About

Suspended floor slabs function differently than ground-bearing slabs. They must resist bending moments that create tension at the bottom of the slab in the middle of the span, and tension at the top of the slab near the supports (walls or beams). This requires a specific reinforcement pattern often involving "cranked" bars or separate top mats.

This calculator estimates the steel required for a one-way suspended slab based on simplified span-to-depth ratios. It accounts for the extra length needed for cranking (bending up) bars at supports and provides a breakdown of Main Bars versus Distribution Bars.

Formulas

The total length of a single cranked bar includes the clear span, the support bearing width, anchorage length, and the additional length from the crank (bent portion).

L_bar = L_clear + 2L_bearing + 2L_d + 0.42D_eff

Total steel weight is derived from:

W = N_bars×L_bar×w_unit

Reference Data

Span Condition	L/d Ratio (Est)	Moment Coeff (Approx)
Simply Supported	20	1/8
Continuous (One End)	24	1/10
Continuous (Both Ends)	26	1/12
Cantilever	7	1/2
Min. Distribution Steel	0.12% - 0.20%	Cross-sectional area basis.
Crank Length Extra	0.42 × D	Added length for 45° bend.
Main Bar Direction	Short Span	Load travels shortest path.

Frequently Asked Questions

Main bars carry the structural load and are placed parallel to the shortest span. Distribution bars are placed perpendicular to main bars (above them) to tie the mesh together and prevent cracking from shrinkage and temperature changes.

In a continuous slab, the top of the slab is in tension near the supports (negative moment). Cranking the bottom bar up allows it to reinforce this top tension zone without needing a completely separate layer of top steel, saving material.

No, this tool uses One-Way slab logic (Load is transferred primarily in one direction). Two-way slabs (where Length/Width ratio < 2) require complex coefficient analysis for both directions.