About bridge · Construction methods

How bridges get built

All 26 construction methods in the TheBridgeEng database, the same one the bridge game uses to judge your choices: what each method is, which decks it suits, the spans it reaches, the plant it needs, and the site conditions where it shines or fails.

Grouped by family. "Best when" and "Not this method when" are the rules the game applies; they are also a fair summary of practice. Spans are for road bridges of normal width.

Cast-in-place concrete 6Precast concrete 6Steel erection 3Marine and heavy lift 3Cable-supported and arch 4Accelerated bridge construction 4

Cast-in-place concrete

Full staging method (ground falsework) 동바리 공법 (FSM)

Formwork supported on scaffold towers or a timber and steel falsework grid built up from the ground, the deck is cast in place span by span or all at once. Cheapest for short bridges with dry, firm ground below and no traffic; impossible over water, rail or live roads.

DecksRC slab, Voided slab, RC T-beam, RC box, PSC box (cast in place), Rigid frame, Concrete arch, PSC box, balanced cantilever, Extradosed, Network tied arch
Spanseconomical 10-50 m, up to 70 m
Cycle30-45 days per span
Plantscaffold towers or shoring frames, formwork, concrete pump, mobile crane
Risksfalsework collapse (the leading cause of construction fatalities in concrete bridges), foundation settlement of towers, flood washout
Best when
  • Dry firm ground, low deck: falsework is the cheap answer.
Think twice when
  • No falsework in water.
  • No falsework over track.
  • No falsework over live lanes unless the road can close.
  • Tall towers get expensive and unstable.
  • Falsework foundations settle on soft ground.
  • Long viaduct: MSS or precast is faster.
Not this method when
  • Ground falsework in a river.
  • Ground falsework over a live railway.
Try it in the game → Watch the animation →

Movable scaffolding system (MSS), overhead or underslung 이동식 비계 공법 (MSS)

A self-launching steel girder carrying the formwork for a whole span, supported on brackets at the piers, casts a span then launches itself to the next. Falsework that never touches the ground: the standard for 30-60 m span concrete viaducts over water, roads and poor ground in Korea and Europe.

DecksPSC box (cast in place), Voided slab, RC box, RC T-beam, RC slab
Spanseconomical 30-55 m, up to 70 m
Cycle7-14 days per span
PlantMSS girder 1.5-2x span long, pier brackets, hydraulic launching, concrete pump
Riskslaunching overturning, bracket failure, casting deflection control
Best when
  • Long viaduct of repetitive spans: MSS.
  • Builds over water and traffic.
  • Underslung MSS passes over track without ground contact (check clearance to the girder).
Think twice when
  • Too few spans to amortise the MSS.
  • Beyond MSS span.
  • Curved MSS possible but slow; consider curved steel or CIP on falsework.
Not this method when
  • MSS far beyond feasible span.
Try it in the game → Watch the animation →

Incremental launching method (ILM), concrete 압출 공법 (ILM)

The box girder is cast in 15-30 m segments in a fixed casting bed behind the abutment and jacked forward over sliding bearings on the piers, with a steel launching nose ahead. Needs a straight or constant-radius alignment and constant depth; ideal over rivers, rail and valleys where nothing can stand below.

DecksPSC box (cast in place), RC box, PSC box, balanced cantilever
Spanseconomical 30-50 m, up to 65 m
Cycle7-10 days per segment 20-25 m
Plantcasting bed with formwork, launching nose 0.6-0.7 x span, jacks and sliding pads, temporary piers if needed
Riskspier reaction and friction forces during launch, cantilever moment at nose landing, geometric tolerance
Best when
  • Straight, repetitive, no ground access: ILM.
  • Launching over rail needs no possession except for the nose passage.
  • Nothing in the river during construction.
  • Tall piers: launching avoids tall falsework, but pier top forces need checking.
Think twice when
  • Variable curvature cannot be launched.
  • Launching moments too high; temporary piers or another method.
  • Too short to set up a casting bed.
Not this method when
  • ILM on a variable-radius alignment.
Try it in the game → Watch the animation →

Balanced cantilever, cast-in-place with form travellers (FCM) 캔틸레버 공법 (FCM 현장타설)

Two form travellers advance symmetrically from each pier, casting 3-5 m segments and stressing cantilever tendons in turn; midspan closure joins the cantilevers and continuity tendons finish the job. No support below, any pier height, spans 80-250 m in concrete.

