Design Aid Curves for Two-Way Post-Tensioned Flat Slabs (ECP 203)

Introduction. Every feasibility study of a post-tensioned (PT) floor asks the same two questions: how far can the slab span, and how much prestressing steel will it need? Answering them still requires a full finite-element model for every candidate geometry, and no primary design aids calibrated to the Egyptian Code of Practice (ECP 203-2020) exist. This study condenses 675 code-compliant designs into curves, a screening equation and a free calculator that answer both questions in seconds.

Methods. A full-factorial parametric grid of two-way PT flat slabs was analysed in RAM Concept, first validated against published deflection measurements of a one-half-scale PT flat-plate test and cross-checked against an independent analysis package. Spans varied from 6.0 to 10.0 m in both directions in 1.0 m steps, with nine superimposed dead/live load combinations (2.0–4.0 kN/m² each) and three concrete strengths (30, 35 and 40 MPa); tendons were uniform in one direction and banded in the other, with the ECP 203-2020 allowable stresses and deflection limits governing the design.

Results. The steel rate is governed by the spans and the total superimposed load — dead and live load contribute almost equally — whereas raising the concrete grade from 30 to 40 MPa reduces it by only about 8%. Plotted against span, the rate is non-linear and non-monotonic, turning over within the studied range rather than following a straight line. Re-expressed in terms of the governing (longer) and shorter span, however, the whole grid is captured by a single screening equation (R² = 0.97, median error 2.6%).

Conclusions. The curves, tabulated grid, screening equation and an open-source estimator with a web calculator let designers select efficient spans, estimate prestressing steel and compare floor options at the feasibility stage without building a single finite-element model.