Construction methods · Finishing, articulation and maintenance

Bridge demolition and deconstruction

Taking a bridge down is construction in reverse with less information: the old drawings may be wrong and the post-tensioning may be corroded. Decks are cut into pieces and lifted, launched back, lowered by strand jacks, or dropped in a controlled sequence; only remote sites allow explosives.

How bridges get built · Finishing, articulation and maintenance · Bridge demolition and deconstruction

Also called: bridge removal, deconstruction, controlled demolition, reverse launching

Bridge demolition and deconstruction — concept diagram — Concept diagram (TheBridgeEng)

How it is done

Investigate the structure: tendon condition, hidden defects, asbestos and lead paint; design the removal sequence with the same rigour as erection.
Cut the deck into pieces with saws or breakers, lift by crane, barge or SPMT; for segmental or launched decks, reverse the erection method.
Protect the road, rail or river below with crash decks and debris control; demolish piers and cut piles below ground.

Where it fits

Every replacement project; the game's lateral slide and SPMT sites include removal of the old bridge.

Where it does not

Cutting post-tensioned members without knowing the tendon state; dropping spans onto navigation routes or live tracks.

Plant, pace and money

PlantSaws, breakers, cranes, crash decks, barges, hydro-demolition.

ProductivityA span per week for controlled removal.

CostUSD 150-400 per m2 of deck removed, more over rail and water.

Risks and controls

What goes wrong

Uncontrolled collapse during cutting (several fatal accidents), falling debris, environmental release.

Quality assurance

Demolition engineering with stage checks, exclusion zones, monitoring during cuts.

Examples

Old Tappan Zee (2017-2019), Hong Kong flyover removals over live roads, Korean overpass replacements in weekend possessions.