Strand jack lifting

How bridges get built · Heavy lift, moving and accelerated construction · Strand jack lifting

Also called: heavy lifting by strand jacks, deck section lifting, lifting gantry

Strand jack lifting — concept diagram — Concept diagram (TheBridgeEng)

How it is done

Engineer the lift: load at each lifting point (by weighing or with calculated tolerances), strand jack capacity with margin, gantry and anchorage design, and the load path into the permanent structure.
Install lifting gantries or frames on the main cables, deck tips, pier heads or temporary towers; mount the strand jacks, power packs and computer control, reeve the strands and fix the bottom anchors to the load's lifting lugs.
Pre-tension all strands, then trial lift: raise the load 100–200 mm clear of its supports, hold, and check loads, deflections and anchorages.
Lift in synchronised strokes with the control system holding level within set limits, monitoring the load at each point and stopping on any deviation.
When lifting from a barge, take the load off quickly at the start so barge motion cannot re-load the strands (snatch loads), and move the barge away once clear.
At final level, align and connect to the structure (temporary hinges, bolts or welds), transfer the load and release the strands gradually.
Move the gantries to the next lift, and inspect strands and wedges between lifts, replacing any damaged.

Key numbers

Strand jack capacityabout 15–1,000 t per jack; systems combine many jacks for loads of several thousand tonnes
Lifting speedabout 5–20 m per hour
Strand working loadcommonly 40–50 % of minimum breaking load
Deck campaign on a suspension bridgeabout one section per day
CostUSD 50,000–150,000 per section; system hire per campaign (indicative)

Where it fits

Suspension bridge deck erection, box girder sections for cable-stayed bridges, arch halves, spans up to 5,000 t or more.

Where it does not

Sites where a crane can do the lift faster; loads without a stable landing structure.

Choosing it

Choose strand jacks over crane vessels when the lift is heavier than available cranes, the water is too shallow, or the lifting point is high above the water (suspension decks, arches, pier-top lifts).
Prefer a land or floating crane for repetitive light lifts where speed matters; strand jacks are slow to rig for each lift.
Use the same system for lowering, sliding and launching; one set of jacks often serves several operations on a project.
Lifting from barges needs a quick take-off and tidal planning; prefer lifting from a fixed platform or quay when available.

Plant, pace and money

PlantStrand jacks (50-800 t each), gantries, power packs, control system.

ProductivityOne section per day in a lifting campaign.

CostUSD 50,000-150,000 per section; system hire per campaign.

Risks and controls

What goes wrong

Strand jack synchronisation failure, gantry overload, barge drift under a partially lifted load.

Quality assurance

Lift procedure with load monitoring, strand inspection, synchronisation tests.

Origins

Strand jacks were developed from post-tensioning hardware by the prestressing firms in the 1970s and became the standard tool for very heavy, slow, precise lifts in offshore, power-station and bridge work.

Examples

Deck sections of Great Belt East, Xihoumen, Yi Sun-sin and 1915 Çanakkale; the Lake Champlain arch lift; launching and lowering of many steel decks.

Case studies

Great Belt East BridgeDenmark · 1998Streamlined box deck sections lifted from barges by gantries running on the main cables.

Golden Horn Metro Bridge, IstanbulTürkiye · 2014Eleven swing-span deck sections of about 300 t each were lifted about 17 m from a barge by two 200 t strand jacks on temporary gantries.

Lake Champlain BridgeUSA · 2011The network tied arch centre span, assembled on shore and floated in on barges, was raised onto its piers by strand jacks.

In the bridge game

What Bridge Master applies when you pick it

Deck types: Orthotropic steel box, Steel arch, Steel truss, Steel box girder, Cable-stayed, Suspension, Extradosed, Steel plate girder, Precast segmental box, Concrete arch, Network tied arch. Spans 100-300 m, up to 500 m.

+30: Central span over a shipping channel: float in and jack up.
-40: Needs barge draft.
-10: A span hanging on strand jacks in strong wind: tight weather windows.
-25: A one-off operation for one span: on a multi-span viaduct it is the exception for the main span, not the method for the deck.

Try it in the game →