DecksPSC box, balanced cantilever, Extradosed, Concrete arch, Rigid frame, PSC box (cast in place), Cable-stayed
Spanseconomical 80-200 m, up to 250 m
Cycle7-10 days per segment pair (2 x 3-5 m)
Plant2 form travellers per pier (4 for two piers at once), temporary pier-deck fixity or twin-leaf pier, tower crane per pier, concrete pump or barge supply
Risksunbalanced load (one traveller ahead), traveller collapse, wind on long cantilever, closure alignment, creep
Best when
  • This is how you build an FCM box.
  • No support below required.
Think twice when
  • Long free cantilevers in strong wind need temporary ties.
  • Too short to justify travellers.
  • Many medium spans: precast segmental cantilever is faster.
Not this method when
  • CIP cantilever beyond any built span.
Try it in the game → Watch the animation →

Incremental launching with temporary piers 가벤트 병용 압출공법 (ILM)

Launching as usual, but temporary steel piers halve the launching span, so 70-110 m permanent spans can be launched with a normal box depth. Common over rivers and valleys where the falsework cannot stand but a few temporary bents can.

DecksPSC box (cast in place), RC box, PSC box, balanced cantilever, Steel box girder, Steel plate girder
Spanseconomical 60-100 m, up to 120 m
Cycle7-10 days per segment 20-25 m
Plantcasting bed and launching jacks, launching nose, temporary steel piers on piles or spread footings, sliding bearings
Riskspier reaction and friction forces during launch, cantilever moment at nose landing, geometric tolerance
Best when
  • Launching over rail needs no possession except for the nose passage.
  • Nothing in the river during construction.
  • Tall piers: launching avoids tall falsework, but pier top forces need checking.
  • Temporary piers make the launching span manageable.
Think twice when
  • Variable curvature cannot be launched.
  • Too short to set up a casting bed.
  • Temporary piers in deep water become a marine job of their own.
  • Temporary piers in a navigation route need permits and protection.
Not this method when
  • ILM on a variable-radius alignment.
Try it in the game →

Falsework on temporary piles (shallow water) 말뚝 지지 동바리 (천수 하천)

Cast-in-place on falsework carried by temporary steel piles driven into the riverbed. Works in slow water up to about 3 m deep outside the flood season; the classic method for small river bridges and canals.

DecksRC slab, Voided slab, RC T-beam, RC box, PSC box (cast in place), Rigid frame, Concrete arch, PSC box, balanced cantilever, Extradosed, Network tied arch
Spanseconomical 20-45 m, up to 60 m
Cycle30-45 days per span
Planttemporary piles and bracing, falsework towers and beams, formwork
Risksfalsework collapse (the leading cause of construction fatalities in concrete bridges), foundation settlement of towers, flood washout
Best when
  • Shallow, slow water: piled falsework is the cheap answer.
Think twice when
  • Too deep for piled falsework.
  • Fast water loads the temporary piles and debris piles up.
  • Only in the dry season; the falsework must be out before the floods.
  • Blocks the navigation route.
Not this method when
  • Piled falsework in 5 m+ of water is not a temporary works design, it is a bridge.
Try it in the game →

Precast concrete

Balanced cantilever, precast segments (crane, gantry or lifting frame) 캔틸레버 공법 (프리캐스트 세그먼트)

Match-cast segments are lifted from barges or trucks by a deck-mounted lifting frame, crane or launching gantry and glued and stressed symmetrically from each pier. Two to four segments a day per pier: the fast way to build 60-150 m spans in quantity.

