World’s first Tensegrity Bridge - Kurilpa Bridge

Introduction:-
Australia's Queensland State Government in 2006 established a design brief on a pedestrian bridge with low budget hardly possible in state capital, Brisbane to establish link with Queensland Gallery of Modern Art (GoMA). Baulderstone(contractor), Arup(engineer) and Cox Rayner(architect) won the design competition with a design, fusion of art and science having array of masts, cables and flying steel spars well suited with locality, structurally efficient and completely original. More on “tensegrity”.

Key statistics

Ø  Bridge deck 430m long x 6.5m clear width between handrails

Ø  500m³ of concrete and 500 tonnes of steel

Ø  Nearly 7km of high strength steel cables

Why “tensegrity” Bridge?

All the possible solution in front of the team and why there were discarded is shown below:-

Restrictions:- Clearance and remote access.

OPTION	HINDERANCE	DECISION
Cable-stayed	Large mast Visually Dominant	No
Arch	Poor soil condition	No
Suspension	Poor soil condition	No
Tube	Promising but difficult to construct	No
Tensegrity mast-and-cable	Satisfies all aspect	Yes

Superstructure form and details

Ø  3 main sections separated from central by expansion joint and bearings:-

1.      Point approach(120m)

2.      Tensegrity itself(3 spans of 58m, 128m and 45m)

3.      Tank street approach(82m)

Ø  Mainly used composite steel (masts, cables, ties, tensegrity canopy) and concrete for deck structure.

Ø  Tensegrity bridge elements:-

1.      Masts:- fabricated tubular steel sections up to 30m long with section 610-905mm diameter.

2.      Major mast cables:- high-strength spiral wound galvanized wire ropes 30-80mm diameter.

3.      Spars:- circular hollow sections up to 23m long with section sizes 457-508mm diameter.

4.      Spar cables:- high-strength stainless steel spiral wound cables 19-32mm diameter.

Ø  Precast deck panels were used which were stitched by in situ concreting.

Ø  Edge Beams separated from deck has fabricated box sections having curved outer face for aerodynamic stability.

Ø  Pairs of major raking tubular steel masts spring from the main support piers on either sides of the main span, setting the locations of an approximately coplanar array of minor secondary masts. The major and minor masts are offsets from the perpendicular both longitudinally and transversely, thus preventing cable/mast or cable/cable clashes and providing the signature “Randomness” without much reducing structural efficiency. Secondary cables connected to flying struts, themselves pure tensegrity elements (only supported by cables), provide lateral restraint to the masts.

Ø  The tensegrity array of flying struts and cables that hovers above and beside the deck fulfils three critical functions:

1.      It laterally restrains the tops of all the masts, preventing them from buckling sideways under the loads arising from the suspension of the deck plus lateral and seismic forces.

2.      It suspends the canopy, allowing it to float above the deck with no apparent means of support.

3.      It laterally restrains the tops of all the masts, preventing them from buckling sideways under the loads arising from suspension of the deck plus lateral and seismic forces.

4.      It works in unison with all the masts and cables to resist twisting and lateral forces arising from patch loads on the deck (i.e. crowds), wind and earthquakes.