Bearing replacement

How bridges get built · Finishing, articulation and maintenance · Bearing replacement

Also called: bearing renewal, jack-and-replace

How it is done

Inspect and record why the bearing failed (seized, cracked, corroded, walked out, split elastomer), survey deck levels, bearing offsets and plinths, and confirm from as-built records that the deck can be lifted at the intended points.
Design the jacking: jack positions on the pier top beside the bearing, on temporary steel brackets or on a trestle; local strengthening of jacking points; lift height; deck stresses with the support line lifted; traffic restrictions during the lift.
Prepare: install brackets or jacking plinths, level the jacking surfaces, set jacks with load cells and locking collars, and set up synchronised control and displacement monitoring on every girder line.
Lift all jacks at a support line together in small steps, holding the load on locking collars or packs, and keep the differential lift between jacks within the specified limit.
Remove the old bearing by cutting the anchors and breaking out the bedding; repair or rebuild the plinth with high-strength mortar or concrete and cure it to strength.
Install the new bearing (often of a different type), level and pre-set it for the current deck temperature, grout the bedding and anchor pockets, and connect the upper plate.
Lower in steps onto the new bearing, release the jacks, check full contact and offsets, record loads and displacements, and fix the cause (leaking joint, blocked drain) or the new bearing will fail the same way.

Key numbers

Lifttypically 3–10 mm, just enough to unload and free the bearing
Jacks50–1,000 t each, normally worked below about 80 % of rated capacity
Differential lift between adjacent jackstypically limited to 1–2 mm per step
Duration2–5 days per support line for straightforward elastomeric replacements; weeks where plinths or pier tops must be rebuilt
Indicative costUSD 30,000–300,000 per pier depending on access and traffic

Where it fits

Any bridge with accessible bearings; the reason the game rewards bearing types that can be replaced.

Where it does not

Bridges with no jacking space or inaccessible bearings, where the pier head must be modified first.

Choosing it

Replace like for like when the failure is local (corrosion under one leaking joint); change the type, for example rocker to elastomeric or spherical, when the original type is obsolete or the articulation was wrong.
Jack from the pier top when there is room beside the bearing and the concrete can take the jack loads; otherwise brackets or trestles are needed and cost and time rise sharply.
On short bridges, consider converting the end supports to semi-integral or integral while the bearings are out; it removes both the bearing and the joint problem.
Close the bridge for a short period rather than lifting under traffic when several support lines must be lifted or the margin on deck stresses is small.

Plant, pace and money

PlantJacks and synchronised control, brackets, grouting kit.

ProductivityA pier in a few days.

CostUSD 30,000-300,000 per pier depending on access and traffic.

Risks and controls

What goes wrong

Cracking the deck by differential jacking, traffic loading during jacking, unknown deck condition.

Quality assurance

Jacking plan, load logs, bearing contact check.

Origins

Bearing replacement became routine in the 1980s and 1990s as the first generation of post-war motorway viaducts reached 30–40 years with seized rockers, corroded rollers and split elastomers. Synchronised multi-point hydraulic lifting made it possible with the deck kept open to restricted traffic.

Examples

Routine on 30-50 year old viaducts; rocker bearings are the usual victims.

Case studies

Forth Road BridgeUK · 2015A seized pin in a truss end link, an articulation that should have rotated freely, led to a cracked member and closure of the bridge to all traffic for about three weeks in December 2015.

Hammersmith FlyoverUK · 2013–15Refurbishment of the 1961 post-tensioned flyover replaced its bearings and expansion joints together with installing new external post-tensioning.