Seismic Retrofitting of RC Circular Columns Using Carbon Fiber, Glass Fiber, or Ductile PET Fiber

Donguk Choi,Sorrasak Vachirapanyakun,Sang-Su Ha,Seongwon Hong,Myung-Kwan Lim

doi:10.1186/s40069-021-00484-7

Abstract

The effectiveness of seismic retrofitting using three different fibers—carbon fiber (CF), glass fiber (GF), polyethylene terephthalate (PET) fiber—and a fiber combination of aramid fiber (AF) and PET fiber (called hybrid fiber reinforced polymer (HF)) wrapped on reinforced concrete (RC) circular columns was experimentally evaluated. A total of 11 RC circular columns were tested: three control columns and eight retrofitted columns in three different test groups. The purpose of fiber wrapping was flexural strength improvement as well as enhancement of rotational capacity in the plastic hinge region. Mechanical properties of CF, GF, AF, and PET were first defined; that is, CF, GF, and AF exhibited linear stress–strain behavior with limited ultimate strain capacity typically less than 3%, while ductile PET exhibited as much as 15% strain and non-linear stress–strain behavior with a very low elastic modulus. In the RC column tests, all three different fibers and the AF + PET fiber combination were effective in enhancing the strength and ductility but resulted in different structural behaviors and failure modes depending on the fiber type and the fiber amount used. The column sections were then analytically studied by section analysis using the behavior of confined concrete, the non-linear relationship of fiber-reinforced polymer (FRP), and the actual material properties of reinforcement. The analytical and experimental results revealed that ductile PET is beneficial, as it demonstrates more ductile behavior with a degree of strength enhancement similar to that of CF and GF.

Highlights

For many existing reinforced concrete (RC) building columns and bridge piers designed and constructed in the 1960s and 1970s in many countries, including South Korea, there is a need to increase flexural and shear capacities, as well as ductility
5 Conclusions In this research, 11 RC circular columns were built and reinforced by carbon fiber (CF), glass fiber (GF), Aramid fiber (AF), polyethylene terephthalate (PET), and HF, and a pseudo-seismic test was performed to investigate the effectiveness of structural seismic retrofitting
The following conclusions were reached based on the experimental results and extensive analyses: 1. In test groups (TGs)-1, compared with the control specimen, the ultimate moment of columns confined by CF and PET was improved by 21% and 28%, respectively, and the displacement ductility of specimens wrapped by CF and PET was increased by 130% and 211%, respectively

Summary

Introduction

For many existing reinforced concrete (RC) building columns and bridge piers designed and constructed in the 1960s and 1970s in many countries, including South Korea, there is a need to increase flexural and shear capacities, as well as ductility. Through an experimental study of 15 sheardeficient square RC piers, they concluded that RC piers wrapped by multiple PET or PEN layers with large fracture strain could efficiently enhance the ductility of RC piers, and PET and PEN could be used for shear strengthening of RC piers lacking transverse reinforcement if an adequate amount of fiber is provided, regardless of their low stiffness. They proposed an analytical model to predict the pier’s deformation capacity based on the experimental results. – The hybrid strand constructed in this study using AF and PET is the first attempt at hybridization of ductile PET and conventional fiber (such as AF) to increase stiffness and constructability

Experimental program

C-3-Control

Test results

Findings

Conclusions