DecksPrecast segmental box, Extradosed, Cable-stayed, PSC box, balanced cantilever
Spanseconomical 60-130 m, up to 150 m
Cycle0.5-1 days per segment pair
Plantcasting yard with match-cast cells, lifting frame or gantry, barges or trucks, epoxy and temporary PT bars
Risksgeometry control errors accumulate, gantry incidents, epoxy in cold or rain
Best when
  • Several medium-long spans: precast cantilever.
  • Segments arrive by barge.
Think twice when
  • Too few spans for a casting yard.
  • Beyond precast cantilever.
  • Span-by-span is faster at short spans.
Not this method when
  • Precast cantilever beyond feasibility.
Try it in the game → Watch the animation →

Span-by-span precast segmental with overhead or underslung gantry 스팬바이스팬 공법 (런칭 갠트리)

A gantry spanning two piers holds all the segments of one span hanging from it, they are glued and post-tensioned together, the span is set on its bearings, and the gantry launches to the next pier. One span every 2-4 days: the fastest viaduct method ever devised.

DecksPrecast segmental box, PSC box (cast in place), PSC I-girder, PSC U-girder, Voided slab
Spanseconomical 30-50 m, up to 60 m
Cycle2-4 days per span
Plantlaunching gantry 2x span long, casting yard, segment delivery by truck on deck or barge, external PT
Risksgantry launching over the next pier, segment delivery logistics, joint quality
Best when
  • Kilometres of 30-55 m spans: gantry span-by-span.
  • Marine or urban viaduct with no ground access.
Think twice when
  • Gantry and yard cannot be amortised.
  • Beyond span-by-span.
  • Gantry geometry on tight curves is awkward.
Not this method when
  • Span-by-span gantry beyond feasibility.
Try it in the game → Watch the animation →

Crane erection of precast girders 크레인 거치 (프리캐스트 거더)

Mobile or crawler cranes on the ground (or on the approach embankment) lift precast girders onto the piers, usually one girder per lift and a span per night over traffic. The reference method: cheapest where cranes can stand beside the pier.

DecksPSC I-girder, PSC U-girder, Voided slab, Spliced PSC girder, Timber deck, FRP deck, Precast segmental box, RC slab, Steel plate girder, Steel box girder
Spanseconomical 15-45 m, up to 60 m
Cycle1-2 hours per girder
Plant200-500 t crawler or mobile crane (two for tandem lifts), haul route for 30-45 m girders, temporary bracing
Risksgirder rolling during lift, crane ground bearing, lifts over live traffic
Best when
  • Cranes can stand at the piers: just lift them in.
  • Night lifts from the verge or in a possession.
Think twice when
  • Cranes cannot stand in water; launcher or barge.
  • No crane positions; use a launching girder.
  • Tall piers exceed reach; launcher.
  • Very heavy girders need large tandem cranes.
Not this method when
  • Land crane erection over deep water.
Try it in the game →

Launching girder (beam launcher) for precast girders 런칭 거더 (빔 런처) 거치

A steel truss two spans long sits on the piers, receives girders delivered along the completed deck, carries them forward and lowers them into place, then moves itself to the next span. Top-down erection over water, wetlands, tall piers and urban streets where no crane can stand.

DecksPSC I-girder, PSC U-girder, Steel plate girder, Spliced PSC girder, Precast segmental box, Steel box girder, Voided slab, Full-span precast box
Spanseconomical 25-45 m, up to 55 m
Cycle2-4 days per span
Plantbeam launcher, girder transporter on deck, pier top brackets
Riskslauncher stability during self-launch, girder transfer
Best when
  • No ground access, many spans: beam launcher.
  • Top-down over the wetland.
Think twice when
  • Too few spans.
  • Cranes would be cheaper.
  • Launcher struggles on tight curves.
Try it in the game →

Spliced girder erection on temporary towers / strongbacks 분절 거더 가설 (가벤트 / 스트롱백)

Haunched pier segments are set on the piers, drop-in segments are supported on temporary towers or hung from strongbacks, splices are cast and the girder is post-tensioned continuous.

