Axial stress distributions in FRP-confined concrete columns : pressure-film measurements and finite element predictions

Abstract

Understanding the stress distribution in fiber-reinforced polymer (FRP)-confined concrete sections remains challenging primarily because no effective technique for direct stress measurement has been developed. This knowledge deficiency may lead to serious errors in current design standards for buildings and infrastructures. In this study, we developed a novel approach for directly measuring axial stress distributions in FRP-confined concrete columns by using digital pressure-sensing films. Measured stress distributions based on the proposed approach after Gaussian smoothing are compared with finite element (FE) results obtained with the evolutionary potential-surface trace (EPT) model at selected load levels. These comparisons showed a reasonably close alignment in terms of overall trend between the smoothed pressure-film data and the FE predictions with localized discrepancies. The differences between the test results and the FE predictions are the largest in the corner regions of square columns (with the maximum difference being 56 %) and at the long-side midpoints of rectangular columns (with the maximum difference being 42 %), although the differences at other locations are generally below 20 %. These findings not only demonstrate the capability of pressure films in measuring stress distributions in concrete columns, but also validate the EPT constitutive model. The combined use of pressure films and FE modeling offers significant potential for understanding and modeling internal stress distributions in structural elements.