costs related not sufficiently reflected.

- Challenging soil conditions, risk of underwater slides - Some unfavorable anchor positions. - Limited experience with taut mooring on these

water depths - Great number of work operations performed on the

fjord.

Rank: 4 3

Reason: Most complex Compromise

K11 K12

Pros: - Known technology, built before (in a smaller scale)

- Simple system, easy to calculate response from loads, ductile behavior

- Known eigenperiods which are difficult to move

- Larger capacity for unknown overloading due to stronger bridge girder

- Installation of complete assembled floating bridge, less work in Bjørnafjorden

- Less maintenance, few “wearing parts”

- Redundant system with double horizontal load-carrying system.

- Largest potential for- and flexibility in designing a robust solution.

- Mooring reduces the response and increases design life compared to K11. Possible to increase design life further with small amount of

additional steel. - Fibre rope mooring gives favorable interaction

with bridge girder. - Linear behavior of mooring without risk of

successive mooring line failure for known load cases

- Installation of complete assembled floating bridge, less work in Bjørnafjorden, simple mooring hook-up

- Few and manageable anchor locations - No joints and bearings

Cons: - Lack of redundancy - Uncertain wind load as turbulence

spectra are normally not applied to structures with long eigenperiods

- Large, concentrated forces at landfalls

- Requires larger clearance between tower legs

- Mooring needs replacement within design life. Complexity and costs related to this operation not sufficiently reflected.

- Challenging soil conditions, risk of underwater slides

- Limited experience with taut mooring on these water depths

Rank: 2 1

Reason: Most simple Most robust

K13 K14

Pros: - Redundancy in mooring - Fibre rope mooring gives favorable

interaction with bridge girder. - Linear behavior of mooring without risk

of successive mooring line failure for known load cases.

- Simplest production. - Potential for moving landfall north onto

the bank outside Gulholmane and obtaining a shorter bridge.

- Redundancy in mooring - Fibre rope mooring gives favorable interaction with

bridge girder. - Linear behavior of mooring without risk of

successive mooring line failure for known load cases.

- No joints and bearings

Cons: - Mooring, part of main load-carrying system, needs replacement within design life. Complexity and costs related not sufficiently reflected.

- Challenging soil conditions, risk of underwater slides

- Many and some unfavorable anchor positions.

- Limited experience with taut mooring on these water depths

- Great number of work operations performed on the fjord.

- Monotonic driving experience - Maintenance of joints and bearings - Noise from joints

- Mooring, part of main load-carrying system, needs replacement within design life. Complexity and costs related not sufficiently reflected.

- Challenging soil conditions, risk of underwater slides - Some unfavorable anchor positions. - Limited experience with taut mooring on these

water depths - Great number of work operations performed on the

fjord.

Rank: 4 3

Reason: Most complex Compromise

K11 K12

Pros: - Known technology, built before (in a smaller scale)

- Simple system, easy to calculate response from loads, ductile behavior

- Known eigenperiods which are difficult to move

- Larger capacity for unknown overloading due to stronger bridge girder

- Installation of complete assembled floating bridge, less work in Bjørnafjorden

- Less maintenance, few “wearing parts”

- Redundant system with double horizontal load-carrying system.

- Largest potential for- and flexibility in designing a robust solution.

- Mooring reduces the response and increases design life compared to K11. Possible to increase design life further with small amount of

additional steel. - Fibre rope mooring gives favorable interaction

with bridge girder. - Linear behavior of mooring without risk of

successive mooring line failure for known load cases

- Installation of complete assembled floating bridge, less work in Bjørnafjorden, simple mooring hook-up

- Few and manageable anchor locations - No joints and bearings

Cons: - Lack of redundancy - Uncertain wind load as turbulence

spectra are normally not applied to structures with long eigenperiods

- Large, concentrated forces at landfalls

- Requires larger clearance between tower legs

- Mooring needs replacement within design life. Complexity and costs related to this operation not sufficiently reflected.

- Challenging soil conditions, risk of underwater slides

- Limited experience with taut mooring on these water depths

Rank: 2 1

Reason: Most simple Most robust

K13 K14

Pros: - Redundancy in mooring - Fibre rope mooring gives favorable

interaction with bridge girder. - Linear behavior of mooring without risk

of successive mooring line failure for known load cases.

