Title:
Confinement Length of R/C Columns Determined Through Image Analysis
Author(s):
Matamoros
Publication:
Web Session
Volume:
Issue:
Appears on pages(s):
Keywords:
DOI:
Date:
4/2/2023
Abstract:
The ACI 318 Building Code requires closely spaced ties at column ends of ordinary and special moment frames, where flexural yielding is likely to occur. Recommendations for the minimum length over which closely spaced ties should be provided were developed by establishing a relationship between the observed length of spalling in ductile columns and loading/geometric parameters, e.g., section height (depth) (h), column length (lc), axial load ratio (P / f’c Ag), and shear span-to-depth ratio (a/d). Spalling length was calculated based on image analysis of digitized photographs of ductile columns subjected to reverse cyclic loading. Two different sets of images and their corresponding column parameters were analyzed. Set 1 had images captured at all levels of deformation, including multiple images of the same column at different levels of displacement. Set 2 comprised a single image for each column captured at the end of the test. Set 1 image analyses showed that spalling length did not increase with increasing deformation after the damage pattern was established. For this reason, design recommendations were based on Set 2. Statistical analyses of spalling lengths in Set 2 showed that axial load ratio, shear span-to-depth ratio, and longitudinal reinforcement ratio were the most important parameters influencing spalling length. Statistical analyses were performed for all columns in Set 2 and for subsets created by separating columns into six different bins according to axial load and shear span-to-depth ratio. A relationship between spalling length and these two parameters is provided and simple design recommendations for the minimum length of closely spaced ties at column ends are proposed.