DecksSpliced PSC girder, PSC I-girder, PSC U-girder, Steel plate girder
Spanseconomical 45-80 m, up to 100 m
Cycle14-28 days per span
Plantlarge cranes or barge cranes, temporary towers, strongbacks, PT equipment
Riskstemporary tower settlement, stability of pier segment before splice
Best when
  • The method for spliced girders.
Think twice when
  • Deep water towers are expensive; use strongbacks.
  • Towers in the rail corridor are hard; strongbacks only.
Try it in the game →

Full-span precast erection with a deck-running gantry 풀스팬 프리캐스트 가설 (갠트리)

A 900 t carrier drives the finished deck with a complete span on its back; a launching gantry at the front sets it on the next pair of piers. One span per shift, kilometres per year. Needs a casting yard, identical spans and a straight run.

DecksFull-span precast box, PSC U-girder, PSC I-girder
Spanseconomical 25-40 m, up to 45 m
Cycle1-2 days per span
Plantcasting yard, span carrier 900 t, launching gantry, gantry cranes in the yard
Risksgantry launching over the next pier, segment delivery logistics, joint quality
Best when
  • Kilometres of 30-55 m spans: gantry span-by-span.
  • Marine or urban viaduct with no ground access.
Think twice when
  • Gantry and yard cannot be amortised.
  • Beyond span-by-span.
  • Gantry geometry on tight curves is awkward.
Not this method when
  • Span-by-span gantry beyond feasibility.
Try it in the game →

Steel erection

Crane erection of steel girders (single piece or spliced) 크레인 가설 (강거더)

Steel girders or box sections delivered in shippable lengths, bolted or welded at field splices on temporary supports or in the air, then decked. Light pieces make this the default for steel over roads and rail.

DecksSteel plate girder, Steel box girder, Steel truss, Orthotropic steel box, Steel arch, PSC I-girder, PSC U-girder, Spliced PSC girder, Network tied arch
Spanseconomical 30-90 m, up to 120 m
Cycle2-7 days per span
Plantmobile cranes, temporary bents for splices, bolting crews
Riskslateral torsional buckling of unbraced girders (Marcy 2002), splice alignment
Best when
  • Standard steel erection.
  • Light lifts in short windows.
Think twice when
  • Use barges or launching.
  • Reach limits; launching.
Try it in the game →

Incremental launching of steel girders 강거더 압출 가설

Steel girders or boxes are assembled behind the abutment and pushed or pulled over rollers on the piers, often with a nose and sometimes with a temporary king-post. Light steel launches far more easily than concrete: standard for rail, river and valley crossings.

DecksSteel plate girder, Steel box girder, Orthotropic steel box, Steel truss, Steel arch, PSC box (cast in place)
Spanseconomical 40-120 m, up to 160 m
Cycle3-7 days per launch of 30-60 m
Plantrollers or sliding bearings on piers, strand jacks or pushers, launching nose, assembly yard
Risksweb crippling over rollers, lateral guidance, cantilever moment
Best when
  • Steel over water, rail or valley: launch it.
  • One short possession for the nose passage.
Think twice when
  • Cannot launch variable curvature.
  • A crane would do it faster.
Not this method when
  • Steel launch on a variable-radius alignment.
Try it in the game →

Cantilever erection of steel (trusses, boxes, arches) 강교 캔틸레버 가설 (트러스 / 박스 / 아치)

Steel members or box segments are added piece by piece from the pier outward using a deck-mounted derrick or creeper crane, with temporary back-stays where needed. The classic method for big trusses and arches over navigable water.

DecksSteel truss, Steel box girder, Orthotropic steel box, Steel arch, Cable-stayed, Extradosed, Steel plate girder
Spanseconomical 100-300 m, up to 550 m
Cycle3-7 days per segment / panel
Plantcreeper or derrick crane, temporary stays and towers, barges
Riskscantilever buckling (Quebec 1907), stay adjustment, closure
Best when
  • Long steel truss or arch: cantilever erection.
  • Keeps the channel open.
Think twice when
  • Simpler methods.
Try it in the game →

Marine and heavy lift

Floating crane / barge lift of whole spans or large segments 해상 크레인 (플로팅 크레인) 일괄 가설

A crane barge of 1,000-4,000 t lifts a whole precast or steel span, or a large box segment, from a transport barge onto the piers. One span per tide: the marine method for viaducts and for the side spans of long-span bridges (Incheon, Busan-Geoje).

