Formwork Cycle Planning

Definition

Formwork Cycle Planning is the discipline of designing, sequencing and resourcing the reuse of formwork across a concrete structure so that the pouring rhythm sets — rather than reacts to — the overall programme. On any cast-in-place building above about six storeys, the floor cycle time is the single largest driver of the programme, and formwork cycle planning is the difference between a 5-day floor and a 12-day floor.

What the Cycle Actually Governs

• Number of complete formwork sets in circulation (typically 2 or 3 for a jump-cycle system).
• Strike time (when the formwork can be removed) — driven by concrete strength gain, temperature, and design load case.
• Back-propping arrangement while lower floors continue to gain strength.
• Formwork clean, oil and set-up time before the next pour.
• Reinforcement fix time within the cycle.
• MEP embedment installation windows.
• Concrete pour rate — trucks per hour, pump capacity, finishing crew.

Why It Matters

On a 30-storey residential tower, a 6-day floor cycle finishes 12 weeks ahead of a 9-day cycle for the same building. The cost of a third formwork set is trivial next to 12 weeks of preliminaries. But the cost of trying to run a 5-day cycle without the right cycle plan — mispiped propping, undersupplied labour, delayed embedments — is a series of cracked slabs and re-worked pours that no amount of catch-up recovers. The plan is where the tradeoff is made honestly.

Real-World Example

On a 24-storey office tower in Sydney, the tender programme assumed a 7-day floor cycle with two sets of table formwork. The controls team modelled the actual cycle in a fragnet — pour, cure, strike, lift, clean, fix rebar, embed MEP, close, pour — and demonstrated the 7-day cycle needed a third set and a two-crew reinforcement gang. The commercial team costed the third set at AUD 380k. The programme benefit was 34 days, worth AUD 2.1m in preliminaries and financing. The third set was purchased before mobilisation. The tower finished five days ahead of the revised programme; the neighbouring project run on two sets ended up on an 11-day cycle and lost the same 34 days it thought it had saved.

Practical Lessons Learned

• Model the cycle as a fragnet, not as a bar. A single "Level 12 cycle" bar hides the constraints that actually drive the duration.
• Concrete strength gain is temperature-dependent. A cycle plan drawn in summer collapses in winter unless the strike time is re-derived for the actual cure temperature.
• Back-propping is design, not habit. The temporary works register owns the arrangement; the cycle plan schedules it.
• Two crews per cycle is often the unlock. One crew stripping while another fixes rebar shortens the cycle without increasing risk.
• Embedments are the hidden constraint. If MEP inserts are not on site when the rebar closes, no cycle plan on paper will help.

Common Mistakes

• Assuming the tender cycle time without modelling the constraints that actually drive it.
• Buying two formwork sets when three would unlock a step change in cycle time.
• Using generic strike times from a supplier catalogue instead of concrete test results from the actual mix and pour.
• Ignoring back-propping loads on the lower floors — a fast cycle can overload a slab that hasn't reached its design strength.
• Planning a 6-day cycle with a 5-day rebar-fix duration.
• No accountability for the cycle — the site engineer says formwork owns it, the concrete engineer says the structural engineer owns it, and nobody drives it.
• Building the cycle around the best-case pour rate rather than the worst-case one.

Expert Tips

• Draw the cycle on one A3 page — every trade, every hour, every constraint. If it doesn't fit, the cycle isn't ready.
• Run a mock cycle on the lowest structural floor. First-cycle problems always exist; discover them before they compound on the tower.
• Interlock with the concrete pour card. The card is the release; the cycle is the plan.
• Publish cycle-day naming (Day 1 = Pour, Day 4 = Strike, Day 5 = Lift, etc.) so every trade uses the same vocabulary.
• Track actual vs planned cycle time weekly. Two consecutive slips of a day each mean the cycle has structurally changed and the plan needs revising, not the crew shouting at.

Key Takeaways

• Formwork cycle time is the primary driver of the programme on any cast-in-place structure of meaningful height.
• The cycle is a fragnet, not a bar; every trade and every constraint sits inside it.
• Strike time is a concrete-strength calculation, not a habit.
• Number of formwork sets is a commercial decision with programme consequences — model both.
• Embedments and back-propping are constraints that quietly break a well-drawn cycle plan.

Related Concepts

Interlocks with Concrete Pour Card, Temporary Works Register, Critical Path Method, Takt Time Planning, and Last Planner System. Cycle-fragnet templates at PMMilestone.org.