The method is particularly suited to viaducts and bridges with consistent span geometry, gentle curvature and limited vertical grade change. The key structural challenge is that the deck passes over each pier in turn — so every cross-section experiences transitory hogging and sagging moments as the support condition changes, requiring flexural capacity for the full reversing bending envelope as the deck advances.
Definition
Incremental launching is a bridge construction method in which the superstructure is fabricated or cast in segments on one bank and then pushed forward over the piers in stages — often in regular casting segments of around 15 to 30 metres for many concrete bridges — until the deck reaches its final position. A temporary steel launching nose extends ahead of the deck to reduce the cantilever moment as each span is crossed. The method allows construction to proceed without falsework in the spans and without obstruction to traffic, rivers or other features below.
The Launching Process
Launching is carried out using hydraulic jacks acting against the rear abutment or purpose-built thrust blocks. The deck slides on temporary low-friction pads or sliding bearings positioned on each pier. Lateral guide systems prevent the deck from drifting off alignment during the push.
The launching nose — a steel fabrication bolted to the leading end of the deck — reduces the cantilever moment as each span is negotiated. Without the nose, the hogging moment as the deck tip crosses mid-span would be prohibitive. Once launching is complete, the nose is removed, temporary bearings are replaced with permanent bearings, and final stressing operations are completed.
The push itself can be driven by hydraulic jacks in either configuration: push systems act from the rear abutment against the deck soffit, while pull systems use strand jacks anchored ahead of the advancing nose. Push is more common on concrete decks; pull is often preferred on long steel launches where rear abutment thrust capacity is limited. Central prestressing tendons carry the deck through the alternating hogging and sagging envelope during launch, with continuity tendons added on completion to provide the permanent in-service condition.
Commercial and Sequence Considerations
Incremental launching concentrates construction risk at the casting yard and launching operation. The civils programme on the spans is eliminated — no falsework, no in-span formwork. But the casting yard must maintain output to feed the launch cycle, and the launch itself depends on pier readiness ahead of the advancing deck.
A pier that is not ready when the deck arrives creates a sequence problem: the deck cannot advance, and any temporary holding position may require verification of the applicable temporary load case. Auxiliary towers or intermediate falsework can provide contingency support in this situation, but at additional cost and programme risk. The dependency between casting yard output, pier programme and launch scheduling is tightly coupled — and commercially consequential if any element falls behind.
Tap to enlarge
Incremental launching — nose advance, pier dependency and erection load envelope
Original diagram — EE&HL Network 2026 · In preparation
Diagram: Original — EE&HL Network 2026
Frequently Asked Questions
Incremental launching is a bridge construction method in which the superstructure is built in segments on one bank and pushed forward over the piers in stages — often in regular casting segments of around 15 to 30 metres for many concrete bridges — until the deck reaches its final position.
A launching nose is a temporary steel fabrication bolted to the leading end of the deck. It reduces the cantilever moment as the deck tip advances toward each pier, preventing excessive hogging stress during the launch.
A pier that is not ready when the deck arrives stops the launch. The deck cannot advance, and any temporary holding position may require verification of the applicable temporary load case — so pier readiness directly controls sequence and commercial exposure.
Push systems use hydraulic jacks acting from the rear abutment against the deck soffit to advance the deck. Pull systems use strand jacks anchored ahead of the launching nose to draw the deck forward. Push is more common for concrete decks; pull is often preferred on long steel launches where rear abutment thrust capacity is limited.
The casting yard is the works area behind the rear abutment where deck segments are cast or fabricated, post-tensioned and prepared for launching. It must maintain continuous output to match the launch cycle, since the launch programme is paced by yard throughput as much as by pier readiness.
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