How bridges get built · Cable-supported and arch bridges · Suspension bridge erection: cables, hangers and deck
Also called: main cable erection, deck erection by strand jack, suspension bridge construction
How it is done
- Build the anchorages (gravity, tunnel or rock) and the towers; install the tower saddles, offset toward the side spans by a calculated amount so the free-standing towers are not overstressed as the cables are loaded.
- Cross the pilot rope (by boat, helicopter or drone), haul up the catwalk ropes, hang the catwalks with their cross bridges, and install the hauling system.
- Form the main cables by aerial spinning or PPWS, adjusting each strand to a reference strand at stable night-time temperature; compact the cables and fit cable bands at the hanger points.
- Install the hangers and lift deck sections from barges (or from the deck below) with lifting gantries running on the main cables, usually from midspan toward the towers; join sections with temporary hinges so the deck can follow the changing cable shape.
- Move the tower saddles toward their final position in steps as deck load builds, jacking them on their bases to keep tower bending within limits.
- When all sections are hung and the profile is right, close the temporary hinges by welding or bolting, working out from midspan; install bearings and expansion joints at the towers.
- Wrap and dehumidify the cables, remove the catwalks, install surfacing and monitoring, and record as-built cable and hanger forces.
Key numbers
- Main spanabout 500–2,023 m (record 1915 Çanakkale, 2,023 m)
- Cable sagabout span/9 to span/11
- Wire5–6 mm galvanised, 1,570–1,960 MPa; main cables up to about 1.1–1.3 m diameter
- Hanger spacingabout 12–25 m
- Deck sectionsabout 20–50 m long and 200–1,000 t per lift
- Programmecable formation 3–8 months; deck lifting 3–6 months for a long span
- Deck, cables and towersUSD 10,000–20,000 per m² of main span (indicative)
Where it fits
- Spans over 800-1,000 m, straits and wide rivers, sites where towers can be founded and anchorages built.
Where it does not
- Sites without anchorage geology or space; spans that a cable-stayed bridge can do (they are cheaper below about 1,000 m).
Choosing it
- Choose a suspension bridge over a cable-stayed bridge for spans beyond about 1,100–1,200 m, or where very tall pylons or deep-water pylon foundations make a stayed scheme costlier.
- Lift deck sections from barges where the waterway can be occupied; cantilever small units out from the towers (Akashi Kaikyo) where shipping cannot be obstructed or the water is too shallow for barges.
- Choose a box deck for aerodynamics and weight; choose a truss where a double deck (road and rail) or high torsional stiffness for rail is needed.
- Consider a self-anchored suspension bridge for spans of about 150–400 m where the ground cannot take an earth anchorage, accepting falsework under the deck.
Plant, pace and money
PlantCatwalk and spinning or PPWS equipment, cable bands, strand jack lifting gantries (2 x 250-500 t), barges, tugs.
ProductivityCable formation 3-6 months; deck lifting 3-6 months for a long span.
CostUSD 10,000-20,000 per m2 of main span for the deck, cables and towers.
Risks and controls
What goes wrong
- Aerodynamic instability of the partially erected deck (Tacoma is the reminder), cable strand damage, deck section drop, hanger misfit.
Quality assurance
Wind tunnel tests of erection stages, cable survey and sag adjustment, section-by-section geometry, hanger force checks.
Origins
The modern sequence (catwalks, cables formed in place, deck hung from the cables) was set by John A. Roebling and his successors on the Niagara (1855) and Brooklyn (1883) bridges; lifting large prefabricated deck sections from barges became the norm with the streamlined box deck introduced at Severn (1966).
Examples
Akashi Kaikyo (1,991 m), Great Belt, Xihoumen, Yi Sun-sin (1,545 m), 1915 Canakkale (2,023 m).
Case studies
Akashi Kaikyo BridgeJapan · 19981,991 m main span; the pilot rope was carried across by helicopter (1993), and the stiffening truss was erected by cantilevering small units out from the towers and anchorages so the busy strait stayed open. The 1995 Kobe earthquake moved the towers apart by about 0.8 m during construction.
Great Belt East BridgeDenmark · 19981,624 m main span; aerially spun cables and streamlined box deck sections lifted from barges by gantries on the cables.
Yi Sun-sin BridgeSouth Korea · 20121,545 m main span over Gwangyang Bay; PPWS cables and steel box deck.
1915 Çanakkale BridgeTürkiye · 20222,023 m main span, the world's longest; PPWS main cables and steel box deck sections lifted from vessels.
In the bridge game
What Bridge Master applies when you pick it
Deck types: Suspension, Cable-stayed. Spans 700-2000 m, up to 2100 m.
- +30: The only way to build one.
Related methods
Aerial spinning of main cablesPrefabricated parallel wire strands (PPWS)Strand jack liftingSteel and composite pylonsCable wrapping and dehumidificationSelf-anchored suspension bridge erectionStress-ribbon bridge constructionStay cable and hanger replacement
Further reading
Gimsing and Georgakis · Honshu-Shikoku Bridge Authority technical reports · Gimsing and Georgakis, Cable Supported Bridges: Concept and Design (3rd ed.)