- Simplest production. - Potential for moving landfall north onto

the bank outside Gulholmane and obtaining a shorter bridge.

- Redundancy in mooring - Fibre rope mooring gives favorable interaction with

bridge girder. - Linear behavior of mooring without risk of

successive mooring line failure for known load cases.

- No joints and bearings

Cons: - Mooring, part of main load-carrying system, needs replacement within design life. Complexity and costs related not sufficiently reflected.

- Challenging soil conditions, risk of underwater slides

- Many and some unfavorable anchor positions.

- Limited experience with taut mooring on these water depths

- Great number of work operations performed on the fjord.

- Monotonic driving experience - Maintenance of joints and bearings - Noise from joints

- Mooring, part of main load-carrying system, needs replacement within design life. Complexity and costs related not sufficiently reflected.

- Challenging soil conditions, risk of underwater slides - Some unfavorable anchor positions. - Limited experience with taut mooring on these

water depths - Great number of work operations performed on the

fjord.

Rank: 4 3

Reason: Most complex Compromise

• Milestones for development and selection- Initial phase: Establish base cases through:

▪ Experience form earlier phases▪ Initial analyses▪ Sensitivities▪ Possible showstoppers▪ Aestetic evaluation

- Development phase▪ Extensive analyses and design, including sensitivity analyses, ship impact, parametric excitation, comfort criterias, hydrodynamic effects etc.▪ Risk analyses▪ Cost estimates based on quantities

- Conclusive phase▪ Supplementary analyses▪ Conclusion on parametric excitation▪ Optimization▪ Risk reduction through continous risk analyses and risk mitigation▪ Updated cost estimated incl. Uncertainties▪ Aesthetics▪ Robustness

Conclusion: K12 is the preferred solution

Concept development and selection

Concept development and selectionAnalyses and special studies

Concept development and selectionAesthetics - Visual Impact

• Horizontal alignment• Landscape

• Vertical alignment• Pontoon, column, bridge deck, tower and cable stay shape/configuration• Walkway• Landscaping

Concept development and selectionCost estimates

Concept development and selectionRisk Analyses

Risk analyses are carried out as a work tool to:• Choose optimal bridge concept- Identification of risk elements- Comparisons of risk elements

between concepts- Comparisons of risk elements

to others• Outline areas/challenges for

further evaluation within theproject (mitigations)- Parametric excitation- Placing of anchors- Ship collosion

Concept development and selectionRanking –K12 superior tothe other alternatives

ChallangesParametric excitation and response

ChallangesParametric excitation and response

ChallangesParametric excitation and response

OON PROPOSAL: CONSERVATIVE DESIGN APPROACH

OON PROPOSAL: CONSERVATIVE DESIGN APPROACH

PARAMETRIC EXCITATIONCALCULATED RESPONSE

CALCULATED RESPONSE HAS A RETURN PERIOD OF APPROX. 700 MILL. YEARS

© Dr.techn.Olav Olsen AS

- End-anchored bridge; known structure without joints or bearings

- Aestethically the best alternative with good horizontal and vertical alignment

- Mooring reduces response and increases robustness and capacity for skew loading

- Quantities, a key cost driver, have «converged», but optimizations are still possible

- Significant development in construction and installation methods

CONCLUSION: K12 IS A ROBUST AND COST-EFFECTIVE SOLUTION

© Dr.techn.Olav Olsen AS

- Two completely independent assessments recommended the same floating bridge alternative, and DNV GL supports the conclusion.

- The recommendations are made on detailed information about the site conditions, given in the design basis prepared by NPRA.

- Uncertainties from previous phases, like parametric resonnance, has been adressed and handled in this project

CONCLUSION: K12 IS A ROBUST AND COST-EFFECTIVE SOLUTION

The NPRA has a solid basis for proceeding with the project

Summary on costs!Concepts considered for Bjørnafjorden

Illustration: Vianova/Baezeni/NPRA

Concept assessed 2015 - 2016: 42,8

Concept assessed 2015 - 2017: 22,9

2012: 14,5

2019: 15,8

Project cost: billions NOK (2019-kroner, incl. VAT)

Concept assessed 2015 - 2016: 27,6

Extra gain! ☺This lagoon saved from NPRA highway E39 ambition!

04.07.2017

Thank you!