This session will showcase the new ACI PRC-ITG-11-24 "Statistical Techniques for Assessment of Existing Concrete Structures". Its target audience includes engineers, technicians, contractors, owners, architects, and anyone planning condition assessments and evaluations of existing concrete structures.
Learning Objectives:
(1) Recognize the need for, and effective implementation of statistically based evaluation.;
(2) Apply available statistical techniques to quantify the condition and reliability of existing concrete structures;
(3) Evaluate the relative merits of repair options using results from statistical assessments;
(4) Review the proposed activities of a new ACI Committee tasked with maintaining this document and further pursuing this initiative.
“A History of Innovation Task Group 11: Statistical Evaluation of Concrete Structures”
Presented By: Peter Barlow
Affiliation: Barlow Consulting
Description: Innovation Task Group 11 was formed in October 2022 with the mission: “To provide a uniform methodology, using a statistical basis, for establishing the minimum requirements of a field investigation.” By August 2024, the ITG published document ACI PRC-ITG-11-24: “Statistical Techniques for Assessment of Existing Concrete Structures.” The aggressive schedule was driven by the goal to publish a document that could be referenced by the next update to ACI 562 Concrete Repair Code, scheduled for publication in early 2025. This presentation will provide a history of how and why the ITG was formed and what steps were taken to efficiently produce the document within the short timeframe.
Preparing a Condition Assessment and Testing Plan using Statistical Methods
Presented By: Nicholas Triandafilou
Affiliation: Brindley Engineering Corporation
Description: The purpose of this presentation is to summarize the methodology for planning and implementing test plans, which is included in publication ACI PRC-ITG-11-24: “Statistical Techniques for Assessment of Existing Concrete Structures.” Licensed design professionals responsible for developing testing plans should consider several factors, including structure age and condition, availability of as-built drawings and test cylinder data, consequence and likelihood of failure, target repair design life, and cost and impact of testing. Balancing these factors to determine an appropriate level of testing for a specific project can be a challenging task that requires collaboration with the owner, a thorough understanding of the project objectives, knowledge of available test methods including their applicability and error sensitivities, and an understanding of reliability-based techniques for analyzing the test results.
Use of Statistics with Large Datasets in Evaluation of the Remaining Service Life of an Existing Structure – A Case Study
Presented By: Ali Inceefe
Affiliation: Tourney Consulting Group, LLC
Description: A large transportation structure built in the 1950s in the Northeast United States is currently in the planning stage for a major rehabilitation effort. Given the size and scope of the project, there has been extensive data collection over almost 10 years, including chloride profiles, compressive strength, and other materials testing. The breadth of the data required the use of statistical approaches to characterize the data. This presentation focuses on chloride-induced corrosion and outlines the approaches used to estimate the service life of different components of the structure so that they can be prioritized as part of the rehabilitation program.
Strength Assessment of an Historic Building
Presented By: Jeremiah Fasl
Affiliation: Wiss, Janney, Elstner Associates, Inc.
Description: Engineering judgment and statistical approaches are available when assessing existing structures. Those approaches will be discussed relative to a strength assessment of a 1920s building where the Owner did not have any available drawings. Multiple nondestructive and destructive techniques were utilized to characterize the structural system (e.g., element sizes, reinforcement locations and sizes, material strengths, etc.) and evaluate the building for design loads. Using techniques presented in ACI PRC-ITG-11-24, this presentation will discuss how the data were analyzed so it could be used in a strength assessment.
Overview of the Reliability Toolkit
Presented By: F. Michael Bartlett
Affiliation:
Description: This presentation will broadly describe the contents of Appendix A “Reliability Toolkit” of ACI PRC-ITG-11-24. This appendix succinctly describes the application of reliability-based principles and techniques to the assessment of existing structures and illustrates these with practical example calculations. The presentation will briefly address:
a) The mathematical definition of the reliability index and its application in the mean load method, which can determine the structural safety without requiring factored load combinations or strength reduction factors.
b) Methods for combining random variables, including simple rules for additive and multiplicative combinations of independent random variables, Monte Carlo Simulation, and the Taylor series linearization approach.
c) Extreme value distributions for transient load effects, including the derivation of statistical parameters for different return periods using log-shift principle.
d) Bayes’ Theorem.
e) The four examples presented in Appendix A.