Going Vertical: Multi-Storey Construction
When we move from single-storey to multi-storey, the structural game changes. Weights multiply, seismic/wind loads become critical, and material logistics get complicated.
1. Suspended Floor Systems
How do we build a concrete floor in the air?
Bondek / Condeck (Composite Steel Decking)
Profiled steel sheeting that acts as both the permanent formwork (so you don't need timber prop boards everywhere) and the tensile reinforcement for the slab. Very common in commercial and apartments.
Post-Tensioned (PT) Slabs
High-strength steel cables are draped inside the formwork and tensioned (stretched) after the concrete cures.
Why? It compresses the concrete, allowing for much thinner slabs and longer spans between columns.
Danger: Never drill into a PT slab without X-ray scanning. Cutting a live cable can explode through the concrete.
2. Transfer Structures
Architects often want a different layout on Level 1 than on Ground. Maybe apartments above a carpark.
A Transfer Slab or Transfer Beam is a massive concrete element that takes the load of the walls/columns above and redirects it to the columns below, which are in different locations. These are thick, heavily reinforced, and expensive.
3. Lateral Stability (Bracing)
Gravity isn't the only force. Wind and Earthquakes try to push the building sideways (Shear).
- Core Bracing: In high-rise, the lift shaft and stairwell are solid concrete cores that act as a rigid spine for the building.
- Shear Walls: Dedicated reinforced concrete walls designed to resist racking.
- Cross Bracing: Steel X-braces seen in industrial sheds or some exposed-structure architecture.
4. Precast & Tilt-Up
Why pour concrete on site (in-situ) when you can crane it in?
Precast: Made in a factory, trucked to site. High quality finish.
Tilt-Up: Poured on the floor slab of the building, then craned (tilted) up into position. Cheaper (no transport), but needs a huge casting bed area.