Precast Concrete Slab

How is a three-leg precast slab installed, and does it need propping?

The three-leg prestressed concrete plank (corrugated plank) is up to 7 cm thick at its thickest part, so it carries load somewhat like a beam and generally needs no propping during installation. It is made to TIS standards and designed to resist fire for at least 1 hour under EIT standard 1009-34.

• If the plank is longer than 4 m, add one temporary prop at mid-span.
• A concrete topping 5 cm thick must be poured over it.
• Bearing on the supporting beam must be no less than 5 cm.
• Reinforce the topping with RB6 bars at 20 cm spacing laid as a grid, or 4 mm welded wire mesh at 20 cm.
• Connect planks by welding the side steel plates (shear keys), as with flat-soffit planks.

Load capacity depends on the number of prestressing wires and the plank length. With no propping needed, it also avoids the termite problem caused by timber props left under ground-floor slabs. Besides the three-leg type, flat-soffit, hollow-core and bridge-deck planks are available for other jobs.