Bridge jacking and lifting

How bridges get built · Heavy lift, moving and accelerated construction · Bridge jacking and lifting

Also called: deck jacking, bridge raising, bearing jacking, synchronised lifting

How it is done

Survey the structure and its current support reactions, by calculation and, where possible, by trial jacking with load cells; assess the deck and substructure for the temporary support condition at the jacking points.
Design jacking points on the pier cap beside the bearings, on temporary brackets or frames founded on the pier or footing, or on temporary towers; add stiffeners or strengthening at the deck jacking positions.
Install jacks with load cells and mechanical locking collars (or packing that follows the lift), connected to a synchronised, computer-controlled pump with displacement transducers at every point.
Lift in small increments, often 1–5 mm per step at the start, checking load and displacement at each point against limits on differential movement; follow the lift with locking collars or packing.
Hold the structure on mechanical locks or packing, never on hydraulic pressure alone, while the work is done (bearing replacement, plinth raising, settlement correction).
Lower onto the new bearings or raised supports in the reverse sequence and confirm reactions after load transfer.
Re-survey levels, inspect for cracking, and reset joints and approach levels.

Key numbers

Jack capacityabout 50–1,000 t per jack
Lift for bearing replacementcommonly 3–15 mm in total
Differential lift between adjacent pointstypically held to a few millimetres
Raising for clearance0.3–2 m in stages on packing or new plinths (Spirit of St. Louis Boulevard overpass, about 0.64 m)
Paceabout one pier per day for bearing replacement
CostUSD 20,000–200,000 per pier (indicative)

Where it fits

Bearing replacement, clearance increases, ILM and slide landing, settlement correction.

Where it does not

Jacking without locks (hydraulic failure drops the deck); jacking a continuous deck at one pier without checking the others.

Choosing it

Choose jacking at the existing piers over deck replacement when the deck is sound and the problem is bearings, clearance or settlement.
Prefer synchronised computer control over manually coordinated pumps for continuous decks or more than a few jacking points.
Prefer temporary towers over brackets when the pier cap lacks space or strength for jacks.
Raise in stages on packing when the total lift is large, and give permanent support with new plinths or extended columns cast under the raised deck.

Plant, pace and money

PlantHydraulic jacks (50-1,000 t), synchronised pumps, load cells, locking rings, brackets.

ProductivityA pier in a day.

CostUSD 20,000-200,000 per pier.

Risks and controls

What goes wrong

Differential lift cracking the deck, jack slippage, bracket failure.

Quality assurance

Jacking procedure with limits per step, load and displacement logs, survey of the deck during the lift.

Origins

Robert Stephenson lifted the Britannia Bridge tubes with hydraulic presses in 1849–50, building packing under them as they rose; computer-synchronised multi-point jacking with load and displacement feedback has been standard practice since the 1990s.

Examples

Bearing replacements on most ageing viaducts; raising of motorway overpasses for clearance (Spirit of St. Louis Boulevard, Missouri); lifting of new spans onto their supports (Fremont, 1973).

Case studies

Spirit of St. Louis Boulevard Bridge over I-64, MissouriUSA · c. 2014Overpass raised about 0.64 m by hydraulic jacks to cure a substandard 4.45 m clearance; reported at about half the cost of replacement, with a 30-day closure instead of six months.

Fremont Bridge, PortlandUSA · 1973The 275 m, about 5,400 t centre arch section was jacked up about 52 m from barges onto the side spans, a record lift at the time.

Britannia Bridge, Menai StraitUK · 1850Wrought-iron tubes floated into position and raised by hydraulic presses, with masonry and packing built up beneath them as they rose so a press failure could not drop them.