Vee Slab Structural Design Supplement

Vee Slabs can be any width between about 600mm and 2400mm. 2400 is the maximum width a precast element can be transported without special provision as is the maximum length of 13500mm The width of Vee Slabs is adjusted to any dimension between these two limits to exactly suit the job. So far we have not cast any portion of a floor insitu on formwork.

The depth of Vee Slabs can vary between 150mm and 400mm The thickness of the base layer can vary between 50mm and 70mm The nominal width of the base of the ribs, WW , is between 120 and 140mm. The angle of the dovetail ribs is 60degrees. Styrene voids are placed between the dovetail ribs but portions may be removed so that the voids typically at the ends of Vee Slabs can be concrete filled to provide connections, enhance shear capacity and also to provide wide solid flanges at supporting beams. Vee Slabs are stressed by posttensioning of cables in 40mm dia ducts, typically one at the base of each rib containing between one and four supa 7 12.7 strands Thus a 2400 wide Vee Slab panel has between 5 and 20 pretressing strands..

The charts and tables in this supplement are all based on 2400mm wide Vee Slabs of depths 150,200,250,300,350 and 400 depth. The prestressing strand numbers for the charts are 5,10,15 and 20 strands., In practice a 2400 mm wide Vee Slab can have between 5 and 20 strands in steps of one.. The depths of Vee Slabs is between 150 and 400 in increments of 25mm. Obviously the chart results can be interpolated for intermediate strand numbers and depths. The charts start at 5m spans as it would be unlikely that Vee Slab would be used at spans less then 5m. Solid reinforced slabs would be more economic for these short spans. The charts go to 18 and 30 m spans. It is unlikely that vee slabs much longer than 13.5 would be made, the excessive length facilitates a more true curve shape at the end of the practical spans.

Strength considerations are not normally the controlling criteria for a bending element. It is usually controlled by deflection criteria and this is the reason for including a spreadsheet for calculating deflections , during construction , immediately after additional dead and live loads are applied and also long term deflections due to shrinkage and creep.