floating bridge – when is the technology ready?€¦ · bergsøysund floating bridge • bridge...

Bruno Villoria

Floating Bridge – When is the technologyready?

Teknologidagene 21.-24. september 201522/09/2015

Teknologidagene 21.-24. september 2015

Table of contents

1. Existing Floating bridges

2. When the technology is challenged - Bjørnafjorden

i. Main conceptsii. Response to environmental Loadsiii. Ship Impactiv. Marine Operations

3. Further investigations

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Floating Bridges - USA

Hood Canal Bridge

• Completion: 1961• Total length: 2398 m • Includes a drawspan• Concrete pontoons• Mooring lines




Hood Canal Bridge

• Sinking during the February 13, 1979 Wind storm combined with an extremely high tideMaintenance hatches were left open

• Criticized design of the pontoon

• Reopened in 1982

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Evergreen Point Floating Bridge

• Completion: 1963• Total length: 2310 m• 33 Pontoons• 58 anchor lines• 70 000 vehicles / day


Floating Bridges in Norway

Bergsøysund Floating Bridge

• Completion: 1992• Total length: 933 m • Main span: 106 m• No mooring line• Truss Deck



Bergsøysund Floating Bridge

• Bridge girder anchored to the shore

• Wave, current and wind loads transferred to the abutments in the form of axial loads



Nordhordland Floating Bridge

• Completion: 1994• Total length: 1246 m • Main span: Cable-stayed Bridge• 10 Concrete pontoons• No mooring line• End Anchoring


Floating Bridges in Norway – Lessons learned


• Observations related to theoperation and maintenance ofBergsøysund and Nordhordland Floating bridges

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Table of contents





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Constraints:

• Allowed speed: 110 km/h

• 4 traffic lanes

• Navigation channel at the centreof the fjord Vertical clearance : 45 m Horisontal clearance: 400 m

• A total length exceeding 4 km

• Depth of the Fjord: 500 m

• Withstand ship impacts

Main concepts

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Curved Bridge– Straight Bridge–

Main concepts

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Straight Bridge

Mooring line Mooring line

Total Length: 4076 m, 18 Pontoons 16 mooring lines required Main Span supported by two cable-

stayed bridges Expansion joint at one extremity

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Straight Bridge

• Cross Section - High Bridge (Height 3.5 m)

Pylons

• Cross Section – Side spans (Height 6.5 m)

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Curved Bridge

Total Length: 4198 m 20 pontoons No mooring line required Fixed end connections

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Curved Bridge

• Twin steel box Girders connected with cross beams (Vierendeel beam) every 62 m

• Width of 60 m

Pylons

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Table of contents


2. Floating Bridge for Bjørnafjorden

i. Main conceptsii. Environmental Loadsiii. Ship Impactiv. Marine Operations


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Prediction of weather conditions

Weather Buoys were installed in January 2015 and continuously collecting data

Use of existing statistics and simulations to predict design values for wind, waves, current and tide in Bjørnafjorden

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Wave loads

Results from statistical simulations (Sintef)

100 year wind and swell waves

Wind environment Reference velocity of 26 m/s and a roughness length of 0.01 m (coastal area) 10 minutes wind velocity at 10 m height: V10,10 = 30.5 m/s

Return Period [years] Hs[m] Tp[s] gamma100 3 3-6 3.3

Return Period [years] Hs[m] Tp[s] gamma100 0.4 12-14 5

Swell waves

Wind Generated Waves

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Wind loads - Procedure

• Load effect evaluated on the basis of the Eurocodes

• Procedure:– Wind taken as a Gaussian process– Elastic behaviour of the structure– Response expected to be also a Gaussian process– Extreme values Gumbel distributed– Characteristic values taken as expected maximum for the Gumbel

distribution– Calculations performed in the frequency domain

• Wind load coefficients for the Bridge girder are based on CFD analysis

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Wind loads - Findings

• The Dynamic effects of wind are dominated by the two first fundamental modes

• Contribution from higher modes non negligible• Certain modes activate pendulum movements of the pontoons

Curved Bridge Straight Bridge

Mode 1 (51.3 s) Mode 2 (39.5 s) Mode 1 (63.7 s) Mode 2 (55.3 s)

