Rotation (swing) construction

How bridges get built · Heavy lift, moving and accelerated construction · Rotation (swing) construction

Also called: rotation method, swing bridge construction, horizontal rotation, vertical rotation

How it is done

Design the rotation system: a spherical hinge or ring track at the pier base between lower and upper caps, temporary support legs around it to limit tilting, and a traction system (strand jacks pulling round a traction ring, or pushers).
Build the lower cap with the hinge, then the upper cap, pier and superstructure in the rotated position (parallel to the railway or river), by balanced cantilever, stayed cantilever or falsework.
Weigh the completed T-structure (jacking or rotation-response test) to find its centre of gravity and the hinge friction, and add counterweight to leave a small designed eccentricity toward the support legs.
Trial-rotate a few degrees before the possession to check friction, traction force and monitoring, and set stop and reverse procedures.
On the day, rotate at about 0.5–1.5° per minute with continuous monitoring of tip levels, plan position and traction force, stopping short and inching into the final position with fine-adjustment jacks.
Lock the structure (wedges or welding), concrete the gap between upper and lower caps to encase the hinge, then cast the closure segments.
Vertical rotation: assemble the half-arch lying at low level, hinged at the springing, and raise it by strand jacks pulling over a temporary tower until it reaches its design angle; then close the crown.

Key numbers

Rotated weightcommonly 5,000–30,000 t; record about 46,000 t (Baoding, 2019)
Spherical hinge diameterabout 2–6.5 m (6.5 m at Baoding)
Rotation angletypically 30–90°
Rotation rateabout 0.5–1.5° per minute (Baoding: 52.4° in 68 minutes)
Design friction at the hingestatic coefficient about 0.05–0.1
Hinge and temporary worksUSD 1–5 million (indicative)

Where it fits

Crossings of live railways and busy waterways where the possession is a few hours; spans 60-300 m; cable-stayed, arch and continuous decks.

Where it does not

Sites where the rotated position conflicts with anything; unbalanced structures without counterweight.

Choosing it

Choose rotation over cantilevering above live tracks when the railway allows only short possessions: everything except the swing happens beside the tracks.
Prefer a lateral slide or SPMT for short spans (under about 40 m), where a whole span can be built to one side and moved quickly.
Choose vertical rotation for arch halves that can be assembled near the springing at low level; it avoids the tie-back towers and stays of cantilever erection.
Avoid it where the rotated position would obstruct something else, or where the pier foundation cannot take the concentrated hinge load.

Plant, pace and money

PlantSpherical hinge (to 30,000 t), strand jacks or pushers, counterweights, survey.

ProductivityRotation in one to two hours; the rest as for the erection method chosen.

CostThe hinge and temporary works USD 1-5 million; saves the possession cost.

Risks and controls

What goes wrong

Unbalanced weight causing the structure to tip on the hinge, friction stalling the rotation, closure misalignment.

Quality assurance

Weighing test to find the centre of gravity, trial rotation, real-time monitoring during the swing.

Origins

Rotating a completed structure about a pivot was used in Europe for some cable-stayed and arch bridges built on a river bank in the 1970s–90s; in China it grew from arch construction into the standard way of building overpasses across operating railways from the 2000s, with rotated weights now above 40,000 t.

Examples

Hundreds of Chinese overpasses across operating railways, including the 46,000 t cable-stayed bridge at Baoding (2019); vertical and horizontal rotation of CFST arch halves (Yajisha, Guangzhou, 2000).

Case studies

Cable-stayed overpass over the Beijing–Guangzhou Railway, BaodingChina · 2019About 46,000 t rotated 52.4° in 68 minutes on spherical hinges of 6.5 m diameter, a record weight.

Yajisha Bridge, GuangzhouChina · 2000360 m CFST arch whose halves were raised by vertical rotation and then swung horizontally into position.

In the bridge game

What Bridge Master applies when you pick it

Deck types: Steel box girder, Steel truss, Network tied arch, Steel arch, Concrete arch, Cable-stayed, Extradosed, PSC box, balanced cantilever. Spans 60-200 m, up to 300 m.

+40: Live railway below: build beside it and swing it in during one possession.
+15: The channel stays open while the span is built on the bank side.
-35: Nothing below to protect: rotation is money spent on a hinge you did not need.
-30: Short spans are lifted in a night with a crane.
+10: Keeps cranes and falsework out of the street.
-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.
not allowed: Too heavy and too long to rotate on one hinge.

Try it in the game →