Title:
Reassessment of Two-way Shear Equation in ACI 440.11 Building Code (Prepublished)
Author(s):
Zahid Hussain, Nima Khodadadi, Antonio Nanni
Publication:
Structural Journal
Volume:
Issue:
Appears on pages(s):
Keywords:
building code; elevated slabs; GFRP reinforcement; reinforced concrete; shear; machine learning
DOI:
10.14359/51749551
Date:
2/13/2026
Abstract:
The two-way shear equation in ACI 440.11 was originally developed nearly two decades ago using experimental data from early FRP materials, most of which are no longer representative of modern GFRP reinforcement. With current GFRP bars exhibiting significantly improved mechanical and surface properties, the validity of the existing equation requires reassessment to ensure practical and economical design. This study evaluates the ACI 440.11 two-way shear provisions using a comprehensive database of 49 GFRP-RC interior slabs and 14 edge column connections. The current code equation was found to be highly conservative, yielding an average test-to-predicted ratio of 2.13. Updated equations are proposed for both interior and edge conditions, reducing the ratio to 1.02 and 1.04, respectively, while maintaining acceptable statistical variation. Additionally, symbolic regression (SR) is used to develop machine-learning-based expressions, which show high predictive accuracy. The proposed models provide reliable, physically grounded, and less conservative predictions of punching shear capacity, supporting broader implementation of GFRP reinforcement in structural concrete applications.