DecksPSC I-girder, PSC U-girder, Precast segmental box, Steel box girder, Orthotropic steel box, Steel truss, Steel arch, Spliced PSC girder, Steel plate girder, Voided slab, Extradosed, Cable-stayed, Network tied arch
Spanseconomical 40-120 m, up to 200 m
Cycle1-3 days per span
Plantfloating crane 1,000-4,000 t, transport barges, load-out quay
Risksweather windows, barge motion during set-down, tide
Best when
  • Deep water viaduct: lift whole spans by floating crane.
  • Navigable river with barge access.
Think twice when
  • Crane barge cannot float.
  • Fast current makes barge positioning dangerous.
Not this method when
  • Floating crane on dry land.
Try it in the game →

Strand jack heavy lift from barge (tandem or from deck) 스트랜드 잭 인양 가설

A whole deck section is floated under the gap on a barge and lifted with strand jacks mounted on the completed cantilevers or on lifting gantries. The method for central sections of cable-stayed decks, arch spans and closure segments in navigable channels.

DecksOrthotropic steel box, Steel arch, Steel truss, Steel box girder, Cable-stayed, Suspension, Extradosed, Steel plate girder, Precast segmental box, Concrete arch, Network tied arch
Spanseconomical 100-300 m, up to 500 m
Cycle1-2 days per lift
Plantstrand jacks 200-700 t each, lifting frames, barge
Riskssynchronisation of jacks, tide timing, channel closure
Best when
  • Central span over a shipping channel: float in and jack up.
Think twice when
  • Needs barge draft.
Try it in the game →

Float-in of a complete tied arch 타이드 아치 일괄 부유 운반 및 거치

The whole tied arch is assembled on shore or a barge, floated to the piers and set down on the bearings at low tide, sometimes with jack-down. The signature method for single-span tied arches over navigable water.

DecksSteel arch, Steel truss, Steel box girder, Network tied arch
Spanseconomical 100-250 m, up to 300 m
Cycle2-5 days per bridge
Planttwin barges, ballast system, tugs, assembly yard
Risksone-shot operation, weather, tidal window, set-down on bearings
Best when
  • Tied arch over a channel: float it in.
Think twice when
  • No draft for barges.
Try it in the game →

Cable-supported and arch

Arch erection by cantilever with temporary stays 아치 사장 가설 (임시 스테이 캔틸레버)

Each half-arch is built outward from the springing with form travellers or precast segments, held by temporary stay cables from a pylon over the pier, then closed at the crown. Standard for concrete and steel arches over gorges.

DecksConcrete arch, Steel arch, Steel truss, Network tied arch
Spanseconomical 100-400 m, up to 450 m
Cycle5-10 days per segment
Planttemporary pylons and stays, form travellers or crane, stay stressing jacks
Risksstay force adjustment, wind, crown closure
Best when
  • Gorge arch: cantilever with stays.
Think twice when
  • Long stayed cantilevers in wind need extra ties.
Try it in the game →

Cable crane (cableway) erection 케이블 크레인 가설

A cableway spanning the gorge between two masts carries precast segments or steel pieces to any point along the arch. Used where the valley is too deep or steep for anything else (Chinese arches, Alpine crossings).

DecksConcrete arch, Steel arch, Steel truss, Precast segmental box
Spanseconomical 150-450 m, up to 600 m
Cycle2-5 days per segment
Plantcableway masts and track cables, carriage 50-200 t, temporary stays
Riskscableway anchorage, wind, segment swing
Best when
  • Very deep gorge: cableway.
Think twice when
  • Only for gorges.
Try it in the game →

Cable-stayed deck erection in free cantilever 사장교 캔틸레버 가설 (데릭 크레인 / 폼트래블러)

After the pylon is climbed, deck segments (steel by derrick crane from barges, concrete by form traveller or precast lifting frame) are added alternately each side and each new stay is installed and tensioned. Continuous geometry and stay-force control until closure at midspan.

