International Concrete Abstracts Portal

Title: Reliability Evaluation of ACI 318 Strength Reduction Factor for One-Way Shear

Author(s): Victor Aguilar, Karina Popok, Pablo Hurtado, Robert W. Barnes, and Andrzej S. Nowak

Publication: CRC

Volume:

Issue:

Appears on pages(s): 75

Keywords:

DOI:

Date: 8/5/2025

Abstract:
A reliability-based calibration of a strength reduction factor for one-way shear strength limit state was not justifiable in the past because of well-founded concerns about the level of safety associated with the ACI 318 traditional one-way shear strength expressions—particularly for large and lightly reinforced beams and slabs—which were first introduced in 1963. After a sustained, collaborative effort of several ACI technical committees (318-E, 445, and 446) to address these safety concerns, improved one-way shear strength expressions were adopted in ACI 318-19. The ACI 318-19 one-way shear design equations are a significant improvement relative to the previous shear design equations in former editions of the ACI 318 building code requirements; however, the reliability of members regarding one-way shear strength limit state remained unknown. Therefore, the objectives of this study were: (1) to provide a statistical basis for improving the strength reduction factor for one-way shear, and (2) to propose a new strength reduction factor for one-way shear, if justified. In this study, relevant test data available in the literature were collected to characterize uncertainties regarding material mechanical properties and cross-sectional dimensions. Although most parameters were statistically represented in the same manner as in previous ACI 318 code calibration, the in-place concrete strength uncertainty was updated, and the considerations for uncertainty in effective depth were specifically revised for one-way shear strength. A large database of the yielding strength of reinforcing bars of sizes commonly used as shear reinforcement was analyzed, and new statistical parameters were developed. In this assessment, data-driven professional factors, which represent the uncertainty in the analytical model, were used instead of expert opinion estimates as in the past. Several scenarios were considered throughout the analyses: small, medium, and large size members; light, moderate, and heavy longitudinal reinforcement; no, light, moderate, and heavy shear reinforcement; and dead to total load ratios from 0 to 1.