Site Engineering Series · @JayStructure
High-Rise Formwork Systems
The temporary structure that determines the permanent one — and why formwork decisions drive the entire construction programme
Construction Systems
Jay Sah
Site Engineer · 5+ years on $300M+ high-rise projects in Sydney
Every concrete element in a high-rise building starts the same way. Steel reinforcement is placed. Then formwork is installed around it. Concrete is poured inside the formwork and left to cure. The formwork is stripped. And what remains is the permanent structure.
The formwork is temporary. But its selection — the system chosen, the cycle time it allows, the sequence it enables — determines the pace of the entire project. A wrong formwork decision on a high-rise is not a minor inconvenience. It is a programme impact worth millions of dollars.
Key Reality
Formwork costs account for
40–60% of the total cost
of a concrete structure
It is temporary. It leaves nothing behind. And it is the single biggest driver of cost and programme in reinforced concrete construction.
The Main Formwork Systems in High-Rise Construction
🗔️
Table Form
Large pre-assembled panels for suspended slabs. Crane-lifted floor to floor. Fast cycle times — typically 5–7 days per floor on repetitive high-rise.
⬆️
Jump Form (Core)
Self-climbing formwork for core walls. Hydraulic rams lift the entire rig without a crane. Covered in the Core Walls article — the heartbeat of the programme.
🛟
Climbing Screen
Perimeter safety screens that climb with the building. Protect workers from falling and falling objects. Required on virtually all Australian high-rise projects by WHS regulations.
📦
Proprietary Column Forms
Reusable steel or aluminium forms for columns. Designed for a specific column size and stripped after minimum concrete strength is reached.
Table Form — The Floor Cycle Engine
On a typical high-rise residential tower, the suspended slab is formed using table forms — large, pre-assembled formwork panels that are lifted as a unit from one floor to the next. The cycle works like this:
The Typical Floor Cycle — 5 to 7 Days
Day 1–2
Strip tables from floor below, crane to next level, set up
Day 2–3
Fix reinforcement, PT tendons, embedments, MEP sleeves
Day 4
Pre-pour inspection, concrete pour, finishing
Day 5–7
Cure, test cylinders, stress PT if applicable, prepare to strip
Repeat · Every floor · For 40+ levels
What the Site Engineer Manages on Formwork
Formwork design compliance
Formwork must be designed to AS 3610. You are not the formwork designer — but you are responsible for ensuring the design exists, has been reviewed, and is being followed on site. Never allow formwork to be erected without an approved design.
Stripping strength verification
Formwork cannot be stripped until concrete reaches the specified stripping strength — typically 15–20 MPa for suspended slabs. This is verified by testing cylinders cured under the same conditions as the structure. Stripping early is one of the most common — and most dangerous — mistakes on site.
Re-propping sequence
After stripping, re-props are installed below the fresh slab to transfer loads back to floors below. The number of re-propped floors, and the sequence in which they are removed, is critical. The structural engineer specifies this — and deviating from it can overload floors that are not yet strong enough.
Inspection before pour
The pre-pour inspection includes checking that formwork is tight with no gaps that concrete can escape through, that props are correctly positioned and not damaged, and that the soffit level is correct. A concrete blowout mid-pour — where formwork fails under concrete pressure — is one of the most costly events on any project.
Key Numbers — Formwork
40–60%
of concrete structure cost
5–7
days per floor cycle
15–20
MPa before stripping
3
floors typically re-propped
Watch the formwork cycle breakdown on YouTube
I walk through a complete table form floor cycle on a real Sydney high-rise — from strip to pour to re-prop.
Table Form
AS 3610
High-Rise Construction
Site Engineering