Suspended Concrete Slabs and Formwork Systems

11 October 2018

According to every engineering handbook, suspended concrete slabs are defined as flat, table-like surfaces, which have no direct physical connection to the ground. Included in the list of challenges faced by a consulting engineer here, there’s the formwork system to create, one that’ll support and buttress the concrete slabs as they’re installed inside a multi-storey structure. With all of the above having been said, where’s this “suspended” feature coming from?

Viewing a Rudimentary Structural Drawing

Engineers have drawn up a cross-sectional view of a structure, you know, for the casual architectural student to check out. On the ground, two elements support the lowest suspended concrete slab. It’s not actually connected to the ground, though, because there’s a big basement underneath the floor. For the next floor, which also acts as the lower level’s ceiling, there are four structural elements anchoring the slab. Two lower framework constructs, plus the vertical beams for the floor above, provide plenty of support all along the slab’s perimeter.

Suspended Concrete Slabs: Formwork Systems

Of course, that quickly scrawled drawing is accurate, but it doesn’t exactly overflow with details. Logistically, a number of formwork components need to be moved up to each floor before the suspended concrete slabs can be poured. Unless this is a precast system, that stage of the project just can’t be avoided. Wooden boards and plywood panels are transported to the required level of the rising edifice. Underneath the formwork panels, temporary beams and frames are incorporated into the slab supporting shoring sets. Concrete is a heavy material. Suspended at height, still uncured, this dangerously mobile construction substance needs the guiding hands of a professional engineering service to ensure the formwork system performs according to all design and safety-oriented criteria, as generated by the head consulting engineer.

Assessing Structural Complications

The least number of shoring components possible goes up to the floor, the panels and temporary beams are fastened, and the concrete is poured according to an engineer’s directions. What about the ground level, the basement, and the floors/ceilings below? They’re absorbing the weight, as carried by the formwork system. Are those lower floors finished and structurally resilient? Can they support the formwork and the uncured concrete as it pushes down from the above floor?

These questions and others all need solutions before the heavy concrete load is discharged. Furthermore, the introduction of post-tensioning fittings, the thickness of the slab and its concrete composition, plus any permanent support systems, must all be determined during the design stage. As for the formwork systems, there are many versatile solutions on the market now, including special panelized slab tables and their inbuilt adjustable steel legs.

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