Construction schedule for a motorway bridge: curing, crane and weather
In which order and when do the construction steps of the bridge run, so that it opens early, the crane is rented briefly and little time is lost to weather?
Drag to rotate, scroll or pinch to zoom. The schedule below plays the whole build, from site set-up to opening. Hover a bar for details. Plan computed with a Timefold model.
The planning question
A fictional motorway bridge with 4 spans of 30 m crosses a river and a farm road. It rests on 2 abutments, the end supports in the embankments, and on 3 piers. Every support stands on bored piles with a pile cap. Precast prestressed girders, 4 per span, carry a deck slab of concrete poured on site. Building starts on 1 March.
Crew 1 builds the foundations, piers and abutments. Crew 2 places the girders with the crawler crane, concretes the deck slab span by span with one formwork set and then lays waterproofing, asphalt and railings. Concrete needs time to cure: 3 days before a pier is built on its foundation, 14 days before girders rest on a pier, 7 days in the deck formwork and 21 days before the waterproofing.
The weather is an assumed calendar for the year: frost in March and from late November, single days of heavy rain and of strong wind. Durations, curing times and the weather are assumptions for this example.
How we plan it
The Timefold model decides a priority and hold days for each of the 22 steps. For every change it builds the whole schedule: the next step is the ready one with the highest priority, and it goes on the earliest working days after its predecessors and their curing, when its crew, the crane and the formwork are free and the weather allows it. A pour needs a day without frost or heavy rain, crane lifts need days without strong wind, waterproofing and asphalt need dry days without frost. From that schedule follow the opening date, the crane rental from the working day before the first lift to the working day after the last, and the working days a step waited for the weather.
The comparison is a span-by-span bar chart, computed with the same code: span 1 is built completely before span 2, no step starts before the step listed before it, and the formwork waits for the deck crew.
What the plan shows
| KPI | Optimized plan | Comparison: span by span |
|---|---|---|
| opening | 2027-11-17 | 2028-04-25 |
| crawler crane rented (days) | 24 −118 | 142 |
| waiting for weather (working days) | 0 −89 | 89 |
Decisions
- order of the steps for each crew, the crane and the deck formwork
- start day of every step, including holding one back on purpose
Constraints
- order of the steps with curing times (piers 14 days before girders rest on them, deck 21 days before waterproofing)
- weather: no concreting on frost or heavy rain days, no crane lifts in strong wind
- one crawler crane, one deck formwork set and one step per crew at a time
Objective
early opening, short crane rental, few working days lost to weather
Questions
Why does the comparison open months later?
Span by span, the last deck slab is poured in late October. The waterproofing then needs 21 days of curing and dry days without frost, and from late November there are few. The plan builds all supports first, pours the last deck slab at the end of September and finishes the asphalt before the frost.
Why is the crane rented for 24 days only?
The plan finishes all piers and abutments before the crane arrives, then lifts the 16 girders in one campaign of about three weeks. Span by span, the crane stays from the girders of span 1 in late May to those of span 4 in October.
Why does the plan never wait for the weather?
The model knows the weather calendar in advance. It puts pours, lifts and waterproofing on suitable days and lets the crews do other work on the bad ones. In practice the forecast changes. The schedule is then computed again from the current day, with the finished work fixed.
Can it plan a bridge on falsework?
Yes. Falsework, the temporary support under the formwork of a deck concreted in place, is another kind of step with its own resource and curing time. The model stays the same.
More use cases
Your planning problem looks different?
Every operation has its own rules. Tell us about yours. We assess feasibility and expected impact in a free initial call.
Book a free call Write to us