Title: Reliability Assessment and Strength Reduction Factor Calibration for Screw Anchors Concrete Breakout

Author(s): Ahmad N. Tarawneh, Eman F. Saleh, and Sereen A. Majdalaweyh

Publication: Structural Journal

Volume: 119

Issue: 2

Appears on pages(s): 113-122

Keywords: first-order reliability method (FORM); Monte Carlo simulation (MCS); reliability analysis; screw anchors; strength reduction factors

DOI: 10.14359/51734190

Date: 3/1/2022

Abstract:
The screw anchor design model was recently adopted in ACI 318-19, and similar strength reduction factors for post-installed anchors were applied to screw anchors despite its reliable performance, which has been proven in experimental studies. Accordingly, this study presents a comprehensive reliability assessment of the safety level for the design of screw anchors governed by concrete breakout. A worldwide database that includes single anchors embedded in cracked and uncracked concrete, anchors with edge effects, and a group of anchors is used in the reliability analysis. Anchor design inherently has different uncertainties related to multiple variables like concrete strength and variability in load. These variables have been modeled using multiple distributions. Furthermore, in this paper, anchors are grouped into three classes based on the installation effort sensitivity classes 1 to 3, where this sensitivity is described in a beta distribution. Based on a 3.5 selected reliability index threshold, the ACI 318-19 strength reduction factors result in conservative reliability indexes that exceed the selected threshold. Thus, revised strength reduction factors (ϕ) are proposed. For anchors embedded in uncracked concrete, the proposed ϕ factors are 0.80 for anchor classes 1 and 2 and 0.75 for anchor class 3. For anchors embedded in cracked concrete, ϕ factors are 0.75, 0.7, and 0.65 for classes 1, 2, and 3, respectively. The study also presents a sensitivity analysis to quantify the effect of each model error parameter on the results.