DecksCable-stayed, Extradosed, Orthotropic steel box, PSC box, balanced cantilever
Spanseconomical 200-800 m, up to 1100 m
Cycle5-10 days per segment pair + stays
Plantderrick cranes or form travellers, stay stressing jacks, pylon climbing forms and tower crane, geometry control survey
Risksconstruction-stage wind on the cantilever (buffeting, vortex), stay installation errors, closure geometry
Best when
  • The way cable-stayed bridges are built.
Think twice when
  • Temporary tie-downs and wind tunnel tests of construction stages.
Try it in the game →

Suspension bridge erection (anchorages, towers, cable spinning or PPWS, deck lifting) 현수교 가설 (앵커리지, 주탑, 케이블 가설, 보강형 인양)

Anchorages and towers first, then a pilot rope and catwalk across, main cables built by aerial spinning or prefabricated parallel wire strands, then deck sections lifted from barges by hangers working out from midspan (or from the towers) in a sequence set by cable geometry.

DecksSuspension, Cable-stayed
Spanseconomical 700-2000 m, up to 2100 m
Cycle4-7 years
Plantcatwalk, spinning wheels or PPWS reels, cable compaction and wrapping, lifting gantries on main cable, barges
Riskscable spinning weather, deck erection aerodynamics (partially erected deck), anchorage construction
Best when
  • The only way to build one.
Try it in the game →

Accelerated bridge construction

Lateral slide (transverse launching) of a complete deck 횡방향 밀어넣기 (ABC 슬라이드)

The new deck is built beside the existing road or track on temporary supports, then slid sideways onto the permanent piers in one weekend or possession. Accelerated bridge construction for replacements and rail crossings.

DecksSteel plate girder, Steel box girder, PSC I-girder, PSC box (cast in place), Steel truss, Orthotropic steel box, Steel arch, PSC U-girder, Spliced PSC girder, Voided slab, Precast segmental box, Network tied arch
Spanseconomical 30-100 m, up to 150 m
Cycle8-48 hours per bridge
Planttemporary supports, slide tracks and PTFE pads, jacks
Risksdifferential friction, alignment, closure overrun
Best when
  • Replace or cross in one possession: slide it in.
Think twice when
  • No reason to slide over open ground.
Try it in the game →

SPMT move (self-propelled modular transporters) SPMT 일괄 운반 가설

A complete span is built off-line and driven into place on computer-controlled multi-axle transporters, then set down on bearings. Hours of road closure instead of months; used over highways and in urban sites with a staging area nearby.

DecksSteel plate girder, Steel box girder, PSC I-girder, Steel truss, Orthotropic steel box, Steel arch, PSC U-girder, Spliced PSC girder, Precast segmental box, Voided slab, Network tied arch
Spanseconomical 30-90 m, up to 140 m
Cycle6-24 hours per span
PlantSPMT modules, jacking towers, staging yard
Riskshaul path bearing, deck stresses at support points, set-down
Best when
  • Overpass with a yard nearby: SPMT.
  • Feasible in a long possession if a haul path crosses the track at grade.
Think twice when
  • SPMTs need ground.
Not this method when
  • SPMT over water.
Try it in the game →

Top-down construction from the completed deck 탑다운 시공 (완성 상판 위에서 전진)

Piling rig, crane and materials travel on the finished spans and build the next pier and span ahead, so nothing touches the ground below. The environmental method for wetlands, mangroves and protected shorelines (long low viaducts).

DecksPSC I-girder, PSC U-girder, Precast segmental box, Voided slab, Spliced PSC girder, Steel plate girder, Steel box girder, RC slab, RC T-beam
Spanseconomical 20-45 m, up to 55 m
Cycle4-8 days per span
Plantdeck-mounted piling rig, launching girder or crane on deck, precast pier caps
Risksdeck capacity under plant, sequence lock-in
Best when
  • Wetland rule: build from the deck.
  • No temporary works allowed below: top-down.
Think twice when
  • Unnecessary where access is free.
Try it in the game →

Precast substructure assembly (columns and caps) 프리캐스트 하부구조 조립

See substructure pier_cap_precast. Listed here as a method so the construction stage can schedule it.

Decksany deck type
Spanseconomical 20-60 m, up to 100 m
Cycle1-3 days per pier
Plantcranes, grouted couplers or PT
Risksconnection grout, tolerance
Best when
  • Precast piers assembled in days.
Try it in the game →