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Wave loads - Procedure

• No guidelines from Eurocodes• Procedure:

o Calculated in OrcaFlex (time domain analysis)o Calculation procedure includes non-linearites in load definitiono Response found to be almost linearo Effect of mooring-lines taken into account

• Characteristic values found byo 10 Simulations of 3 hrs storm conditions on the relevant contour lineo Simulate wind generated waves and swell generated waves simultaneous

(two-peaked spectrums)o Extreme values taken as mean of the 10 maxima found in the simulations

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• Stresses dominated by bending moments about the weak axis

• Observed pendulum motions of the pontoons cause large bending and torsional moments in the Bridge girder

• An accurate environmental design basis can help avoid triggering some pendulum

• A large number of Eigen modes coincide with wave excitation frequencies

• Wave loads transferred to the bridge girder depend on pontoon geometry

Wave loads - Findings

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Combined Wave and Wind loads

• Based on characteristic values for:o Wind aloneo Waves aloneo Marginal load effects from current (only incorporated in static calculations)

• Analysis of combined effects of wind and waveso Extreme values evaluated for different stochastic processes with different

frequency content and different response behaviouro Unlikely that the structure is subjected simultaneously to the extreme loads

from wind and waveso Correlation is to be assessed

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Pontoon Design

• Purpose: o To reduce forces transferred to the bridge

girdero To ensure that displacements and

accelerations remain within allowable limits

• The following criteria have been chosen

• Different pontoon geometries have been considered

Parameter Criterion criteria Type of criteria Limiting parameter

Width1 degree roll angle for 80%

eccentric trafficImposed by

Design GroupMinimum roll stiffness

Area Deflection < Linfluens/350 EurocodesMinimum heave

stiffness

Displacement>20 000 t (side spans) >70 000 t (main span)

Ship impactMinimum

displacement

Pontoon Design

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Ship Impact - Methodology

• Analysis of the existing traffic and prediction of ship traffic in the area(Monte Carlo Simulations)

• Determination of an accepted risk

• Determination of a design ship• A relevant indentation curve has to be

used.Energy transferred to the pontoons can then be evaluated

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Ship Impact - Methodology

The ship impact analysis can be subdivided into two main steps:

1. Impulse loads from the impacting ship estimated from local dynamic analyses of the considered pontoon (USFOS)Centric and eccentric impact scenarios are considered

2. The global response of the bridge is then evaluated in Orcaflex (time domain simulation)

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Ship Impact – Findings

The following elements affect greatly the response of the bridge Mass of the hit pontoon Restoring stiffness Mooring stiffness

Higher utilization of the abutment for the straight bridge solution

Maximum utilization under centric impacts

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Production of the pontoons High competences in Norway: the production of pontoons is expected to

take place in Norway

Productions methods will be the same regardless of the chosen solution

Challenging to find facilities with sufficient capacity

A barge or a floating dock could be built

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Towing of the pontoons

Potential towing route:165 km at a towing speed of 3 knotTotal duration: approx. 30 hours

Weather restricted operation

Powerful Anchor Handling Tug vessels (AHT) could perform the towing operation

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Production and transportation of the Bridge girder

Production can take place in many countriesWelding robots can help guarantee a certain levelof quality

The girder elements have to be transported to the assembly yard in the vicinity of Bjørnafjorden

The bridge elements would then be weldedtogether and transported to the planned bridgelocation

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Assembly of side spans

Assembly of columns and pontoons

The assembled girder element is then lifted and held in position while the pontoon with columns is positioned under the girder.

Side spans can be towed to the bridge site (3large sections)

Stability has to be investigated at every stage

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Assembly of high bridge

The complete High Bridge segment will consist of four pontoons and the two towers.

Towing to Bjørnafjorden

Supporting barges can be introduced prior to transportation Temporary ballast is considered

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Environmental load calculations :

Dynamic wind response has to be further evaluated (correlation length, coupled fundamental modes)

Assessment of the correlation between wind and wave loads Effect of floating supports on the divergence and flutter stability of the

bridge girder

Model tests and Software development can help address these issues

Ship Impact calculations : New indentation curve for the design ship Finalize the ship collision risk analysis Evaluate the potential for weak links or fenders

Alternative Solution: Navigation channel positioned closer to the shore

Further investigations

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Challenging but feasible

Thank you for your attention

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floating bridge – when is the technology ready?€¦ · bergsøysund floating bridge • bridge...

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