Floating Bridge When is the technology ready?

Floating Bridge When is the technology ready? Bruno Villoria

Table of contents 1. Existing Floating bridges 2. When the technology is challenged - Bjørnafjorden i. Main concepts ii. Response to environmental Loads iii. Ship Impact iv. Marine Operations 3. Further investigations

Floating Bridges - USA Hood Canal Bridge Completion: 1961 Total length: 2398 m Includes a drawspan Concrete pontoons Mooring lines

Floating Bridges - USA Hood Canal Bridge Sinking during the February 13, 1979 Wind storm combined with an extremely high tide Maintenance hatches were left open Criticized design of the pontoon Reopened in 1982

Floating Bridges - USA 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

Floating Bridges in Norway Bergsøysund Floating Bridge Bridge girder anchored to the shore Wave, current and wind loads transferred to the abutments in the form of axial loads

Floating Bridges in Norway 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 the operation and maintenance of Bergsøysund and Nordhordland Floating bridges

Main concepts Constraints: Allowed speed: 110 km/h 4 traffic lanes Navigation channel at the centre of 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 Curved Bridge Straight Bridge

Straight Bridge Mooring line Mooring line Total Length: 4076 m, 18 Pontoons 16 mooring lines required Main Span supported by two cablestayed bridges Expansion joint at one extremity

Straight Bridge Cross Section - High Bridge (Height 3.5 m) Cross Section Side spans (Height 6.5 m) Pylons

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

Curved Bridge Twin steel box Girders connected with cross beams (Vierendeel beam) every 62 m Width of 60 m Pylons

Table of contents 1. Existing Floating bridges 2. Floating Bridge for Bjørnafjorden i. Main concepts ii. Environmental Loads iii. Ship Impact iv. Marine Operations 3. Further investigations

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

Wave loads Wind Generated Waves Return Period [years] Hs[m] Tp[s] gamma 100 3 3-6 3.3 Results from statistical simulations (Sintef) Swell waves Return Period [years] Hs[m] Tp[s] gamma 100 0.4 12-14 5 100 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: V 10,10 = 30.5 m/s

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

Wind loads - Findings The Dynamic effects of wind are dominated by the two first fundamental modes Mode 1 (51.3 s) Mode 2 (39.5 s) Mode 1 (63.7 s) Mode 2 (55.3 s) Curved Bridge Straight Bridge Contribution from higher modes non negligible Certain modes activate pendulum movements of the pontoons

Wave loads - Procedure No guidelines from Eurocodes Procedure: o Calculated in OrcaFlex (time domain analysis) o Calculation procedure includes non-linearites in load definition o Response found to be almost linear o Effect of mooring-lines taken into account Characteristic values found by o o o 10 Simulations of 3 hrs storm conditions on the relevant contour line Simulate wind generated waves and swell generated waves simultaneous (two-peaked spectrums) Extreme values taken as mean of the 10 maxima found in the simulations

Wave loads - Findings 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

Combined Wave and Wind loads Based on characteristic values for: o Wind alone o Waves alone o Marginal load effects from current (only incorporated in static calculations) Analysis of combined effects of wind and waves o o o Extreme values evaluated for different stochastic processes with different frequency content and different response behaviour Unlikely that the structure is subjected simultaneously to the extreme loads from wind and waves Correlation is to be assessed

Pontoon Design Purpose: o o To reduce forces transferred to the bridge girder To ensure that displacements and accelerations remain within allowable limits Pontoon Design The following criteria have been chosen Parameter Criterion criteria Type of criteria Limiting parameter 1 degree roll angle for 80% Imposed by Width Minimum roll stiffness eccentric traffic Design Group Minimum heave Area Deflection < Linfluens/350 Eurocodes stiffness Displacement >20 000 t (side spans) >70 000 t (main span) Ship impact Minimum displacement Different pontoon geometries have been considered

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

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)

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

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

Towing of the pontoons Potential towing route: 165 km at a towing speed of 3 knot Total duration: approx. 30 hours Weather restricted operation Powerful Anchor Handling Tug vessels (AHT) could perform the towing operation

Production and transportation of the Bridge girder Production can take place in many countries Welding robots can help guarantee a certain level of quality The girder elements have to be transported to the assembly yard in the vicinity of Bjørnafjorden The bridge elements would then be welded together and transported to the planned bridge location

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 (3 large sections) Stability has to be investigated at every stage

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

Further investigations 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

Challenging but feasible Thank you for your attention